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   FOUS11 KWBC 292040   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   340 PM EST Sat Nov 29 2025   
      
   Valid 00Z Sun Nov 30 2025 - 00Z Wed Dec 03 2025   
      
      
   ...Northern High Plains through the Midwest into the Northeast...=20   
   Days 1-2...   
      
   ...Significant winter storm unfolding across the Midwest today...   
      
   A pair of 500mb vorticity maximums are interacting with one another   
   and helping to carve out a negatively-tilted 250-500mb layer trough   
   over the Midwest this afternoon. A coupled 250mb jet streak setup   
   is further strengthening the ongoing storm system at the surface,   
   while at the same time, strong 850-700mb WAA ahead of the storm is   
   promoting 290K isentropic glide over the Midwest that is fostering   
   highly saturated profiles within a mesoscale environment that is   
   ripe for heavy snow bands. ECMWF ensembles show S-SWrly 850mb winds   
   in excess of 60 kts over the Middle MS Valley, which are topping=20   
   the 99.5 climatological percentile for late Nov and early Dec. This   
   exceptional LLJ is feeding a slug of 850-500mb moisture northward=20   
   that will wrap around the storm system and sufficiently saturate=20   
   the DGZ over the Midwest. WPC's Snowband Probability Tracker, which   
   utilizes HREF members, shows a band of 1-2"/hr snowfall rates from   
   central IA today that heads east across the MS River and towards=20   
   the Great Lakes this evening.=20   
      
   Snow will persist throughout the Great Lakes tonight with snow=20   
   arriving over the Northeast and central Appalachians Sunday=20   
   morning. LES bands will develop within broad cyclonic flow off=20   
   Lakes Superior and Michigan and continue through Sunday evening.   
   LES bands will stick around a little longer downwind of Lakes Erie   
   and Ontario but eventually taper off by Monday morning as high   
   pressure moves in. Locally heavy snowfall is possible in parts of=20   
   the Tug Hill on Sunday, as well as the White Mountains above   
   2,000ft where steady SWrly upslope flow within an atmosphere   
   remaining sub-freezing.=20   
      
   WPC probabilities depict moderate-to-hgih chances (50-80%) for   
   additional snowfall totals >6" along and east of the MS River from   
   eastern IA and southern MN to the Mitten of Michigan. There are   
   some low chance probabilities (10-30%) for snowfall totals   
   exceeding 12" in coastal areas of southeast WI, the Chicagoland   
   metro area, southwest MI, and northern IN where LES bands may   
   contribute enough snowfall to where over a foot of snow has   
   accumulated by the time the LES machine concludes. Downwind of Lake   
   Erie, parts of the Chautauqua Ridge have moderate chances (40-60%)   
   for snowfall totals >4" through Monday Sunday night. In the   
   Northeast, the Tug Hill and White Mountains sport moderate-to-high   
   chances (50-80%) for snowfall accumulations >6" with localized=20   
   totals approaching 12" possible by the time this winter storm=20   
   concludes. The WSSI continues to summarize this storm well,=20   
   highlighting Moderate to locally Major impacts from central IA on=20   
   east through the Milwaukee/Chicago metro areas and into northern IN   
   and southern MI. Expect considerable disruptions to travel in=20   
   these areas as travelers are likely to encounter numerous travels=20   
   delays by both road and by air today and lingering through tonight.   
      
   Key Messages remain in effect for this system (Key Message 2=20   
   below).   
      
      
   ...Central Rockies through the Ohio Valley, Ice in the Ozarks...=20   
   Days 2-3...   
      
   A positively titled 500mb trough diving south from the Northwest   
   into the Central Rockies on Sunday will contain both sufficient   
   synoptic-scale lift and 700-300mb mean layer moisture to support   
   rounds of mountain snow from central OR and the northern Great   
   Basin on east across the Wasatch and into the CO Rockies. The   
   heavier totals in the Great Basin and Wasatch will generally=20   
   reside above 8,000ft, while the CO/northern NM Rockies are most=20   
   likely to see their heavier snowfall totals above 9,000ft. WPC=20   
   probabilities show these listed elevations as having >50% chances=20   
   for snowfall >8" with localized totals >12" in the peaks of the CO=20   
   Rockies.=20   
      
   As snow continues across the Central Rockies Sunday night, the   
   aforementioned 500mb trough will begin to eject east into the   
   Central Plains. A strengthening surge in 700mb WAA and the 500mb=20   
   PVA will foster a blossoming area of snowfall from the central   
   Plains to the Middle MS Valley. Snowfall totals are most likely to   
   range between a coating-3", although WPC probabilities do show low   
   chances (10-30%) for snowfall totals >4" over northeast KS,   
   southeast NE, and northern MO through Monday morning. This narrow=20   
   plume of snow races east across the Lower Great Lakes and OH Valley   
   Monday evening with similar snowfall totals.   
      
   Farther south, as low-level WAA and moisture over-run an air-mass   
   that features sub-freezing temperatures and dry dew points, a setup   
   for freezing rain unfolds from the ArkLaTex on across much of AR,   
   northern MS, western TN, and southern MO. The plume of low-level   
   moisture does not last too long, but 290K isentropic ascent sticks   
   around long enough for some disruptive ice accumulations in parts   
   of these areas on Monday. WPC probabilities show low chances   
   (10-30%) for ice accumulations over a tenth of and inch, but there   
   are moderate chances (40-60%) for at least a hundredth of an inch.   
   The WSSI-P does show up to 40% odds for Minor Impacts as a result   
   of this freezing rain setup on Monday across much of central AR.=20   
      
      
   ...Central Appalachians, Mid-Atlantic, & Northeast...   
   Day 3-3.5...   
      
   ...A complex & potentially disruptive winter storm to affect these   
   regions on Tuesday and into Tuesday night...   
      
   Summary: The first accumulating snowfall and disruptive ice event=20   
   of the season is likely to occur from the Central Appalachians and=20   
   interior Mid-Atlantic to the Northeast. There remain ongoing=20   
   changes and disagreements in guidance with snowfall totals, who=20   
   sees the heaviest totals, and timing all still lower in confidence.   
   Those in these regions should monitor the forecast from WPC and=20   
   their local WFOs over the next 24-48 hours.=20   
      
   Analysis: As the Central Plains disturbance tracks east Monday=20   
   evening, there are three other disturbances that are influencing=20   
   this complicated setup. The first is a weak feature over South TX=20   
   that is running just out in front of the main upper trough over the   
   Central Plains. Second: a fast moving 500mb trough over south-=20   
   central Canada racing southeastward through the Great Lakes by=20   
   Monday night. Third:the departing system over the Northeast on=20   
   Monday that races east of Atlantic Canada Monday night. Where=20   
   guidance is in agreement is that the primary trough over the=20   
   Central Plains works in tandem with the ejecting Deep South=20   
   disturbance to direct a plume of 700-300mb moisture at the East=20   
   Coast. This moisture source will overrun a residual sub-freezing=20   
   air-mass Monday night over the Central Appalachians and Mid-=20   
   Atlantic that will support disruptive ice accumulations. However,=20   
   the dome of high pressure is departing as the storm approaches. For   
   areas west and north of I-95 in the Mid-Atlantic, boundary layer=20   
   wet-bulb temperatures will support at least a brief period for=20   
   accumulating snow. By 18Z Tuesday, a coupling 500mb jet streak=20   
   setup will support strong vertical ascent aloft that deepens a=20   
   coastal low as it tracks off the coast. To the north of the storm=20   
   track, heavy-banded precipitation to the north of a 850-700mb FGEN   
   band will transpire with snow most likely to occur north of I-95=20   
   in the higher terrain.   
      
   This is where the agreements in the overall setup end. Guidance   
   members such as the ECMWF show a less amplified Middle MS Valley   
   feature and less phasing with the Great Lakes disturbance, with   
   that Great Lakes feature suppressing the storm tracks with its   
   ensemble membership over the GEFS. Meanwhile, the GEPS are north   
   and more amplified compared to the GEFS, making the GEFS the   
   middle ground in storm position. Notably, the EC-AIFS ensemble   
   means is stronger with the surface low as it reaches the East=20   
   Coast on Tuesday and its QPF footprint is farther up the coast than   
   the EPS membership is. At the moment, the ECMWF is on the drier=20   
   side of guidance, while other like the CMC/NAM are much more=20   
   amplified. What today's trends have favored, as of this discussion,   
   is a slightly faster solution that would allow for precipitation=20   
   to arrive sooner on Tuesday morning.=20   
      
   With the cold air-mass retreating on Tuesday, the expectations for   
   those from northern VA and northern MD on north and east through=20   
   southeast PA, the Delaware Valley, and into southern New England   
   was to favor lower SLRs, which should make for a heavy/wet snow.=20   
   That said, the storm track is critical in determining how far north   
   the rain/snow line gets. As is the case in marginal boundary layer   
   temperature environments with fast moving coastal lows that are=20   
   unable to develop a robust deformation zone, plus baking in=20   
   climatology for the time of year, it should be the higher=20   
   elevations north and west of I-95 that are most favored for=20   
   accumulating snowfall. This setup favors interior New England for=20   
   heavy snow, although should the Great Lakes disturbance act to=20   
   suppress the storm track, this could shift farther south to the=20   
   Catskills and higher terrain of southern New England.=20   
      
   WPC probabilities show moderate-to-high chances (50-70%) for=20   
   snowfall totals >4" from east-central PA on north and east through=20   
   the Poconos, Catskills, Berkshires, Green, and White Mountains.=20   
   Farther south, the Philly/Baltimore/DC metro areas may start out=20   
   briefly as snow, but transition to a wintry mix on Tuesday. There=20   
   is a possibility for a more icy scenario should cold-air damming=20   
   (CAD) stick around longer on Tuesday before transitioning to plain   
   rain. Speaking of CAD, the Central Appalachians will see sub-=20   
   freezing surface temperatures persist long enough to support a=20   
   treacherous freezing rain event. WPC probabilities depict=20   
   moderate-to-high chances (50-80%) for ice accumulations over a=20   
   tenth of an inch from the Blue Ridge of western NC on north through   
   the WV/VA Appalachians and Shenandoah Valley with low chances=20   
   (10-30%) for over a quarter inch of ice. The WSSI-P shows a swath=20   
   of >50% chances for Minor Impacts from the Central Appalachians on=20   
   north and east through the WV Panhandle, along and west of Parrs'=20   
   Ridge in northern MD, through east-central PA, northern NJ,   
   southern NY, and interior New England. Key messages are ongoing=20   
   for this system (Key Message 3 below).=20   
      
      
   Mullinax   
      
      
      
   ...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!_sInBjlekP6pjNLeRE9LcvsU1nax_MbMvx1zivFGkr4Rq=   
   k-U2PID8H1T0KDpJqo1tgG6WZCgot_ZewEEuM12DI18XNw$=20   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_3.png__;!!DZ3fjg!_sInBjlekP6pjNLeRE9LcvsU1nax_MbMvx1zivFGkr4Rq=   
   k-U2PID8H1T0KDpJqo1tgG6WZCgot_ZewEEuM12uPpTWiE$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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