Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Dec 03 2025 20:15:41 FOUS11 KWBC 032015 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 315 PM EST Wed Dec 3 2025 Valid 00Z Thu Dec 04 2025 - 00Z Sun Dec 07 2025 ....Southern/Central Rockies...=20 Day 1... The sharp, positively-titled trough currently over the Four=20 Corners states will continue to translate eastward tonight before=20 ejecting into the central/southern Plains on Thursday. Forcing for=20 ascent downstream of this trough (in response to height falls and=20 modest divergence) will be enhanced by a strengthening jet streak,=20 especially tonight into Thursday morning. Meanwhile, Canadian high=20 pressure dropping into the Plains will result in impressive upslope flow as cold N/NE winds develop in response. Moisture within the=20 region is progged to be around to slightly below normal as=20 reflected by NAEFS ensembles, but the impressive overlapping ascent will still be favorable to support heavy snow. This will=20 especially be the case above 4000-5000 ft, with snow levels falling in conjunction with waning snowfall intensity later tonight into=20 Thursday morning. The latest WPC probabilities continue to show=20 moderate to high chances (40-80%) for additional accumulations of=20 >6 inches across portions of the southern San Juans and Sangre de=20 Cristo mountain ranges, with low to moderate chances (20-50%) of >8 inches. ....Great Lakes & Northeast... Days 1-3... Progressive flow across the Northeast will manifest in response to a large gyre centered near Hudson Bay, which will shed periodic=20 shortwaves from the Great Lakes through the Northeast leading to=20 occasional enhanced ascent and lowered heights throughout. In=20 response to this evolution, multiple rounds of snowfall, sometimes=20 heavy, are expected through the period.=20 The first event will be associated with an arctic cold front=20 dragging southeast beneath a shortwave aloft. This front will move=20 rapidly across the eastern Great Lakes tonight, and then across the Northeast on Thursday. Along and ahead of this front, the=20 environment continues to suggest an increasing threat for snow=20 squalls, especially across Upstate NY and New England on Thursday.=20 With 0-2km fgen maximizing along the front into elevated RH and=20 SBCAPE as high as 300 J/kg, widespread linear squalls are likely.=20 While total snowfall will be minimal in any squall, rapidly=20 changing conditions due to heavy snow and gusty winds will create=20 periods of dangerous travel Thursday afternoon and evening. As a=20 result, WPC has initiated Key Messages to highlight this event. See the link below for more details. Behind this front, as well as behind a subsequent shortwave on=20 Friday, increased CAA will spread across the Great Lakes leading to periods of lake effect snow (LES). The progressive flow will=20 support shortwave ridging between the two impulses, so the duration of any LES with each shortwave/front should be somewhat limited.=20 However, 850mb temps falling to between -15C to -20C Thursday, and=20 then between -10C to -15C late Friday into Saturday, will create=20 steep lapse rates and deepening inversion depths to support bands=20 of heavy LES. The heaviest LES snowfall accumulations within the=20 LES bands are expected in the typical NW snow belts across the U.P. of MI, the NW L.P. near Traverse City, and then along the=20 Chautauqua Ridge and into the Tug Hill Plateau. In these belts,=20 3-day snowfall of 6-12 inches is possible, highest across the U.P. ....Mid-South to the Mid-Atlantic...=20 Day 2... Plenty of uncertainty heading into Day 2 with respect to a strung- out shortwave exiting the Central Plains and becoming embedded=20 within the more zonal flow to the east. Although this shortwave is=20 expected to be of modest amplitude and fast moving, the=20 accompanying upper jet is progged to be powerful at over 150kts=20 across the Mid-Atlantic, leading to surface low pressure=20 development across the Southeast. This low will then race E/NE,=20 producing a swath of at least light wintry precipitation from the=20 Tennessee Valley to the Mid-Atlantic states.=20 There has been at least a modest northward shift/trend in the=20 MSLP/QPF fields from the various global ensembles the past few=20 runs, with the ECMWF and various machine learning suites the=20 farthest north. While it still remains too early to iron out the=20 details, WPC probabilities of 1+ inches of snow across the Central=20 Appalachians and into eastern VA/MD have increased to 20-60%, with=20 the highest chances in the higher terrain of WV/VA. WPC=20 probabilities for 2+ inches are between 10-20% from eastern WV to=20 central VA. South of the potential moderate snow, an axis of light freezing rain is also possible where a p-type transition occurs underneath a stubborn layer of low-level cold air. The latest WPC=20 probabilities maintain a 10-30% chance for at least 0.1" of ice=20 across northern NC and into southern VA. ....Northern to Central Rockies...=20 Days 1-3... The next chance for heavy snowfall totals in the northern Rockies=20 will develop as a low amplitude shortwave slides off of the top of=20 the Pacific ridge into the region late Thursday into Friday,=20 coincident with the LFQ of an impressive upper jet streak swinging=20 across the Northern Pacific. This will result in favorable mid to=20 upper level forcing along with a notable influx of Pacific=20 moisture, sufficient for some heavy totals, especially above around 5000 ft as snow levels rise coincident with this moisture plume=20 moving into the area. Heavy snowfall accumulations are likely from=20 the WA Cascades through the terrain of NW WY near Yellowstone NP as reflected by WPC probabilities that suggest a high risk (>70%) for 4+ inches, with impacts to many of the area passes becoming=20 likely. Probabilities become even more impressive Day 2 and 3 across the=20 higher terrain from Glacier NP through Yellowstone NP including=20 portions of the Sawtooth/Salmon River ranges, Absarokas, terrain of NW WY, northern Utah, and into the Park Range of CO. Here, WPC=20 probabilities Day 2 and 3 reach above 70% for 8+ inches, and Day 2=20 and Day 3 snowfall could be impressive above generally 6000 ft=20 where locally 1-2 feet is possible. Miller/Weiss ....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!4ONBRMdITod6KQZeFxmplUpEcL6FhhdNmsyM3cstn2js_= 1Nv2iBrrRRCa5z0OsCbPZ1yd7WcRTVv4VpGUAMNxmUzroo$=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .