Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/10/21

Area Forecast Discussion
National Weather Service La Crosse WI
958 PM CST Thu Dec 9 2021 .UPDATE... Issued at 955 PM CST Thu Dec 9 2021 A dynamic forecast continues to transpire for Friday afternoon`s and night`s winter storm as increasing CAM guidance arrives. Major changes to the headlines included the backing up of the warning/advisory for much of the day on Friday as the available CAM guidance all tracks the leading def zone precipitation wing further to the north, leaving much of the area dry through the early to mid afternoon. Added Clayton and Fayette to the advisory as the loss of ice in the dry slot and ongoing surface CAA may lead to the development of freezing drizzle late Friday night. May need to add Grant County as well, but confidence in impacts was not as high given the longer persistence of the warmer surface airmass. Also nudged the warm nose further north with the continued northward shift in the track, with the threat for freezing rain knocking on La Crosse`s door Friday evening. Finally, added the mention of thundersnow to the forecast with a solid region of negative EPV or even pure upright instability noted in CAM/CPM soundings within the band of heaviest snow. && .SHORT TERM...(This evening through Friday night) Issued at 205 PM CST Thu Dec 9 2021 Attention squarely focused on the upcoming winter storm. Water vapor satellite shows the system taking shape over the Desert Southwest and this will take a northeast track coming across the region with a positive tilt Friday night. The precipitation looks to be focused in the three time frames, initial band comes in Friday morning, second looks to be later Friday afternoon into the first part of the evening followed by a third round late Friday evening into the overnight. The first round looks to be primarily forced by a band of moderate mid-level frontogenesis in the 750-600 mb layer that comes across central/southern Minnesota into northern/central Wisconsin. The second round looks to have the strongest period of forcing with it. Another band of moderate to strong mid-level frontogenesis looks to take shape in the 750-500 mb layer, positioned a bit farther south over southern Minnesota into western and north-central Wisconsin. This lift from this frontogenesis will be aided by strong up glide on the 285K isentropic surface along with good jet dynamics in the right entrance region of the a departing 300 mb jet streak and in the left exit region of the next incoming jet streak. This is when the 09.12Z HREF probabilities for greater than one inch an hour snowfall rates jump into 70 to 90 range with a small signal for some rates to exceed 2 inches an hour. This round of forcing looks to be off during the mid-evening hours only to be replaced by yet another mid-level frontogenesis in the 700-550 mb layer late Friday evening which again looks to mainly be over southeast Minnesota into western and north-central Wisconsin. The HREF also shows some potential for this band to hourly rates in excess of 1 inch but the probabilities are lower, generally in the 20 to 30 range. The heavy snow band will set up underneath this round of forcing with the highest confidence of amounts exceeding warning criteria from southeast Minnesota into western and north-central Wisconsin. Some potential that there could also be some convective snows in the heavy snow band with the RAP showing a bit of slantwise instability above the frontogenesis bands. If this were to occur, the potential for hourly rates to exceed to 2 inches will jump up dramatically. South of the main snow band, the precipitation types get to be a bit more dicey. Forecast soundings show a distinct warm nose aloft working in that would be enough to cause partial to complete melting. This will set up a zone of mixed precipitation where some sleet and freezing rain could occur. Output from the HREF does suggest the possibility of some minor ice accumulations across northeast Iowa into southwest Wisconsin. The Winter Storm Watch has been converted over the warnings and advisories this afternoon. Much of the watch along the Iowa/Minnesota border in the Interstate 90 corridor in western Wisconsin has been upgraded to a warning. Band of heaviest snow is expected from about Dodge County Minnesota over the Clark County Wisconsin where some totals could exceed a foot. Farther south, the watch has been upgraded to an advisory for a few counties in northeast Iowa and southwest Wisconsin where snow amounts will not be as high but a better potential for the wintry mix to occur. .LONG TERM...(Friday night through Thursday) Issued at 205 PM CST Thu Dec 9 2021 Taking a quick look out into next week, there looks to be the potential for another storm to impact the region around the middle part of the work week. Current indications suggest this system will take a more northwest track putting the local area into the warm sector. The 09.00Z NAEFS indicates the potential for temperatures at 700 and 850 mb to be 1 to 2 standard deviation above normal which would push surface temperatures in the 40s and 50s. Some spots could even reach the lower 60s! This system also looks to have the potential to bring a pretty good slug of moisture with it. Again looking at the NAEFS data, both the precipitable water and specific humidity could be in the 4 to 5 standard deviations above normal range. At this time, looks to be a warm, rainy system falling on top of the existing snow pack. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 533 PM CST Thu Dec 9 2021 An initial band of 600 to 700 mb frontogenesis will produce some light snow at KRST by 10.16z. The snow will then pick up intensity between 10.20z and 10.22z. Snowfall amounts by evening will be in the 2-4 inch range. Most of this snow will fall after 10.20z. The total snowfall amount by Saturday morning will likely range from 9 to 13 inches. Meanwhile, at KLSE the snow will likely not accumulate until after 10.21z. Snow amounts between 10.21z and 11.00z will likely range between 1 and 2 inches. May also have watch for a wintry mix, but confidence was not high enough to include at this time. he total snowfall amount by Saturday morning will likely range from 5 to 9 inches. If more of wintry mix occurs, these totals may be on the lower end. Once the snow starts to accumulate, ceilings and visibilities will quickly become IFR/MVFR. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Weather Advisory from 3 PM Friday to 6 AM CST Saturday for WIZ054-055. Winter Storm Warning from 3 PM Friday to 6 AM CST Saturday for WIZ041>044-053. Winter Storm Warning from noon Friday to 6 AM CST Saturday for WIZ017-029-032>034. MN...Winter Storm Warning from 3 PM Friday to 6 AM CST Saturday for MNZ095-096. Winter Storm Warning from 9 AM Friday to 6 AM CST Saturday for MNZ079-086-087. Winter Storm Warning from noon Friday to 6 AM CST Saturday for MNZ088-094. IA...Winter Weather Advisory from 3 PM Friday to 6 AM CST Saturday for IAZ010-011-018-019-029-030. Winter Storm Warning from 3 PM Friday to 6 AM CST Saturday for IAZ008-009. && $$ UPDATE...Skow SHORT TERM...04 LONG TERM...04 AVIATION...Boyne
Area Forecast Discussion
National Weather Service Denver/Boulder CO
836 PM MST Thu Dec 9 2021 .UPDATE... Issued at 808 PM MST Thu Dec 9 2021 Water vapor shows a steady plume of moisture going over western Colorado which is producing snowfall in the mountains this evening. The forecast for the mountains remains on track with the Park Range and Rocky Mountain National Park receiving the highest totals. There is plenty of clearing from South Park to Denver to Sterling and areas southeast this evening with no snow expected through much of the night. A cold front will move southward out of Wyoming overnight tonight which will eventually moisten the low levels. The latest model guidance has come in drier than the previous runs on the CAMs. The HRRR barely shows an upslope component to the wind across the I-25 corridor and has basically no snow accumulation for that area. The NAM and NAM Nest have taken away snowfall in the 00Z runs. On the contrary, the 18Z global ensembles continue to have 80-90 percent of the members showing accumulating snow at DIA. In summary, the upslope flow looks bleak for the I-25 corridor to receive snowfall but a jet streak overhead with ample moisture aloft will typically produce something in our area. PoPs were lowered slightly across the Denver metro and Palmer Divide tomorrow morning but the overall forecast of a trace to inch of accumulation remains the same. There is low confidence in whether the snowfall will impact the morning commute but the chance of poor travel conditions in the morning seem to be decreasing. && .SHORT TERM...(This evening through Friday) Issued at 241 PM MST Thu Dec 9 2021 A strong moist southwest flow aloft ahead of an upper level trough over California will bring heavy snow to the western and northern mountains tonight. Based on water vapor satellite imagery and radar, best moisture is just arriving to the northern mountains. An additional 8 to 16 inches are expected for the northern mountains. Over the Park range in western Jackson county an additional 2 feet of snow will be possible. The I-70 corridor east of Vail Pass will be somewhat sheltered from the heavier snowfall while southwest flow aloft prevails. The upper level trough weakens and quickly moves eastward overnight. Once the trough axis shifts east of the mountains, better orographic lift will prevail for the I-70 corridor. Light snow fall is expected to prevail for most of Friday under west to northwest flow aloft. Will continue with the Winter Storm Warning for the northern mountains. For the mountains east of Vail Pass, the Winter Weather Advisory will remain in effect where 4 to 10 inches of snow will be possible. If traveling in the mountains tonight and Friday expect snow covered roads and hazardous travel conditions. For the foothills, Urban Corridor, and eastern plains, expect cloudy skies, but dry conditions to prevail for most of the night. A cold front pushes south through eastern Colorado after midnight, ushering in colder air for Friday. The air behind the front will be cold enough for all precipitation to fall as snow. Lift from the trough, right entrance region of the jet, and upslope slope flow is expected to produce a period of snow Friday morning. Snowfall amounts are expected to be light with most locations seeing less than an inch. Could see a little more snow along the Palmer Divide. Northern areas from Fort Collins to Fort Morgan could miss out on the snow due to the northerly downslope component off the Cheyenne Ridge. .LONG TERM...(Friday night through Thursday) Issued at 241 PM MST Thu Dec 9 2021 Mountain snowfall will continue to wind down through the overnight hours with west/northwest flow aloft. A few of the favored northwest aspects in the Park Range could pick up another couple of inches of snow overnight with little to no additional accumulation elsewhere. Most snow should end by about midnight as a large area of subsidence spreads across the region. Gusty winds will continue across the high terrain tomorrow night with perhaps a weak mountain wave developing in the 40-50kt cross-barrier flow. An upper level ridge will begin to build this weekend as a drier pattern returns. Temperatures will rebound a bit on Saturday with highs in the upper 40s across the plains, aided by light downslope westerly winds. Cooler air should stay trapped across the high country with highs still in the upper 20s to low 30s for the mountain valleys. Gusty winds are likely to continue for the higher elevations with some gusts up to 50-55 mph possible. We should return to a pattern of well above normal temperatures Sunday through the first half of next week. A robust ridge is expected to develop across the Central Great Plains/Mid- Mississippi Valley region by the start of next week. 500mb Heights from the NAEFS and ECME are above the maximum values in climatology across those areas for a remarkably long period of time. On our side of the ridge, warm southwesterly flow will lead to temperatures reaching the low 60s both Monday and Tuesday. By mid-week uncertainty in the forecast increases substantially as a potent trough approaches from the Pacific coast. Models are in good agreement that this trough axis should arrive by Wednesday, but beyond that details are hazy. The overall pattern would favor a quick moving snowfall across the western slopes while most of the plains stay dry. The main impacts across the Front Range and plains would likely be winds. The 12z GFS reflects a higher end wind event across the forecast area with a nearly textbook setup for a strong mountain wave with a stout stable layer just above the ridgetop along with 70-110kt cross barrier flow between 700mb and 500mb. The position of the trough is less favorable among the other global models, but at the very least the potential for strong winds/elevated fire danger should be watched closely over the next few days. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 808 PM MST Thu Dec 9 2021 Ceilings will lower after a cold front moves through around 9-10Z tonight. There may be some snow showers that develop behind this front from roughly 12-16Z but the chances of this seem to be lowering. The biggest impact during the afternoon will be strong northwesterly winds that develop with gusts up to 38 knots possible. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 PM MST Friday for COZ034. Winter Storm Warning until 5 PM MST Friday for COZ031-033. && $$ UPDATE...Danielson SHORT TERM...Meier LONG TERM...Hiris AVIATION...Danielson
Area Forecast Discussion
National Weather Service Cleveland OH
939 PM EST Thu Dec 9 2021 .SYNOPSIS... High pressure will move off the east coast overnight as an upper level system moves through the upper lakes. Low pressure will develop over the Central Plains on Friday and deepen and track into the northern lakes Friday night and Saturday. High pressure will build into the region early next week. && .NEAR TERM /THROUGH FRIDAY NIGHT/... Starting to see some indications of patchy dense fog and low stratus developing late tonight into Friday morning as low level moisture significantly increases with warm air advection. The best chance of dense fog will be in western and southern zones where winds may become light enough for fog development. Will need to monitor for potential fog related headlines overnight, but opted to only mention the hazard in the HWO until confidence increases. A more optimistic outcome will occur if winds do not decrease overnight. No other changes needed with this update. Previous Discussion... Rather abrupt changes are expected in the weather during this period with a quick warm up with storms followed by rapid windy cooling on Saturday. Into Friday we can expect rather quiet weather as high pressure moves off the east coast and a southerly flow prevails. A short wave will lift northeast of the Great Lakes this evening. Very light precipitation associated with this feature will move through the area this evening with a little precipitation which is mostly aloft that may produce a few sprinkles or flurries. Once that feature lifts to the northeast our attention focuses on the developing low pressure over the plains that is expected to deepen and move into the Great Lakes Friday night and Saturday. Very strong wind fields are associated with this low pressure. Initially warmer and increasingly humid air will be drawn into the region Friday night with dewpoints rising to 55-60F by Saturday morning. Modest amounts of CAPE in the 200-400 J/KG range with rather intense wind shear is expected from 06Z to 12-15Z ahead of a cold front that is expected to sweep east through the region on Saturday. SPC extended the risk of severe weather northward into the southwest portion of the region and that looks reasonable. Some experimental guidance that processes the HRRR model called the NCAR Neural Network convective Hazard Forecasts indicates a high likelihood of severe weather across the western and central part of the CWA before 12Z Saturday and over the eastern third of the area between 12Z-15Z. There is some potential for tornadoes given the high shear low CAPE situation. Following the cold front passage, cold advection will overspread the region with rapidly falling temperatures from the 60-65 degree range. Strong winds will mix down to the surface and a wind headline will likely be needed post frontal for several hours. The showers and storms will quickly exit the region after the frontal passage and there could be more precipitation toward dark as temperatures drop into the 30s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... After analyzing the latest 18z high resolution model guidance, we have issued a High Wind Watch for the lakeshore areas of northern Ohio Saturday morning through Saturday evening. The potential of damaging wind gusts up 60 or 65 mph is increasing along and behind a cold front on Saturday. The highest wind gust threat will be closer to the lakeshore and on top of hilly terrain. Previous Discussion... Post frontal environment leaves the region in diminishing winds as the low pressure system lifts out to the northeast and the front heads for the east coast. As strong as the system was, being Pacific in nature, the cold air advection will not be all that impactful. Temperatures on the back side will be in the 40s for the most part, and there will be a noticeable lack of lake effect. Skies clear and winds continue to subside into Sunday night as high pressure builds to the south over the Ohio Valley. && .LONG TERM /MONDAY THROUGH THURSDAY/... Upper level ridge begins to build over the northern Gulf Coast into the middle of next week, signifying increasing heights into our region and resulting in a warm up once again. Models indicating disturbance riding around the top of the ridge, and will see low POPs enter the picture. There could also be a warm front during this period of time as well extending from the next surface low developing in the lee of the northern Rockies. Thursday temperatures could be pushing the 60 degree mark again. && .AVIATION /00Z Friday THROUGH Tuesday/... VFR conditions continue for the next several hours, but expect southerly flow to usher a surge of moisture into the local area overnight into Friday. Deteriorating ceilings will spread northeast across the area after around 06Z tonight. Low stratus and fog will likely produce IFR to LIFR ceilings and visibilities at KTOL/KFDY/KMFD for much of the day Friday, and can`t rule out similar conditions at KCLE/KCAK for the same timeframe. Showers will begin to move northeast into the area on Friday evening, but the best chance of rain will likely occur after the TAF period. Winds will generally be out of the southeast at 8 to 14 knots tonight, but western terminals may become more light and variable overnight. Winds become southerly to southwesterly on Friday. Will need to monitor for some gusty downslope winds to 25 to 30 knots at KERI overnight into Friday morning. LLWS may develop towards the end of the TAF period, but not confident enough to add into this update. Outlook...Non-VFR likely in showers/storms Friday evening into Saturday morning. Strong wind gusts are expected with the approach and passage of a cold front on Saturday. && .MARINE... Gale Watch and Storm Watch Saturday into early Saturday night. Offshore wind flows ahead of the next frontal system, which will quite powerful as it approaches the region. Winds really begin to ramp up Friday night in the warm sector where winds will veer from SE to SW. Cold front expected to enter the western basin after 15Z Saturday, and will have exited by 21Z Saturday. There will not be much of a notable wind switch with the passage of the front, but sustained 20-25kt winds ahead of the cold front will become greater than 40kt sustained winds in the wake of it for Saturday afternoon into early Saturday night. As mentioned, Gale Watches in effect, and a Storm watch for the eastern basin of Lake Erie. Waves in the central basin eastward are expected to exceed 12ft, possibly as high as 18ft. Waves fall below 10ft basin wide after 06Z Sunday and winds below 20kts by 12Z Sunday. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...High Wind Watch from Saturday morning through Saturday evening for OHZ003-007>012-089. PA...High Wind Watch from Saturday afternoon through Saturday evening for PAZ001. MARINE...Gale Watch from Saturday morning through Saturday evening for LEZ142>144-162>164. Gale Watch from Saturday morning through Saturday evening for LEZ145>148-165>168. Storm Watch from Saturday afternoon through Saturday evening for LEZ149-169. && $$ SYNOPSIS...LaPlante NEAR TERM...LaPlante/Maines SHORT TERM...26 LONG TERM...26 AVIATION...Maines MARINE...26
Area Forecast Discussion...UPDATED
National Weather Service Gray ME
957 PM EST Thu Dec 9 2021 .SYNOPSIS... A weak disturbance will bring some very light snow to the region on Friday before we await a more significant system...which will arrive on Saturday. This storm will bring a period of freezing rain that will change to rain as temperatures warm during the day Saturday. Temperatures will continue to warm Saturday evening before a cold front sweeps through the area Saturday night with gusty winds and seasonably mild temperatures for Sunday. Temperatures remain above normal through much of next week with dry weather expected through Wednesday. && .NEAR TERM /UNTIL 7 AM FRIDAY MORNING/... Update...Currently a rather robust looking regional radar mosaic showing the narrow band of snow forecast to cross the area tonight is not doing a whole lot at the surface. It is a struggle to find many automated obs of snow...let alone any appreciable accumulation. However snowfall is forecast to pick up in intensity...especially E of Lake I do not see any reason to deviate significantly from the previous forecast. The best chances of snow amounts approaching 1 inch will be in the mtns where upslope may enhance lift and along the Midcoast where some ocean effect may work inland for a time as flow reverses. Previous discussion...A few scattered instability flurries and snow showers will diminish soon after sunset, except across the mountains where they`ll likely linger into the evening. High clouds from our next system are already moving into southwest New Hampshire, and will continue to progress across northern New England overnight tonight. Temperatures will mostly fall this evening and then stabilize once the cloud cover thickens. Northern and eastern areas will be the last to see the clouds arrive, and are therefore expected to be the coolest. Warmer air is already starting to move in aloft, and this trend will continue through the overnight hours. With this warm air advection, a band of light snow will likely progress northeastward into New Hampshire toward daybreak. Overall the best chances for snow are across northern and western New Hampshire overnight tonight where snow showers are likely, with decreasing chances toward the Seacoast. && .SHORT TERM /7 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... The band of snow showers will continue to progress into Maine tomorrow morning. Precip will mostly shut off across New Hampshire by mid morning. Accumulations near an inch are possible across northern areas and the higher terrain, but elsewhere generally a half inch or less are expected. The band of snow showers will progress through Maine during the daylight hours tomorrow morning. Similarly to New Hampshire, accumulations near an inch are possible across the northern areas of Maine, while generally lighter amounts are expected elsewhere. The one exception to this may be along the Maine MidCoast. High res guidance on the NAM 3km and HRRR has consistently been hinting at some ocean enhancement of snow along parts of the MidCoast. A weak area of convergence offshore will likely serve as the focus for some ocean effect snow showers. With the difference between sea surface and 850mb temps between 17C to 20C tomorrow morning, greater than the 13C absolute instability benchmark, it looks likely that these snow showers will develop. Whether or not they make it onshore is the biggest question, but there is fairly good agreement among the high res guidance that they will as winds turn onshore. This would enhance the snow totals along parts of the MidCoast, with the Camden Hills area standing the best chance to pick up 1-2 inches of snow. Also during the day tomorrow, cold air damming looks like it will begin to dig in its` heels across the region. After an initial push of mild air off the ocean sends temps into the upper 30s along the coastline, light northerly winds from high departing high pressure across the Canadian Maritimes will likely thwart the warm air and keep temperatures locked in the 20s and low 30s from late tomorrow afternoon through the overnight hours. During the initial warm up some light rain and snow showers are possible near the coast, but by the overnight hours tomorrow the precip types will likely become either rain, freezing rain, or sleet. A dry period is likely later tomorrow afternoon into the overnight hours. But after midnight more showery precipitation is likely to begin moving in and bring some light mixed precipitation after midnight. Chances will continue to increase toward daybreak Saturday morning as the cold airmass gradually moderates toward freezing. Overall precip amounts greater than a few hundredths will likely hold off until daybreak on Saturday, but some light coatings of ice are possible before this time, especially across southern New Hampshire. && .LONG TERM /SATURDAY THROUGH THURSDAY/... High Impact Weather Potential: * A period of freezing rain primarily Saturday morning will bring travel impacts. * Gusty winds late Saturday night into Sunday. * No significant weather impacts beyond Sunday. --Pattern and Implications-- Strong jet over the eastern Pacific early this afternoon /+EPO/ with little downstream blocking east of the region /+NAO/ will allow for a progressive pattern through the long term forecast period. +EPO correlates to warmth over the northeastern United States given the ample amount of Pacific air that will be present over the lower 48 and that is evident in the deterministic and ensemble guidance which favors at or above normal high temperatures throughout the entire long term forecast period. As for sensible weather...pretty much the entirety of the weather impacts will come to open the period Saturday and Saturday night as a Great Lakes low pressure system passes well north of the forecast area dragging a cold front through the region Saturday night. High pressure largely dominates the Sunday-Wednesday period with another frontal system approaching the region to end the forecast period Thursday. --Daily Details-- Saturday - Saturday Night: The period opens with low pressure over lower Michigan deepening about 10mb in 12 hours as it moves northeast through the day. Surface pattern looks similar to the event on Monday...but the overall airmass aloft will be significantly warmer...roughly 5C warmer at H8. By 18Z Saturday T8s push above +10C with model soundings suggesting +10C air existing in a deep layer from 800mb to 925 mb. As we start to get some high resolution model output for this period...the overall trend is for ankle-deep cold air to hold very persistently for areas south of the mountains through the day and given this trend /which matches pattern recognition/ have continued to trend temperatures downward. However...with the amount of warm air aloft...expect temperatures to be higher than our Monday event which will likely leave many locations in the 30s for much of the day...but too warm to support significant freezing rain. Guidance supports two rounds of along the advancing warm front in the morning before a potential break Saturday evening before the cold front arrives overnight Saturday night. Can/t rule out a rumble of thunder along the front Saturday evening with some elevated parcels seeing 100-200 J/kg of CAPE. Beyond the front...attention will turn to the winds in strengthening cold advection scenario as isallobaric component lines up well after midnight with 40kt at H9 suggesting gusts 30-40 mph are possible. Ice Amounts: Expect any icing across the southern half of NH to be over early /7-8am/ with no more than very light coating. Given the QPF is possible that temperatures rise before meaningful precipitation arrives. Further north and east...however...confidence is increasing in a short period of freezing rain before temperatures move into the mid 30s. Generally 0.10" of icing or less...which suggests travel as the primary impact Travel impacts look to be confined to the morning with nearly all areas above freezing /though still in the 30s/ in the afternoon. Expect winter weather advisories will be needed for some of the area...but will await increasing confidence in precip timing/location before issuing. Will continue to message this potential in the afternoon Hazardous Weather Outlook. QPF: Progressive warm and cold frontal passages will limit overall precipitation potential despite PWATs moving above 1.25" as the elevated warm front lifts north of the region. Mesoscale guidance /09.12Z NAM Nest...NAM and RGEM/ is coming in drier than the global guidance...with the best totals over the mountains where the advancing warm front is best aligned with mid level forcing. Have trended the forecast a bit in this drier direction...generally 0.40- 0.80 from south to north. Sunday - Monday: Quick shot of cold air arrives Sunday behind departing cold front with a blustery and somewhat cooler /though not cold/ day expected. T8s fall back to around -8C in the post frontal airmass. Model soundings suggest that we will be close to mixing to H8...which would allow high temps to reach into the lower to perhaps middle 40s from the coast into the foothills...with 30s expected in the mountains. Arriving airmass will be dry...with any residual mountain snow showers coming to and end. Model profiles indicate around 35kt of flow at the top of the mixed layer, so wind gusts over 30 mph are likely. High pressure settles south of the region for Monday with a substantial gradient remaining overhead though now in a warm advection regime. Expect highs mostly in the 40s with a few lower 50s possible over the south as shallower mixing will offset some of the increasing warmth in the column. Tuesday - Wednesday: Flow over North America gradually amplifies with a longwave ridge axis taking shape from Hudson Bay south through the Appalachians. With the mid level ridge axis to our west...this keeps our area susceptible to impacts from the northern stream and ensemble +T8 anomalies actually decrease from Monday into the midweek as models hint at a dry cold frontal passage sometime on Tuesday. T9s look to remain similar on Tuesday as Monday...then fall behind the front back to the negative single digits on Wednesday. This should take highs down about 5 degrees from the upper 30s to upper 40s from north to south on Tuesday to the mid 30s to mid 40s on Wednesday with continued dry conditions. Northwest winds will continue...though somewhat lighter than earlier in the week. Thursday: High pressure ridge axis begins to push east of our longitude as we reach the end of the long term forecast period on Thursday. This should allow for renewed warm advection with modest ensemble agreement that another low pressure system will track into the Great Lakes region with some potential for warm frontal precipitation to impact our area. Best ensemble support for precipitation at this range is in the mountains and will follow the National Blend of Models depiction in this regard. As for temperatures...the overall consensus is that the greatest positive temperature and height anomalies arrive at the end of the week and will therefore push temperatures upward with mid 40s to mid 50s from north to south and can make further adjustments from here. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Short Term... VFR conditions will gradually deteriorate to MVFR or IFR toward daybreak tomorrow. IFR conditions are expected across northern and eastern terminals tomorrow, with MVFR ceilings across southern terminals. A few hours of light snow is possible tomorrow morning, which could reduce visibility to IFR briefly. Ceilings will linger near MVFR into tomorrow night, and then fall to IFR with lowering ceilings and possible fog. Light freezing is also possible late tomorrow night. Long Term...Widespread LIFR/IFR in stratus/fog with early morning freezing rain changing to rain. Rain...with a few embedded rumbles of thunder is possible Saturday night with conditions improving to VFR with strong westerly winds /gusts over 30kt/ developing and continuing through the day on Sunday. VFR Monday-Tuesday with moderate westerly winds continuing. && .MARINE... Short Term... High pressure will lead to diminishing seas and winds tonight through tomorrow. Seas will begin to build again tomorrow night ahead of an approaching low pressure center. Long Term...Southerly winds strengthen on Saturday with gale force gusts possible by evening. Winds shift westerly with gusts to gale force likely continuing through Sunday. In coordination with neighbors...have issued a gale watch for the period of highest winds late Saturday through Sunday. Small crafts will likely be needed for Monday and possibly Tuesday as westerly winds gradually diminish and waves subside. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Gale Watch from Saturday afternoon through Sunday afternoon for ANZ150>154. && $$ NEAR TERM...Legro
National Weather Service Wilmington OH
852 PM EST Thu Dec 9 2021 .SYNOPSIS... Mainly dry conditions are expected tonight, with a few sprinkles possible from time to time. Warmer temperatures will overspread the region Friday and Friday night, with showers and storms expected Friday night through Saturday morning. Windy conditions are expected Saturday before cooler and calmer conditions evolve for Saturday night into Sunday. A slow warming trend is once again expected early next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Plentiful moisture is advecting NNE through the Ohio Valley this evening, and there is evidence of a sharp gradient in temperature at the surface -- with 8PM readings of 56 at CVG and 46 at DAY. This is a fairly strong setup for fog development later tonight, as this moisture leads to saturation on the cooler side of the surface boundary. HRRR visibility plots remain very aggressive in developing fog (likely dense in spots) during the 06Z-12Z time frame from southern Illinois through western and central Ohio. This remains the primary concern for the overnight hours, and fog potential has been expanded slightly in the grids to account for it. Temperatures were also adjusted, to show a sharper gradient than before -- slightly cooler values in the northern and northeastern ILN CWA, and slightly warmer values in the southwest. Predictive dense fog advisories are always a significant challenge, but the evolution of upstream observations over the next 4-6 hours will be crucial in determining how things may develop over the ILN forecast area closer to daybreak. Previous discussion > Mid/high level clouds are gradually pulling away from the region this afternoon, with some light echoes still appearing on regional mosaic radar imagery. Quite a bit of LL dry air sampled on the KILN 09.12Z RAOB, and am not seeing any sites reporting pcpn reaching the ground, so anticipate that we may see more of a virga situation for this afternoon with just a small chance for a few sprinkles as we progress into the evening hours. However, most spots will remain dry. In fact, are seeing skies trend clearer briefly for late afternoon into early evening, especially for locations south of I-70, before the onset of more robust LL moisture advection begins late this evening through the overnight. Are already seeing the manifestation of an more potent LLJ nosing north into the region with a surge of LL moisture back across IL/IN. Will see this moisture advection continue to expand N/NE into the ILN FA by mid/late evening, with OVC conditions settling in area-wide for the overnight period. In fact, will see setup evolve by late tonight into Friday morning that suggests the potential for some fog development, especially west of I-75 into parts of IN where the LL moisture advection will be the strongest. Could even see some patchy fog linger into the afternoon on Friday with a rather soupy setup until eventually the LL thermal gradient is pulled far enough north and enough mixing can start to take place by the evening Friday. Lows tonight will range from the upper 40s in N KY to lower 40s in central OH. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/... We will likely be contending with quite a bit of cloud cover and even some fog Friday morning into the afternoon before eventually enough mixing can take place for the VSBYs to improve by later in the day. The OVC conditions will inhibit temps from warming too quickly, especially through early afternoon, with daytime highs ranging from near 60 degrees in N KY to the upper 40s in central OH. These temps will continue to rise through the evening and overnight ahead of the impending system set to impact the region Friday night into the day on Saturday. Broad/large-scale troughing across the central CONUS will promote SW flow aloft from the s-cntrl plains to the OH Vly early Friday with stronger deep-layer WAA to becoming during the daytime. Lee side cyclogenesis will be underway by early Friday in the s- cntrl plains, with the attendant theta-e boundary arcing to the NE across the mid MS/OH Rvr Vlys early in the day. With the deepening of the system as it ejects east into the mid MS Rvr Vly by Friday evening, will see robust theta-e advection begin to evolve by late in the day into the overnight near/E of the MS Rvr. This will place the local area well within the broadening open warm sector of the system, with tremendous moisture and mass transport north into the region by late in the day through the evening hours. Moisture depth will initially be rather shallow in nature during the heart of the morning and afternoon hours on Friday (likely indicating a fog/drizzle potential moreso than anything else, especially through about 21z. Have kept PoPs largely in the chance category until mid afternoon before the depth of moisture availability becomes such that the isentropic lift is able to generate a NW to SE band of SHRA, which will pivot NE, mainly for areas NW of I-71, during the late afternoon and early evening. At this juncture, we shift our focus to Friday night into the day on Saturday -- a setup that continues to be concerning for the region. There are several items to break down as we discuss the expected evolution and potential impacts locally, so an attempt to do so follows here: We have just reached the time window for which we can analyze some of the various CAM solutions. And one thing that continues to stick out, from a CAM /and/ a synoptic-based deterministic and ensemble perspective, is the depiction of a stronger/deeper system, which in turn would make the overall progression of it eastward... a bit slower. This trend is significant for several reasons, most notably a corresponding depiction of slightly stronger LL wind fields (and corresponding LLJ maxes), as well as an indication that the threat for strong to severe storms will linger past daybreak on Saturday. This is a climatologically-favorable track that is /generally/ supportive of a severe threat across parts of the OH Vly. A slowly-deepening sfc low is fcst to track from N MO to Lake Michigan from Friday afternoon into Friday night. Deep lows on this track have a rather long history of being supportive for at least some severe weather across the OH Vly. And although the low will be pulling away/N through MI by the time the FROPA actually occurs locally late Saturday morning, it will continue to deepen as it does so. Both deterministic and ensemble solutions have trended toward a deeper system, with the prospect of a sub-985mb low in MI Saturday morning seeming more and more likely. The overall track and deepening of the sfc low as it progresses from MO to MI puts the region squarely in a favorable zone for robust isallobaric and LL mass field response, aiding in enhanced convergence and large-scale ascent, especially after 06z. And with this track and a very favorable dynamic and kinematic environment, traditional thermodynamic evolution, such as instby, tends to become slightly less important as the mass transport/response can often be sufficient to produce strongly- forced vertical ascent amidst an increasingly-frontogenetic response. Looking more closely at some of the ingredients... the effective shear of 50+ kts will be /more/ than supportive of storm organization, likely manifesting itself in a SSW-NNE linear convective structure for the overnight period, especially considering the /largely/ unidirectional profile with favorable vertical speed shear in place. A /very/ robust H9 LLJ of 45-50kts and H8 LLJ of 60-65+ kts will overspread the ILN FA toward midnight and beyond, supporting tremendous LL mass response and ascent. It does appear there will be at least /some/ cross component of the LL bulk shear vector to the front itself, helping enhance LL shear and SRH, supporting circulations within any QLCS structure that is able to develop (likely closer to the front very late in the night). Anticipate that the magnitude of the LL shear (45-50kts) may be sufficient to overcome the larger angular overlap with the initiating boundary. As for the instby... this may be one of the main limiting factors, despite the impressive theta-e advection/LL moisture transport north into the area ahead of the front (with sfc DPs in the upper 50s and lower 60s and PWATS approaching 250-300% of seasonal norms). It is likely that one or more convective lines may develop along a pre-frontal trough or LL confluence axis, initially to the west of the ILN FA, with the front itself hanging back even further to the west across MO after midnight. Synoptic-based deterministic and ensemble guidance continues to depict a narrow ribbon of several hundred J/kg SBCAPE nosing north into IN and parts of N KY and W OH after 06z. This narrow ribbon of slightly more favorable thermodynamics will likely overlap, at least in a small spatial and temporal capacity, with the most favorable kinematic environment in place as the core of the strongest H8/H9 LLJs translates NE through the region between 06z-12z. Regarding storm evolution, there remains some uncertainty at this juncture regarding the coverage /and intensity/ of prefrontal activity in the 06z-12z time frame. Sounding analysis from a variety of synoptic and CAM guidance suggests that a LL isothermal layer or cap may remain in place across parts of the area through at least 08z (and perhaps even several hours longer). Eventually, the strong forcing and large-scale ascent will be enough to overcome this, allowing for convection to become more surface-based as we progress later into the night and beyond. If /and this remains a BIG IF at this juncture/ the prefrontal activity is able to become more sfc-based between 08z-12z, the severe threat would likely be maximized a bit earlier (opposed to just along/ahead of the front itself). So taking this all in from strictly a setup and ingredients- based fcst perspective, there is certainly some concern that the OH Vly may be subjected to one or more slightly elevated (or even surface based) rotating clusters before daybreak and morning QLCS (around/after daybreak). At this juncture, strong straight- line winds will remain the primary concern, but any convectively- driven sfc wave development could allow (with some favorable LL shear orientation as well as some brief backing of the winds), for circulations to develop with any activity that moves through. This would indicate a tornado potential in the ILN FA, at least in a small spatiotemporal manner. Will continue to highlight this threat in the HWO, and could very well see /additional/ upgrades/expansion of SPC convective outlooks to encompass more of the ILN FA as we get closer to Friday night and we have a better look at some of the CAM guidance and can further hone in on the timing and overlap of parameter spaces. The other item, and it is not an insignificant one, will be the robust synoptic-based winds Friday night and especially during the day on Saturday. With the trend of a stronger system, it is appearing more and more likely that a Wind Advisory will eventually be needed for parts of the ILN FA, mainly for the daytime Saturday. In the WAA advection Friday night ahead of the FROPA, could very well see sustained winds of 20-25kts, especially near/N of I-70, which in-and-of itself would be close to advisory-level criteria. Behind the front during the day/afternoon on Saturday, within the increasingly-well mixed BL environment, we could see gusts 30-40+ kts at times, again favored for locations further north. A stronger and slightly slower system evolution would naturally favor more enhanced synoptic-scale wind/gusts on Saturday, with indications for 40+ kts very possible across parts of the area. Additionally, with a very moist and strongly- forced environment, any training convective activity may yield localized flooding, despite the progressive nature of the system as a whole. With /some/ overlap between the steering- layer flow and the initiating boundary, some briefing training of activity will be possible, even with individual elements moving quickly within the overall evolution. However, anticipate the overall flood/flash flood threat will be limited and isolated in nature. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... High pressure southwest of the region will build into KY on Sunday with southwest flow over much of the region. This will limit the strength of the cold air in the post-frontal atmosphere and permit Sunday`s highs to reach into the mid 40s. Slightly warmer overnight lows will be found Sunday night - near 30 versus Sat night`s low in the upper 20s. The high lingers over the Appalachians through Tuesday as surface flow shifts from the southwest to southerly early on. An upper disturbance may bring some light rain Tuesday night and early Wednesday, moreso near a developing warm front north of Ohio/Indiana. The southerly flow persists and remains generally light, leading to a gradual yet persistent warming trend over the region. After the coldest day starting the forecast period (still above normal), readings will slowly warm to the upper 50s for highs on Wed/Thurs, and mid 40s for overnight lows at the end of the forecast. Thursday is showing the next probable chance for rain over the region as a cold front behaving more like a windshift strings out sw- ne along the Ohio River. As of now it would provide a focus for increased moisture with good zonal southwest flow getting wrung out somewhere in the Ohio Valley, potentially a good soaker of a rain. Deterministic models are showing similar features with this system but remain well too far out in time to do anything other than increase the pops for this period and speak to it in this discussion. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... While VFR conditions will begin the TAF period, conditions will deteriorate significantly through the overnight. Ceilings are expected to lower as the night progresses, ending up with IFR/LIFR ceilings at all TAF sites by morning. As this occurs, visibilities will also drop. While MVFR visibilities are the most likely scenario, some IFR visibilities are possible, and even likely at KDAY. In fact, there is some potential for dense fog to develop at KDAY. As this occurs, there will also be a chance for some very light rain or drizzle, but the main impacts will not be from any precipitation. Winds overnight will start out southerly, shifting to the southeast by morning. Tomorrow, while visibilities may improve some through the morning, ceilings are expected to remain very low -- IFR to LIFR. If there is going to be any slight improvement in ceilings, it will be late in the afternoon, but currently it appears that conditions will remain IFR through the entire TAF period. Chances for rain showers will also increase tomorrow afternoon, though there is low confidence on specific timing or placement. Thus, this will be handled with a VCSH in the TAFs. Finally, winds will increase after the tail end of the TAF period, and LLWS is likely. LLWS has been included in the extended portion of the CVG TAF. OUTLOOK...MVFR/IFR conditions will continue into Friday night and Saturday morning, and MVFR conditions may continue well into Saturday. LLWS is expected Friday night. Thunderstorms are possible late Friday night through Saturday morning. Sustained southerly winds of 20-25kts expected Friday night, with sustained westerly winds of 20-25kts and gusts to 30-40kts expected Saturday. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...None. KY...None. IN...None. && $$ SYNOPSIS...KC NEAR TERM...KC/Hatzos SHORT TERM...KC LONG TERM...Franks AVIATION...Hatzos
Area Forecast Discussion
National Weather Service Lincoln IL
829 PM CST Thu Dec 9 2021 .SYNOPSIS... Issued at 212 PM CST Thu Dec 9 2021 A strong storm system will move across the region Friday night. Ahead of it, areas of fog are expected over central and southeast Illinois, then an increasing threat of showers and scattered thunderstorms Friday afternoon and evening. Some potential exists for severe thunderstorms south of a Champaign to Taylorville line Friday evening. As the storm departs, expect a very windy period late Friday night into Saturday, with wind gusts exceeding 40 mph. && .UPDATE... Issued at 817 PM CST Thu Dec 9 2021 This evening, a number of sites are reporting calm winds as a col area is spreading across the lower Illinois River Valley. Meanwhile, satellite imagery shows thicker mid and high clouds over northern MO and central/southern IA moving east into Illinois. Cloud cover looks to be most prevalent along and north of the I-72 corridor but should gradually lift from the south. Clearing skies, light/calm winds, and high dew points in the lower 40s will set the stage for fog development overnight. Still have some concerns a dense fog advisory may be needed overnight. && .SHORT TERM...(This evening through Saturday) ISSUED AT 212 PM CST Thu Dec 9 2021 Lots to discuss in this part of the forecast. The developing storm system is starting to take shape over Colorado this afternoon, and should intensify as an upper wave currently in California moves across the 4-corners region. Model guidance is in good agreement with the surface low tracking to near Milwaukee by Saturday morning. 1) Fog potential: Concern has been increasing recently over the potential for dense fog overnight near and east of I-55, southeast of where the warm front will be setting up. Increasing surface moisture will bring dew points into the 40s in this area with a low level inversion noted on forecast soundings. High-res model guidance brings dense fog as far northwest as the Illinois River, but that area`s a little more uncertain. Have added areas of fog into the forecast into this region tonight and Friday, and will monitor closely over the next few hours for a potential dense fog advisory. 2) Severe potential: Latest SPC Day2 outlook brought the slight risk up to a Pana-Danville line with the enhanced risk edging into our highway 50 counties in southeast Illinois. Warm front is expected to lift north of the CWA late afternoon. In the warm sector to the south, HREF 0-1km storm relative helicity reaches the 200-400 m2/s2 range with CAPE`s 500-1000 J/kg depending on the model. HRRR model is slower with focusing the 8-midnight time frame for the best severe threat, with the ARW and NAM Nest mainly after midnight. QLCS type environment is more favored with wind damage and brief tornadoes possible. 3) Wind potential: Behind the storm system, wind gusts 40-45 mph likely after midnight Friday night and continuing much of Saturday morning. BUFKIT soundings suggest some potential for 50+ mph north of I-74. A wind advisory may be needed as we get closer. 4) Temperatures: Passage of the warm front will result in some non-diurnal temperature trends later Friday, with Friday high temperatures occurring in the evening and Saturday`s highs not too long after midnight. .LONG TERM...(Sunday through Thursday) ISSUED AT 212 PM CST Thu Dec 9 2021 Focus on the longer range remains with the unseasonably mild as we get toward mid week. Temperatures of 15-30 degrees above normal continue to be advertised by the GFS/European ensembles. Low temperatures Wednesday and Thursday mornings are likely to be well above the normal highs for mid December. Upper ridging amplifies as a developing storm system emerges from the central Rockies, bringing the peak of the warmup. The core of the storm system should track northeast, with a trailing front bringing some showers toward Wednesday night and Thursday. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 506 PM CST Thu Dec 9 2021 Main concern is with expected low clouds and fog as a warm front sets up over central Illinois overnight. High-res guidance continues to focus on expansion after 06Z potentially as far west as KPIA. Will lower ceilings to below 500 feet at all sites except KPIA, but IFR conditions likely there as well on the edge of the stratus deck. Visibility around 1/2 mile appears likely elsewhere late tonight into Friday morning, until the front lifts north. Most improvement in visibility will be in the period after 18Z, though clouds expected to remain below 1,000 feet in the afternoon. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Deubelbeiss SYNOPSIS...Geelhart SHORT TERM...Geelhart LONG TERM...Geelhart AVIATION...Geelhart
Area Forecast Discussion
National Weather Service North Platte NE
538 PM CST Thu Dec 9 2021 .SHORT TERM...(This evening through Friday night) Issued at 408 PM CST Thu Dec 9 2021 The main forecast challenge through Friday night revolves around the incoming winter storm. Upper level zonal flow over Nebraska will transition to southwest through the night as the trough currently centered over California will dig into the Great Basin and Four Corners. The trough then bisects the forecast area late Friday and take on a more neutral tilt. At the surface, a low pressure near the Denver metro is starting to deepen as of this afternoon. Not much movement is expected overnight, but it really picks up steam tomorrow as it ventures onto the Plains and ultimately reaches the Quad Cities IA/IL area tomorrow night. Other factors compounding this system are a strong H3 jet with speeds 120kt+ that eventually becomes coupled late tomorrow and a deepening H7 low that tracks right across the Sandhills. As of 21z, the beginning of the baroclinic leaf is noted on water vapor imagery, stretching from the Pacific Coast up to the Laramie Range. Radar echoes in western Nebraska are showing the enhanced mid- level moisture and cloud deck. Expect this activity to eventually become the main deformation band as H5-7 frontogenesis ramps up tonight. Isentropic upglide is rather strong, most notable at 290K, which roughly corresponds to H7-85. Surface and low level winds are also transitioning to more easterly flow. In addition to enhanced moisture advection, upslope winds will aid in some forcing/lift. In response, steadily increased PoP after 00z across northwest Neb. Most of Sheridan and W.Cherry should receive moderate snow by 03z, and the band beginning to stretch east along the Hwy 20 corridor by 06z. Will need to monitor the development of this band as dry air reigns supreme in the low levels currently, as shown by 20-30F surface dew point depressions at KGRN, KVTN, KONL. It will take some time for the column to fully saturate, especially for areas east of the panhandle. Checked forecast soundings for potential freezing drizzle at the onset, but found little evidence. Still cannot be completely ruled out, especially for the eastern zones where low and mid level saturation will occur tomorrow morning and a surface inversion capable of trapping moisture. Thinking the 06z-12z timeframe will be crucial for snow accumulation for the western half of the Winter Storm Warning areas. Forecast soundings suggest ample lift in the H5-7 layer, which directly correlates to the majority of the DGZ. Some solutions also show the classic isothermal layer developing, increasing time for aggregates in the DGZ. Additionally, cross sections indicate some slight theta- E folding and negative EPV values from KCDR to KVTN. Snow rates may exceed 1"/hr at times, leading to quick accumulations. Cold air advection later in the night will help increase SLR`s from around 8:1 up to 14:1. One caveat in this setup is the northward trend in the latest model guidance. The highest confidence for significant snowfall (6-10") is generally along and north of Hwy 20. After 12z Friday, things get more tricky, especially relating to the widening/weakening of the main deformation band, the formation of a second band, dry air intrusion, and the extent of wrap-around moisture. Used a blend mainly consisting of HREF, NAMnest, RAP to capture a general picture of timing, location, and qpf. The bulk of the heavy snow should shift into South Dakota after sunrise, but enough forcing at H5-7 remains across Nebraska to support a southward extent of light to moderate snow. Forecast soundings suggest at least a six hour window of appreciable precip as far south as I-80 with the peak accumulation occurring mid-morning through early afternoon. The thermal profile is not as supportive of dendrites or heavy rates compared to the far north, but impacts will likely still be felt. Bouts of stronger lift and variations in the H85-7 temp that increase the DGZ may lead to pockets of heavier snow embedded in the main batch of light snow. The second primary deformation band may brush far north central Neb, generally Holt and Boyd Cos, mid to late afternoon as the system strengthens over the Upper Midwest. Thinking the greatest wrap-around activity will affect far northern and northwest Neb, which may also be enhanced by orographic lift along the Pine Ridge. Some light snow showers may linger into the late evening hours over north central Neb, but all snow should be done by 06z Sat. All in all, confidence decreases in snow amounts outside the Warning area as there will likely be a steep/narrow gradient of 6"+ and 1-2" amounts. With that said, made no change to current headlines. .LONG TERM...(Saturday through Thursday) Issued at 408 PM CST Thu Dec 9 2021 The long term pattern in the extended period will be characterized by broad height rises over the middle part of the country through the weekend as the Friday system exists the area, resulting in a quasi-zonal flow aloft transitioning to southwesterly flow as the next long wave trough develops off the CA coast. Weekend temperatures are expected to rebound fairly quickly under large scale subsidence and sunshine, except of course where snow cover will ultimately exist. Temps likely to remain below average in the north and closer to average in the south Saturday (low-mid 40s), but returning to above average for this time of year by Sunday. Strong ridging and subsequent downstream jet streak intensification, followed by anticyclonic wave breaking in the northern Pacific will teleconnect to a building ridge by Monday into Tuesday and the first part of Wednesday in the Plains. Model ensemble clustering suggests differences in timing of the very quick moving upper low from the 4 corners region Tuesday into Wednesday. A general track of the upper low moving across the northern Plains looks favored for now which would put much of western and north central NE in the warm sector of this approaching storm system Wednesday. While some instability is suggested for Wednesday the trend for significant moisture return is uncertain to support widespread rain with embedded thunderstorms at this time. Precip chances have been included and will be fine tuned as guidance refines moisture availability. There is high confidence in very strong winds for Wednesday, both in the warm sector and behind the cold front. Wind gusts over 35 mph looks likely at this point. The anomalous ridging developing across the Plains in the Tuesday/Wed time frame may support record or near record high temps once again, though timing differences in ensemble solutions yields only medium confidence in that. But well above average temps for that period does look likely. The anomalously warm temps and strong winds on may well provide a critical fire weather period Tuesday afternoon, but especially Wednesday afternoon. As forecasts become more refined those details will be updated as well, but the pattern suggests some concern in that time frame. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 537 PM CST Thu Dec 9 2021 KVTN: Flight conditions will be deteriorating as snow starts to move in from the southwest. Expect conditions will go below VFR early this evening as vsbys and cigs lower, then reach IFR after Midnight. Snow will be heavy at times but will wait for more definitive radar trends to develop before introducing more specific timing. May see precipitation lighten up for a period before daybreak but that will fill back in. Wind increases and blowing snow develops with poor flight conditions throug the latterportion of the valid period. KLBF: Main band of snowfall will become established to the north of KLBF, leaving VFR conditions through daybreak. However easterly flow will enhance with wind gusts over 25kt expected by early tonight. Snow and lower cigs arrive after daybreak with a period of IFR conditions mid morning into early afternoon. Winds will shift to a northwesterly direction and become gusty Friday afternoon as low pressure moves off to the east with gusts over 30kt at times. && .FIRE WEATHER... Issued at 408 PM CST Thu Dec 9 2021 Despite the strong system on Friday, a rapid recovery in temperatures in the far southwest part of the state to some degree Saturday, but especially Sunday will still yield relative humidity values dipping below 20 percent again in the far southwest part of the state, assuming little to no snow cover. Winds for Saturday and Sunday should remain below 20 mph for the most part however which should lessen critical fire weather conditions. As referenced in the long term section, anomalously warm temps and strong winds on may well provide a more critical fire weather period Tuesday afternoon, but especially Wednesday afternoon. As forecasts become more refined those details will be updated as well, but the pattern suggests some concern in that time frame. While relative humidity forecasts are more uncertain at this time, there is decent confidence in very strong winds especially Wednesday ahead of the strong system, and a potential wind shift from west to northerly as well later as the system passes. && .LBF WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 6 PM CST /5 PM MST/ Friday for NEZ004- 094. Winter Weather Advisory until 6 PM CST /5 PM MST/ Friday for NEZ022>024-035-036. Winter Storm Warning from midnight CST /11 PM MST/ tonight to 6 PM CST /5 PM MST/ Friday for NEZ005>010. Winter Weather Advisory from midnight tonight to 6 PM CST Friday for NEZ025>029-037. && $$ SHORT TERM...Snively LONG TERM...Stoppkotte AVIATION...MBS FIRE WEATHER...Stoppkotte
Area Forecast Discussion
National Weather Service Marquette MI
652 PM EST Thu Dec 9 2021 .SHORT TERM...(This evening through Friday) Issued at 401 PM EST THU DEC 9 2021 Water vapor imagery and RAP analysis show a southern stream shortwave lifting into the Upper Great Lakes this afternoon, and as expected, forcing from this wave is causing a flare up of system snow, especially into central Upper Mi. The forcing from this wave will also provide lake enhancement of snow into the se portion of the cwa and over the tip of the Keweenaw in a se flow. I issued a winter wx advisory earlier this afternoon for Delta/southern Schoolcraft and advisories still continue for Ontonagon thru Keweenaw counties thru 00z this evening. Expect additional snow amounts of 1 to 2 inches through early evening for the advisory areas. Could maybe see isolated amounts of 3 inches in Delta/southern Schoolcraft with the added boost from lake enhancement. A second northern stream shortwave moving from Manitoba into Ontario will push the sfc trough east across the fcst area this evening as winds shift from southerly to southwest or westerly behind it. At the same time, snow will be tapering off from west to east this evening. Expect fairly quiet and dry weather late tonight into much of Friday as high pressure builds in from the west. Some light snow ahead of a more significant storm system approaching from the CO Rockies could spread into south central zones late Friday. Min temps tonight will range from the mid to upper teens interior west to the 20s elsewhere. Highs Friday will be in the lower to mid 30s. .LONG TERM...(Friday night through Thursday) Issued at 355 PM EST THU DEC 9 2021 Main attention in the extended period is the potential for a winter storm Friday night into Saturday. Shortwave currently making its way into Nevada will continue eastward tonight. Its progged to exit the Rockies and then lift northeast toward the Upper Great Lakes tomorrow. By 0z Saturday, guidance suggests its surface low will be near the Iowa/Missouri stateline. There are some differences among the 12z guidance as to how deep the system will be initially, but the consensus among the guidance suite is that the system will continue deepening as it continues to interact with favorable upper level jet dynamics while entering the Upper Great Lakes. From there, the feature will begin taking on a negative tilt just downstream late Saturday as it enters Ontario. As the system lifts toward the region, strong isentropic and low-mid level fgen forcing ahead of the system will support snow showers spreading over the forecast area by Friday evening. With the strong low level q-vector signal and the deepening moisture, expecting snowfall to become moderate to heavy across mainly the central and eastern UP during the evening and through the night. As the low approaches, the flow will become northeast which will bring an opportunity for lake enhancement for areas along the Lake Superior lakeshore. This flow pattern and an added terrain boost will also help Lake Superior lakeshore communities see some of these higher snow amounts, particularly across Marquette and Alger counties. 6z GFS suggested enough WAA on the system`s eastern flank could be enough to support a ptype change over to rain or freezing rain late Friday night/Saturday morning along the Bay/Lake Michigan lakeshores and east. The 12z guidance continues to suggest this potential, and even the Canadian is suggesting a switch to rain by the end of the event in the east. 9z SREF Plumes also suggest the potential for mixed ptype. Outside of the likely snow though, this ensemble system suggests a switch over to rain would be more likely then freezing rain, albeit this probability still remains low (~20 percent or so). This appears consistent with the NBM v4.1 as well. If this does occur, icing accumulations look light, but could be something to watch as new guidance arrives. At the moment, snow totals look to vary between 8 and 12 inches across the central and east, with some potential above a foot in the higher terrain just west and south of Marquette. The west looks to be largely spared from a majority of the snow given the tightly wrapped nature of the comma structure that`s expected to move over the region, but 3 to 5 inches of snow still looks possible. Opted to upgrade the watch to Winter Storm Warnings and Winter Weather Advisories for the event. The system will pull away Saturday, with CAA and a tight pressure gradient to follow. This will result in strong winds and areas of blowing snow. Because the snow is expected to be wetter and heavy, not only will driving conditions be hazardous and snow removal require more effort, but power outages can`t be ruled out. After this system lifts out, the jet stream is progged to retreat north. This will be accompanied by ridging extending over much of central CONUS and near zonal flow over our region Sunday through at least Wednesday. GEFS 500mb height spaghetti plot shows good agreement among its various members, so confidence is high that the expected warming period is still on track. The beginning of next week looks to start off with highs near 40F and then by mid-week, potentially some mid 40s. Snow melting should be slow to occur given overnight lows dropping below freezing across the board, low sun angle, and daytime dewpoints not much above freezing, except perhaps Wednesday. Beyond this there are differences among the guidance. At the moment, there is the potential for another notable system Wednesday night or Thursday. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 643 PM EST THU DEC 9 2021 As a system pulls away to the east tonight, conditions will improve at all terminals from west to east. Conditions have already improved to MVFR at CMX and IWD and should return to VFR by Friday morning. IFR conditions at SAW will improve to MVFR in a couple hours and then to VFR Friday morning. Another system will move across Upper Michigan Friday night through Saturday morning, likely bringing IFR to LIFR conditions at all terminals. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 401 PM EST THU DEC 9 2021 Ahead of an approaching surface trough, southerly winds have increased today. Into early evening, southerly winds of 20-30kt with maybe a few gale force gusts to 35kt will continue west with gales to 40 kts central and east. As the trough passes tonight expect w to nw winds to 20-30kt for a time in its wake. A weak high pres ridge reaches Lake Superior by late Fri aftn, providing a period of light winds under 15kt. Deepening low pres will then track ne, passing near the Straits of Mackinac Sat morning. N to NW gales of 40kt will likely occur across the e half of Lake Superior on Sat as the deepening low continues lifting ne. Would not be surprised to see even a few high-end gale gusts to 45 kts. W to sw winds of 20-30kt are then expected Sat night into Sun as another low tracks e toward northern Ontario. Could be a few gale force gusts across western and north central Lake Superior on Sun. As a sfc high pressure ridge builds over the lake, expect winds to generally be 20 kts or less by Mon afternoon into Tuesday. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Winter Storm Warning from 7 PM EST /6 PM CST/ Friday to 10 AM EST /9 AM CST/ Saturday for MIZ002-009-084. Winter Storm Warning from 7 PM Friday to 4 PM EST Saturday for MIZ006-007-013-014-085. Winter Weather Advisory until 7 PM EST this evening for MIZ001>003-013-014. Winter Weather Advisory from 9 PM Friday to 10 AM EST Saturday for MIZ001-003. Winter Storm Warning from 7 PM EST /6 PM CST/ Friday to 1 PM EST /noon CST/ Saturday for MIZ004-005-010>012. Lake Superior... Gale Watch from Saturday morning through Saturday evening for LSZ251-267. Gale Warning until 7 PM EST this evening for LSZ244-245-249>251- 264>267. Gale Watch from Saturday morning through Saturday afternoon for LSZ249-250-266. Lake Michigan... Gale Watch from Saturday morning through Saturday afternoon for LMZ221-248-250. && $$ SHORT TERM...Voss LONG TERM...JP AVIATION...JAW MARINE...Voss
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
810 PM MST Thu Dec 9 2021 .UPDATE... Issued at 810 PM MST Thu Dec 9 2021 Current surface analysis shows cold front well south of the region now, with an area of low pressure developing along it across eastern CO. High pressure is centered over north central SD. Upper level analysis shows near zonal flow across much of the region, with a potent shortwave now over ID and western UT. Strong jet and increasing upper level moisture to the east of the wave is moving east-northeast across the central Rockies and into the high Plains. Skies have clouded over across much of the area, with the lower clouds over southern portions of the region. Drier air to the north and northeast of the Black Hills is holding strong on the back side of the surface high. The burst of snow that developed across the central and southern Black Hills this afternoon has tapered off some, with mostly areas of light snow and flurries across southwest SD at this time. Regional radars show the heavier snow developing across southeast WY into the NE panhandle over the last couple of hours, and will start to move into southern parts of northeast WY and southwest SD over the next few hours. Forecast still looks to be on track for the most part through tonight and into Friday morning. The heaviest snow will fall overnight and into Friday morning across the warning areas, with 6 to around 12 inches, highest amounts generally toward the NE border in southwest SD. Amounts will taper off pretty sharply toward the Interstate 90 corridor and especially over extreme northeast WY and northwest SD. The only change to the headlines was to put the central Black Hills in a warning, with some areas along the eastern slopes from Hill City and Pactola to Keystone and Rockerville likely seeing around 6 inches of additional snow on top of the 1 to 3 inches from this afternoon. Otherwise, only minor adjustments made to the forecast for tonight at this point. && .DISCUSSION...(This Evening Through Thursday) Issued at 115 PM MST Thu Dec 9 2021 Most recent upper air analysis shows the long-wave trough situated over the rockies, with the low poised over Colorado moving east northeast that will support frontogenesis this evening into Friday morning. Latest HRRR and SREF runs show potential for weak development over the Black Hills this afternoon, but more widespread snow will move into the area as the wave moves into the CWA later this evening. Deterministic models all agree on broad FGEN band along the SD/NE border creating the highest amounts (6"+) over the forecast area. Snowfall amounts drop off further to the north, especially north of I-90, with 850mb models showing much drier air the northern half of SD. Snow will taper off from west to east Friday morning and afternoon. Have kept with the trend of lowering temperatures for Friday night, in areas where snow pack is expected. Looking ahead through the weekend and into next week, upper ridging moves into the western CONUS and brings a warming trend, with temperatures reaching back into the 50s and possibly 60s Mon-Weds. Models hint at another strong low pressure system moving into the upper plains middle of next week, and we may see another drop in temperatures, along with strong winds and snowfall potential. && .AVIATION...(For the 00Z TAFS Through 00Z Friday Evening) Issued At 437 PM MST Thu Dec 9 2021 Snow and MVFR/IFR conditions will gradually spread east-northeast across much of northeast WY, the Black Hills area, and southwest SD through the evening hours, and eventually into south central SD overnight. VFR conditions are expected across much of northwest SD tonight into Friday, especially the far northwest. Snow will taper off and conditions will gradually improve from west to east across northeast WY and southwest SD on Friday. The heaviest snow and worst conditions will be across far southern SD overnight into Friday morning. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Winter Weather Advisory until 11 AM MST Friday for SDZ024-026- 031-072. Winter Storm Warning until 2 PM MST Friday for SDZ027>030- 041>044-074. Winter Storm Warning from midnight tonight to 6 PM CST Friday for SDZ046-047-049. WY...Winter Weather Advisory until 11 AM MST Friday for WYZ055-057- 058. && $$ Update...26 DISCUSSION...Dye AVIATION...26