Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/11/16

Area Forecast Discussion
National Weather Service La Crosse WI
911 PM CST Sat Dec 10 2016 .UPDATE... Issued at 911 PM CST Sat Dec 10 2016 we are with the event underway and some questions still remain regarding snow amounts overnight. Overall, am starting to get a little nervous that our snowfall amounts may be a touch too high across southern areas and thus a little too low near the I-90 corridor. Radar trends the past 2 hours are telling, with a pronounced narrow but intense frontogenetic snow band laid out across southern MN and WI, and really stretching back into western SD as well. Recent RAP trends seem to have caught onto this feature, most pronounced in the 700-500mb layer, which also just happens to be completely in the DGZ, supporting the growth of dendrites and thus some pretty high snow-liquid ratios. Per reports/observations under this band, snow ratios are generally 20-25+ to 1 (not surprising at all with a 300+mb deep DGZ), while outside of it where there is minimal lift through the DGZ, ratios are much closer to 12 to 1. That makes for a very tough forecast heading through the night, not only with regard to snowfall amounts but also placement of the narrow FGEN band, especially considering some spots under that band have already picked up 2-4" of fluffy snow the past 6 hours. Hard to ignore reality and short term model trends which agree that the FGEN axis may well end up a little farther north than earlier thought. This is especially true with recent RAP runs, showing the elongated FGEN axis pretty much stationary as a subtle lead 700mb wave passes the next few hours, followed by the more pronounced upper feature toward morning, with the latter also helping induce a nice deformation field bisecting the CWA near the I-90 corridor. That setup does leave some question about how far south additional precip redevelopment will occur, especially too far south of the FGEN axis (as well as areas north of I-94 on the downward branch side...also fighting some dry air). All told, not ready to bite on the need for any upgrades to the current advisory area farther north, but it may be needed with little advance notice pending trends overnight. Ahhh...the joys of winter weather forecasting! && .SHORT TERM...(This evening through Monday night) Issued at 220 PM CST Sat Dec 10 2016 It now appears that the southern parts of the forecast area will have a decent shot of getting some heavier snow and plan to upgrade to a warning to handle this. The 10.12Z models have come in with a slightly stronger short wave trough to cross the area as it deepens once it crosses the northern Rockies tonight. This allows the frontogenesis zone to become stronger, especially in the 06Z to 12Z time frame tonight in the 750-600 mb layer. With this stronger forcing signal, the resulting qpf amounts and snow amounts will be bumped up and it now appears that 8 inches of snow could fall in a 24 hour period. In addition, the surface low looks like it will take a more northeast track Sunday which could linger some light deformation snows a little longer over southwest Wisconsin. This may not add all that much snow as the qpf amounts look to be pretty light in the deformation zone, but again, could be enough to bump some areas into the warning category. Thus will take all of our northeast Iowa counties along with the 3 southwest Wisconsin counties and upgrade to a winter storm warning through Sunday. Otherwise, very little overall change in the expected conditions for the remainder of the area. Snowfall amounts of 6 to 8 inches north of the warning up to Interstate 94 still look on track as does the 4 to 6 inches for north central Wisconsin. There may also have to be some adjustments made on the back side of the system to the end times for the Wisconsin part of the advisory. It looks like the snow could be winding down by late afternoon or early in the evening, which could necessitate ending the advisory a little sooner. There is also a signal on the back side of the system of a potential loss of ice before the precipitation ends. However, think the models have a bit of a bias toward taking the ice out too fast as systems are pulling away from the region and will stay with just snow for now. Cold, arctic air is still on track to spill into the Upper Midwest early next week. The arctic cold front will move through the region Monday afternoon and evening. Another pacific short wave trough looks like it will zip across the region in conjunction with the cold front. This wave looks to be strong enough to generate a short period of weak to moderate pv advection in the 500-300 mb layer. The QG convergence looks to be weak but extend through a deep layer from 1000 up to 300 mb. This may be enough to squeeze out some light snow as the cold air moves in and will carry a small 20 to 30 percent of snow Monday afternoon and evening. Temperatures Monday night look to bottom out in the single digits above and below zero. Wind chill values will become a concern with values dropping into the single digits and teens below zero. However, it does not look like an advisory would be needed at this time. .LONG TERM...(Tuesday through Saturday) Issued at 220 PM CST Sat Dec 10 2016 The cold air will remain for much of the week with some slow moderation expected by the end of the week into the upcoming weekend. Wind chill advisories may be needed Tuesday night/Wednesday morning across north central Wisconsin and again Wednesday night/Thursday morning for much of the area. Overnight lows during this period generally look to be in the single digits below zero with west winds of 5 to 15 mph. The next chance for snow will come for the end of the week into the weekend as the arctic high pressure moves off to the east. The models are currently showing a positive tilt long wave trough moving across the Rockies with southwest flow and embedded short wave troughs over the Midwest. Decent agreement that a surface low in the pattern will track between the local area and the Ohio River Valley into the eastern Great Lakes with the potential to drop some more snow on the area. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 530 PM CST Sat Dec 10 2016 Periods of snow have begun across the area and will continue overnight and into Sunday, with the heaviest period of snow still expected later tonight into Sunday morning. Overall, IFR conditions will prevail (especially visibility), though a few periods of LIFR are possible during any bouts of heavier snowfall. It still appears that RST and LSE will pick up between 5 and 8 inches of snow by the time it tapers off Sunday afternoon, with the snow initially of a lighter, more fluffy variety gradually replaced by a slightly wetter snow with time. As the snow departs (or at least lightens up in intensity) Sunday afternoon and evening, widespread IFR ceilings appear probable, with even a small risk for a little freezing drizzle, though confidence in that is very low. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Storm Warning until 6 PM CST Sunday for WIZ054-055-061. Winter Weather Advisory until 9 PM CST Sunday for WIZ032>034- 041>044-053. Winter Weather Advisory until 9 PM CST Sunday for WIZ017-029. MN...Winter Weather Advisory until 6 PM CST Sunday for MNZ079-086>088- 094>096. IA...Winter Storm Warning until 6 PM CST Sunday for IAZ008>011-018- 019-029-030. && $$ UPDATE...Lawrence SHORT TERM...04 LONG TERM...04 AVIATION...Lawrence
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
638 PM CST Sat Dec 10 2016 .DISCUSSION...Updated for latest aviation discussion below. && .AVIATION...The 00z BRO sounding shows a pretty saturated airmass in place this evening with a fairly strong low level inversion persisting. This is resulting in a mixture of VFR/MVFR conditions around the RGV early this evening. The latest NAM forecast soundings maintains the saturated low level inversion in place over the region through the night which will reduce the ceilings back down to IFR levels. Some fog has started to form over the northern and western counties and as the surface winds start to slacken later tonight expect this fog to progress further south lowering vsbys for the RGV airports. The low level wind flow tomorrow will finally shift around from the south which will increase the WAA and the low level mixing allowing for the ceilings/vsbys to improve back up to VFR levels. && .PREV DISCUSSION... /issued 250 PM CST Sat Dec 10 2016/ SHORT TERM (Now through Sunday night): Zonal flow aloft will dominate Deep South Texas, and indeed, most of the CONUS, through the short-term period. After one more cool night, southerly winds return on Sunday for a quick warm-up. For the near-term, through 00Z, trimmed back PoP`s per recent radar trends. Picking up some light (15 dBZ) echoes near the Lower Valley and association with convergence into the coastal trough...but have yet to see any evidence of this reaching the ground. Mid-Lower Valley locations warmed up a few degrees more than expected today, when the sun shone for a couple hours, as per previous AFD update. Forecast trend overall has remained the same, but 12Z runs of NAM and GFS showing some timing differences with regard to SSE flow setting up overnight. Both models show NW winds of past couple of days finally backing around to light SW this evening, which allows temps to actually rise a few degrees through the night. However, GFS brings the more moist flow back inland around 03-06Z, whereas the NAM is about 6 hours slower...and shows a more sudden jump in dewpoints mid-morning on Sunday. Latest RUC and HRRR lend more support to the NAM solution, so based on that, and the fact that it`s capturing current temps/dewpoints better, will lean pretty heavily on it for the forecast. With the slower moisture return, have backed off some on fog potential tonight. Will still word patchy coverage over most areas, but delay onset until after 06Z. Can`t rule out some isolated light rain overnight along the coast, but all other areas should stay dry. Moving into Sunday, the spring-like warmup kicks in, especially once a weak trough aloft passes during the morning, swinging upper winds to more WNW. H85 winds turn SW, ahead of a front moving into the TX Panhandle. Depth of moisture will trend down from its current 700- mb level down to 850mb or perhaps even lower. Upshot will be more sun with temps reaching the low 80s in the mid-Valley with mid-upr 70`s elsewhere. Dewpoint in Brownsville reaches 70F by late afternoon, so the muggy feel will return. Low temps for early Monday looked good and so were retained...from near 60 NW to near 70 SE. MOS guidance hitting fog potential pretty hard for late tomorrow night as well. Will introduce areas of fog across all land areas and the Laguna Madre for now. Dense fog potential would seem to be better over the NW counties where winds will die off more so than nearer the coast. Continued 8 to 10 second swell period with a still brisk east to northeast onshore flow has continued tidal run-up to the dune line at high tide this afternoon per webcams on S. Padre Island. Don`t see a need to extend the Coastal Flood Statement at this juncture as water levels (both observed and residual vs. prediction) are running a bit lower than this time yesterday. Next high tide will be minor, and by then winds offshore should have shifted to SE, which should calm down the swell. LONG TERM (Monday through Saturday): The lastest GFS/ECMWF are in better agreement through the forecast period. A nearly zonal flow aloft will prevail through much of the week. Southerly flow at the surface will allow moisture to increase across the area and warming temperatures through mid week. A cold front will move into central Texas on Monday but will stall well north of the area. Another cold front will approach Deep South Texas Wednesday night before stalling near the northern Ranchlands on Thursday. By late week, a sharp 500 mb short wave trough will dive south through the Pacific Northwest and lift across the Great Basin. This will result in mid level flow becoming southwest over the forecast area. Above normal temperatures will prevail Monday through Wednesday. High temperatures each day will be in the 80s with overnight low temperatures generally be in the 60s. Slight chance of rain will develop Wednesday night through Thursday night with increasing cloud cover as a cold front approaches and stalls across area. Temperatures will recover Friday and Saturday as southeast winds return and push warm Gulf air back over the area. MARINE (Now through Sunday): Conditions at Buoy 020 as of 150pm CST were reported as E winds of 18G21KT, with seas near 7 ft. Extended SCA for the outer Gulf Waters only through 9pm. Winds veer SE by this evening, but stay at around 16-20 knots. SCA may need to be extended, again for the outer waters, into Sunday morning as latest wave guidance keeps seas right around 7 ft. out there. SCEC likely for the nearer-shore waters. Conditions on the Laguna Madre should remain relatively favorable with some moderate southerly breezes by Sunday afternoon. Seas on the Gulf finally subside to around 5 ft. by later Sunday night, though moderate S winds may require SCEC. Monday through Thursday...Broad surface high pressure across the Gulf will support light to moderate south to southeast winds and low to moderate seas through the period. Isolated to scattered showers are expected across the coastal waters Wednesday night into Thursday as a front approaches and stalls across the area. && .BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...Small Craft Advisory until 9 PM CST this evening for GMZ170-175. && $$ This product is also available on the web at: HTTP://WEATHER.GOV/RGV Short Term...60 Long Term...69 Graphicast/Upper Air...56
Area Forecast Discussion
National Weather Service Wilmington OH
925 PM EST Sat Dec 10 2016 .SYNOPSIS... A low pressure system will eject northeast from the Plains into the Great Lakes Sunday into Monday. Snow will develop ahead of this system tonight and then a mix of rain and snow is expected Sunday before precipitation ends early Monday. High pressure returns late Monday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Not many changes to current forecast as widespread WAA/ isentropic upglide has allowed a band of snow to move into our northern zones with a couple of sites already reporting. The main question is that dry air remains in the low levels and will take a little bit of time to saturate as the band heads north. Latest HRRR run then has snow filling back in across the northern zones early Sunday morning. Latest run of the NAM also hints at this while advertising a sharp cut off. Have kept forecast advertising accumulating snow along and north of Interstate 70. New zones out. Prev Discussion-> Still have a few flurries flying across the CWA this afternoon, particularly across west central Ohio and east-central Indiana. No accumulation is expected from the flurries through sunset. Focus then shifts to the next system which will begin to affect portions of the CWA tonight. Low pressure will eject out of the Rockies and into the central Plains tonight. And as high pressure over the Ohio Valley moves into the Mid-Atlantic, a return flow will set up, allowing the low levels to moisten up and warm advection will also start to kick in and produce more clouds. Isentropic lift will also promote the development of snow, although much of our guidance suggest a fairly sharp southern cut off where accumulating snow will occur. At this point in time, the highest confidence in accumulating snow looks to be just north of the Interstate 70 corridor, favoring a GFE/SREFS blend. Highest snowfall accumulations are forecast to reside across our northern most counties, namely Auglaize, Mercer and Hardin and a Winter Weather Advisory has been issued. Further south of this area toward the Interstate 70 corridor, snowfall accumulations are expected to remain below Advisory criteria but enough to potentially result in slick travel late tonight/early Sunday. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/... Snow continues Sunday morning mainly across the far northern portion of the CWA, but precipitation will overspread the entire area during the afternoon/evening as a favorable jet develops over the CWA ahead of low pressure which will move into the upper Midwest by days end. In addition to supporting precipitation, the southwesterly jet will also result in the rain/snow line shifting north through the day where much of the CWA is likely to experience rain by late afternoon, except for perhaps the extreme northern counties within the Advisory area. Surface temperatures will likely continue to rise into the overnight hours, with rain being the primary p-type across the CWA. Then, as low pressure moves through the Great Lakes late Sunday night, this will allow a cold front to move through from the west, ending the precipitation chances Monday morning. The remainder of Monday dries out and clouds may even break for some sunshine later in the day. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... With the departing frontal system leaving the area becoming under the influence of a shallow ridge over the southern CONUS...but low level moisture will linger for Monday night. So despite Cold air advection over especially the northern half of the forecast area,there will only be occasional breaks in cloud cover. There will be a pretty tight gradient of temperatures on especially Tuesday into Tuesday night with the passage of the upper low over central and then SE Ontario, with the weak ridging in the south. The only potential for precipitation will come in the form of light snow showers in NW flow with the passage of the upper low, but limited moisture available. More significant Cold advection and dry conditions will continue the below normal temperatures through the work week, with single digit overnight lows Wednesday night and Thursday night. For Friday into Saturday, moisture returns to the region with the passage of another shortwave, with precipitation onset beginning as snow and then changing over to rain during the day on Saturday. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... Light returns are moving across the western taf sites this evening with no snow being reported. There are some reports of snow in the KIND area. Looking at MPING reports are sparse. Widespread WAA lift will continue this evening with most of the snow remaining north of the TAF sites. Looking at forecast soundings KDAY and KCMH/KLCK have the greatest chance of observing snow with KCVG/ KLUK likely remaining south of the snow. As this initial band of snow heads northeast it will push north of all the TAF sites by 12z. Looking at high res guidance shows all TAF sites remaining VFR with this initial band. In any heavier snow bands that due form reductions in visibilities will be possible. Sunday afternoon surface low pressure will head northeast towards the Great Lakes with another band of precipitation moving in from the west. Looking at GFS and NAM forecast soundings thermal profiles quickly warm Saturday afternoon with precipitation starting right on the border of the rain/ snow line across the north. The precipitation will then continue into early Monday morning. Cigs and visibilities will then start to fall Sunday night. OUTLOOK...MVFR/IFR ceilings and visibilities possible Sunday night into Monday morning. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...Winter Weather Advisory until 6 PM EST Sunday for OHZ026-034- 035. KY...None. IN...None. && $$ SYNOPSIS...Haines/BPP NEAR TERM...Haines/BPP SHORT TERM...BPP LONG TERM...JDR AVIATION...Haines
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
859 PM CST Sat Dec 10 2016 .UPDATE... 855 PM CST Evening Update... No changes planned to forecast or headlines at this time, though will be making some minimal changes to near term pops based on radar/obs trends. Initial region of warm-advection forced light snow overspread the region late this afternoon as anticipated, with heavier (mainly moderate) snowfall within a region of frontogenetically-forced northwest-southeast bands. Recent radar trends show this banding has weakened and lifted northeast across southeast WI, Lake Michigan and northern IN at this time. However, 00Z DVN sounding depicts a fairly deeply saturated column with nice veering wind profile signature associated with strong warm-advection. Within this region of persistent upglide, latest high-res guidance continues to support regeneration of transient f-gen banding which should continue to result in periods of moderate or greater intensity snowfall. While we`re currently in a lull in radar returns especially across the western parts of the cwa, stronger returns are blossoming across portions of eastern IA, and would expect an uptick in coverage and intensity later this evening/overnight as forcing and moisture advection persist. With the first band working to moisten initially dry low-levels, will likely see additional bands more efficient in lowering vis and producing heavier snow, and latest RAP soundings suggest a decent period of deeper dendritic growth after 05-06Z. Initial bands of snow have produced 2+" of new snow in many spots across the warning area, which is in line with going forecast amounts through 06Z. Thus not inclined to make any big changes at this time, with expected redevelopment and increase in snow coverage and intensity later tonight. Ratzer && .SHORT TERM... 309 PM CST Through Sunday Night... The main forecast concerns with the winter storm continue to revolve around total snow amounts, as well as the extent of the mixing/changing to rain in my far south later Sunday into Sunday evening. Not much has changed in the overall thinking in terms of snow amounts, with only minor tweaks made from the updated snow amounts from this morning. Generally this will continue to result in the highest totals of generally 8 to 12 inches north of I-80. Amounts still look to tapper off into the 1 to 4 inch range over my far southern counties (Livingston, Ford, Iroquois and Benton counties). As a result, no changes are planned to the current headlines. An impressive band of moderate snow continues to develop east- northeastward over eastern Iowa and western Illinois in association with an initial band of frontogenesis along the leading edge of the increasing isentropic upglide (warm air advection). This area of snow should begin to result in a quick onset of moderate snow from west to east over the area within the next few hours. This could result in up to a quick inch of snow through early this evening, especially over north central Illinois. Once this snow onsets, it appears that it will continue at times through the night and into Sunday morning over northern Illinois and northwestern Indiana as warm air advection continues. Mesoscale banding will also continue to be possible over northern Illinois overnight as steep mid-level lapse rates remain in place above 650 MB. As a result, snow amounts tonight alone could be in the 3 to 6 inch range, especially north of I-80 where higher ratios of around 15 to 1 will be likely. Periods of moderate snow look to continue Sunday morning, though there could end up being a break, or a period of lighter snow during the morning, before another period of wetter snow onsets in the afternoon in association with the approach of the mid-level disturbance. This could again result in periods of moderate, to possibly at times heavy snow over the area into early Sunday evening. Temperatures still could get warm enough in my far south for a mix or transition to a period of rain late Sunday into the evening, though it appears areas farther north would remain mainly snow. Snow ratios will likely be lower (around 10 to 1) during the day, but another 3 to 6 inches will still be possible. The snow should gradually come to an end from west to east during the evening on Sunday. There could also be some patchy blowing snow Sunday night as the winds pick up a bit on the back side of the surface low. However, given the wet nature to the snow on Sunday, blowing snow would likely be a minor impact. KJB && .LONG TERM... 249 PM CST Monday through Saturday... Concerns in the long-term portion of the forecast include the potential for dangerous cold Tuesday night through Thursday night, as well as a few opportunities for snow. Late next week, a more significant storm system could take shape, with accompanying accumulating wintry precipitation. Anomalous mid and upper ridging across the Aleutians and northeastern Pacific near Alaska will favor a very cold pattern continuing through the upcoming week, as true Arctic air plunges southward across the country. A piece of the polar vortex will drop to near Hudson Bay, supporting 500 mb heights of near or below 480 DM. Meanwhile, the fast progressive jet stream pattern will remain as well, with low amplitude clipper type disturbances possible Monday evening and again Wednesday. With the Arctic air mass in place, any snow from these potential systems will be of the fluffy/high-ratio variety. Thus, while the current operational guidance would not suggest any significant events, snow will easily accumulate on surfaces for at least some travel impacts. Also, some previous model runs have offered potential for more energetic disturbances and more notable accumulations, so cannot rule this out either. Again, latest forecast suggests that period of interest for potential fast moving snow producers are Monday evening and Wednesday. Returning to the potential for dangerous cold in the mid-late work week period, behind the possible Wednesday system, shortwave around impressive ~480 DM mid-level low near James Bay will send a potent thermal trough our way. Models have exhibited run to run variance in the magnitude of the cold air mass that reaches our latitude, though there was consistency in today`s guidance in 850 mb temperatures of -20 Celsius or colder Wednesday afternoon through early Thursday. With deep snow pack in place, this thermal profile will easily support temperatures barely budging and then falling Wednesday afternoon followed by widespread subzero readings Wednesday night/early Thursday. Expansive high pressure spreading toward area will also add a westerly wind component to support wind chill values of -20F or colder (advisory criteria or colder) for at least a portion of the area. Weak "warm" advection will ensue aloft on Thursday, though frigid start and no mixing under the high could keep temperatures in the single digits area wide, if not colder in a few spots. Finally, despite long lead time, concern is increasing for a significant winter event later in the week. A very impressive thermal gradient will exist across the Plains with Arctic high pressure to the north. At the mid and upper levels, there is decent guidance continuity in the idea of deep trough carving out into the intermountain West, with a temporary surge of height rises for the eastern 2/3 of the CONUS. Associated surface cyclone will be working with aforementioned impressive thermal gradient, as well as very strong WAA ahead of it, potentially supportive of mixed precip for at least portions of the area. This will depend on low pressure track and how far north warm surge makes it. Cold northerly flow supplied by Arctic surface high over the northern Plains, as well as deep snow pack locking in the cold increase the concern. With it being 5-6 days out, however, have maintained snow as precipitation type in the Friday-Saturday period. There is enough confidence in precipitation occurring for likely PoPs Friday night. Will need to watch this period closely as it draws closer. Castro && .AVIATION... For the 00Z TAFs... 554 pm...Main forecast concern is snow through the period with significant challenges trying to determine the time periods of lowest vis/cigs associated with bursts of moderate/heavy snow. Light snow continues to spread across the terminals this evening and while this timing and trends have worked out well...colder temps and lower dewpoints have resulted in a dry snow which has struggled to lower vis below 1sm. There may still be some vis reductions below 1sm this evening but not confident on how prevailing vis under 1sm will become. Models seem to be converging on additional bands developing later this evening which may continue to support vis around 1sm or perhaps lower as the low levels fully saturate. Will need to monitor trends this evening and may need to make changes with the 03z updates. If this banding...more moderate snow doesn/t materialize later this will likely develop overnight toward dawn. Added a tempo for lower conditions during this time period but confidence remains low and changes here can be expected. Beyond this time period...maintained previous forecast as trying to pin down periods of moderate/heavy snow is difficult. Trends would support a lull mid/late Sunday morning with perhaps a period of heavy snow Sunday afternoon but not confident enough to make any changes with this forecast. Even if a lull does occur... its likely vis/cigs would improve no more than low ifr. Back edge of the snow does appear to become fairly progressive Sunday evening with snow ending after 00z but this timing will likely need adjustment with later forecasts. Winds have become south/southeast at most locations and will remain southeast through Sunday morning with speeds gradually increasing overnight into Sunday morning. Winds will eventually turn more to the southwest Sunday afternoon but confidence on this timing remains low. Some gusts into the upper teens/near 20kts are possible Sunday morning into Sunday afternoon. cms && .MARINE... 330 PM CST An active pattern is in store on the lake through the upcoming week. The pressure gradient between a weak surface low approaching the lake from the west and high pressure departing to the east will support south-southeast winds increasing tonight and topping out at 30 kt on Sunday. The low will track northeast Sunday night, with trailing cold front sweeping across the lake and resulting in winds shifting to west-northwest up to 30 kt, though likely remaining sub-gale. Westerly winds will diminish on Monday and briefly shift southwest ahead of another cold front Monday night, bringing another period of west-northwest winds to 30 kt. A brief period of gales can`t be ruled out in this period given the very cold air mass and deeply mixed unstable conditions. Yet another Arctic front will cross the lake Tuesday evening, and this frontal passage could set the stage for a fairly extended period of westerly gales through early Thursday. An even colder air mass will support very unstable conditions and deep mixing, along with the pressure gradient remaining tight as high pressure spreads eastward from the northern Plains. Despite the lake waters still being mild for mid December, will need to watch for freezing spray potential Wednesday and Thursday. Finally, to close out next week, a stronger storm system could take shape and affect the region as expansive high pressure spreads southeast across the Plains. Regarding headlines, have issued a Small Craft Advisory from early Sunday morning into Monday, for the strong southerly winds shifting to westerly. Hazardous conditions for small craft will subside by mid to late Monday morning for the Illinois shore as west winds diminish, and by mid to late afternoon for the Indiana shore after winds and waves diminish. Castro && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Winter Storm Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010- ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022 UNTIL MIDNIGHT Monday. Winter Weather Advisory...ILZ023 UNTIL MIDNIGHT Monday. IN...Winter Storm Warning...INZ001-INZ002 UNTIL MIDNIGHT Monday. Winter Weather Advisory...INZ010-INZ011 UNTIL MIDNIGHT Monday. LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...4 AM Sunday TO 9 AM Monday. Small Craft Advisory...LMZ743-LMZ744-LMZ745...4 AM Sunday TO 3 PM Monday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
Area Forecast Discussion
National Weather Service Medford OR
301 PM PST Sat Dec 10 2016 .DISCUSSION...The latest IR image shows the front that brought steady precipitation last night and this morning is just south of the area. Meanwhile a shortwave is swinging through Vancouver Island and a surface trough is just offshore. This feature will move inland in the next couple of hours and places like Coos County and northwest Douglas County will have an uptick in shower activity. Elsewhere at the moment showers are far and few in between. A look at the high res short range HRRR model shows showers increasing along the coast late this afternoon, then moving inland early this evening west of the Cascades. Snow levels this evening will be around 3500 feet along the Cascades, so accumulating snow is most likely to occur at Crater Lake and Diamond Lake where showers are expected to be most frequent. Could not rule out a inch or two near Lake of the Woods and an inch or less at Siskiyou Summit tonight. A strong westerly 100+ kt jet at 300mb will remain over the region through early next week. This will keep our weather active most of the time. The flow at the mid levels will also remain westerly with disturbances riding along it. Therefore we can expect showers to continue mainly west of the Cascades Sunday into Monday morning. Snow levels are expected to start out around 3000 feet Sunday the morning, then rising to around 3500 feet Sunday afternoon. Same for Monday morning and Monday afternoon. This type of flow at the mid levels typically results in higher precipitation amounts along and west facing slopes of the Cascades. However its not expected to be excessive, even for areas like Crater Lake and Diamond Lake. We`ll catch a relative break in the action Monday afternoon into Monday night with weak ridging building into the area, then a good slug of moisture (IVT related) could impact Northern Cal Tuesday morning. The models vary with respect to the tining and northward extent of the heavier precipitation. However they do agree that the heaviest precipitation should remain south of our area. If the core of the heavier precip ends up further north, say into southern Modoc and Siskiyou county, then we could be dealing with significant snow accumulations. As previously mentioned, it`s still a ways out so we`ll have to keep a close eye on this in the days to come. -Petrucelli .Long Term...Wed, Dec 14th - Saturday, Dec 17th... The long term period will bring with it the possibility of significant precipitation amounts across Northern California and portions of the East Side, followed or accompanied by the intrusion of an Arctic airmass into the region. This will set the stage for the possibility of low elevation snowfall west of the Cascades late int the week. However, it should be noted that there has been a tremendous amount of run to variability in the forecast models on timing and amount related details for this entire extended period. What there is fairly high confidence in is Arctic air spilling onto the East Side late week and moderate confidence in this also affecting the West Side. More specifically, on Wednesday, ESRL reforecast analog data from the 00Z GEFS indicates a 90th percentile (of climatology for this time of the year) precipitation event for the Northern Sierras from Monday night through Thursday afternoon, while, for our area, it indicates a 50-70 percent chance of a 90th percentile event in portions of eastern Siskiyou and Modoc Counties. Meanwhile, for Wednesday, the operational GFS and ECMWF 12Z runs indicated an atmospheric river affecting the Northern Sierras with precipitation pushing northward into our area into at least Eastern Siskiyou and Modoc Counties. During that time period snow levels appear they will be in the 4.5-5.5kft range. How much precipitation falls in our area certainly depends on the details and, while the operational models and reforecast analogs look promising for significant amounts, guidance has wavered on whether or not this will be a significant event. The 18Z GFS has just come in, and indicates 0.50" to 1" of water late Wed afternoon through late Thu afternoon for the mentioned areas in northeastern California. I would not be surprised if the guidance continues to waiver here for a couple more days. On Thursday and Arctic airmass intrudes from the north, spilling mostly out of the Columbia Basin, but also in modified form on the West Side. Models have periodically indicated (every other run or more for the day) a shortwave trough riding through Thursday night into Friday with 850mb temperatures falling from -4C to -8C. This brings a possibility of another round of West Side snowfall, possibly lower than was observed in the past week. It should be noted that some guidance simply shows the cold air working in on the West Side and not much else. A very cold air mass will then settle in for the weekend, with the next frontal system expected to dive in from the northwest early next week. It appears that temperatures on the East Side are very likely to fall into the single digits or lower for lows this upcoming weekend, with low in the 10s to lower 20s expected for most of the West Side. BTL && .AVIATION...10/18Z TAF CYCLE...VFR along the coast and in the Umpqua Basin is expected to lower to MVFR mid-afternoon as another round of showers move in, likely falling to IFR overnight into Sunday morning. Across the remainder of the West Side IFR to MVFR is expected to improve to VFR this afternoon and then IFR to LIFR is expected to develop overnight into Sunday morning. All high terrain areas west of the Cascades will experience at least partial terrain obscurations. East of the Cascades VFR and partial terrain obscurations will generally prevail, though areas of MVFR area expected this morning. The freezing level, between 5,000 and 6,000 feet, late this morning, is expected to lower to 4,000 to 5,000 feet through this evening. BTL && .MARINE...Updated 905 AM PST Saturday 9 December 2016...Periods of enhanced west to southwest winds are expected through Sunday evening. Winds will remain at or just below small craft advisory levels throughout this time. Meanwhile, west swell will combine with the resulting wind waves to produce steep seas in nearly all of the coastal waters. Have maintained a small craft advisory for both winds and seas throughout this time period, as conditions will be hazardous to small craft, but the confidence in the exact location and timing of winds is low. Beyond Sunday, winds and seas will become relatively calm for much of the week under high pressure and east winds, with a stronger system forecast to arrive by the weekend. BTL/BPN && .MFR WATCHES/WARNINGS/ADVISORIES... OR...None. CA...None. Pacific Coastal Waters...Small Craft Advisory until 10 AM PST Monday for PZZ350-356-370-376. $$ MAP/MAP/MAP
Area Forecast Discussion
National Weather Service Melbourne FL
920 PM EST Sat Dec 10 2016 .DISCUSSION... Tonight...Surface high pressure center will push to the middle Atlantic coast and cause low level winds to slowly veer to easterly. This will gradually raise dew points, then some isentropic lift will occur especially across the south half. This should support an expansion north of the stratocumulus that have been rather prevalent along the Treasure Coast. Satellite imagery did not support our previous cloud forecast though and have trimmed values except in the south. Precipitable water values are forecast to rise to about 1.3 inches along the Treasure Coast and support small rain chances, but it looks too dry farther north for any POPs. Don`t anticipate much change for min temps, though the evening mostly clear skies in the north will necessitate a downward tweak. Sunday...Surface high shifting offshore will cause winds to veer to east/southeast at the surface and southerly in the 850-700 mb layer. This will allow higher precipitable water values to lift northward, but the 18z GFS only showed values 1.4-1.5 inches along the south coast and 1.3-1.4 inches along the Brevard coast. The HRRR model is rather skimpy on shower coverage spreading north while the local WRF is more generous especially south of Orlando and Cape Canaveral. The ECMWF showed a 1.5 inch bullseye of precip along the Treasure Coast. Our forecast hitting coastal areas south of Canaveral with 40 percent chances looks good for now. Cannot rule out locally heavy rain amounts with the breezy low level flow possibly enhancing convergence. Elsewhere rain chances look low but expect more cloudiness. Overall air mass moderation should result in max temps about 3-5 degrees more mild than today. && .AVIATION... Stratocumulus ceilings expected to be most prevalent KMLB-KSUA and especially so KFPR-KSUA where some showers may produce MVFR tonight. Chances for showers will elevate in those areas Sunday morning into afternoon and a few periods of MVFR should occur. Elsewhere, expect mainly VFR, but there should be more extensive ceilings at or above FL035. && .MARINE... Tonight-Sunday...Pressure gradient has decreased in the north due to the proximity of an inverted trough. The gradient is tighter in the south, as evidenced by some still gusty coastal winds. The inverted trough is forecast to dissipated by Sunday morning and the overall pressure gradient should tighten over most of the waters. The small craft advisory expiring at 4 am for the central zones may need to be extended through the day. Even in the north conditions for small craft operation look poor, and possibly hazardous offshore. && .MLB WATCHES/WARNINGS/ADVISORIES... FL...None. AM...Small Craft Advisory until 4 AM EST Sunday for Volusia-Brevard County Line to Sebastian Inlet 0-20 nm-Volusia-Brevard County Line to Sebastian Inlet 20-60 nm. Small Craft Advisory until 4 PM EST Sunday for Sebastian Inlet to Jupiter Inlet 0-20 nm-Sebastian Inlet to Jupiter Inlet 20-60 nm. && $$ Lascody/Blottman
Area Forecast Discussion
National Weather Service Marquette MI
1019 PM EST Sat Dec 10 2016 .UPDATE... Issued at 1018 PM EST SAT DEC 10 2016 ...Warnings for Alger and Luce Counties cancelled... The MQT radar indicates the les bands that have been impacting ern Alger and nrn Luce Counties are shifting offshore as the llvl winds at even Grand Marais have turned to the sw, shifting the axis of stronger llvl cnvgc out over the open lake. So the warnings that were in effect until 05Z for Alger and Luce Counties have been canx. && .SHORT TERM...(This evening through Sunday) Issued at 409 PM EST SAT DEC 10 2016 ...Lake effect snow ends tonight then widespread system snow moves in on Sunday... Lake effect snow continues but the areas affected have become less over the last 24 hours. Persistent sfc trough over southern Lk Superior is main focus with one or two dominant bands of snow over parts of Keweenaw and multiple dominant bands with some connection to Lk Nipigon converging over eastern Alger and northern Luce. Over water instability remains favorable for lake effect with inversions over western Lk Superior around 5kft/h85 with inversion top temps to -20c and up to 8kft/h75/-25c over eastern Lk Superior. Winds back steadily to the WSW-SW this evening over Keweenaw so expect heavier snow to remain on the move and will not extend the warning or advy there. However, convergence remains strong into far eastern Alger and northern Luce so extended warning there until midnight when HRRR indicates blyr winds turn SW enough to push heavier lake effect offshore. Away from the lake effect this evening skies should be mostly clear allowing temps to fall off toward zero this evening for the interior west. Mid-high clouds increase overnight as low pressure system over eastern WY and CO this aftn pushes across the central Plains. Min temps will depend how quickly the clouds move in but a few zero to 5 below readings for favored cold spots seems likely. Low pressure system crosses IA and WI/northern IL on Sun morning. WNW flow aloft and lack of very tight baroclinic zone at h85 should keep stronger isentropic ascent snow mainly south of cwa into Sun morning. However by aftn shortwave trough that is currently over Pacific NW moves across Dakotas and northern MN. Deep layer q-vector convergence increases markedly through the aftn and that forcing along with increasing moisture advection ahead of low pressure trough over WI (mixing ratios at h7 up to 2g/kg) running into cold airmass should start to produce light to moderate snow. H85 low tracking across northern WI as the shortwave moves through also increases larger scale lift and there is some mid-level fgen on northern edge of this low. That forcing along with SE winds off Lk Michian and E winds off Lk Superior should result in lake enhancement with h85 temps -8c to -10c and water temps around 5c. Overall snow amounts with this system should fall into advy range of 3 to 5 inches in 12 hours (12z-24z/7 am ET to 7 pm ET) along WI border, but lake enhancement could add to the totals for scntrl Upper Michigan and across the Keweenaw Peninsula. Highlighted this potential in the WSW statement and it is possible eventually could need warnings but will start with advy for now. Does look like after this event all areas of Upper Michigan will have at least light snow cover. .LONG TERM...(Sunday night through Saturday) Issued at 435 PM EST SAT DEC 10 2016 The medium range models suggest that the blocking ridge through Alaska will favor pattern amplification with an intrusion of very cold arctic air into the CONUS as the deep mid level low moves into nrn Ontario. This will bring an extended period of wrly flow LES and low wind chills across the region. Sunday night, although the stronger isentropic lift will shift off into the ern cwa during the evening a period moderate to strong 700- 300 mb qvector conv associated with the shrtwv moving out of the nrn plains will help sustain the light to moderate snow through the evening. In addition, convergent se winds off of Lake Michigan and easterly winds on Lake Superior will bring some higher snow amounts into s cntrl Upper Michigan and the Keweenaw. As the sfc trough moves off to the east another period of lake enhanced snow may affect the nw cwa. QPF values in the 0.10-0.15 inch range will favor another couple of inches for most of the cwa with local amounts of 5 inches or more over the Keweenaw. Monday, once the lingering snow over the nw ends expect mainly dry weather. Winds backing to the sw will keep most of the additional LES potential west of the Keweenaw. Monday night into Tuesday, the arctic front is expected quickly move through the nrn Great Lakes. A period of light snow associated with qvector conv ahead of the mid level trough may bring a period of light snow through the cwa Monday night with heavier lake enhanced snow or LES over the Keweenaw as winds veer to the west. Temps will fall or remain steady through the single digits Tuesday. Wednesday-Friday, after the initial surge of arctic air, a reinforcing batch is expected to move in wed into wed night. This will bring a slight veering trend with the low level flow which may push the LES into a greater portion of the nrn cwa, especially from p53 eastward. LES will continue through the period, but the intensity will be limited as the very cold air limits snow growth. However, low vsby will prevail through most of the period downwind of the wrly flow. Wind chill values may approach 25 below both Wed and Thu, especially inland west, farthest from any moderating influence of Lake Superior. Saturday, GFS/GEFS/ECMWF maintain the idea of that sw mid level flow in response to trough into the Rockies will favor the development of a broad waa pattern which could bring widespread snow into the region. However, confidence in any details is low. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 620 PM EST SAT DEC 10 2016 As the llvl winds shift to the sw over the Keweenaw this evng, band of heavier les impacting CMX wl shift to the n and allow for VFR conditions to dvlp at that site later in the evng. Dry llvl air at SAW and IWD wl result in VFR conditions at both those locations even as mid/hi clds begin to increase overngt ahead of the next lo pres advancing toward the Upr Midwest. Sn in advance of this lo pres wl overspread Upr MI on Sun, resulting in IFR conditions by the aftn at all 3 sites. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 435 PM EST SAT DEC 10 2016 Expect NW winds up to 25 kts to diminish under 20 kts tonight but may increase to around 25 knots as a trough lifts into Upper Michigan Sunday. A steady WNW wind to 30 kts with potential for brief periods of gales Mon night into Thu following a strong cold frontal passage that will introduce arctic air into the Upper Lakes. Expect some heavy freezing spray over at least portions of the Lake on Tue night/Wed as this arctic air moves into the area and waves at the end of fetch build to at least 10 feet. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Winter Weather Advisory from 10 AM EST /9 AM CST/ Sunday to 1 AM EST /midnight CST/ Monday for MIZ002-004>007-009>014-084- 085. Winter Weather Advisory from 1 PM Sunday to 7 AM EST Monday for MIZ001-003. Lake Superior... None. Lake Michigan... None. && $$ UPDATE...KC SHORT TERM...JLA LONG TERM...JLB AVIATION...KC MARINE...JLB
Area Forecast Discussion
National Weather Service Charleston WV
1013 PM EST Sat Dec 10 2016 .SYNOPSIS... A low pressure system crosses Sunday night and Monday. A cold front crosses toward midweek bringing another arctic blast and ushering in a more unsettled pattern through next weekend. && .NEAR TERM /THROUGH SUNDAY/... As of 1010 PM Saturday.. Used the latest runs of the HRRR and RAP to give the POPs, QPF, and snow grids some TLC along the far northern tier of the CWA beginning tonight through 18Z Sunday. The changes do not amount to all that much, and max out the totals to around 1.5 inches, but for only a very small area up in far northern Perry County. As of 200 PM Saturday... Clouds will be increasing tonight as mid and high level moisture advect into the area ahead of the next system. WAA will be increasing over the upper Ohio Valley on low level SW flow. Some good isentropic lift will develop as well, which will allow snow to overspread portions of the upper Ohio Valley. It still appears most of this will fall just north of the RLX CWA, perhaps clipping Perry/Morgan over to Clarksburg/Elkins later tonight. The consensus in the hi res models though keeps all of precip north of the CWA with the GFS/ECMWF showing QPF over the aforementioned areas. Given the amount of low level dry air in place...tend to favor keeping the precip north of the area but will leave a tight gradient of POPs across our northern fringe counties for some wiggle room. The best chance for any accumulations would across Perry/Morgan where a tenth or two is possible. This all pushes north Sunday morning with mainly a dry forecast for the daylight hours in broad SW flow aloft/SE flow at the surface. Expect some sunshine in the afternoon across SW VA and a good portion of WV. This along with downsloping should allow temps to approach 50 in the typical banana belt areas along US 119/I 79 corridor. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 250 PM Saturday... The period starts with another front knocking on our doorstep. Continuing WAA will push H85 temps to near +10C ahead of this system, so predominantly a rain event for most areas. There will be a small window for brief frozen precip in/near the mountains from late Sunday evening into the pre-dawn hours Monday before too much warm air moves in aloft. Forecast soundings show low level thermal profiles favoring brief SN along the taller ridges with ZR possible in mountain valleys. While a light glaze of ice is possible, the changeover to rain should occur relatively quickly Monday morning with all rain across the area before dawn. Temperatures will remain cool but relatively mild compared to the previous several days and rain should end west-to-east late Monday into Tuesday with sfc high pressure building back in. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 250 PM Saturday... Confidence remains low concerning overall pattern evolution for the long term. Regardless of spatial and temporal discontinuities in model guidance, it does appear that another arctic airmass will filter in by mid week. Multiple rounds of precipitation are also possible through the period with any waves embedded in the larger scale flow. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... As of 630 PM Saturday... For the area terminals, forecast is VFR ceilings and visibilities with winds turning southerly less than 10kts. Off the surface, low level flow to increase steadily through the period. Warm front will develop north of the terminals with light snow overspreading the region. Again, this will fall north of the PKB- CKB-EKN line, and will end up in warm advection warm sector flow through the period. Rain will move in from the west northwest towards the end of the period, but will lie just beyond the temporal scope of the TAFs. FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z MONDAY... FORECAST CONFIDENCE: Medium SE OH/N WV. High elsewhere. ALTERNATE SCENARIOS: Light snow tonight may sneak into northern TAF sites which would bring MVFR into play. EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY OF WFO FORECAST TO AVAILABLE MODEL INFORMATION: H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS. L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL. DATE SUN 12/11/16 UTC 1HRLY 03 04 05 06 07 08 09 10 11 12 13 14 EST 1HRLY 22 23 00 01 02 03 04 05 06 07 08 09 CRW CONSISTENCY H H H H H H H H H H H M HTS CONSISTENCY H H H H H H H H H H H M BKW CONSISTENCY H H H H H H H H H H H M EKN CONSISTENCY H H H H H H H H H H H M PKB CONSISTENCY H H H H H H H H H H H M CKB CONSISTENCY H H H H H H H H H H H M AFTER 00Z MONDAY... IFR possible in rain developing Sunday night. && .RLX WATCHES/WARNINGS/ADVISORIES... WV...None. OH...None. KY...None. VA...None. && $$ SYNOPSIS...30/DTC NEAR TERM...30/26 SHORT TERM...DTC LONG TERM...DTC AVIATION...26