Subj : HVYSNOW: Probabilistic Heavy Snow And Icing Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Nov 25 2025 07:51:02 FOUS11 KWBC 250750 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 250 AM EST Tue Nov 25 2025 Valid 12Z Tue Nov 25 2025 - 12Z Fri Nov 28 2025 ....Significant winter storm to impact parts of the Northern Plains and Upper Midwest/Great Lakes through Wednesday before lake effect snow intensifies on Thanksgiving. Key Messages have been issued=20 for this storm... ....Northern Plains/Upper Midwest/Great Lakes... Days 1-3... Shortwave trough moving through the northern Plains this morning=20 will continue eastward today. The sharpening upper jet across the=20 US/Canada supports a strengthening area of low pressure that will=20 move from the Plains to the Upper Midwest and western Great Lakes=20 over the next couple of days. An inverted trough over ND will act=20 as a focus for modest snow this morning, then translate east- southeastward today as the surface low deepens over southeastern=20 MN. Trend in recent guidance was to bring this swath of light to=20 moderate snow farther south than just 12hrs ago, down the I-94=20 corridor into the Twin Cities. As the mid- level shortwave starts=20 to then close off, a TROWAL should form on the western side of the=20 storm as warmer air wraps northward and westward around the low.=20 This could allow for >1"/hr snowfall rates along with gusty winds=20 over 30mph, causing some blowing/drifting snow and low visibility=20 at times. By tonight into early Wednesday, the low will lift toward the U.P. with northeasterly flow off Lake Superior, aiding in=20 enhancing moisture into the region just north of the 850mb low=20 (eastern central MN into northern WI).=20 By Wednesday night into early Thursday, the system will reach its=20 peak intensity over Ontario and take the bulk of its snow with it.=20 However, northerly to northwesterly flow will transition the lake-=20 enhanced snow to lake effect snow over northern WI into the U.P.=20 where the 850-lake temperature difference will be >15C (-10 to -14C at 850mb and a lake temperature around 5C). Lake effect snow=20 will eventually break out across the rest of the Great Lakes by=20 Thursday morning and continue through the day and into Friday=20 morning. With 850mb temperatures < -10C and Lakes Erie/Ontario=20 SSTs around +10C, intense lake bands will persist on WSW to W to=20 WNW flow as the cyclone pulls farther away from the region. Single banded snow will drop southward and become more multi-banded=20 downwind of Lake Erie but may retain a stronger single band off=20 Lake Ontario. Multi-banded snow will persist across the Upper=20 Great Lakes as well through early Friday.=20 For the synoptic event D1, WPC probabilities for at least 6 inches of snow are >30% from southeastern ND and northeastern SD eastward across much of central MN from the Twin Cities northward to the=20 Arrowhead. Higher probabilities >70% exist across central MN and=20 northern WI to the U.P. of Michigan. After the surface low passes=20 and the snow becomes driven by lake effect (mostly D2-3), WPC=20 probabilities for at least 12 inches of snow are >50% from near=20 Ironwood eastward across the northern portion of the U.P. near the=20 Huron Mountains. This region is also where major impacts due to=20 snow amounts are possible as three day snow totals could be in=20 excess of two feet. Over northwestern Lower Michigan, lake effect=20 snow could yield in excess of a foot of snow as well (probabilities are >50% just east of Traverse City). Residents and visitors in=20 the Upper Midwest/Great Lakes are advised to check the latest=20 forecast before traveling this week. Lake effect snow will pick up in earnest over western and northern NYS on Thursday (Thanksgiving) and continue into Friday. WPC=20 probabilities for at least 8 inches of snow are >70% over=20 northeastern OH, northwestern PA, and western NY as well as the Tug Hill Plateau downwind of Lake Ontario. Areas that see stronger=20 snow bands hold the longest may see totals in excess of 18 inches,=20 especially over northwestern PA where WPC probabilities are already >50%.=20 ....Pacific Northwest/Northern Rockies... Days 1-3... An active North Pacific jet will send in two systems into the=20 Pacific Northwest and northern Rockies over the next three days.=20 The first will be today as the upper jet dips south across=20 Washington and a cold front (with a leading warm front) move in=20 from the west/southwest. Another system will form west of 140W=20 tomorrow and travel along the lead stationary/moisture boundary=20 into Washington on Thursday. Snow levels will start low today with=20 colder air in place but then rise on Wednesday as milder air wins=20 out across the region. The second system will push into the Rockies late Thurs/early Fri. For D1, colder sheltered locations along/east of the Cascades may=20 see some freezing rain as moisture moves in from the west.=20 Otherwise, snow levels initially near 2000-4000ft (north to south)=20 along the Cascades will slowly rise over the northern WA Cascades=20 but rise much quicker over the southern WA/northern OR Cascades to=20 over 6000ft by early Wednesday. Thereafter, snow levels will rise=20 well above 5000-6000ft Thursday as the second system moves in. WPC=20 probabilities of at least 6 inches of snow D1 are >50% above about=20 3000-4000ft in the WA Cascades (which includes Stevens and=20 Snoqualmie Passes). For D2-3, WPC probabilities for at least 8=20 inches of snow are >50% above about 5000ft. Farther east, much of=20 northwestern MT above 6000ft or so across the Lewis and Flathead=20 Ranges show probabilities of at least 8 inches of snow above 50%. The probability of significant ice across the CONUS is less than=20 10 percent. 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!4LDjCV1VJ-Jt_mbQyvEw7p95f8ihrIq4NbocPm8O4o_KN= 9w-OXp-MvmkFlPWbEc22b1dUNJdhbzUHBf4SUOwBb9sSDw$=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) .