Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jan 10 2025 08:34:26 FOUS11 KWBC 100834 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 334 AM EST Fri Jan 10 2025 Valid 12Z Fri Jan 10 2025 - 12Z Mon Jan 13 2025 ....Mid-South/Southeast into the Mid-Atlantic... Day 1-1.5... ....Major winter storm continues to progress eastward through the=20 Mid-South today with hazardous winter conditions into portions of=20 the Mid-Atlantic overnight...=20 A strongly positively-tilted longwave trough, with its axis back=20 into Mexico, will continue to help develop low pressure along the=20 Gulf Coast today on the southeast side of a 170kt jet. Gulf=20 moisture continues to stream northward into the Mid-South atop a=20 cold surface layer, yielding snow on the north side of the=20 expansive precipitation shield and a wintry mix of sleet and=20 freezing rain to the south (and plain rain toward the Gulf Coast).=20 Mid-level FGEN will drive moderate snow rates (~1"/hr at times)=20 over Tennessee this morning and early afternoon with a broader=20 shield of light snow to the north and northeast. Much of the region from southeastern MO and across most of TN has at least moderate=20 probabilities (>40%) of seeing at least 4 inches of snow. To the=20 north, a general 1-3" of snow is forecast as additional northern=20 stream energy moves through the Midwest.=20 To the south, milder air aloft will move northward up and over the cold surface layer, creating a mix of sleet and freezing rain over northern AL/GA that will continue E/NE through SC into=20 central/eastern NC as the system evolves later tonight. Where the=20 surface cold air is most stubborn beneath the >0C air aloft,=20 several hours of ZR may accrete to near/over 0.25" esp over N GA.=20 There is a large area from northern AL to central NC where WPC=20 probabilities of at least 0.10" ice are >30% with an embedded area=20 of 20-50% probs for at least 0.25" of ice.=20 By this evening, upper trough will be stretched and elongated and=20 become dominated by the northern stream approaching the central=20 Appalachians. Low pressure will reform along the Carolina coast and light northeastward overnight, spreading snow across interior NC=20 into VA with lighter snow extending northward into the Northeast.=20 Low pressure near Cape Fear 09Z Sat will quickly move northeastward and deepen, with a potential modest band of snow on the northwest=20 side across southern/southeastern VA and the southern DelMarVa. WPC Snowband Tool shows several members with ~1"/hr rates early Sat=20 morning (06-12Z) before the system finally scoots out to sea.=20 Though the probabilities for at least 4 inches are low (10-40%),=20 there is potential for some enhanced banding per a couple 00Z Hires members.=20 Lastly, across the central Appalachians, orographic upslope will=20 help wring out several inches of snow over the higher terrain from=20 the Laurel Highlands southward down to the Smokey Mountains, where=20 WPC probabilities for at least 4 inches are >50%.=20 ....Northwest to the Upper Midwest/Great Lakes... Days 1-3... Fairly sharp mid-level shortwave and sfc front will enter the=20 PacNW starting Friday morning with mostly higher elevation snow but lowering snow levels (from ~4500 to ~3000ft) as the front moves=20 past the Cascades. The shortwave will move southeastward beneath a=20 weakening upper jet, but the combination of height falls and=20 upslope enhancement will maximize snow over the mountains, from the Bitterroots to the Tetons and western MT today then into the=20 Big/Little Belts into the Bighorns and eventually the Black Hills=20 Saturday afternoon/evening as the stronger height falls move=20 through. WPC probabilities for at least 12 inches of snow D1-2 are=20 >50% above ~5000-6000ft or so (west to east) where two-day totals=20 could exceed 18-24 inches above 6000-7000ft (40-70% chance).=20 Farther south, with height falls digging into CO, areas in the=20 Rockies above ~8000ft have >50% chance of 8 inches of snow. Additionally, on D2, an Alberta clipper will move into the=20 northern Plains/Upper Midwest with a swath of generally light snow=20 via WAA and FGEN on the northern side of an area of low pressure=20 moving through central ND into southern MN by late Sat/early Sun.=20 Amounts should generally be on the lighter side of a couple/few=20 inches, with moderate probabilities (40-70%) of at least 2 inches=20 of snow from northern ND eastward across northern MN. This low will intensify during the Day Sunday when it moves over northern=20 Wisconsin and the U.P. before curling back to the northeast across=20 the U.P. and into Quebec by early Mon. A reinforcing upper level=20 low will rotate into northern MN by the end of the period, helping=20 to slow the progression of the sfc low over the U.P. or over Lake=20 Superior. This should act to enhanced low-level convergence over=20 the western U.P where several inches of snow are likely and WPC=20 probabilities for at least 4 inches of snow on D3 are 30-80%.=20 Southerly flow ahead of the front will tap some moisture off Lake=20 Michigan and help enhance totals on the southern side of the=20 eastern U.P. where WPC probabilities for at least 4 inches are >50% (in a rather unusual setup).=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_2.png__;!!DZ3fjg!4s1ryLm6VsyGK0LRFvb_6hsTzOrckqx-A4ltM_YB8oe3d= 9lQrmFQHIuYJ1yve7kwxpkHCnfKHDyQxduNUlOrJAXskVY$=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. 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