Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/11/21

National Weather Service Albany NY
1045 PM EST Fri Dec 10 2021 .SYNOPSIS... An approaching storm system will bring some light rain to the region towards daybreak Saturday. Some sheltered areas could briefly see this start out as light freezing rain. With milder temperatures moving into the region, rain showers and gusty winds are expected throughout the day on Saturday. Behind the storm`s cold front, strong winds are expected for Saturday night as rain ends, with some cooler temperatures moving back into the region. Breezy and dry weather is expected for Sunday with temperatures closer to seasonal levels. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A Winter Weather Advisory for freezing rain is in effect for 3 to 8 am Saturday for southern Adirondacks and Glens Falls area including northern Washington County of eastern New York and for southern Vermont. Update 1015 PM EST...Temperatures have dropped off a bit more than expected in some locations. However, clouds will continue to increase and lower across the area and winds will pick overnight resulting in temperatures beginning to rise. With precipitation not expected until late at night don`t see a need to expand the winter weather advisory. Update 7 PM EST...Forecast is on track with warm air advection precipitation not expected to develop across the area until late at night. It`s mild for an early December evening with temperatures in upper 20s to upper 30s across the forecast area. Temperatures will drop some before stabilizing then beginning to rise late at night. Skies across the southern part of the forecast area have become mostly clear but clouds will move back in as the night progresses. Only some minor adjustments were needed. Previous Discussion 353 PM EST...Upper level ridging over the far southeastern US extends northeast offshore into the Western Atlantic. Meanwhile, a large upper level trough is shifting from the Rockies towards the High Plains for tonight. As a result of this pattern over the CONUS, our region is under the influence of broad west-southwest flow aloft. Surface high pressure has been in control of the weather through the day today, but will be departing off to the east for tonight. IR satellite imagery continues to show plenty of clouds in place over the region, although there have been some breaks from time to time. Skies may initially be partly cloudy this evening which will allow for temps to fall. After midnight, however, clouds will start increasing once again, as a surface warm front off to the southwest starts approaching. With a developing light south to southeast breeze, temps will stop falling and actually hold steady or even start to rise. Lows around midnight should be in the upper 20s to low 30s. Some light rain will start moving into the area from the southwest after about 5 or 6 AM or so. While most areas will be above freezing when precip begins, some sheltered areas of the Adirondacks and southern Greens could see surface temps right at 32 degrees, allowing for a brief period of freezing rain. While ice amounts will only be a trace to a hundredth or two, it may be enough to make any exposed surfaces slick. A Winter Weather Advisory is in effect for these areas beginning at 3 AM (although best chance for seeing freezing precip will likely be a short duration after 5 or 6 AM). && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... The warm front will continue to lift northward across our area on Saturday morning as the strong surface storm lifts towards the Great Lakes. A period of steady light rain looks to occur, with any lingering freezing rain within the sheltered mountain valleys changing to plain rain by 8 or 9 AM. The light rain associated with the warm advection/isentropic lift should be ending towards Noon. Behind the warm front, a gusty southerly winds will take over for Sat afternoon, allowing for surface temps to warm considerably, despite the clouds and calendar showing December. Most of the area will be well into the 50s by Saturday afternoon, with some spots in the mid Hudson Valley coming close to 60 by late in the day. The southerly winds will be gusting up to 30 mph at times, although the strong inversion around 900 hpa will prevent winds from getting too strong ahead of the approaching frontal boundary. While there may be a few patches of drizzle or light showers during the afternoon, most of the time should be fairly dry as our area will be between the best forcing. By the evening hours, the storm`s cold front will be approaching from the west as the surface low pressure lifts into southern Canada and a more organized line of showers will be heading towards the area. According to both the 3km HRRR and NAMNest, it should be crossing from west to east from 7 to 10 PM. Some locally heavy downpours may accompany the fine line of showers that moves across the area. Model sounding shows some elevated instability, so can`t rule out a rumble of thunder as well and have included that slight chance in the forecast as well. Some gusty winds may accompany the showers as well, although the best chance for gusty winds looks to be immediately behind the boundary. As cooler air moves in aloft, both good mixing and a strong pressure gradient in place will allow for strong westerly winds for Saturday night, especially for areas north and west of the Capital Region. Some gusts may reach 50 mph, especially for the Adirondacks, Mohawk Valley, Greater Capital Region and Berkshires. Some downed trees/power lines are possible and a Wind Advisory is in effect for much of the area for Sat evening into Sat night. Precip should shut off for most areas as the front crosses, although some lingering lake-effect rain/snow showers can`t be ruled out for the western Adirondacks for the late night hours, where a light dusting of snow is possible as well. Temps will fall into the mid 20s to mid 30s, although most larger valley areas will remain above freezing for Sat night. Drier, breezy and cooler weather is expected for Sunday into Sunday night. Any lingering lake effect activity over the Adirondacks or Mohawk Valley should wind down on Sunday morning and skies will be clearing out. Surface high pressure will be passing by to the south, so enough of a pressure gradient will remain in place to keep it fairly breezy through the day on Sunday, with some gusts still up to 25 mph. Daytime temps will range from the mid 30s to mid 40s. Skies should remain fairly clear into Sunday night, although a light breeze may linger. With the light breeze and lack of snow cover, it won`t be too cold for Sunday night, with lows in the upper 20s to low 30s. && .LONG TERM /MONDAY THROUGH FRIDAY/... Weak cold front with little to no moisture tracks through Monday into Monday night and high pressure will build in from Canada Tuesday, exiting SE Canada Wednesday. Highs Monday in the mid 40s to around 50 with around 40 higher terrain. Highs Tuesday behind the cold front, in the mid to upper 40s with upper 30s higher terrain. Warm advection begins Wednesday and based on the low level ridging in SE Canada building offshore New England, onshore low level flow and boundary layer warming and moisture advection could increase the clouds very quickly late Tuesday night through Wednesday, limiting the sun. So, highs Wednesday in the mid to upper 40s with upper 30s to around 40 higher terrain. Strengthening warm advection and moisture advection as well as isentropic lift Wednesday night into Thursday as a strong upper impulse and associated cold front approach our region. Spotty mixed precipitation is possible late Wednesday night. Then a potential warm up to temperatures in the 50s Thursday with showers ahead and along a strong cold front. Temperatures near 50 in higher terrain. The front tracks through Thursday afternoon and night and weak cold advection returns Friday. Based on the long wave pattern, the cold advection will be similar to past cooldowns in recent weeks, with temperatures cooling to near or a little above normal because the deepest and coldest air is still locked up well north of the U.S. lower 48 states. Highs Friday in the mid 40s to around 50 with upper 30s to around 40 higher terrain. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... Area of partial clearing tracking into our region with some scattered variable clouds at around 5000 feet and higher. This area of scattered variable broken cloudiness will exit our region as the leading edge of developing precipitation and solid cloud cover approaches from central and western PA/NY. So, VFR conditions until about 10Z, when the leading edge of the clouds and precipitation begin to affect the TAF sites. Temperatures around KGFL will be near freezing, so while the highest probability is for rain to begin at KGFL around 10Z, there could be a few hours of freezing rain between 10Z-13Z, where a PROB30 is included. Elsewhere, precipitation should start as just rain. Temperatures will warm by around 13Z to change any freezing rain at KGFL to just rain. Rain will be fairly widespread through about 15Z-18Z with MVFR ceilings and visibilities at all TAF sites. Some intervals of steadier precipitation may continue at KGFL into the afternoon, but at KALB, KPSF and KPOU, a lull in the steadier precipitation is likely until the showers associated with the cold front approach by around 21Z-22Z. Just keeping VCSH from around 18Z-21Z until the showers with the cold front move in. So, during the lull, still, some MVFR ceilings but visibilities will trend to VFR. Then once the showers move in to all TAF sites with the cold front around 21Z, visibilities trend to borderline MVFR/IFR and ceilings drop to IFR. The MVFR/IFR conditions and showers continue through 24Z. Winds tonight from the southeast to south at 10 Kt or less, sometimes less than 3 Kt at KPOU, KGFL and KPSF. Then around daybreak, steady south winds at around 10 Kt, increasing to 15 to 20 Kt by afternoon. KALB and KPSF could gust around 25 to 35 Kt in the afternoon. WInd shear is expected at all TAF sites by around 10Z as winds at 2000 feet should be south to southwest at 40 to 55 Kt through the day. Once surface winds become gusty at KALB in the afternoon, the wind shear should end, but wind shear continues at all other TAF sites through the day. Outlook... Saturday Night: High Operational Impact. Windy. Definite SHRA. Sunday: Low Operational Impact. Breezy. Sunday Night through Wednesday: No Operational Impact. NO SIG WX. && .HYDROLOGY... Although dry weather is expected this evening, a frontal system will begin bringing some light rainfall to the region towards daybreak Saturday. It may initially begin as freezing rain in some sheltered areas, but the majority of the precip will be just plain rain with this system. Showers will occur during the day Saturday, especially just ahead of the storm`s frontal boundary during the evening hours. Total precipitation amounts will range from around a third of an inch across southern areas to a little over an inch across the Adirondacks. This rainfall will lead to rises on rivers and streams, but no flooding is expected. Drier weather returns Sunday into early next week, which would allow river levels to gradually recede. For details on specific area rivers and lakes, including observed and forecast river stages and lake elevations, please visit the Advanced Hydrologic Prediction Service /AHPS/ graphs on our website. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Wind Advisory from 5 PM Saturday to 4 AM EST Sunday for NYZ032- 033-038>043-047>054-058>061-063-082>084. Winter Weather Advisory from 3 AM to 8 AM EST Saturday for NYZ033-041>043-082-083. MA...Wind Advisory from 5 PM Saturday to 4 AM EST Sunday for MAZ001- 025. VT...Winter Weather Advisory from 3 AM to 8 AM EST Saturday for VTZ013>015. && $$ SYNOPSIS...IAA/Frugis NEAR TERM...IAA/Frugis SHORT TERM...Frugis LONG TERM...NAS AVIATION...NAS HYDROLOGY...Frugis
Area Forecast Discussion
National Weather Service Gaylord MI
957 PM EST Fri Dec 10 2021 .UPDATE... Issued at 947 PM EST Fri Dec 10 2021 Strong surge of warm air advection driven precipitation driving north across the area this evening...well ahead of deepening surface low across southeast Iowa. Leading edge of this precipitation across northern lower Michigan taking the form of a wintry mix, with a quick transition to just plain rain as surge of elevated warm air spreads north. Expect this precipitation to continue to expand north into eastern upper Michigan, where snow will remain the primary precipitation type for much of the overnight. Expect several inches of wet snow for this area, especially across northwest Chippewa County. Warm nose does make it into eastern sections of eastern upper Michigan late, supporting a transition to a wintry mix of precipitation. Expect a full transition to rain for areas south of the big bridge, but not before an inch or two of slop falls across interior areas in the tip of the mitt. May even hear a few rumbles of thunder late across our southeast counties as that area gets into the warm sector with surface low tracking into northwest lower Michigan toward morning. Per coordination with Grand Rapids forecast office, have gone ahead and expanding inherited wind advisories to all of northern lower Michigan late Saturday morning and afternoon. Latest HRRR guidance shows widespread wind gusts of over 40 mph within surge of cold air advection behind departing deepening surface low. && .NEAR TERM...(Through Tonight) Issued at 336 PM EST Fri Dec 10 2021 ...Messy winter storm arrives this evening... High Impact Weather Potential...High. Accumulating snow in portions of Eastern Upper. The main wave continues to dig through the central Rockies this afternoon with a 120kt jet extending from it into the Great Lakes. The 990mb surface low has moved into southwest Iowa, and is forecast to intensify and track into central Lake Michigan just after midnight tonight..supported along by great dynamic support thanks to the incoming wave and UL jet. Convection has broken out over Missouri and Illinois along the warm front which has been slowly moving northward...with some midlevel moisture over-running it into the Chicago/southern Michigan region. Still believe we`ll take a while to saturate the column given the quite dry antecedent mid- level air this morning. Better forcing ahead of the wave arrives in our area right around 00Z...this area of forcing is currently supporting the convection in NO/IL. Thus believe we`ll see some decent rainfall overnight. PWAT`s approach 0.90" overnight in the southeastern third of the CWA, which is much above normal (by 3 to 4 St. Dev!) for mid-December. One question is when exactly rain moves into the southwest counties this evening. Guidance has been fairly consistent with the column saturating by 00Z, but don`t know if we could squeeze out some precip before this given the amount of moisture and forcing beginning to move into the area. Also, precip intensity may allow precip to initially fall as very wet snow for a couple hours over Nrn Lower this evening before switching over to rain. Precip marches to the northeast through the evening, reaching E. Upper as snow by 9 or 10pm. (One caveat here is the assumption the current snow band moving northeast through Wisconsin doesn`t stretch over to Ern Upper before this.) Another big question is how much evening/early overnight lows drop before warmer air moves in. Most recent guidance shows the interior portions of Nrn Lower hovering either right at or a degree above freezing for a brief time around 00z. Thus a brief period of freezing rain is possible in the higher terrain this evening. Ern Upper is a different story with temperatures hovering at the freezing mark throughout much of the night, with most of the precip tonight expected to fall as a slushy wet snow. A tight gradient may arise (in temperature and precip types) through central Chip/Mack counties as warm air surges northward late night/early Saturday morning, changing precip over to rain/freezing rain. Otherwise, still expected snow amounts of generally one or two inches for Nrn Lower (locally higher right at the tip of the mitt potentially). Chip/Mack counties can expect 3 to 6 inches with the highest totals in far western portions of these counties. && .SHORT TERM...(Saturday through Monday) Issued at 336 PM EST Fri Dec 10 2021 ...Very windy Saturday with mixed precip... High Impact Weather Potential...High. Winter storm conditions continue in parts of eastern upper MI Sat. Very windy. A rapidly deepening surface low will lift across northern lower MI Sat morning, a few hours slower than it appeared yesterday. A dry slot will scoot quickly eastward across northern lower MI in the morning, with wraparound/deformation precip continuing in central/eastern upper MI and pushing back into northern lower MI. But this will all exit to the ne fairly abruptly late in the afternoon into the evening. Precip and wind trends are the primary concerns. Morning starts out with a dry slot over much of northern lower, on up into Drummond Isl. Leftover synoptic precip may still linger in the far se. But wraparound/deformation will be continuing over central/eastern upper MI, and will wrap back into nw lower. Precip will continue thru midday, then gradually diminish and end in the afternoon and early evening. A bit of lake enhancement will develop on the tail end of synoptic precip, with 850mb temps quickly lowering to -8/-9C. Initially, most areas will be just rain, with wintry precip (FZRA and snow) in the west half of Chip/Mack Cos. Colder air will make more abrupt inroads beginning mid morning, with precip mixing with and turning to snow before ending. Mixed precip will linger along the nw lower MI coastline all day long, even while the higher elevations inland will have turned back to all snow. Highest snowfall amounts will be in far western Chip/Mack Cos, with 2-4" west of a Bay Mills-Epoufette line. In northern lower MI, 1-2" accums occur in the higher terrain snowbelts from Kalkaska to GLR. Lesser snow amounts elsewhere. High winds will arguably be a bigger story than wintry precip. An initial surge of isallobaric post-frontal sw winds arrives in the morning. The highest winds with this will be largely downstate, though the plume of strongest winds eventually spreads into our se zones, especially along Saginaw Bay. A wind shift to nw occurs midday into the afternoon, and these will be quite gusty across all of northern MI. Gusts of 40-45mph will be common from midday into very early evening. Will be issuing wind advisories for essentially all of the northern lower MI coastline (excluding Gd Trav Co, including Beaver Isl). Gusts to or in excess of 45mph will be most confidently felt here. Things are more marginal inland; in addition, the combination of snow and winds might make winter wx advisories a better choice of headline in some interior counties. Will decline to issue anything for these areas at this time, but additional wind/winter headlines are a distinct possibility for Saturday. Sunrise temps will range from the lower 30s in western Chip/Mack, to the mid 40s near Saginaw Bay. Temps will be in the 30-35f range by early evening. Much quieter wx for the rest of the short term. Fastest 500mb westerlies migrate north into Canada, with 500mb heights steadily building across the central/eastern CONUS. Sprawling high pressure covers the OH/TN Valleys and mid Atlantic states, ushering in mild Pacific air. Dry and mild wx is in the offing Sunday into Monday. Max temps will be mainly near 40f to the mid 40s both days. Mostly sunny skies Sunday, with a bit more cloud cover Monday (especially north of M-32. .LONG TERM...(Monday night through Friday) Issued at 336 PM EST Fri Dec 10 2021 ...Unseasonably warm midweek... High Impact Weather Potential...Minimal. Unseasonably mild Pacific air will cover the region most of next week. The faster 500mb flow will remain north of the area, as 500mb ridging will be overhead by Wed morning. Energy eventually ejects from the sw states, displacing the ridge and returning precip and cooler temps to the area. Rain showers are likely by late Wed, and a rain-snow mix is possible by late Thursday as cooler air filters back in. We could well flirt with record high temps at all sites on Wednesday, when northern lower MI looks to be in the 50s, and eastern upper MI upper 40s to around 50f. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 625 PM EST Fri Dec 10 2021 Conditions expected to deteriorate to IFR overnight into Saturday morning as band of rain and br/fg overspread the area from the southwest. May see precipitation begin as a wintry mix initially overnight, perhaps bringing some minor snow accumulations. Rain transitions back to snow on Saturday, once again likely bringing some minor accumulations. Band of wind shear tonight gives way to very gusty northwest winds on Saturday, with gusts likely exceeding 35 knots during the afternoon. Cigs will rise/scatter out heading toward later Saturday afternoon. && .MARINE... Issued at 336 PM EST Fri Dec 10 2021 Strong low pressure will move ne across northern lower MI Sat morning. Southerly winds ahead of the low will veer sw early Sat, and then nw midday into the afternoon. Those winds will be very strong Saturday, with at least gales on all waters. Have upgraded the waters either side of Presque Isle Lt on Lk Huron to storm warnings for a short period Sat afternoon, where gusts to circa 50kt are likely in an area of favorable coastal convergence. Winds will weaken Sat night. && .APX WATCHES/WARNINGS/ADVISORIES... MI...WIND ADVISORY from 10 AM to 8 PM EST Saturday for MIZ016>018- 020>036-041-042-098-099. WINTER STORM WARNING until 4 PM EST Saturday for MIZ086-087. WINTER WEATHER ADVISORY until 4 PM EST Saturday for MIZ095-096. LH...GALE WARNING from 9 AM to 9 PM EST Saturday for LHZ345-346. STORM WARNING from 9 AM to 8 PM EST Saturday for LHZ349. STORM WARNING from 3 PM to 8 PM EST Saturday for LHZ347-348. LM...GALE WARNING from 9 AM to 9 PM EST Saturday for LMZ323-341-342- 344>346. LS...GALE WARNING from 9 AM to 9 PM EST Saturday for LSZ321-322. && $$ UPDATE...MB NEAR TERM...STJ SHORT TERM...JZ LONG TERM...JZ AVIATION...MB MARINE...JZ
Area Forecast Discussion
National Weather Service La Crosse WI
844 PM CST Fri Dec 10 2021 .UPDATE... Issued at 839 PM CST Fri Dec 10 2021 Continued assessment and extrapolation of the deformation zone arcing out of the Mid-Missouri River valley has increased confidence just enough to lower the already marginal warning-level snowfall totals for a few counties. Thus, have transitioned the warning to an advisory for four counties, including La Crosse. The gradient in the snowfall axis will still be tight and bifurcate these counties. Cannot 100 percent rule out some 6 inch snowfall reports in the northern portions of these counties, but the vast majority of the population should see less than 6 inches and have adjusted the headlines accordingly. The impacts, nonetheless, will change little. Expect slippery roads through the night, especially with freezing rain mixing in at times across the advisory. UPDATE Issued at 607 PM CST Fri Dec 10 2021 Given the trends in radar/satellite/CAMS, have pulled forward the end time of the eastern warning/advisory from noon to 9am. Also have blended in more HRRR QPF to the near-term QPF fields to tighten the southern end of the snow band. La Crosse remains situated on the very edge of the snow band, thus snowfall amounts remain the most uncertain through this belt. && .SHORT TERM...(This evening through Saturday) Issued at 220 PM CST Fri Dec 10 2021 In the overall big picture, not a lot has changed with the winter storm. Water vapor satellite shows the upper level system is coming across the central Rockies with a nice baroclinic leaf forming out ahead of. This wave will continue to track northeast, coming across with a positive tilt during the overnight hours. This looks to produce a period of moderate to strong pv advection in the 500 to 300 mb layer. There also looks to be a period of some decent jet dynamics late this afternoon into the evening with the area coming under the right entrance region of a departing 300 mb jet and the left exit region of the next incoming jet streak. The first band of mid-level frontogenesis has come in and produced the first round of light snow across southeast Minnesota into western Wisconsin. This frontogenesis will continue to work on the atmosphere as it lift off to the northeast through the rest of the afternoon. It will quickly be replaced by another band which looks to be stronger and not quite as migratory as the first. The lift from this band will be augmented by the jet dynamics, increasing pv advection ahead of the wave and good isentropic up glide on the 285K surface. This all looks to combine to produce the period of highest snowfall rates from late this afternoon through much of this evening. The 11.12Z HREF continues to show a strong signal for hourly snowfall rates in excess of 1 inch with a signal for some 2 inch an hour rates as well. This signal has shifted northwest from this time Thursday with it now looking to be along our forecast border with MPX or just into their area. The 2 inch per hour rate signal does look to be almost all into MPX`s area at this time. This looks to have shifted the highest band of snowfall amounts just a little farther northwest. Farther to the south, with the slight northward shift, the warm nose aloft looks to have more an influence over our southeast counties to create more of wintry mix than just snow. Based on the thermal profiles depicted in the RAP forecast soundings, a period of sleet and freezing rain or rain (depending of surface temperatures) will occur along with some snow. Some ice accumulations could occur with the highest probabilities for these being from northern Richland County into the southern sections of Adams and Juneau Counties. Amounts should be just a glaze to less than a tenth of an inch. The final hazard from this system will occur overnight. Another band of frontogenesis will occur, although this does not look to be a strong or as big in areal coverage, but enough to produce a burst of snow. This will likely occur as the winds are swinging around to the northwest on the back side of the surface low with gusts up to 35 mph possible. This will be enough to move some of the fresh snow around to create drifting and some pockets of visibility reductions from blowing snow. Everything looks to wind down pretty quick Saturday morning as the system pulls away from the region. At this time, no additional changes are planned to the layout of warning and advisory. Some of the counties on the southern edge of the border may not get all the way to six inches, but when combined with the wind and blowing/drifting potential, enough impacts to justify not making any more adjustments. .LONG TERM...(Saturday night through Friday) Issued at 220 PM CST Fri Dec 10 2021 Just taking a cursory glance out into next week shows that another system looks to move across the Upper Midwest sometime in the middle of the week. Starting to see some differences now between the models on the timing and potential strength of this system. Most models continue to show the area getting into the warm sector of this storm with the 10.00Z NAEFS still showing the specific humidity and precipitable water running 4 to 5 standard deviations above normal. Plenty of warm air coming in as well, with temperatures at 925 and 850 mb having the potential to be about 2 standard deviations above normal. This should help to push high temperatures Wednesday into the 50s and maybe even some lower 60s possible for portions of northeast Iowa into southwest Wisconsin. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 607 PM CST Fri Dec 10 2021 Widespread aviation impacts continue tonight due to heavy snow and a wintry mix over much of the area. Expect widespread IFR to LIFR conditions through the overnight hours, improving from west to east between 09-15Z. Gusty northeast winds back to the northwest late and then continue backing to the WSW by midday on Saturday. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Weather Advisory until 9 AM CST Saturday for WIZ041>044- 053>055. Winter Storm Warning until 6 AM CST Saturday for WIZ032. Winter Storm Warning until 9 AM CST Saturday for WIZ017-029-033- 034. MN...Winter Weather Advisory until 6 AM CST Saturday for MNZ096. Winter Storm Warning until 6 AM CST Saturday for MNZ079-086>088- 094-095. IA...Winter Weather Advisory until 6 AM CST Saturday for IAZ009>011- 018-019-029-030. Winter Storm Warning until 6 AM CST Saturday for IAZ008. && $$ UPDATE...Skow SHORT TERM...04 LONG TERM...04 AVIATION...Skow
Area Forecast Discussion
National Weather Service Denver/Boulder CO
847 PM MST Fri Dec 10 2021 .UPDATE... Issued at 846 PM MST Fri Dec 10 2021 A few snow showers are still ongoing in the mountains but in the majority of areas the snow has stopped. There will be some blowing and drifting snow tonight across the higher mountain passes as the winds increase. It will take a few hours for the stability to increase over the mountains but after midnight, a strong mountain wave will develop with wind gusts up to 75 mph in the foothills. The highest winds will occur during Saturday night with the best flow aloft and the development of a mean state critical layer. Otherwise, it will be a very chilly night with wind chills below zero across much of the forecast area. && .SHORT TERM...(This evening through Saturday) Issued at 158 PM MST Fri Dec 10 2021 RAP mesoanalysis and water vapor satellite indicate that the current trough axis is located over northeastern Colorado and is continuing to lift to the northeast. Gusty winds have developed this afternoon with strong northwesterly flow aloft, with a few gusts into the 45-50 mph range noted over the eastern Plains. While it hasn`t been as windy for the Denver metro, winds are slowly picking up, and there should be a brief window of 30-45 mph gusts as subsidence on the backside of the trough helps push some of these stronger gusts to the surface. Across the mountains, light orographic snow continues, particularly over the Park Range. Light snow will gradually taper off this evening and overnight, with just a couple of additional inches expected. With diminishing snow, we`ll allow the Warnings/Advisories to expire at 5pm this evening. Tonight will be mostly quiet and cold across the plains and urban corridor, with lows dropping into the low 10s to single digits. The usual cold spots like Limon could fall to near 0. Over the mountains, strong winds are likely to develop tonight as a mountain wave develops. Sangster forecasts are bullish with the win potential through Saturday night, though deterministic guidance shows more of a marginal event. The current forecast leans more towards the ingredients based approach and calls for warning-criteria gusts beginning tonight. We may see an initial burst of stronger gusts late this evening/early tonight corresponding to the mid- level subsidence crossing through the area, and thus we`ve pulled the High Wind Warning start time up to midnight tonight. Gusty winds should continue into Saturday evening. Otherwise, tomorrow will be quieter for most of the forecast area as zonal flow develops and temperatures warm up a bit. Highs should reach the 40s over the plains with 20s to 30s common for the high valleys. Outside our typical mountain wave clouds it should be a mostly sunny start to the weekend. .LONG TERM...(Saturday night through Friday) Issued at 158 PM MST Fri Dec 10 2021 On Saturday night a good bet of high winds continuing into Sunday morning for the mountains and Front Range foothills. Cross sections showing 40-65kt cross barrier flow along with mountain top stable layer resulting in a modest profile for an amplified mountain wave. In addition...hefty progged surface gradient of 13-17mb across the state through this period with local high wind program in the warning category. High resolution models showing peak winds in the 50-70kt range. Considering the above parameters will upgrade the high wind watch to a warning and will extend it further in time through Sunday morning. High resolution models (HRRR/WRF) showing peak winds 60-75kt range. For the later Sunday through Tuesday time frame; expect a return to dry conditions along with a warming trend through the period. The flow aloft will shift more southwest for Monday and Tuesday with temperatures bouncing back into the upper 50s/60s across the plains. The next significant system is expected to pass across Colorado sometime in the Tuesday night through Wednesday night time frame. There is some timing and amplitude differences amongst the models with the Euro/Canadian runs faster with less amplitude than the GFS. There is a chance of snow with this system, especially in the mountains but the bigger potential may be the wind. Especially given the GFS scenario with an ejecting closed upper low moving to the northeast across the state and deepening across Nebraska. QG omega fields showing very strong downward forcing of 40-60mb/hr rises while cross sections showing 50-65kt of cross barrier flow developing as the low kicks out northeast. Still positioning and amplification still in question so overall wind strengths will be quite varied depending on low positioning. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 846 PM MST Fri Dec 10 2021 VFR conditions expected throughout the TAF period. Moderate westerly winds are expected to weaken and turn towards drainage in a couple hours at DEN and APA. Winds will be light during the day tomorrow. As for BJC, there will be sporadic gusts up to 35 knots possible throughout almost the entire TAF period. Stronger winds will come and go. && .BOU WATCHES/WARNINGS/ADVISORIES... High Wind Warning from midnight tonight to noon MST Sunday for COZ033>036. && $$ UPDATE...Danielson SHORT TERM...Hiris LONG TERM...Entrekin AVIATION...Danielson
Area Forecast Discussion...UPDATED
National Weather Service Corpus Christi TX
1001 PM CST Fri Dec 10 2021 .DISCUSSION... Pacific front/dryline was near the northern Hill Country while the strong cold front was diving south over northwest Texas. Front still on pace to reach south Texas during the overnight hours. Colder air and stronger winds will arrive after daybreak Saturday. Adjusted temperatures to show non-diurnal trend behind the front. Scattered convection still possible over the coastal plains as the front moves through early Saturday morning. No changes with the current PoPs forecast. Elevated fire danger conditions will be possible over the Brush Country to the Coastal Bend as drier air and gusty winds linger over the region Saturday afternoon. && .MARINE...Moderate to strong south winds and elevated seas will continue over the offshore waters until 06Z. Timing of cold front still on track to move into coastal waters around 13Z with winds increasing to very strong with gusts to gale force after 16Z. Kept Gale Watch in place and let night shift make to decision to upgrade. May be able to keep the bays out of Gale Warning. No changes were made to PoP forecast with convection increasing with the cold front. && .PREV DISCUSSION... /Issued 555 PM CST Fri Dec 10 2021/ AVIATION...00Z TAFs Winds will diminish early this evening as the low level jet moves off to the east with the trough/dryline moving toward the region. Shallow moist layer will remain over the coastal plains in advance of the boundary. MVFR ceilings have persisted in the VCT area and expect will continue this evening. Stratus will develop over the Coastal Bend by 06Z with fog forming over the inland coastal plains as winds diminish. Expect MVFR vsbys will be prevalent but there could be IFR vsbys periodically until the winds shift. Expect the initial wind shift to reach COT by 07Z and CRP by 13Z. Stronger winds with the arrival of the cold air will occur around 15Z Saturday with winds gusting to near 30 knots over the coastal plains. There will be a brief period along and behind the front when showers (possibly a thunderstorm) could occur over the coastal plains. Then conditions will improve to VFR with ceilings around 5 kft lingering over the coastal plains through the afternoon. PREV DISCUSSION... /Issued 354 PM CST Fri Dec 10 2021/ SHORT TERM (Tonight through Saturday Night)... Big changes tonight and Saturday as a strong cold front moves across S TX. The cold front is currently moving south into the TX Pan Handle while a dryline is moving east across W and Central TX. The cold front is expected to surge south and southeast through the evening and is expected to reach the northwest portions of the CWA close to midnight. Models have been consistent in bringing a southwest to northeast oriented frontal boundary through S TX overnight, reaching Laredo and Victoria between 07Z to 10Z. The boundary is progged to reach the southern Coastal Bend between 10Z- 14Z. As the boundary approaches VCT, showers and a few thunderstorms are forecast to develop ahead and along the boundary, then more thunderstorms are expected to develop and spread southeastward with the front. The best chance for thunderstorms will be along the coast and over the gulf waters where moisture is deepest and instability is strongest. Models prog the strong capping inversion in place across S TX to diminish along the cold front. Moderate CAPE values around 1300J/kg across the Coastal Bend up to around 2400J/kg across the gulf waters are progged for tonight. Strong low level moisture convergence with the frontal boundary combined with increasing diffluence aloft as a strong upper jet sinks south and places the RRQ of the jet over S TX, will contribute to deeper convection. The combination of these features will be conducive for some storms to become strong along the coastal areas and across coastal waters. Gusts to around 40 mph are possible across the Coastal Bend. As the line moves across the coastal waters, gusts may reach 40-45 knots. The inhibiting factor will be just how quickly the cap weakens. Behind the cold front on Saturday, strong gusty north winds will develop and bring drier and cooler conditions into the area through the day. Could see the high temperature in the morning with falling temps during the afternoon. The Rap and HRRR show light precip behind the cold front with mid level clouds remaining across the area. This looks reasonable given that the main upper trough will be working its way across the region. Am expecting that any precip that does fall will likely be virga due to dry low levels. Skies finally clear out from northwest to southeast Sat night along with diminishing winds. This will enhance radiational cooling with lows expected to dip down into the upper 30s across the northern CWA to upper 40s along the coast and low 50s across the islands. LONG TERM (Sunday through Friday)... High pressure builds over the area Sunday and remains in place for the long term period. Onshore flow bringing increased moisture with PWAT`s around 1.40-1.50" combined with a developing coastal trough will increase chances for showers and thunderstorms Monday into Tuesday. Then on Wednesday a mid-level low over the Desert SW will slide off to the north east but not expecting a cold front to reach South Texas despite model discrepancy with this feature. Currently have slight PoPs extending from offshore inland over the Victoria Crossroads area, Thursday through Friday due to some isentropic lifting. Temperatures are expected to start the week in the 60s and warm back to the low to mid 80s for the week with lows near 50 also warming to the mid 60s. MARINE... Winds are expected to decrease to more moderate levels tonight with advisory conditions diminishing by midnight as a cold front approaches the region. Foggy conditions will be possible once again tonight over the bays and nearshore waters ahead of the advancing boundary. The cold front will be moving through the area early Saturday morning creating a strong to very strong offshore flow through the day. Frequent gusts to gale force are expected and a Gale Watch is in effect for Saturday across the bays and coastal waters. Scattered showers and thunderstorms will be possible late tonight, becoming numerous early Saturday morning as the front moves across the waters. Strong offshore flow will continue Saturday evening, with gusts to gale force expected. Conditions will improve late Saturday night and Sunday. Moderate northeast flow on Sunday will turn to onshore flow Monday and become weak to moderate. This flow will continue into the week. Isolated showers and thunderstorms will be possible Monday and Tuesday as a coastal trough develops along the Middle Texas Coast. && .PRELIMINARY POINT TEMPS/POPS... Corpus Christi 67 69 45 66 55 / 30 30 0 0 10 Victoria 60 62 39 65 49 / 50 10 0 0 10 Laredo 66 70 43 70 53 / 10 10 0 0 0 Alice 66 69 40 69 51 / 20 20 0 0 10 Rockport 64 68 43 66 57 / 50 50 0 0 10 Cotulla 61 66 40 71 49 / 0 0 0 0 0 Kingsville 69 70 44 67 53 / 30 30 0 0 10 Navy Corpus 68 69 51 67 60 / 40 60 0 0 10 && .CRP WATCHES/WARNINGS/ADVISORIES... TX...None. GM...Gale Watch from Saturday morning through Saturday evening For the following zones: Bays and Waterways from Baffin Bay to Port Aransas...Bays and Waterways from Port Aransas to Port O`Connor...Coastal waters from Baffin Bay to Port Aransas out 20 NM...Coastal waters from Port Aransas to Matagorda Ship Channel out 20 NM...Waters from Baffin Bay to Port Aransas from 20 to 60 NM...Waters from Port Aransas to Matagorda Ship Channel from 20 to 60 NM. Small Craft Advisory until midnight CST tonight For the following zones: Waters from Baffin Bay to Port Aransas from 20 to 60 NM...Waters from Port Aransas to Matagorda Ship Channel from 20 to 60 NM. && $$ TMT/89...SHORT TERM
Area Forecast Discussion
National Weather Service Des Moines IA
929 PM CST Fri Dec 10 2021 ...Updated for Near Term Weather Trends... .UPDATE... Issued at 929 PM CST Fri Dec 10 2021 No changes planned to the current warning and advisory. The deformation band of snow from Lincoln through our northwestern forecast area and up toward the Twin Cities is being aided by 700mb frontogenesis, which shows up well on the latest SPC mesoanalysis. RAP cross section along this shows the moderate lift with saturation through much of the dendritic growth zone. This lift will wane from southwest to northeast over the next 6 hours or so and the accumulating snow will be done by daybreak Saturday. Forecast has continued a slight northward shift with the snowfall amounts to better line up with the path of the deformation zone. Thus, blended in some HRRR time lagged QPF earlier this evening to lower snow totals slightly, but not greatly enough to change any headlines. With surface low pressure over southeastern Iowa now, winds across central Iowa are from the north or northwest and increasing. Gusts nearing 40 mph are occurring at EST with 25 to 35 mph gusts more common at this point across northern Iowa. Of course, these winds with falling snow will reduce visibility. Farther south, have also been monitoring visibility reduction under a mile due to areas of fog. Issued an SPS earlier this evening that will end shortly over south central Iowa and with winds increasing should also see visibilities come up above a mile. Lastly, have been monitoring the drizzle and near freezing temperatures here in the metro and points west. Concern has been for freezing drizzle with air temperatures near or just below freezing, but with road conditions from Iowa DOT ranging from 32F at Adair to the mid-30s in the Des Moines metro have not seen this materialize so far. && .DISCUSSION.../Tonight through Friday/ Issued at 325 PM CST Fri Dec 10 2021 Key Messages: -Significant winter storm impacting portions of the forecast area through daybreak on Saturday. -Dry and much warmer into early next week with possible record warmth by midweek. Surface low is currently across eastern Kansas and is continuing to deepen. Warm front across Missouri is surging northward in advance of the low and is approaching southern Iowa late this afternoon. It is likely to advance into the southeast prior to the surface low arriving. Therefore, temperatures are likely to continue to rise in the southeast late this afternoon and early evening prior to the arrival of the low. Visibilities have also fallen as dewpoints have continued to climb into the mid 40s and these reduced visibilities are likely to persist until the low passes this evening. In addition, some instability is likely to clip the southeast corner of the forecast area and have included a brief few hours of thunder when the low passes. The storms may also produce some small hail but the threat of severe weather likley passes just southeast of the area. Otherwise, cold advection is increasing in the northwest and this begins to overspread the area as the evening continues and the surface low moves into northern Iowa. Snow is expected to persist across the far northwest into tonight with the deformation zone eventually push east into the rest of central Iowa overnight. There may be some light drizzle or even freezing drizzle prior to the arrival of the deformation zone in central and southern portions of the state this evening but should transition to snow the column saturates. Overall amounts appear somewhat lighter with totals of 7 or 8 inches in the far northwest near EST to an inch in the southern portion of the advisory area. Winds become more north to northwest overnight and quite strong at 15 to 25 mph with gusts of over 30 mph at times. This will lead to poor visibilities, especially in areas that have over 2-3 inches of snow on the ground. At this time, blizzard conditions may occur briefly in the north, but a sustained period is not expected at this time and have left all headlines "As Is" at this point. The precipitation is expected to end around daybreak on Saturday as the system departs with the wind slowly diminishing through the day as the sun returns to most locations. Guidance continues to indicate a broad upper ridge developing across the central United States during the second half of the weekend into the middle of next week. This allows warm air to spread into the state as thermal ridging develops across the Plains. It remains plausible for record highs on Tuesday into Wednesday next week with Wednesday being the warmest day. Otherwise, a shortwave in the southwest US ejects rapidly into the Midwest later Wednesday into Wednesday night with associated surface boundary passing through the state during this time. Instability remains evident in guidance across the state by Wednesday afternoon, therefore the timing of the boundary through Iowa the possibility of convection at a given locations. Otherwise, cooler air arrives through the end of the work week but with readings still above normal for this time of year. && .AVIATION.../For the 00Z TAFS through 00Z Saturday evening/ Issued at 547 PM CST Fri Dec 10 2021 Nearly all reporting sites across central Iowa are IFR or LIFR and these conditions will prevail overnight as winds from the northeast early this evening rotate counter-clockwise and become from the northwest as they increase overnight. Snow will continue much of the night at MCW and FOD with blowing snow possible as the winds increase. A transition from drizzle or light rain to snow is expected at ALO and DSM near or after midnight. While it is low confidence and not included in the official TAFs, a short period of light freezing drizzle is possible at both sites dependent on liquid precipitation occurring as air and surface temperatures fall this evening. Conditions will improve into VFR Saturday morning with brisk winds from the northwest persisting through the day. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 6 AM CST Saturday for IAZ039-049- 050. Winter Storm Warning until 6 AM CST Saturday for IAZ004>007- 015>017-023. Winter Weather Advisory until 6 AM CST Saturday for IAZ024>028- 033>038-044>048. && $$ UPDATE...Ansorge DISCUSSION...Cogil AVIATION...Ansorge
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
704 PM CST Fri Dec 10 2021 .UPDATE... At 7PM the cold front was moving south through the Panhandle. A dry line extended from near Fort Worth all the way southwest to near Rocksprings and Del Rio. The cold front is forecast to accelerate southward late this evening moving through the CWA overnight, with a pre-frontal wind shift ahead of it. Latest HRRR runs still depict a broken, thin line of convection developing from just east of Austin south to near Seguin between midnight and 2AM, then quickly moving southeast into the Coastal Plains between 2AM and 5AM. Windy behind the front through the morning and into the early afternoon on Saturday, with some gusts up to 35 mph. Appears sustained winds will stay just below Wind Advisory criteria. Wind speeds gradually weaken late afternoon the fall off quickly after sunset and with cirrus shield exiting east this should setup good radiational cooling night. We have lowered low temperatures Sunday morning slightly, a blend of the previous forecast and the NBM 25th percentile. This will place all of the Hill Country in a freeze and potentially some drainage areas just south of U.S. 90 as well as east of I-35. A Freeze Warning is likely coming for the Hill Country by tomorrow. && .PREV DISCUSSION... /ISSUED 534 PM CST Fri Dec 10 2021/ AVIATION (00Z TAFs)... VFR conditions prevail across South Central Texas this evening. Guidance indicates MVFR ceilings may try and develop just east of an AUS-HYI-BAZ line 04Z-06Z, before being swept eastward overnight with the pre-frontal wind shift and cold front. Convective allowing models still indicate the possibility of a broken and thin line of convection developing east of I-35 and I-37 between 06Z-10Z. At this time it looks like SHRAs and TSRAs will remain east of AUS/SAT/SSF. Gusty north winds develop behind the cold front overnight and persist through the morning and early afternoon Saturday, then gradually weaken late afternoon. Wind gusts between 25-30KT are forecast in many areas. PREV DISCUSSION... /ISSUED 213 PM CST Fri Dec 10 2021/ SHORT TERM (Tonight through Saturday Night)... Skies have cleared out for the most part with just some scattered to clouds in the eastern half of the area as southwest flow prevails at the surface. This southwest flow will lead to an unseasonably warm today with possible record highs across the area. Temperatures are already into the middle 80s in some locations. A strong upper trough is passing through the Central Plains with the surface low in northeastern Oklahoma. As the system moves east, there should be a wind shift from the northwest that comes into the CWA this evening ahead of the actual Canadian cold front. This feature should lead to a thin line of showers and perhaps a thunderstorm for our eastern counties. There is a chance of a strong storm, if the convection is able to become rooted and sustained in the boundary layer but overall chances of this are very low. The actual cold front with the better drop in temperatures is expected to move into the area after 2 AM overnight and will be through the CWA by 8 AM. Winds behind the front during the morning will be in the 15 to 20 mph range with higher gusts. The wind speeds will lessen a bit as we progress through the day. This will help keep the period of strongest winds to not line up with the period with the lowest afternoon humidity. Therefore, think the western areas will only see elevated to near critical fire weather conditions, and do not think any headlines will be needed. For the eastern areas tomorrow, some mid-level moisture and lift will move overhead which could lead to some elevated showers, but the low- levels will be very dry and will not mention anything in the forecast at this time, but there should be at least some nice virga around. Highs tomorrow will be much cooler today, or about 25 degrees cooler than today. Winds are expected to weaken tomorrow night and skies should also clear. This could lead to the first freeze for a decent portion of the Hill Country, and portions of the I35 corridor away from the city centers. If the trends in the forecast, a Freeze Warning will likely be issued at a later time. LONG TERM (Sunday through Friday)... Sunday morning will start off cold with temperatures near freezing with an extension of the surface high overhead. This high will quickly move to the east, establishing southerly return flow across the area. Isentropic upglide over the retreating shallow cool air will result in cloudy skies and reduced diurnal heating on Monday, so morning lows will be quite a bit milder, but afternoon highs near or slightly below those on Sunday. The southerly return flow will deepen and strengthen through the week as another cyclone moves through the central Plains. This will bring a climatologically familiar pattern with a warming and moistening trend. Expect the return of morning fog and drizzle/showers by Wednesday, then continuing into Friday. A stalling front/boundary in the wake of the central Plains cyclone will end up along or north of our northern border Friday night into next Saturday, potentially bringing rain back into the area. However, this is too far in the future for more than low chance PoPs and relatively light QPF at this time. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 52 59 36 64 43 / - 0 0 0 0 Austin Bergstrom Intl Airport 51 60 30 64 40 / 10 0 0 0 0 New Braunfels Muni Airport 53 61 33 65 42 / 10 0 0 0 0 Burnet Muni Airport 48 57 31 64 42 / 0 0 0 0 0 Del Rio Intl Airport 55 66 38 67 44 / - 0 0 0 0 Georgetown Muni Airport 49 57 31 63 41 / - 0 0 0 0 Hondo Muni Airport 54 63 32 66 42 / - 0 0 0 0 San Marcos Muni Airport 52 60 32 64 41 / 10 0 0 0 0 La Grange - Fayette Regional 54 61 35 65 45 / 40 - 0 0 0 San Antonio Intl Airport 55 61 35 64 46 / - 0 0 0 0 Stinson Muni Airport 57 64 37 67 46 / - 0 0 0 0 && .EWX WATCHES/WARNINGS/ADVISORIES... None. && $$ Short-Term/Aviation...76 Long-Term...Brady
Area Forecast Discussion
National Weather Service Grand Rapids MI
1025 PM EST Fri Dec 10 2021 LATEST UPDATE... Update/Marine .UPDATE... Issued at 1023 PM EST Fri Dec 10 2021 Main concern tonight is the wind, but it is not the only concern. We considered upgrading to a High Wind Warning across portions of our area for Saturday, but in the end decided to hold off based on coordination and the latest guidance coming in. The 18Z 3km NAM was more bullish on winds reaching warning criteria, but the 00Z came in and backed off just a bit. It may have just nudged the winds south into the I-94 corridor. The HRRR remains fairly close to warning criteria gusts with each run. The area of most concern in the HRRR stretches from Grand Haven/Holland/South Haven northeast towards Mt.Pleasant/Lansing/Alma (essentially the heart of the forecast area). The HRRR is trying to indicate gusts in this area around 55 mph if not 60 mph. Bottom line the overnight shift will be looking into whether or not we need to upgrade anywhere. We did add the remainder of the CWA into the Wind Advisory, namely the counties that were not in the headline up along U.S. 10 across Central Lower Michigan. Most of the models are in the advisory range when it comes to the wind gusts, but its the higher resolution models that are the ones flirting with warning criteria. The message is certainly out that we are expecting high winds tomorrow. The winds will come up suddenly out of the southwest between 700 AM and 1000 AM on Saturday morning. The high winds will continue all day, backing off Saturday evening. We are still expecting the threat of thunderstorms tonight into Saturday morning. The highest MUCAPE values in the 500-1000 j/kg range nose up into our area between 100am and 1000am. Cannot rule out a few higher end gusts given the winds that are present in the profile. && .DISCUSSION...(This evening through next Friday) Issued at 300 PM EST Fri Dec 10 2021 - Wind Advisory for much of the CWA later tonight through Saturday Ensemble model trends have shown a lowering of the max wind gusts for this system tonight into Saturday. At this time only low confidence exists for a high wind warning event. That being said...this is a very anomalous event with intense winds showing up around 500 mb...topping 120kts 15z to 18z Saturday. Cross sections still show a trop fold event is likely to occur which could help this system reach a greater magnitude of impacts. This system will be strengthening on top of us...which will also result in some uncertainty as to the overall impact. We are going to start the headline up around 05z. We used this earlier time to account for the potential for high gusts with the bands of showers and storms that will be starting to move in then. Several models are showing 60 knots or higher winds not too far off the ground. With SPC showing a marginal day 1 risk for southern parts of the is possible that severe thunderstorm warnings could cover any short duration severe convective wind gusts. Either way...scattered power outages are expected with numerous outages still possible for later tonight through much of Saturday. - Period of snow Saturday afternoon/evening As the storm pulls away from the CWA the wrap around moist will be drawn in from the west. Temperatures will drop off quickly changing the rain to snow late in the morning into the afternoon. Models are showing the potential for 1 to 3 inches of snow. Road temperatures will be wet and relatively warm to start with the bulk of the accumulations expected on colder surfaces. It may struggle for surface temperatures to fall below freezing before the snow ends. For now we are not highlighting winter impacts with this system. - Considerable warmup for next week Deep warm air advection moves in for mid week. Temps at 850 mb are shown to climb above 10 deg C with 925 mb temps into the teens. It looks likely that temps will climb through the 50s and perhaps into the 60s. One limiting factor for how warm it gets could be the low clouds. RH forecasts for 925 mb show a surge of moisture lifting up from the Gulf and into MI then. The low cloud cover would limit the mixing heights and ultimately the max temperatures for the day. Just from advection alone though...well above normal temperatures are predicted. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 718 PM EST Fri Dec 10 2021 Significant winds expected at all TAF sites on Saturday. Winds will be strong for night time hours tonight as they veer from southeast to south-southwest. Tonight`s winds will be of the 15-30 knot variety. A stark and sudden increase in wind will be noted across the entire area between 700am and 930am Saturday morning. The strong winds will first be seen down towards BEH around 700am and then sweep north and east through LAN and JXN around 900am. Winds will increase to 20-30 knots out of the southwest with gusts into the 40-50 knot range. Wind gusts over 40 knots will be common all day on Saturday, with peak gusts nudging up towards 50 knots. Winds will shift from the southwest Saturday morning to more of a westerly direction Saturday afternoon, so north/south runways will have a significant cross wind. As for other aviation conditions, they will be equally as poor. Ceilings are in the process of dropping to the IFR and LIFR categories as of 700pm. These low ceilings will remain in place through roughly 100am. There may be some lifting of the lower ceilings across the southern TAF sites along I-94, but at best an improvement to only MVFR is expected. IFR and MVFR ceilings will be present most of Saturday with a rapid improvement to VFR towards 700pm. Rain showers will move through the area this evening, followed by scattered showers and possibly thunderstorms overnight. Precipitation will become mixed with and change over to snow during the late morning and early afternoon hours of Saturday. Bottom line...less than ideal conditions expected the next 24 hours with low ceilings and visibilities tonight, along with a chance for some thunderstorms, followed by significant wind on Saturday. && .MARINE... Issued at 1023 PM EST Fri Dec 10 2021 Maintained the Small Craft Advisory through 500 AM and the Gale Warning thereafter. Big Sable Point is already flirting with 30 knot gusts. Winds will ramp up significantly over the lake late tonight and continue throughout the day on Saturday. Solid high end gales to 45 knots are expected through the day on Saturday. The winds will be strong all day, not falling below gale force until into the evening hours, near or slightly after 700 PM. Could see the gale needing to be extended through 1000 PM Saturday evening. In terms of the waves, 10-15 foot waves look likely in most nearshore zones, which is typical of a high end gale. Highest waves per a local model run based on HRRR winds would be near Grand Haven towards sunset, in excess of 15 feet. It still appears lakeshore flooding issues should not materialize given the lower water levels. The FVCOM model is indicating water levels reaching the 580-581 range. Flooding issues starting above 582.50 feet. So, while there will likely be moderate beach erosion, flooding should not be a big concern. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Wind Advisory until 7 PM EST Saturday for MIZ037>040-043>046- 050>052-056>059-064>067-071>074. LM...Small Craft Advisory until 5 AM EST Saturday for LMZ844>849. Gale Warning from 5 AM to 7 PM EST Saturday for LMZ844>849. && $$ UPDATE...Duke DISCUSSION...MJS AVIATION...Duke MARINE...Duke
Area Forecast Discussion
National Weather Service Huntsville AL
813 PM CST Fri Dec 10 2021 .NEAR TERM...(Tonight) Issued at 813 PM CST Fri Dec 10 2021 Evening soundings indicate a very volatile atmosphere in place, although capped in our area at the moment. The combination of significant CAPE and strong bulk shear are exceptionally strong for this time of year over the region, especially over MS, AR, and western TN. Supercell and tornado indices from SPC all are indicating the potential for strong tornadoes if deep convection can develop, especially in northwest AL into middle TN. Earlier showers in northeast MS were not able to overcome the cap and intensify just yet without a significant forcing mechanism. Currently, a few showers are in northwest AL, but appear to be struggling as well. So we may be fortunate for the next several hours. A wedge was still holding in northeast AL where temperatures are still in the upper 50s. This will eventually be overcome by the very warm and moist flow further west. In contrast, KMSL was up to 73 degrees with a dew point of 68. Successive HRRR runs indicate that convection may be held at bay for several more hours until storms develop again in northern MS through western TN after 06Z, moving into northwest AL after 08Z. Wind fields may become more parallel with the line toward morning which may slow the progress of the line east into southern middle TN and north central AL along the I-65 corridor until after 12Z. Shear will remain quite strong, so the threat of severe weather remains once these arrive. So for now, really no significant changes made to the forecast. Will maintain the Wind Advisory as well. .SHORT TERM...(Saturday afternoon through Sunday) Issued at 247 PM CST Fri Dec 10 2021 Behind the cold front, the severe weather threat will come to an end by early Saturday afternoon as winds shift to the northwest. In its wake, strong cold air advection will result in a sharp temperature decrease as the mercury will plummet some 30-35 degrees from the mid 60s Saturday morning to the low to mid 30s by Saturday night into early Sunday morning. Clouds will be slow to clear initially Saturday afternoon/evening, but rapid clearing should occur by late Saturday night into Sunday morning as a drier air mass finally pushes in. High pressure will build into the region on Sunday, resulting in a mostly sunny, dry, and pleasant day. Northwest winds will make it feel quite chilly despite the sunshine with temperatures struggling to climb above the low to mid 50s. .LONG TERM...(Sunday night through Thursday) Issued at 247 PM CST Fri Dec 10 2021 Tranquil weather will continue through much of the upcoming work week as high pressure becomes established across the Deep South. Deep southerly flow will become established under this regime, resulting in a marked warm up as highs return to the mid to upper 60s with lows in the upper 40s to lower 50s. Overall, very pleasant weather for mid December with plenty of sunny, warm days to enjoy. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 439 PM CST Fri Dec 10 2021 Through most of tonight, ceilings will remain below 020agl at KMSL and northwest AL (MVFR), and below 010agl (IFR) in southern TN and northeast AL including. LLWS is also included as southerly flow rapidly increases this evening into the overnight. Isolated to scattered SHRA are possible, with perhaps a TS as well, so have kept VCSH ahead of the main line of TS. This line arrives toward 12-13Z at KMSL and 15-16Z at KHSV with the potential of strong to severe wind gusts. The cold front will shift winds to the west-northwest by 16-18Z with gusts of 25-35kt possible. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Wind Advisory until noon CST Saturday for ALZ001>010-016. TN...Wind Advisory until noon CST Saturday for TNZ076-096-097. && $$ NEAR TERM...17 SHORT TERM...AMP.24 LONG TERM...AMP.24 AVIATION...17 For more information please visit our website at
Area Forecast Discussion
National Weather Service Indianapolis IN
1012 PM EST Fri Dec 10 2021 .Forecast Update... Issued at 1012 PM EST Fri Dec 10 2021 ...Significant Severe Weather Event Ongoing/Evolving Across MS/OH Valleys Tonight... Rapidly strengthening low pressure is located near the Iowa/Illinois/Missouri border as of 9 PM EST. The low will continue to lift northeast, with a more favorable low level thermodynamic environment advecting into central Indiana over the next few hours. Some isolated to widely scattered prefrontal convection is currently over the area, but mesoanalysis indicates it is likely still elevated above a shallow stable layer, so marginally severe hail may be the most likely severe threat in the next hour to 90 minutes with the strongest cores that are also able to exhibit some midlevel rotation thanks to the extreme deep layer shear values. As the warm sector continues to expand into central Indiana, effective deep layer shear values of 50 to 80KT and significant to extreme low level storm relative helicity values in excess of 200- 400 m2/s2 will move into the area, along with the development of fairly significant (especially for the time of year) surface based instability around 500-1000 J/kg, and this will set the stage as expected for a significant damaging wind threat and an enhanced tornado threat as well, particularly across south central Indiana, as the southern end of the line appears to be remaining more supercellular at this time. This activity to our west appears to be the main threat for central Indiana, although some weak convective initiation appears to be ongoing across southern Illinois just ahead of the line that could complicate matters. For the moment, continue to expect the prime severe window to be through roughly 4 AM, although there remains the chance for a secondary wind threat immediately ahead of the front a bit later in the night. However, latest HRRR runs have been less aggressive with development along the boundary. && .Short Term...(This evening through Saturday night) Issued at 246 PM EST Fri Dec 10 2021 Quick Overview: --There will be a risk of severe thunderstorms, including tornadoes, this evening and overnight, with the greatest threat roughly between 10pm and 4am. --Impacts include; tornadoes, damaging winds (up to 80 mph possible), and a secondary risk of hail (in most cases not exceeding quarter size). --This will be a nocturnal event during a time of year that traditionally sees a low frequency of severe storms, so pre-event messaging and emphasis of the danger of overnight storms is important (see messaging section below). Forecast Challenges/Uncertainties: --Warm front position/timing, and where (how far north) specifically the low-level thermodynamic environment will be supportive of tornadoes. --Whether prefrontal confluence quasi-discrete activity can evolve into our area (conditional), or exclusively frontally-forced QLCS. --In the best case scenario, upstream initiation of pre-frontal discrete truly surface based convection and higher-end tornado threat occurs mostly south of the area, but damaging winds and QLCS tornadoes remain possible late tonight. --In the worst case scenario, upstream pre-frontal confluence zone initiates convection that remains at least quasi-discrete into our area and interacts with a rapidly destabilizing PBL, resulting in a more substantial tornado threat, followed by a QLCS wind/tornado threat later. Meteorological Analysis: We won`t belabor the synoptic scale pattern/processes as we`ve talked extensively about it the past few days. In short, a strong mid-latitude system with the surface low this evening, falling to 990-mb or below by late evening. Anomalously strong and moist southerly low-level flow is ongoing and will strengthen further. Our environment will rapidly transform through the evening. This will precondition the environment for deep/moist convection as forcing for ascent increases with the approach of the trough. Such rare/strong warm advection will result in a non-diurnal temperature curve today, with our high temperature being at midnight. The record for Indianapolis for 12/10 is 66, and may be approached around midnight. Tomorrow`s record high is also 66 and could be approached around and just after midnight. Some important details with the trough geometry are that it is positively tilted, and thus mean flow/deep shear vector orientation is aligned oblique enough to the cold front for linear evolution. For the linear convection along the front later in the night, we`ll be watching particularly closely for rear inflow jets and surges within the line as these reorientations are often where tornadoes are favored. From the apex of the bows northward is where concern is often highest for QLCS mesovortices and tornadoes. Also, it`s worth noting that winds aloft will be particularly strong and momentum transfer resulting in severe gusts will not be difficult to achieve, even with weaker convection. Preceding the QLCS threat, there is concern for open warm sector convection driven by pre-frontal confluence area (similar to the October 24th event in Missouri). These are usually linked to either the old Pacific front that has become diffuse at the surface, and/or the leading edge of stronger DCVA and its subtle surface reflection that may not be particularly baroclinic, at least relative to the aforementioned lagging primary front. Or, a subtle lead shortwave trough. The warm sector is broad and a 2m theta-e surge in tandem with steepening low-level lapse rates are seen in the models rapidly overspreading the area early-mid evening. This is a classic signature associated with many past nocturnal tornado events. Prior to this occurring, convection should be relatively weak and nontornadic, owing to a stable PBL north of the warm front. Nevertheless convection could become fairly widespread where isentropic ascent is maximized north of the warm front. However, a dangerous parameter space will evolve once the warm sector spreads into southern and central Indiana during the evening with strengthening low level jet, causing surface-based buoyancy to increase and support tornadoes. Further adding to the concern is hints of an elevated mixed layer and associated steeper midlevel lapse rates resulting in larger instability and stronger parcel acceleration and more robust convection. So, no argument that when coupled with strong deep layer and low- level shear values, the parameter space is favorable for severe storms and tornadoes this evening into the night. The concern then goes back to pre-frontal storm mode and evolution. We attempt to assess this potential below, but there remains uncertainty: Water vapor channel imagery shows a lead shortwave trough over northern Oklahoma with the main mid-upper trough now emerging from the central Rockies onto the High Plains. Pinning down the exact timing and magnitude of influence of this lead wave and/or CFA/prefrontal convergence to delineate a more focused corridor of concern is difficult. Hi-res guidance/HREF members reaffirm this uncertainty with varying depictions but most do show at least some pre-frontal development. More members than not are focusing this to our southwest, and perhaps into southern Indiana, and this would be along/near the favored 570-dm 500-mb height contour, which is old school but it often works. This suggests that portions of northeast Arkansas, southeast Missouri into southern Illinois, west Kentucky and far southwest Indiana will have greater concern than our area. Sometimes large convective blow-ups to our south can result in dynamic PV adjustment and locally enhance subsidence limiting convective potential. Even if this scenario were to happen, we shouldn`t minimize the threat in our area as again we will at least see some damaging wind and QLCS tornado potential with squall line during the predawn hours. Storm motions if prefrontal warm sector convection moves into our area will be east-northeasterly at around 60 mph, and eastward progression of the late night line of convection will be nearly as fast. Storms should be fairly progressive but could produce locally heavy rainfall amounts in portions of southern Indiana that saw heavy rainfall earlier in the week, with depressed flash flood guidance. Flooding isn`t expected to be a primary concern, but heavy amounts in areas that experience two or more storms could cause localized flooding, particularly where the ground is saturated. We will watch observational data closely through the late afternoon and evening upstream and once we see the character and expansiveness of upstream convection, we will be able to refine timing and speak more confidently about severe magnitude. Mesoanalysis will be critical later today and tonight. To Our Partners/Messaging: We`re asking our partners to help stress the danger of the overnight severe potential. There are only a handful of days per year we ask people to be particularly vigilant at night. Furthermore, December is outside of our typical severe season and so overall awareness may be low. Some ideas for items to stress today are to consider turning on WEA alerts on phones if they`ve disabled them in the past, check the status of warning devices such as weather radios and broadcast media/private apps (multiple ways to get warnings are key), charge devices ahead of time. Also, review sheltering plans, clean out closets for sheltering, etc. Emphasizing that storms will be moving fast (55-65 mph) and warning lead time could be a challenge, especially for any QLCS tornadoes. Thanks to our partners and your critically important roles, and please never hesitate to contact us directly if you need anything before, during, or after this severe weather event. Saturday and Saturday Night.... Precipitation... Around sunrise tomorrow morning, a strong cold front will pass through central Indiana, providing chances of thunderstorms for locations upstream (See Friday discussion for details on severe threat). Current high resolution models are indicating the front should be through central Indiana prior to noon EST. The near surface layer behind this front is significantly drier, and should limit any chances of wrap around moisture reaching the ground. Temps... Pre-frontal temperatures will be in the upper 50s to low 60s tomorrow morning. Following the passage of the cold front, temperatures will plummet 20+ degrees, resulting in afternoon temperatures near 40. Dew point temperatures in the 20s and clear skies should create an efficient environment for diurnal cooling, allowing temperatures to fall quickly Saturday night. This will lead to lows in the mid 20s; a shocking difference with temperatures 35- 40 degrees warmer just 24 hours prior. Winds... Near surface will increase significantly as well Saturday within the drier, cooler airmass. The low will be nearing an efficient cyclogenesis zone along a steep thickness gradient Saturday morning; of which should allow for sharp surface pressure falls. This will create a steep pressure gradient over the Great Lakes and Northern Ohio Valley. This in combination with an expanding PBL in the presence of increasing dew point depression in the late morning will provide prime conditions for high winds and wind gusts. Sustained winds should be between 20-30MPH for most of central Indiana tomorrow morning. Sounding analysis shows momentum transfer from around 2000 feet (just above the LCL), resulting in gust upwards of 50MPH in northern portions of central Indiana. && .Long Term...(Sunday through Friday) Issued at 246 PM EST Fri Dec 10 2021 A much quieter weather pattern will settle in for the latter part of the weekend lasting through much of the upcoming week as surface and upper level ridging dominate across the region. Winds will back to southwest as early as during the day Sunday with the center of the surface high passing through the Tennessee Valley. This will enable a return to a warm advection regime with mild temperatures quickly back in the Ohio Valley as early as Monday. Highs in the 50s will be common Monday and Tuesday with low to mid 60s again possible on Wednesday ahead as southerly flow intensifies ahead of another developing low pressure system over the central Rockies. The aforementioned low will intensify as it interacts with a sharpening upper level trough and tracks northeast midweek. One difference with this system versus the current one will be a track further to the north and west with forcing aloft displaced to the northwest of the region as well. The trailing cold front will bring showers and perhaps some thunder Wednesday night into Thursday with another cooldown to follow to end the week. But that being said...the cooler temperatures will be just much closer to normal for mid December than earlier in the week. There are some hints of the cold front getting hung up just south of the area next weekend which may lead to more unsettled weather and possibly a surge of colder air that may enable some snowflakes to mix in with rain. Ultimately...winter showing no signs of appearing across the region within the next 7 days. && .Aviation...(00Z TAF Issuance) Issued at 628 PM EST Fri Dec 10 2021 IMPACTS: * IFR or worse ceilings will continue this evening into the overnight, with fluctuations in both ceiling and visibility likely, particularly with thunderstorm activity. * Convection will develop later this evening and impact all terminals through the predawn hours * Southerly wind gusts will increase to near 30kts by late evening...higher winds possible in and near thunderstorms * Low level wind shear this evening into the overnight. * winds will veer to westerly with the cold frontal passage early Saturday: gusts at 30-40kts expected throughout much of the day Saturday Discussion: Poor flying conditions will be the rule this TAF period as rapidly strengthening low pressure pushes northeastward into the Great Lakes and drags a strong cold front through the area. Widespread restricted ceilings, primarily IFR or worse, are expected in the warm sector overnight, although there will likely be fluctuations in both ceiling and visibility, particularly in thunderstorm activity. Expect convection to continue to develop to our west and southwest this evening and begin to impact the terminals after about 03Z or so, and have used TEMPO groups to try to better define impact windows, although uncertainty remains in the high shear, relatively low instability environment. Surface winds are likely to become gusty in short order, although will still carry low level wind shear given extremely strong southerly/southwesterly flow just off the surface overnight. After the front passes late tonight into early Saturday morning, there may be a brief period where ceilings improve before widespread MVFR stratus redevelops. Winds will become quite strong on Saturday with gusts at times well into the 30KT to near 40KT range, strongest to the north. These gusts will dissipate very late in the period in typical diurnal fashion. && .IND WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 7 AM to 5 PM EST Saturday for INZ021-028>031- 035>042. && $$ Update...Nield Short Term...BRB/Updike Long Term...Ryan Aviation...Nield
Area Forecast Discussion
National Weather Service North Platte NE
922 PM CST Fri Dec 10 2021 .UPDATE... Issued at 922 PM CST Fri Dec 10 2021 Current radar trends and surface observations have indicated that the threat for accumulating snow has ended across western and north central Nebraska. Winds have diminished to 10 to 15 MPH with gusts up to 20 MPH noted at O`Neill and Broken Bow over the past hour. With the threat for accumulating snow ending and diminishing winds, will be canceling winter headlines for the area at 9 PM CT. Temperatures will be cold tonight, particularly in the west, where some limited clearing has occurred over the past hour. UPDATE Issued at 603 PM CST Fri Dec 10 2021 Recent satellite imagery indicates some drier air trying to work into southwestern Nebraska and the southeastern Nebraska panhandle over the past 1 to 2 hours. This has ended the snow threat across our panhandle counties and far SW Nebraska. However, radar returns over the past hour have increased over the sandhills into northern Nebraska. With the increasing radar returns and some support from the HRRR and NAMNEST reflectivity products, decided to extend a winter weather advisory across portions of the eastern Sandhills and north central Nebraska through 10 PM CT. The winter storm warning for Holt and Boyd counties as well as the winter weather advisory for Garfield and Wheeler counties will continue through midnight CT. Updated headlines and forecast has been sent out. && .SHORT TERM...(This evening through Saturday night) Issued at 410 PM CST Fri Dec 10 2021 The main forecast challenges heading into the weekend relate to the latter part of the winter storm and yet another big warmup. Winter weather headlines remain in effect for northern Nebraska as accumulating snow continues and extended the Advisory for Garfield and Wheeler through 06z. The western half of the headline area should be good to let expire at the planned 00z. In the wake of the storm, a broad upper ridge builds back into the Central US, allowing temperatures to rise well above normal (at least for those without significant snowpack). This evening and tonight... The surface low currently (as of 21z) over eastern KS zooms northeastward, reaching western MI by sunrise. The upper trough moves nearly as quickly with its axis passing through all of Nebraska by midnight and the ridge taking over by morning. The second main deformation band is underway, stretching from near KGLD to past KFSD. Extended PoP across central Neb to account for this activity. Could still experience some bursts of heavier snow, especially invof KONL where forecast soundings indicate decent lift and saturation within the DGZ. There`s also a window of 2-3 hours of an isothermal layer in the DGZ to really help bump of SLR`s and quick accumulation. Potential still exists for an additional 4-6" in Boyd and Holt Counties and 1-3" in surrounding areas. Farther west, expect continued waning of snowfall as isentropic downglide takes over and mid-level dry air filters in. However, there may be enough remnant forcing, especially near the Pine Ridge, for wrap-around snow showers. Some higher res solutions suggest this potential through 03z until the trough finally kicks out. Northerly winds will also be gusty due to rapid surface pressure changes with the departing low, strong H7-85 flow, and a nearby PV anomaly. Gusts will taper somewhat after sunset, but may remain high enough overnight to inhibit full boundary layer decoupling. Made some adjustments to the min temp forecast to reflect the recent deep snowpack, most notably extending the much colder lows around the Pine Ridge farther east. Forecast values in the single digits are a good 5-10F below guidance, which seem reasonable given eventual clearing of clouds. Reports from observers near KGRN and KVTN indicate 8-12" of fresh snow. In the southwest and mainly the river valley, dropped temps slightly in case winds relax enough. For central Neb, raised lows slightly due to later snowfall and slower clearing of clouds. Lows range from around 2F at KGRN to around 10F in the Platte Valley to mid teens north central. Saturday and Sat night... The upper ridge gains more influence over the High Plains, placing Nebraska into northwest flow. Meanwhile, a large surface high pressure system takes over with one centroid over the western Rockies and another in the southern Plains. These factors along with notable WAA at H85 will provide fair conditions and moderating temperatures, at least across southwest Nebraska where snowpack is minimal. Bumped up max temps along/south of I-80 into the lower/mid 40s, which is at the top end of NBM envelope but middle of MOS guidance. To the north, kept highs in the 30s where it will take some time to melt off 6"+ of snow. Wind will be rather gusty in the afternoon as the H3 upper jet passes by and drives some stronger flow into the mid levels. Downsloping west winds at H85 at 30kts will mostly mix to the surface, resulting in gusts of 25+ mph. The somewhat mild temps in the far southwest will actually drive humidity values down below 20%, and when combined with gusty winds, there is an elevated fire weather risk. Overnight lows will be another dance between warm air advection and southwest winds in the low levels, remnant snowpack, and mostly clear sky. For now, used a general blend with upper teens to lower 20s. .LONG TERM...(Sunday through Friday) Issued at 410 PM CST Fri Dec 10 2021 Next week, the main upper ridge spreads into the Eastern US and amplifies while a trough digs into the Desert Southwest. Some long range solutions close off a low and swings it right through the central Plains mid next week, accompanied by a rapidly deepening lee side surface low. This setup is big forecast concern as it will likely bring strong winds to western Nebraska and another chance of precipitation, some of it wintry. Some guidance hints at 50kt+ gusts on Wednesday, which would necessitate High Wind products and will definitely need to be monitored. The other big story is the warmup that comes with the ridge. Strong southerly flow and continued WAA will drive H85 temps to near 15C, which may translate to highs well into the 50s and even lower 60s. Fire weather concerns will also be heightened in the southwest where antecedent conditions are mainly dry and humidity values will be lower. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 525 PM CST Fri Dec 10 2021 Recent radar trends show enhancement with light snow filling in across central Nebraska. Expect this will keep conditions MVFR tempo IFR at both KLBF and KVTN for the first few hours of the valid period. May even see a brief period of LIFR vsbys at KVTN through 02Z. However, conditions will be improving rapidly this evening with snow moving off to the east and cigs rising to VFR before Midnight. VFR will then prevail through the end of the valid period. Winds will be gusty mainly at KLBF this evening. As skies clear and the surface cools quickly expect winds will decouple early tonight and bring an end to gusty conditions through the overnight period. Will see some gusts return Saturday afternoon but generally under 25kt. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Buttler SHORT TERM...Snively LONG TERM...Snively AVIATION...MBS
Area Forecast Discussion
National Weather Service Louisville KY
750 PM EST Fri Dec 10 2021 .Forecast Update... Issued at 750 PM EST Fri Dec 10 2021 Tornado Watch #554 has been issued for the western two-thirds of our CWA until 3 AM EST. Scattered pre-frontal convection has already developed across the lower Ohio/Mississippi River confluence and will quickly race northeastward into our western CWA within the next hour. The VAD wind profiler data from VWX/HOP radars have shown increasing low level wind shear resulting in very strong helicity in the lowest 1 km (resulting in >400 m2/s2). Model soundings along our far western CWA do show a bit of an inversion and farther east toward the I-65 corridor we are seeing that inversion show up on AMDAR soundings. RAP soundings over the next few hours show dew points slowly increasing west of I-65, which may be enough to allow those storms to become surface based when they move into the CWA. Do want to convey that we expect another Watch will be needed farther east in our CWA for the pre-dawn and around sunrise time frame, but that will likely come at a later time tonight. && .Short Term...(This evening through Saturday) Issued at 344 PM EST Fri Dec 10 2021 ...SIGNIFICANT EPISODE OF SEVERE WEATHER EXPECTED TONIGHT AND EARLY SATURDAY MORNING... ==================================== Synoptic Discussion ==================================== Deepening mid-level trough axis over the Plains will translate eastward this evening and overnight. The trough axis is forecast to remain positive to neutrally tilted as it moves toward our region. Initial mid-level vorticity lobe moving NE across KS/OK this afternoon will lead to initial convective development across MO/AR/WKY/WIN/SCIL as early as late this afternoon/evening. Deep tropospheric wind fields are expected to overspread the Ohio Valley along with a strengthening low-level flow that will transport deep/rich Gulf moisture northward into the region. The net result of this combination of increasing instability and shear will lead to a severe weather episode over the Ohio Valley tonight and early Saturday morning. Damaging winds in excess 60 MPH and isolated to scattered reports of tornadoes are expected. In addition, copious amounts of moisture will lead to heavy rainfall which may result in some minor flooding issues across the area. ==================================== Meteorological Technical Discussion ==================================== Surface warm front is rather diffuse this afternoon, but boundary looks to be crossing through the region at this time, based on band of elevated convection oriented from W/C IN southeast through eastern KY. This activity will continue to move to the northeast this afternoon. Once this activity clears out, we will be in the open warm sector with moisture advection continuing through the evening hours. Dewpoints are currently in the mid 50s across the region but are approaching 60 in our southwest areas. A stronger dewpoint surge is currently in progress out along the MS river and dewpoints have already risen into the upper 60s over far southwest Kentucky. In the near term, a mid-level short wave evident in the GOES moisture channel was moving NE across OK/KS. This feature will translate northeastward into the Midwest this evening. This feature will likely lead to initial convection firing over AR/MO/WKY/WTN and SCIL later this afternoon/evening. Further east over our area, continued moistening and theta-e advection will continue across our region. The front edge of a strong low-level jet axis will work northeastward into very lower part of the Ohio Valley. As this occurs, additional cooling aloft is expected to overspread portions of SWIN/WKY which should allow higher instability to develop as mid- level lapse rates steepen. These two items will also help erode the elevated mixed layer of warm air aloft and result in a possible uptick in surface based convection across our western CWA this evening. Given the parameter space, initial cells that develop will like be discrete/scattered and given the shear profiles a mix of multicell and supercells are expected. These storms will likely race off to the northeast at 55-60 MPH. Threats with this activity will be damaging winds, perhaps some marginally severe hail, and isolated tornadoes. Many members of the various short range ensemble models generally support this idea, i.e., more members that not. However, the eastward extent of pre-frontal convective development this evening remains uncertain due to unknowns involving how much of the EML will erode and whether surface based convective inhibition will remain. In general, the best chances of convective development this evening will be in areas along and west of the I-65 corridor. Later in the overnight, it appears that additional convection will develop given the instability and deep forcing resulting in more of a linear QLCS. Given the strong shear and substantial front- parallel components of the deep layer flow, downward momentum transfer should yield instances of wind damage within the convective line. Additionally QLCS mesovortices within the squall line where bows and surges develop may produce several instances of embedded tornadoes. This line will work through region during the late night hours and continue into our eastern sections after sunrise Saturday. The expected progressive nature of this line should result in generally short residence time of heavy rainfall over any one particular area. Additional QPF information may be found below in the Hydrology section of the discussion. We will continue to monitor observational data closely this afternoon and evening especially upstream. As cells develop and the convective evolution becomes more certain, we will be able to update our timing and speak a bit more confidently with regards to the possible magnitude of this severe weather event. ==================================== Important Messaging ==================================== As we have mentioned over the past 24 hours, we want to stress the danger in the overnight severe weather potential. Historically, tornadic and widespread severe weather events in the month of December are rare, although we`ve had a couple of events in the last 10 years (12/2013 and 12/2015). We would like to emphasize the following topics: 1. Have multiple ways to get warnings overnight. Leave your cell phone on and have WEA alerts turned on. Check the status of your weather radio and make sure it is functioning. Charge/replace batteries in your alert devices. 2. Review your severe weather plans for your household. Review where your lowest level interior rooms in your home are and have space ready in there to shelter. Put as many walls as you can between you and the outside of your home. If you have a basement, make sure a shelter space in an interior room or under substantial framing is available and ready in the event of a warning. Stay away from exterior windows and doors. 3. If you live in a mobile home, consider finding a more substantial shelter this evening with friends and/or family. Even in non- tornadic winds, gusts of 60+ MPH can easily flip mobile homes whether they are tied or bolted down. 4. These storms will be moving quickly with speeds of 55 to 60 MPH. Warning lead time on these storms could be a challenge especially involving mesoscale vortices within the anticipated squall line. ==================================== Forecast Confidence ==================================== Tornado Threat: West of I-65: Medium-High East of I-65: Low-Medium Wind Threat: High confidence across our region Flooding Threat: Medium confidence across our region .Long Term...(Saturday night through Friday) Issued at 320 PM EST Fri Dec 10 2021 After an stormy start of the weekend, the latter part of the forecast will certainly be more relaxed. Ejecting upper wave will give way to anomalous ridging aloft and surface high pressure for the easternmost two-thirds of the CONUS. Meanwhile, upstream flow will feature a series of digging troughs which will slowly advance towards the central US by midweek, eroding the high-pressure dome. Sunday-Monday... Morning temperatures both days will be below freezing thanks to a combination of CAA and radiational cooling. Afternoon highs will gently move from the upper 40s on Sunday to the lower 50s at the start of the work week. A dry air mass in place secures clear skies and plenty of sunshine as the surface high pressure moves to the Mid Atlantic states and an West Coast trough moves to Central Plains. Tuesday-Wednesday...The aforementioned large scale configuration imposes a southerly wind and accompanying increased theta-e advection. As a result, temperature readings will progressively climb and the forecast reflects maximum temps around the upper 60s south of the Parkways by midweek. Expect winds to start picking up on Wed with gusts in the 10-15 mph range while cloud coverage spread our area. Thursday-Friday...As the Central Plains trough progresses to the Midwest/Great Lakes region, it pushes an attendant cold front to the Ohio Valley. However, strong ridge aloft anchored over the SE CONUS will inhibit further southward momentum of the baroclinic zone, therefore, it could stall south of our area or right above us. There is still some timing uncertainty with this evolution as noted in the WPC mid-level EOF cluster patterns. That being said, there is increasing agreement for warmer temps on Thursday which could result in record high low for SDF. The latest NAEFS ESA guidance has 850-mb temps around the 90th climo percentile. Winds gusts will be blowing from the southwest around 15-20 mph on Thursday as the front sweeps by central KY and diminishing by Friday. Finally, precipitation is boosted for the end of next week and probably next weekend with the frontal passage and subsequent stalling nearby. This scenario is also reflected by the slight risk of heavy precipitation delineated by CPC during the Dec 17-20 timeframe as return flow from the GoM leads to high rain chances. && .Aviation...(00Z TAF Issuance) Issued at 649 PM EST Fri Dec 10 2021 IMPACTS: - Low stratus early this evening with scattered showers - Southerly winds increase become gusty tonight - Gusts tonight and overnight of 30-35kt - Strong to severe thunderstorms moving through overnight - Strong/gusty southwest to west winds will be seen on Saturday behind a cold front DISCUSSION: A strong storm system will approach and pass the region during this TAF cycle, strong & impactful storms, gusty gradient winds, low ceilings at times. In addition, the most intense thunderstorms will briefly reduce visibilities below 2 SM. For the evening and overnight period, we expect scattered convection to develop over the next 1 to 2 hours across western KY and southwest Indiana. After scattered storms (some supercells), these storms are expected to organize into a well developed squall line that will race across the region. While not explicitly defined in the TAFs, localized gusts over 50kts can be expected in this line in some areas. Additionally wind fields aloft are very strong and LLWS is expected at all the terminals this evening and into the overnight period. Convection should clear the terminals around or just after sunrise Saturday however, scattered rain showers and gusty southwest to westerly winds are expected throughout the day. CONFIDENCE: Medium-high on all elements. && .Hydrology... Issued at 320 PM EDT Fri Dec 10 2021 Deep, moist SW flow characterized by PW~1.5" is being advected along the warm sector ahead of an amplifying upper-level trough. Attendant cold front will swing through our area Friday night/Saturday morning bringing a strong-to-severe line of thunderstorms. Heavy rain from this event might provoke localized flooding and river flow rises, especially streams that experienced flow peaks during the last event. Current forecast package is considering QPF in the 1-1.5" range associated with the main frontal passage. Meanwhile 3-hr FFG sits between 2-3" area-wide and the 0-40 cm soil moisture is still average per the latest NASA SPORT analysis. Therefore, rainfall should be largely managable giving minimal runoff. Additionally, HREF 1-hr probabilities for QPF greater than 1" is less than 20%, which aligns well with the progressive nature of the system. Only problem for stagnant water is in poor drainage areas and low-lying locations. WPC still manintains a Marginal Risk (1 out of 4) of excessive rainfall due to the strong linear forcing, theta-e advection, and any localized areas of training convection given the alignment and strenght of the LLJ and the cloud-layer mean wind. Another factor to consider is the antecedent hydrological conditions of rivers that experienced flooding/rises this past Monday and respond quicly to short periods of heavy precipitation, such as: Rochester Ferry, Paris, Peaks Mill,and Boston. Other rivers worth monitoring during the next 24 hours per the lastest AHPS/HEFS forecast are the Green and White Rivers. It is important to mention that the OHRFC does not expect any widespread risk of significant river flooding. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...BJS/DM Short Term...MJ Long Term....ALL Aviation...BJS Hydrology...ALL
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
953 PM CST Fri Dec 10 2021 .MESOSCALE DISCUSSION... Issued at 952 PM CST Fri Dec 10 2021 Warm front has surged north and lies roughly from Chicago west- southwest to southern DeKalb/northern LaSalle County. Modifying recent ACARS soundings from MDW for observed T/Tds in the warm sector over our CWA suggests there is a weak near surface inversion present with very weak instability. Despite the minimal instability and weak inversion near the surface, the strongly forced convection is taking full advantage of the extreme low and strong deep layer shear. Have seen transient circulations developing within the small short line segments. Have also seen some near severe/isolated severe gusts with these short line segments, which isn`t surprising given 50kt winds about 1500ft agl on the KLOT VWP. Over the next 1-2 hours, storms should continue moving eastward into northwest IN and into a very similar environment that they are in now. Given this, not anticipating much if any weakening. Primary threat should continue to be locally damaging wind gusts. While there is a weak near surface inversion, the extreme shear and strong dynamics suggests that the subtle inversion could be overcome with more intense convection. Will need to closely watch for any transient circulations or developing mesovortices for tornado potential over the next hour or two. - Izzi Issued at 655 PM CST Fri Dec 10 2021 No significant updates early this evening as we continue to monitor upstream convective trends as well the evolution of low- level thermodynamics ahead of and along a warm front over central Illinois. At this point, the rapidly develop convection west and northwest of St. Louis is of most interest as the associated airmass quickly advects NE into central Illinois over the next few hours. The potential for surface-based convection into the CWA remains unclear even at this hour. Near-term CAMs still show variability in overall convective evolution, but the fairly consistent trends in the HRRR along with reasonable depiction of how convection has developed thus far supports leaning more toward its guidance for this evening. Our greatest severe threat will likely be tied to any upscale growth/congealing of the recent convection in northeast Missouri. Any mature convective line will have the capability of punching stronger winds through any existing shallow inversion, and may even have enough micro/mesoscale dynamic influence on the environment to weaken existing near-surface stability immediately ahead of the line. Additionally, recent convective growth with some surface-based potential in southeast Iowa indicates low-level stability can quickly be overcome within this dynamic environment. Even more, gravity wave packets within the significant shear across the frontal inversion have been evident on radar this evening. these features can be of concern for convective initiation or potentially helping to bring down stronger winds with any slightly elevated convection. With all that said, concerns for severe convective winds into the CWA, primarily south of I-88, remains warranted through at least midnight, with the greatest focus in the 9pm-midnight period. The potential for local thermodynamic modification by any mature convection bears close monitoring for low- level rotation under any enhanced updrafts, especially south of the Illinois/Kankakee River Valleys. Kluber && .SHORT TERM... Issued at 320 PM CST Fri Dec 10 2021 Through Saturday... Multi-faceted hazards into Saturday with the strong storm system impacting the region, including: * Dense fog threat into early evening * Thunderstorms and associated severe threats later this evening into the early overnight * Strong winds from the southwest to west pre-dawn Saturday through the early afternoon * A period of wind blown mainly light snow Saturday morning for portions of northern Illinois Regarding the going Wind Advisory, main change was to expand the Advisory to include Winnebago, Boone, Lee, and Ogle Counties, in effect from 3 AM to 12 PM. [Dense Fog] After the visibility improvement in the late morning, starting to see visibility creeping back downward for locales south of I-80 and also deteriorating visibility on webcams in downtown Chicago. As the warm front sharpens into the early evening, we may well need to issue a new Dense Fog Advisory that could also include counties farther north. May need to start with some initial counties in an advisory in the near term (within next hour or two) if trends continue and then assess from there. [Thunderstorms and Severe Threat] Lead warm advection wing showers spreading east-northeast as of this writing have had isolated embedded thunder, so have included slight chance/isolated wording over the next few hours with this activity. Shifting to the severe weather threat tonight, SPC outlook 20z update maintained the level 3 (Enhanced) risk into areas south of US-24, with no changes on northward extent of level 2 (Slight) and level 1 (Marginal) risk areas that were expanded northward earlier this morning. As can best be gleaned from guidance trends and plausible scenarios, there is solid agreement in robust deep moist convection initiating in the early to mid evening (00z-02z) near the MS River and then quickly tracking east-northeastward. Then toward through a few hours after midnight immediately ahead of the sharp system cold front, there is another window of thunderstorms. See below for more details, but in summary, the evening round could be mainly elevated but have a wind threat. Window for surface based severe threat would be tied to the 2nd potential round, with this also having a damaging wind threat and possibly a brief tornado threat. All in all, the presence of sufficient MUCAPE tonight for a high shear low CAPE setup amidst very strong dynamics and kinematics supports the level 1-3 risks from SPC. And speaking of the shear and low level SRH, it is extreme as you`d expect for a wintertime setup. We`re still not in the realm of mesoanalysis for the local area yet being well north of the warm front, but there continue to be some key elements to watch as the warm front advances northward. An exceptionally juicy (upper 60s-lower 70s Td) air mass resides in the open warm sector in AR, far southern MO, and TN. The 60F isodrosotherm has pushed to or just north of the latitude of St. Louis as of this writing. Guidance varies on how far north the 60F+ dew points get this evening, and HREF CAMs currently have a decent handle, so it`s too soon to say which guidance is on the right track, though we did lean toward the slightly more aggressive HRRR. Also have questions on how much if any role the existing fog/very low stratus bank has on evolution of the air mass and available instability this evening. Would think that initially prior to stronger pressure falls, the fog would somewhat inhibit northward advance but then quickly strengthening southerly flow aloft should advance it northward. If anything, the existence of this very low cloud cover and obvious low level inversion may shorten the time window in which severe weather is possible this evening/tonight. A consistent item seen in poring through model forecast soundings south of the warm front this evening is a pretty distinct low level inversion around 900 or 925 mb. This seems to be tied to the extreme warmth at 925 mb (+17C at LZK/Little Rock and +16C at SGF/Springfield MO) set to advect over our area. Most recent SPC/RAP Mesoanalysis shows +15C isotherm at 925 mb reaching KSTL. Even with the unseasonably warm and moist air mass in the warm sector, this magnitude of warmth at 925 mb is not being overcome by surface warming through the bulk of the evening. This leaves low-level inversion in place and providing rather large SBCIN except for maybe a very short 1-2 hour window where that capping can be overcome. As mentioned earlier, the likely evening round, depicted as a QLCS type or mixed with semi-discrete supercells on some recent HRRR runs, quite possibly could remain mostly elevated. Temperature trends will need to be closely monitored, as observations being just a few degrees warmer would lessen the inversion. The above being said, think the modeled low level inversion does present uncertainty as to the magnitude and mode of the severe threat within the CWA. At this time, think the primary threat will be damaging winds in QLCS storm mode during the evening, as the tremendous momentum aloft could be mixed down through the inversion (perhaps not in a widespread manner). Suspect that any tornado threat would be mainly of the QLCS variety, though it`s tough to say how that antecedent low level inversion would play into the tornado threat. In low topped supercell storm mode, decent likelihood of discrete/ semi-discrete cells remaining elevated may limit severe threat aside from rear-flank downdraft punch and perhaps marginally severe hail. Then overnight (~05z-08z), immediately ahead of and along the front, strong low level advection could help the environment recover for a short 1-2 hour window of a surface based severe threat, per consensus on forecast soundings. SPC outlook is a reasonable approximation of the relative threat during this time as well, with points south more favored. Confidence is a bit lower by this time, as we`ll need to see how much the air mass gets worked over, and if the threat truly becomes surface based. We may also start to see some drying and rising LCL heights at this time, suggesting that perhaps damaging wind threat will be primary again. The tornado threat, while certainly not one to completely discount given the extreme low level shear profile, is low confidence. Needless to say, and to reiterate, observational trends will need to be closely monitored this evening, as to how well the models are handling the temperature profile and dew point surge. In addition, ILX will be launching a special RAOB sounding at 02z or 03z, which hopefully will help get a better handle on the environment that will be in place in the mid-late evening. For the 00z sounding, they will still be north of the warm front. Finally, the cold front sweeping across the area toward and beyond 09z will end the convective threat and shift our attention to the strong southwest to west winds. Castro [Wind and Wind-blown Light Snow Threat Saturday] Intense pressure rises on the order of 12+ mb/6 hrs coupled with strong cold air advection and a 50 to 60 kt low level jet aloft will generate strong winds late tonight through early Saturday afternoon. This will be as the surface low deepens into the low- mid 980s mb over central Lake Michigan by 12z Saturday. Forecast soundings indicate that winds of 45 to 50 mph are expected to be mixed down to the surface across the CWA, with a potential for gusts to exceed 50 mph right on the leading edge of the rapid onset of CAA with pressure rise/fall couplet, as well as in the deeper mixing during Saturday morning. The strongest gusts and best chance for ~50-55 mph gusts (and non-zero threat for 60 mph gusts) are most likely across the southeastern half or so of the CWA, but recent forecast guidance does support gusts around 40 to 50 mph occurring in Winnebago, Boone, Ogle, and Lee counties late tonight through Saturday morning. Because of this signal, the wind advisory starting at 3 AM CST on Saturday has been expanded to include Winnebago, Boone, Ogle, and Lee counties until noon on Saturday. The rest of the area will remain under a wind advisory until 3 PM CST Saturday afternoon. The winds will slowly begin to ease late Saturday afternoon and throughout the evening with gusts around 15 mph expected Saturday night. The strong short-wave trough axis will be pivoting overhead Saturday morning, so during this time, still looks like a flip to mainly light snow is plausible near and north of I-80 and especially for northern tier where highest PoPs are. Model soundings vary on how deep saturation gets, with some models pretty dry in DGZ and some sufficiently saturated up to -12 to -13C. This suggests that the snowflakes will be poor quality/small. Temperatures will crash to the lower-mid 30s behind the cold front, with profile quickly becoming snow supportive, so the main question is the aforementioned saturation depth. Given such mild temperatures late tonight ahead of the cold front, think that road accumulations are pretty unlikely and main impact would be reduced visibility. Can`t rule out some slick spots on elevated surfaces, with accumulation primarily a coating to a few tenths on grassy surfaces. The precipitation will end by mid day, with clouds quickly eroding west to east yielding sunny breaks before sunset. Castro/Yack && .LONG TERM... Issued at 123 PM CST Fri Dec 10 2021 Saturday night through Thursday... Forecast thinking has not changed during the period. Please reference the previous discussion below for details. The main forecast point of note in the long term is the pronounced warmth next week, with all days looking to be above normal and a period midweek with 20 to 25 degrees above normal, including possibly a record high on Wednesday and warmest December day in several years (at least since 2017). As has been the case for several weeks, the upper air pattern this coming week remains notably progressive across the country, even with strong synoptic lows and highs. For the latter half of this weekend, a 1030 mb high south of the area will be scooting quickly to the east. This will keep the CWA under the pressure gradient on its north promoting breezy southwest winds on Sunday. Both Sunday and Monday should be sunny as well, and support highs near 50. Monday may even overperform given 850-925 mb temperature climatology for this time of year and the dry air mass. Have leaned toward warmer guidance as has been the forecast trend for this period. Neither of the days stand out as a fire weather concern based on the stronger gusts on Sunday and lower relative humidity values being on Monday. On Tuesday into Wednesday, an upper level ridge will build northward through the Great Lakes, with highly anomalous heights values at 500 mb. Deep low pressure in the lee of the Rockies will strengthen over the northern High Plains area. A warm front will approach and then lift north of the area, replacing the dry- ish air mass that starts the work week with a very moist one for this time of year on Wednesday. Tuesday should see increasing mid and high clouds at least as warm front lifts north, so temps may be similar if not a degree or two warmer than Monday in spots. Increasing pressure falls Tuesday night will result in increasing southerly winds and rising temps, providing a springboard for Wednesday`s near record or record warmth. It will be windy with southerly gusts up to 30-35 mph, with strong surface advection of the warmth and moisture. At least low-mid 50s Td appears likely and any higher would increase upside potential for high temps. Conceptually, this pattern still continues to favor low stratus due to strong south-southwesterly flow. With isentropic ascent from strong WAA, could even see some sprinkles or drizzle break out. The 850 mb temps of at least 10-15C are still shown for Wednesday and this again is near top of the charts for December, so with all the above factors in play, comfortable with the 61-66F range from the NBM. Daily record high on Wednesday (12/15) for Rockford is 58F and is 64F for Chicago, both set in 1971. Strong south- southwesterly winds look to result in a positively spring-like Wednesday night likely not dipping below 50F ahead of the cold front. Uncertain timing of the cold frontal passage will dictate how warm temps get until the frontal passage, with mid-upper 50s in current forecast. Should be a band of strongly force showers, possibly even with a few storms with the front, so chance PoPs in gridded forecast appear reasonable, though would be shorter-lived than in the current blend-provided, broad-brushed grids. MTF/Castro && .AVIATION... For the 00Z TAFs... Concerns for the near term include low cigs and vsbys in the rain shield ahead of an approaching center of low pressure. Current values are not quite as low across the area as expected earlier, so elected to bump the initial vsbys up to MVFR in the 3 to 5 mile range. Thunderstorm chances are not great early this evening, but do ramp up somewhat as midnight approaches, more for the Chicago terminals than RFD, and with MDW and GYY probably favored a bit more than ORD and DPA. Winds veer from easterly early this evening to southerly by later this evening, around to southwesterly by midnight, then to the west during the morning. The flip from south to southwest toward midnight will be accompanied by a significant increase in speeds and gusts as a cold front pushes through. These magnitudes are expected to persist through late morning and very gradually subside during the afternoon. Before the surface winds increase this evening, and before they really ramp up behind the front in the early overnight hours, winds riding over the stable surface layer will be quite strong, so we have maintained a mention of LLWS. The last item to mention is the chance of some light snow toward mid-morning as an upper level wave of energy behind the low swings across the area. At this time this is not expected to produce much more than flurries, but there could be a brief period of vsby reductions. Lenning && .MARINE... Issued at 123 PM CST Thu Dec 9 2021 ...Higher end westerly gales Saturday morning... A strong and deepening low pressure system will track northeast over the southern half of the lake very late tonight through Saturday morning. Ahead of this system, southerly winds will be blowing near or into Small Craft Advisory this evening into early overnight before the cold front arrives. Also in the hours ahead of the cold front, convection is likely, and some of this will potentially be strong and mix down winds in excess of 35 kt. After the cold front passes around 3-4 A.M., solid westerly gales of 40-45 kt will occur with continued high confidence. A few storm force gusts may even materialize during Saturday morning. Winds will slowly ease during the afternoon into evening on Saturday. No major changes have been made to the going forecast, and thus the Gale warning remains in effect from 3am through 3pm Saturday. MTF/KJB && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Wind Advisory...ILZ005-ILZ006-ILZ011-ILZ012-ILZ013-ILZ019-ILZ020- ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-ILZ104-ILZ105- ILZ106-ILZ107-ILZ108...3 AM Saturday to 3 PM Saturday. Wind Advisory...ILZ003-ILZ004-ILZ008-ILZ010...3 AM Saturday to noon Saturday. IN...Wind Advisory...INZ001-INZ002-INZ010-INZ011-INZ019...3 AM Saturday to 3 PM Saturday. LM...Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...3 AM Saturday to 6 PM Saturday. Small Craft Advisory...nearshore waters until 3 AM Saturday. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
640 PM CST Fri Dec 10 2021 .UPDATE... Issued at 640 PM CST Fri Dec 10 2021 A narrow band of intense snow stretches from New Ulm, to the southern Twin Cities metro, eastward to New Richmond and approaching Ladysmith. It is within this band rates are now 1 to 2 inches per hour. The band is nearly stationary and is pivoting as the system advances to the east. Increased QPF within this corridor to highlight the mesoscale heavy snow band. Amounts have already reached 6 inches in places in the south metro and it`s highly likely now that some will exceed a foot by late tonight. Farther to the south, while radar may be some beam overshooting some of the more intense echos, visibilities also indicate the snow isn`t as intense there. Didn`t change too much in those locations yet, but it`s expected the heaviest totals will be along the aforementioned axis farther north. && .DISCUSSION...(This evening through Thursday) Issued at 141 PM CST Fri Dec 10 2021 Key Messages: Winter storm remains on track to cause significant travel impacts across parts of Minnesota and Wisconsin. 1) Periods of 1 inch per hour snowfall rates likely late this afternoon and evening under the heaviest band. 2) Totals of 8-12" likely within that band of snow by the time the snow ends late tonight into Saturday morning. 3) Northerly winds of 20 to 30 mph will lead to some blowing and drifting snow. TODAY AND TONIGHT`S WINTER STORM - No significant changes from the previous forecast. The Upper Level wave driving this system was located over Nebraska. An area of isentropic ascent and frontogenesis developed along the thermal gradient ahead of this wave. Snowfall amounts under this band will be in the 8 to 12 inch range, with locally higher amounts near 14 inches possible. HREF guidance shows high probabilities of snowfall rates of at least an inch per hour, with some signal for 2 inches per hour. The intensity of the snowfall is probably going to be the most impactful part of this storm. Some thundersnow is possible as the system develop later this evening. The snow should quickly dissipate from west to east overnight. Another aspect of the storm is the northerly winds. The surface low drops from 994 to 987 mb as it tracks from Kansas up towards southern Wisconsin. This strengthening system will support stronger surface winds, but the cold air advection never moves across southern the region. As a result, winds will be breezy, with easterly gusts near 25 mph, and northwesterly gusts near 30 mph, but they should top out around there. That means areas of blowing and drifting snow, but not expecting blizzard condition. The reduced visibility will be more so a result of the aforementioned snowfall rates, and less a result of blowing snow. In summary, HiRes guidance from the early afternoon runs of the HRRR did reduce the QPF across the Twin Cities metro, but there is enough other guidance such as the HopWrf and HREF that maintains a band of 8 to 12 inches of snow. SATURDAY AND SUNDAY - A few lingering snow showers are possible across western Wisconsin on Saturday morning, but otherwise expect dry conditions with mostly sunny skies. Highs on Saturday will be in the upper 20s to near 30 with light westerly wind. On Sunday there will be a few clouds in the sky, and surface winds will be more southwesterly. This will lead to warmer temperatures, with highs on Sunday in the mid 30s across the region. SUNDAY NIGH THROUGH WEDNESDAY - The forecast looks rather quiet. We`ll see zonal flow aloft develop on Sunday where downsloping flow on the leeside of the Rockies will warm 850 mb temperatures in the Central & Northern Plains. This will promote broad, subtle ridging across the central CONUS early next week. The warmer 850 mb temperatures signal that warmer temperatures are likely early next week, as a majority of the guidance continues to show. The new snowpack has warranted a slight downward adjustment for temperatures early next week across southern Minnesota, but the warmth will eventually prevail on Wednesday. The ridging becomes more pronounced Tuesday afternoon into Wednesday as low-level southerly flow develops across the Plains. This occurs in response to an amplified trough over the west coast. With the southerly flow contributing to strong WAA into the Northern Plains, forecast models suggest 850 mb temperatures of at least 10C across the CWA Wednesday. As such, some models have highs Wednesday approaching (or even exceeding) 60 at MSP. This highlights the potential of a highly anomalous pattern with potential record breaking temperatures across the region. We`ve opted to go cooler, with highs only in the upper 40s and lower 50s on Wednesday. As the aforementioned trough travels east into the central CONUS, models depict a surface cyclone rapidly developing somewhere over the Plains. This system travels northeast Wednesday into Thursday but, spread between low track and timing within the models is still high. It seems like we could have another chance at precipitation mid-next week but exact placement, timing, and type of precip remain large questions. More certain is cooler weather following the low to close out the end of next week with a return to near-normal temperatures forecast. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 640 PM CST Fri Dec 10 2021 Moderate to heavy snow continues across southern/eastern MN into WI for the next several hours. LIFR conditions expected, but a quick improvement to VFR will occur soon after the snow ends. Clearing skies for Saturday with northwest winds shifting southwest in the afternoon. KMSP...Snow rates of 1 to 2 inches per hour will continue through 03-04Z, then intensity will slowly taper off in the late evening and overnight. /OUTLOOK FOR KMSP/ Sun...VFR. Wind SW 5-10 kts. Mon...MVFR/IFR in BR/FG possible. Wind E 5 kts. Tue...MVFR/IFR in BR/FG possible. Wind SE 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...Winter Storm Warning until 6 AM CST Saturday for Blue Earth-Brown- Carver-Dakota-Faribault-Freeborn-Goodhue-Hennepin-Le Sueur- Martin-McLeod-Nicollet-Ramsey-Rice-Scott-Sibley-Steele-Waseca- Washington-Watonwan. Winter Weather Advisory until 6 AM CST Saturday for Anoka-Chisago- Isanti-Sherburne-Wright. Winter Storm Warning until 3 AM CST Saturday for Redwood-Renville. Winter Weather Advisory until 3 AM CST Saturday for Chippewa- Kandiyohi-Meeker-Yellow Medicine. WI...Winter Storm Warning until 6 AM CST Saturday for Barron-Chippewa- Dunn-Eau Claire-Pepin-Pierce-Polk-Rusk-St. Croix. && $$ UPDATE...Borghoff DISCUSSION...BPH/JRB AVIATION...Borghoff
...Updated Aviation Forecast Discussion...

.DISCUSSION... Issued at 306 PM CST Fri Dec 10 2021 The well-advertised winter storm was in progress across the area this afternoon, with the primary snow band stretching from central NE into northeast NE and southeast SD and northwest IA as of 3 PM. In addition, some drizzle had developed across eastern Nebraska and western Iowa, though latest road temperatures across said area were still in the upper 30s to lower 40s. However, the colder air is certainly make progress southward, with many spots dipping down toward freezing, and KOFK and KTQE showing some light ice accumulation. Given current road temperatures, not anticipating much in the way of widespread ice accumulation prior to snow, though still could see some light glaze in some spots, especially on untreated and elevated surfaces such as bridges and overpasses. Going forward, surface low pressure was analyzed over central KS and will continue its track northeastward this evening, with the primary precipitation band continuing to overspread the area. CAMs continue to suggest potential for a narrow enhanced band of precipitation to the southeast of the main deformation band, which would likely move through southeast Nebraska during the evening commute. Looking in a bit more detail, 10.18Z RAP guidance does show the presence of a frontogenesis/frontolysis "couplet" at 700 mb, which would suggest the CAMs are on to something with that heavier band. Model soundings do show a shallow dry layer that would need to be overcome for snow to occur, but given the strength of the forcing, would think there should be no problem switching to snow rather quickly. In addition, with the CAMs hinting at some convective elements, could see some sleet at times. Finally, should this heavier band play out, surface temperatures would likely cool slightly faster than previously thought, meaning any wet roads could become slick with ice and/or accumulating snow that much faster. Certainly a small scale feature to keep a very close eye on late this afternoon into early evening, especially with gusty winds and temperatures cooling rather quickly below freezing. As it stands, not much change with snowfall amounts along the main deformation band, with totals of 5 to 8 inches in far northeast Nebraska. Amounts will be less as you go south and should largely be less than 1 inch south of I-80. The main questions on snowfall totals remain tied to that aforementioned small-scale banding. Did already increase amounts by an inch or so within that band, but may need to further increase them this afternoon. In addition, may need to eventually expand the Winter Weather Advisory slightly farther south, but confidence in southern extent of that band is not very high at this time. Snow should exit east of the area shortly after midnight with skies clearing out and setting up for a rather sunny weekend. Temperatures should top out in the 30s and 40s Saturday followed by 40s and 50s Sunday. Large scale ridging will then build in for the first part of the work week, with temperatures increasing to perhaps record levels Tuesday (50s and 60s) and Wednesday (60s to around 70). While raw model output is quite warm for Wednesday, there is pretty good agreement of a fairly potent shortwave trough moving through sometime Wednesday/Wednesday night, which could lead to increasing clouds or precip which would impact our temperatures. In addition, that system could bring some rather diverse weather across the area, with potential for widespread strong winds, snow in part of the area, and perhaps some thunderstorms in another part. Plenty of time between now and then to work out the details, but it does look like it could be our next chance for impactful weather in the forecast area. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 509 PM CST Fri Dec 10 2021 There likely is patchy freezing drizzle at KLNK with temp of 32, but transitioning to snow by 00z. And it`s 33 with drizzle at KOMA, and freezing drizzle may not develop there. Otherwise, IFR conditions with snow at all TAF locations, along with northerly winds at 18 to 26 knots. Snow tapers off by 04-07z, and sky conditions eventually become VFR by 07-09z. Gusts diminish by 09-12z. Storm total snow at KOFK around 2-3", 1-2" at KOMA, and around an inch at KLNK. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory until midnight CST tonight for NEZ015- 018-030>034-042>045-050>053-065-066. Winter Storm Warning until midnight CST tonight for NEZ011-012- 016-017. IA...Winter Weather Advisory until midnight CST tonight for IAZ043- 055-056-069. && $$ DISCUSSION...CA AVIATION...DeWald