Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Nov 30 2024 19:23:37 FOUS11 KWBC 301923 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 223 PM EST Sat Nov 30 2024 Valid 00Z Sun Dec 01 2024 - 00Z Wed Dec 04 2024 ...Great Lakes... Days 1-3... *** Heavy Lake-Effect Snow event into early Tuesday *** Broad cyclonic flow from the upper levels to the surface will=20 continue across eastern Canada and across the Great Lakes through=20 Tuesday when the trough will finally start to move out of the=20 Northeast. With Great Lake SSTs well above average for this time of year (+8C to +14C per GLERL) and 850mb temps around -10C, the=20 sfc-850 delta-T will remain ~20C which supports strong/intense=20 uplift/instability. The sometimes extreme instability will support=20 cellular convection embedded within well-formed lake-effect bands=20 and may include thundersnow. The cyclonic flow and continued moisture influx will also favor=20 broad atmospheric lift irrespective of the lakes. This favorable=20 atmosphere will maximize each lake's ability to continue producing=20 heavy lake-effect snow. The general northwesterly flow will also=20 allow for the upper lakes to feed the lake-effect off the lower=20 lakes. This will be a large contributor to the prodigious snow=20 totals forecast southeast of the lower lakes. Lake Superior and=20 Georgian Bay (part of Lake Huron) will feed into Lake Ontario's=20 lake band, while the bulk of Lake Huron will feed into Lake Erie's=20 lake-effect bands. Lake Erie will be increasingly dependent on Lake Huron's support as the winds shift more northwesterly and become=20 more perpendicular to the long axis of the lake. Upslope into the=20 terrain of far northwest Pennsylvania and far western NY for Lake=20 Erie's bands and into the Tug Hill east of Lake Ontario will=20 locally further enhance the lift and ability of the bands to=20 produce incredibly heavy snowfall -- at times exceeding several=20 inches per hour. Storm total snowfall could approach 6 feet east of Lake Ontario=20 and 3-4 feet southeast of Lake Erie. Off of the upper lakes, the=20 broader geography of the larger lakes makes single band formation=20 much more difficult, so multiple smaller bands of moderate to=20 occasionally heavy snow are likely to impact portions of the U.P.=20 and the northwestern lower peninsula. Snowfall amounts over a foot=20 are expected in the eastern U.P. and far western U.P. as well as=20 east of Traverse City. WPC probabilities of at least an additional=20 18 inches of snow are high (>70%) near Watertown-Fort Drum through=20 Sunday afternoon. Over southwestern NY, WPC probabilities for at=20 least an additional foot of snow are high (>70%) just south of=20 Buffalo along I-90. The latest Winter Storm Severity Index values show extreme impacts through Monday in the Watertown, NY area east of Lake Ontario and=20 along the I-90 corridor from the Buffalo southtowns through=20 Ashtabula, OH, including through Erie, PA southeast of Lake Erie.=20 Travel will remain extremely dangerous to near impossible with=20 numerous road closures.=20 By Tuesday, the upper trough will finally start to shift eastward=20 with its axis moving east of 70W by the afternoon, helping to=20 slowly diminish the lake effect snowfall. Upstream, another weak=20 disturbance will move out of southern Canada into the northern=20 Plains/Upper Midwest with light snow spreading across northern MN.=20 Amounts look fairly light at this time, and WPC probabilities for=20 at least 4 inches of snow are around 10% through 00Z Wednesday=20 right along the Canadian border. The ongoing lake-effect snow is a subject of the Key Message=20 linked below. ....Southern IN/northern KY to West Virginia...=20 Day 1... Broad upper troughing over the eastern CONUS will carry a weak=20 disturbance out of the MS Valley this evening and across TN tonight as it slowly weakens. Attendant surface front and weak area of low pressure will promote a light west-to-east axis of snowfall along=20 the I-64 corridor east of MO tonight. Recent guidance has trended=20 just a tick south and lighter with QPF (thus snowfall), and WPC=20 probabilities for at least 2 inches are low (10-40%) mostly over=20 southern IN and somewhat across northern KY. Farther east, upslope=20 into the central Appalachians will be the main driver for heavier=20 amounts and WPC probabilities for at least 4 inches of snow are=20 >70% above 1500ft or so.=20 The probability of significant ice across the CONUS is less than=20 10 percent.=20 Fracasso/Wegman ....Winter Storm Key Messages are in effect. Please see current=20 Key Messages below... https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_1.png__;!!DZ3fjg!9oslp7Gz5btZZ6TW0FkEUMLCGx5PGPlDZm90ljG7WgmXO= twhkXQCAaerv_Fbq5QHI3thZNmfl9dYUI00cYDgbZbManA$=20 $$ =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .