Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jan 06 2025 20:30:32 FOUS11 KWBC 062030 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 330 PM EST Mon Jan 6 2025 Valid 00Z Tue Jan 07 2025 - 00Z Fri Jan 10 2025 ....Mid-Atlantic... Day 1... Trailing mid-level shortwave behind the outgoing major winter=20 storm will pass quickly through the Mid-Atlantic early this=20 evening, spurring another inch or two of snow east of the=20 mountains. Over central WV, some upslope enhancement will help=20 squeeze out perhaps a few inches, with WPC probabilities for an=20 additional 4 inches of snow after 00Z around 30-50%. Snow will=20 taper off there by Tuesday afternoon. ....Great Lakes and Northeast... Days 1-3... A large, sprawling, and multi-pronged circulation over=20 southeastern Canada will send mid-level shortwaves into the eastern Great Lakes and Northeast over the next few days, maintaining high chances of at least light snow over the higher elevations (NY and=20 northern VT/NH) and also downwind of the Great Lakes in general=20 owing to the broad cyclonic flow.=20 For D1, a compact closed low near Montreal this evening will swing through northern NY/VT overnight with some terrain enhancement=20 over the northern Adirondacks and into the Green Mountains. WPC=20 probabilities for at least 4 inches of snow tonight through Tuesday are 50-80% there. By D2, with already cold 850mb temps below -12C or so, a=20 reinforcing shot of cold Canadian air (via another short wave out=20 of Canada) will steepen lapse rates and reinvigorate lake effect=20 snow off the western Great Lakes, especially along the western=20 shore of Lower Michigan, and also off Lakes Erie/Ontario on NW=20 flow. WPC probabilities for at least 4 inches of snow D2 are=20 highest south of Muskegon right along the lake short, but will be=20 dependent on the fetch and trajectory of the band.=20 For D3, one last shortwave will push through the eastern Great=20 Lakes and New England, maintaining additional light snow off Lake=20 Ontario on NW flow and additional snow for the northern Adirondacks and Green Mountains. WPC probabilities for at least an additional=20 4 inches of snow are moderate (40-70%) over these areas. ....Intermountain West, Rockies, and Southwest... Days 1-3... Broad height falls moving through the Great Basin tonight will=20 sharpen into a closed low over the lower CO River Valley late Tue.=20 With high pressure nosing down out of the northern Plains, upslope=20 snow will expand across the CO Front Range via an easterly low=20 level flow along with a relatively low DGZ. However, the snow=20 should not last too long as the upper low will likely move into=20 northwestern Mexico by the end of the period. This will help to=20 drag the snowfall southward as well through the Mogollon Rim,=20 Sangre de Cristos, Sacramento Mountains, etc. Models continue to=20 vary on QPF (and thus snow) over parts of the Southwest but at=20 least a large footprint of light snow is expected. For the D1-3=20 period, WPC probabilities for at least 4 inches of snow are >50%=20 over the Front Range into the CO Rockies, San Juans, and higher=20 elevations in AZ/NM above 8000ft or so.=20 Farther north, a shortwave moving out of Canada through Montana on Wednesday will touch off some light to locally moderate snow over=20 much of the state that will push into Wyoming and the Black Hills=20 on Thursday. WPC probabilities for at least 4 inches of snow are=20 highest (>50%) over the Little Belts, Gallatin Range, and into the=20 Bighorns. ....Southern Plains... Day 3... As the aforementioned upper low closes off over the Southwest=20 Thursday and continues to dig into northwestern Mexico Friday it=20 will become anomalously deep (below the 0.5th climate percentile=20 per the NAEFS ESAT). Meanwhile, a separate shortwave rounding the=20 far eastern Pacific ridge is forecast to dive southward through=20 Utah and interact with this feature and spawn strong southwest flow containing rich moisture and prominent upper divergence from an=20 increasingly buckled jet. Given the strong high situated to the=20 north over the Central Plains and a cold low-level airmass in=20 place, snow and mixed precipitation is expected over much of=20 western and north-central TX late Wed and through Thursday,=20 expanding eastward to the Ozarks by the end of the period. Thermal=20 uncertainty is high (as expected) due to the upstream players=20 (timing, depth, etc.) and the NBM ptype probabilities show a zone=20 of maximum uncertainty from near the Big Bend northeastward to=20 around TexArKana.=20 All ptypes are in play -- snow/sleet/freezing rain and plain rain=20 to the south -- and each will likely not be stagnant in location.=20 For now, the highest probabilities of snow lie on the northwest=20 side of the precipitation shield in the deeper colder air from the=20 Permian Basin across Northwest TX into North TX (near and northwest of the D-FW Metroplex). There, WPC probabilities for at least 4=20 inches of snow are around 30-50%. To the southeast, within the zone of maximum uncertainty, probabilitiesfor accumulating snowfall=20 decrease while probabilities for ice increase. Areas from near=20 Austin northeastwardthrough the Piney Woods into the Hill Parishes=20 of LA show the highest chance of at least 0.1 inches of ice=20 accumulation (30-60%). This system has prompted the issuance of a new set of Key Messages which are linked at the bottom of the discussion. Fracasso/Snell ....Winter Storm Key Messages are in effect. Please see current Key Messages below... https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late= stKeyMessage_2.png__;!!DZ3fjg!_p-d5kX8NzvPiea0SkbIvk3YnMjHKOh2q0s4iASxMHzCr= TEx8epFDhVUmnjbsdroCOxm3zPaNswlrn58foeDVnjrYAg$=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) .