TZUTC: 0000   
   MSGID: 167886.weather@1:2320/105 2db2aaec   
   PID: Synchronet 3.21a-Linux master/123f2d28a Jul 12 2025 GCC 12.2.0   
   TID: SBBSecho 3.28-Linux master/123f2d28a Jul 12 2025 GCC 12.2.0   
   BBSID: CAPCITY2   
   CHRS: ASCII 1   
   FORMAT: flowed   
   FOUS11 KWBC 231852   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   152 PM EST Tue Dec 23 2025   
      
   Valid 00Z Wed Dec 24 2025 - 00Z Sat Dec 27 2025   
      
   *** Strong Atmospheric River followed by low pressure systems to   
    impact California and the Sierra Nevada through Friday ***   
      
      
   ...Northeast...   
   Days 1 & 3-3.5... Maximum impact level from Day 1 WSSI: Major. Day   
   3-3.5 WSSI-P Minor Maximum Probabilities: 90%.   
      
   A sharpening 500mb shortwave trough in southern Ontario heads towards   
   the Northeast U.S. this afternoon as the diffluent left-exit region   
   of a roaring 150kt 300mb jet streak adds healthy divergence atop   
   the atmosphere. A ribbon of 850-700mb WAA and resulting FGEN is   
   responsible for the ongoing shield of snow across the Northeast   
   today and, once it becomes quasi-stationary over eastern MA on   
   north to the Gulf of Maine, will become the defacto train-tracks   
   for the 850mb low as it tracks from the St. Lawrence Valley tonight   
   to off the MA Capes by Christmas Eve morning. Periods of snow will   
   continue, falling heavily at times tonight, from the Adirondacks=20   
   and the rest of the northern New England mountains, on east to the=20   
   coast of Maine as the 850mb low strengthens and a Nor-lun trough fosters   
   heavy snow north and east of Portland. Burst of heavy snow cannot=20   
   be ruled out as far south as the MA Capes on Wednesday, but the=20   
   deepening storm system south of Nova Scotia will quickly race east=20   
   and all but end any accumulating snowfall by mid-afternoon. WPC=20   
   probabilities show east-central ME as having >50% odds for snowfall   
   totals >8" through Wednesday afternoon. The WSSI generally shows=20   
   Moderate Impacts from the Portland area on north and east along the   
   east-central ME coast with localized Major Impacts in areas where   
   snowfall totals exceed 12". WPC probabilities also depict high=20   
   chances (>70%) for snowfall totals >4" in portions of the=20   
   Adirondacks, Green, and White Mountains, as well as much of=20   
   interior ME. WSSI shows widespread Minor Impacts from this=20   
   snowfall, implying some inconveniences to travel are likely with=20   
   winter driving conditions. Those traveling today and Christmas Eve=20   
   in the interior Northeast should use caution while driving in these   
   areas.   
      
   In wake of a fast moving clipper system over northern New England   
   on Christmas Day, strong 850mb CAA ahead of a strengthening dome of   
   Canadian high pressure will result in a cold-air-damming signature   
   (CAD) to become positioned briefly over the Northeast by Friday   
   morning. To the west, a progressive 500mb shortwave trough over the   
   Great Lakes will approach and strong 850mb WAA will accompany   
   sufficient 290K isentropic ascent to produce precipitation over the   
   Northeast. Healthy mid-to-upper level ascent will also be supplied   
   in the form of healthy 700mb Q-vector convergence Friday afternoon   
   and evening. This classic "over-running" setup with a burgeoning   
   warm nose of >0C air at low-levels but sub-freezing wet-bulb   
   temperatures at the surface (due to a cold and very dry boundary   
   layer at the onset) will allow for an icy wintry mix of   
   sleet/freezing rain to fall from western PA and northern MD on east   
   across southern PA and towards the Delaware Valley. Meanwhile,   
   areas farther north of the storm track and areas with more=20   
   elevation; such as northern PA, the Poconos, NY Finger lakes,   
   Catskills, northern NJ, and potentially the NYC metro on north and   
   east through southern New England, are showing better odds of   
   remaining mostly snow for Friday afternoon and into Friday night.   
      
   Through 12Z Saturday, WPC probabilities show low-to-moderate chances   
   (20-50%) for snowfall totals >4" in northeast PA, southern NY,=20   
   northern NJ, western MA, and western CT. Meanwhile, WPC ice=20   
   probabilities show moderate-to-high chances (50-70%) for ice=20   
   accumulations over a tenth of an inch along the Laurel Highlands=20   
   and central Appalachians. The same mountain ranges also show   
   moderate chances (>50%) for ice accumulations greater than a   
   quarter inch. Light ice accumulations and some accumulating sleet   
   is expected as far east as northern MD, southern PA, and the   
   DC/Baltimore metro areas. There remains ongoing fluctuations in=20   
   the forecast track which could result in additional changes in=20   
   which areas see the most snow and ice. Regardless, WPC's WSSI-P=20   
   show >50% odds for Minor Impacts from western PA to as far east as=20   
   the Tri-State area between 1AM Fri - 1AM Sat. Residents and=20   
   travelers following Christmas will want to keep a close eye on this   
   forecast over the next couple of days.   
      
      
   ...Great Lakes...   
   Days 2.5-3... Maximum chances of at least minor impacts from=20   
   WSSI-P: 70%   
      
   An impressive plume of Pacific and subtropical moisture ejecting=20   
   out of the robust longwave trough off the West Coast will travel=20   
   around the northern periphery of the ridge axis over the south-   
   central U.S. and head for the Great Lakes on Thursday. Guidance is   
   in agreement on strong 850-700mb WAA over the north-central U.S.   
   Thursday afternoon with a band of snow developing along the 700mb   
   front. This is likely to result in a combination of snow and some   
   embedded sleet/freezing rain across northern ND and northern MN   
   Thursday night, then across northern WI and the U.P. of MI early   
   Friday morning. The strong but transient 850-700mb WAA will cause a   
   stout warm-nose of >0C temperatures over MI that cause a wintry mix   
   to engulf much of Michigan's Mitten on Friday, with the same icy   
   potential just east of Lakes Erie and Ontario Friday afternoon. The   
   progressive nature of this disturbance will help to cap snowfall   
   totals to generally <4", with the lone exceptions being the MN=20   
   Arrowhead and northern half of MI's U.P. where WPC probabilities=20   
   how low-to-moerate chances (20-50%) for snowfall totals >4".   
   Otherwise, ice is of concern across central and southern MI,   
   northeast OH, northwest PA, and far eastern NY. WPC probabilities   
   show moderate-to-high chances (50-70%) for ice accumulations of at   
   least one-tenth of an inch in these areas on Friday, including the   
   greater Detroit metro area. There are also low-chance   
   probabilities, of a more impactful event with over one-quarter of   
   an inch. WSSI-P shows the tip of the MN Arrowhead having moderate=20   
   chances (40-60%) for at least Minor Impacts due to snowfall from=20   
   this system, while central and southern MI sport moderate-to-high=20   
   chances (50-70%) for Minor Impacts due to ice.   
      
      
   ...California/Sierra Nevada...=20   
   Days 1-3... Maximum impact level from WSSI: Extreme   
      
   The next Atmospheric River (AR) pushes across the CA coast   
   tonight, with heavy precipitation suddenly reaching the=20   
   central/southern Sierra Nevada around midnight with 3-4"/hr rates   
   (per the 12Z HREF) above the snow levels of 7500ft/8500ft through=20   
   the heaviest precip Wednesday morning. Snow becomes more showery=20   
   with moderate rates and lower snow levels of 6500/7500ft Wednesday=20   
   afternoon/night in the continued southerly flow behind the main AR=20   
   plume. The next moisture plume arrives early Thursday morning with=20   
   snow levels around 6000ft and heavy snow rates of 2-3"/hr into the=20   
   afternoon before rates decreased a bit in showery conditions and=20   
   snow levels dipping below 5000ft through Friday morning.=20   
      
   These rounds of heavy snow with lowering snow levels will lead to=20   
   increasing travel and infrastructure impacts. Storm total snowfall=20   
   in excess of 4ft can be expected above 6500ft along the extent of=20   
   the Sierra Nevada.   
      
   Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect   
   heavy snow above 7000ft tonight and above 5000ft Wednesday   
   afternoon through Thursday. Moderate snow above 4000ft can be   
   expected Thursday night through Friday as low pressure lingers near   
   Cape Mendocino. Some snow impacts to I-5 near Mt Shasta are   
   possible.   
      
   Snow levels remain around 10,000ft in Southern CA through the main   
   AR plume Wednesday before dropping to around 7000ft Wednesday night   
   into Friday. Impactful snow looks to remain higher than Big Bear   
   Lake.=20   
      
      
   Key Messages for the CA atmospheric river and subsequent low that=20   
   maintains impacts through Friday are linked below. CPC has Key   
   Messages for the Pacific Northwest into California through early=20   
   January.   
      
      
   ...Pacific Northwest, Great Basin and Rockies...=20   
   Days 1-3... Maximum impact level from WSSI: Moderate=20   
      
   The remnant first AR, with an axis from far northern CA to western   
   MT this afternoon, continues lifting north as surface low pressure   
   rides along from SW OR up the Cascades tonight into Wednesday. Snow   
   levels rise on the WA Cascades from around 3000ft this evening to   
   4000ft by 12Z Wednesday. Moderate snow rates around 0.5"/hr can be   
   expected through Wednesday morning above those snow levels on the=20   
   WA Cascades. Day 1 PWPF for >4" above pass level are 40-80%.=20   
      
   The next AR surges through CA tonight and across the Great Basin   
   Wednesday, reaching the western Rockies Wednesday night. Snow=20   
   levels are high in this moisture shield, 8000-9000ft over the Great   
   Basin and the Rockies through central ID and WY with much lower=20   
   precip and snow levels of 6000-7000ft in northern ID and MT. Day=20   
   1.5 snow probs for >6" are 40-80% in the highest central NV ranges,   
   the Sawtooths, Wind Rivers, and Uintas.=20   
      
   The following moisture surge through CA Thursday brings widespread   
   precip at lower rates than before across the Great Basin and=20   
   western Rockies with lower snow levels around 6000-7000ft. Day 2.5   
   snow probs for >6" are 30-70% again for the highest central NV ranges,   
   the Sawtooths, Wind Rivers, Uintas, as well as western CO ranges   
   and the Absarokas.   
      
   The upper trough comes ashore Friday in northern CA up through the   
   PacNW with moderate precip rates and Cascades snow levels around=20   
   2500ft in WA and 3500ft in OR. Day 3 snow probs for >6" are 40-70%   
   in the WA Cascades, including Snoqualmie Pass, and around 30% for   
   the OR Cascades including Santiam Pass. Snow will continue in   
   earnest for the Rockies into Saturday.   
      
      
   Mullinax/Jackson   
      
      
      
   ...Winter Storm/Atmospheric River Key Messages are in effect and   
   linked below...   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_1.png__;!!DZ3fjg!748M92R3xI_pv1iK1Rxjk-4CcKjFg89ad5izP-Qu4FuJA=   
   U0nVasQbx7qHo4hN9wCFbI8WQwj7qA1HBLzwHvxS0diFjc$=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: Capitol City Online (1:2320/105)   
   SEEN-BY: 1/19 100 16/0 19/10 37 104/119 105/81 106/201 114/10 120/302   
   SEEN-BY: 123/130 128/187 129/14 142/104 153/757 7715 154/10 30 50   
   SEEN-BY: 154/110 700 201/0 203/0 218/700 840 220/10 20 30 90 221/1   
   SEEN-BY: 221/6 360 226/18 30 44 50 227/114 229/110 134 206 300 307   
   SEEN-BY: 229/317 400 426 428 470 664 700 705 240/5832 266/512 280/5003   
   SEEN-BY: 291/111 301/1 320/119 219 319 2119 322/757 762 326/101 335/364   
   SEEN-BY: 341/66 342/200 396/45 423/81 460/58 633/280 712/848 902/26   
   SEEN-BY: 2320/0 105 304 3634/12 5020/400 5075/35   
   PATH: 2320/105 154/10 221/6 1 320/219 229/426