Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Feb 15 2025 08:04:13 FOUS11 KWBC 150803 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 303 AM EST Sat Feb 15 2025 Valid 12Z Sat Feb 15 2025 - 12Z Tue Feb 18 2025 ....Rockies...=20 Day 1... The upper trough centered across the Four Corners will continue=20 eastward today, with the last trailing vorticity pushing through=20 the CO Rockies this afternoon. Light to modest snow over the higher peaks of CO into southeastern WY will diminsh through the day with an additional 4-8+" likely and much lighter snow into the valleys=20 and Front Range.=20 ....Corn Belt/Midwest/Great Lakes/Northeast...=20 Days 1-3... Trough in the Rockies will exit today with a long extension to the northeast into the Upper Midwest. Base of the trough will lag=20 through TX but additional height falls out of Canada will slow the=20 northern stream, alloiwing the trough to recongeal as it heads into the Ohio Valley and then the Northeast. The setup will be broad=20 WAA-driven snow into the Great Lakes and Northeast but as the=20 trough sharpens and jet becomes more S-shaped along 80W, low=20 pressure will deepen and surge mild air far northward toward the=20 Canadian border, allowing snow to change to sleet/freezing rain and just rain through Sunday with the main low into western NY. By=20 that time, a new area of low pressure will start to take shape and=20 eventually take over southeast MA into the Gulf of Maine,=20 essentially halting the northward surge in milder air into/through=20 New England as the low finall then lifts northeastward along the=20 Maine coast and into Atlantic Canada by early Monday.=20 For D1, strengthening jet across Michigan into Canada will act to=20 maintain snowfall over Lower MI today where WPC probabilities for=20 at least 4 inches of snow are >50% for the central/eastern 2/3rds.=20 Into the Northeast, WAA-driven snow will overspread the region this morning/afternoon where temperatures are cold. Could capitalize on good WAA for this front-end thump of snow but strong southerly=20 surge will drive the mixed ptype zone northward from the Mid-=20 Atlantic later this afternoon into tonight. WPC probs for at least=20 4 inches of snow are highest (>50%) farthest north where the cold=20 air will hang on the longest -- north of I-90 into the Adirondacks=20 and Green Mountains as well as into the Berkshires and Worcester=20 Hills. To the south, temperatures are sub-freezing thanks to high=20 pressure overhead this morning but aloft it is near and just above=20 0C. Any snow will turn to sleet or more likely freezing rain from=20 across the Midwest and especially into the central Appalachians (SW VA into central PA then up into the Southern Tier of NY). Ice=20 accumulation will depend on how long the cold surface temperature=20 can resist the strong surge in mild air from the south. WPC probs=20 for at least 0.25" icing are at least 30% along the WV/VA line=20 northward to the I-99/US 220 corridor.=20 Into D2, low pressure over southeastern OH will track=20 northeastward toward western/central NY by the afternoon as the=20 coastal low takes shape, which should stop the northward push of=20 the mix ptype zone but not before it may reach all the way to the=20 Canadian border (NY/VT) and into Downeast Maine. The remaining cold air will be largely confined to northern Maine where WPC probs for at least 6 inches of snow are >50% north of I-95. Ice=20 accumulations will be primarily over eastern NY and north of I-95=20 into New England, especially into the Berkshires and Monadnocks=20 where ice probs for at least 0.25" are at least 20%.=20 By D3, storm will be well out into the Atlantic but with a broad=20 cyclonic flow back across the Great Lakes, supporting lake-effect=20 snow off all the lakes but especially off Lake Ontario on WNW flow. This could support a healthy single band into the northern SYR=20 suburbs from Oswego toward Rome/Utica where at least several inches of snow are possible.=20 ....Pacific Northwest/Rockies/Central Plains...=20 Days 1-3... The next multi-vorticity lobe upper low in the northeast Pacific=20 will send a cold front into the Pac NW later today with snow levels around 3000-4000ft for the WA/OR Cascades. With the upper jet=20 nosed into southern OR for the next two days or so, onshore flow=20 will continue to provide Pacific moisture to the region and into=20 the Great Basin/northern Rockies, overriding cold air on the east=20 side of the Divide. There, lower level convergence should enhance=20 snowfall over western MT D2 into D3 with two-day WPC snow=20 probabilities for >12" >70%. Snow into the Cascades will affect=20 the passes esp D1-2 until the trailing upper low finally reaches=20 the coast.=20 Farther southeast, moisture will spread back into the central/CO=20 Rockies with additional amounts of at least 6 inches likely by D3.=20 Onto the Plains, incoming vort maxes in the quick WNW flow atop=20 lower-level WAA will favor light snow stretching from western NE=20 southeastward toward the MS River Valley including much of KS. The=20 air mass will be fairly cold thanks to high pressure starting to=20 assert itself across southern Canada into the Dakotas, supporting=20 SLRs ~15:1. Through 12Z Tue, WPC probabilities for at least 4=20 inches of snow are 40-60% over the northern half of KS into=20 southern NE with more to follow.=20 Fracasso ....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!88-PewK77Ur9LQ3bDMbolWcFPOOPt3JbpybhL-du-PAE9= G0-mE1kk-tfUKhgRYRKy0o4fX0a7nfggdpfTjViwTJcQp4$=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) .