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   FOUS11 KWBC 252105 AAA   
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   Probabilistic Heavy Snow and Icing Discussion...UPDATED   
   NWS Weather Prediction Center College Park MD   
   405 PM EST Thu Dec 25 2025   
      
   Valid 00Z Fri Dec 26 2025 - 00Z Mon Dec 29 2025   
      
   *** Continued Heavy Snow on the Sierra Nevada through Friday ***   
      
   *** Heavy Wintry Mix tonight through Friday night from the Great   
    Lakes through the Northeast and Mid-Atlantic ***   
      
      
   ...Great Lakes to Northeast...   
   Days 1-2... Maximum impact level from WSSI: Moderate   
      
   Quasi-zonal flow continues to direct a plume of moisture=20   
   originating from the West along the US/Canadian border=20   
   leading to WAA- driven snow over the MN Arrowhead into the U.P. of   
   Michigan. With cold sub-32F sfc temps over parts of MN/WI/Lower MI   
   at precip onset tonight, some freezing rain is likely with minor=20   
   accumulations over MN/WI. WPC probabilities for at least 4 inches=20   
   of snow are low to moderate (20-60%) over the Keweenaw Peninsula   
   into the eastern U.P.=20   
      
   Into D2, shortwave will push through northern Lower MI with its=20   
   sfc reflection over IN/OH and the 850mb low moving through BUF. The   
   sfc low will weaken as it approaches the Appalachians, getting too   
   far behind the mid-level shortwave, and ultimately jumping into=20   
   the Atlantic by 12Z Sat. From Friday to Saturday morning, a variety   
   of ptypes are expected over the region (central Appalachians/Mid-=20   
   Atlantic to the Northeast). The stubborn cold surface air will hold   
   tight over Lower MI and especially into the Laurel Highlands in=20   
   western PA where significant freezing rain is possible. WPC=20   
   probabilities of at least 0.10" icing are high (>70%) from central   
   to southeast MI, including Detroit, as well as into western=20   
   PA/western MD. 40 to 70% probabilities of at least 0.25" icing=20   
   exist over southeast MI down through northwest PA into the Laurel=20   
   Highlands. Light icing is likely on either side of this zone of=20   
   maximum probabilities -- on the south side along the I-66 corridor=20   
   (DC) and into eastern WV. To the north/northeast, deeper cold air=20   
   at the surface will allow for sleet to be a dominant ptype over=20   
   central/eastern PA with up to an inch of sleet possible.=20   
      
   To the north, from central NYS through northeast PA into the=20   
   Catskills/Poconos and to the NYC Metro area, an axis of moderate to   
   locally heavy snow is increasingly likely, driven by the stronger=20   
   height falls at the nose of the incoming 130kt jet. Beginning to=20   
   see numerical guidance fall in line on the axis of greatest=20   
   snowfall potential with the NAM shifting further south compared to=20   
   its placement at 00z. Rest of the dynamical guidance is keying on=20   
   the area from southern NY state down through the Lower Hudson to=20   
   NYC and 50-75 miles on either side seeing at least 4" with >6"   
   becoming a greater likelihood around the Catskills into the Lower   
   Hudson Valley to the north of NYC.=20=20   
      
   WPC probabilities for at least 4 inches of snow are still >50% in   
   a zone bounded between I-890/Rt 17/I-476 to the west, the southern   
   Adirondacks on the north side, Berkshires/I-91 to the east, and=20   
   into the NYC Metro/Long Island to the south. Probabilities for at   
   least 6" are now between 50-70% for that area of central NY state   
   down through southern NY, including the Catskills/Lower Hudson/NYC   
   corridor south and east of I-88. Though the system will be=20   
   progressive, combination of higher SLRs and upslope could yield=20   
   more than 8 inches of snow into the southern Catskills where areal   
   average maxima is currently positioned with some deterministic   
   indicating >10" on their outputs.   
      
   Fracasso/Kleebauer   
      
   ...California/Sierra Nevada...=20   
   Day 1... Maximum impact level from WSSI: Extreme   
      
   *** Heavy Snow Continues on the Sierra Nevada through Tonight ***   
      
   The final round of widespread heavy snow arrives early this evening   
   to the northern Sierra Nevada then works its way down the length=20   
   of the Sierra Nevada through the overnight. Expect a few hours of=20   
   2-3"/hr rates (per the 12Z HREF) above the snow level of 5000ft=20   
   (north/central Sierra) to 6000ft (southern Sierra) with an=20   
   additional 12-18" overnight.   
      
   Moderate snow showers continue into Friday evening with snow=20   
   levels dropping to 4500ft. The upper trough which had been offshore   
   finally shifts east to the Great Basin Friday night, cutting off=20   
   Sierra snow by 12Z Saturday.   
      
   Far northern CA ranges (Shasta Siskiyou/Klamath/etc) can expect=20   
   two more rounds of heavy snow: this evening above 4000ft and early   
   Friday down to 3500ft. Snow impacts to I-5 near Mt Shasta are=20   
   likely Friday. Some moderate snow linger Friday night before=20   
   ending by 12Z Saturday.=20   
      
   For SoCal, snow levels remain around 7000ft through Friday morning=20   
   and most of the additional precip. Snow levels do drop below=20   
   6000ft Friday afternoon with some 1"/hr rate potential around Big=20   
   Bear Lake into the evening before tapering off.   
      
   Jackson   
      
   ...Pacific Northwest, Great Basin and Rockies...=20   
   Days 1-3... Maximum impact level from WSSI: Moderate to Major   
      
   Deep low pressure off CA will continue to infuse moisture across=20   
   the West with a separate trough pushing down the BC coast Friday=20   
   and over the northern Rockies Saturday providing a final focus for=20   
   precipitation and ending the active pattern.=20   
      
   Ongoing snow over the Cascades tapers off this evening with=20   
   moderate to locally heavy snow for the length of the Cascades=20   
   Friday and Friday night with snow levels dropping on the WA=20   
   Cascades from 3000ft to 1000ft and over the OR Cascades to 2000ft.=20   
   Day 1.5 snow probs for >8" are 50-90% on the WA/OR Cascades=20   
   including for the Snoqualmie and Santiam passes.   
      
   The next round of moisture from CA arrives into the northern=20   
   Rockies this evening with prolonged moderate to heavy snow until=20   
   the cold frontal passage Friday night. Snow levels drop from=20   
   6000/7000ft to 3000/4000ft through this time leading to increasing=20   
   travel impacts. Day 1.5 snow probs for >8" are 50-80% over the=20   
   Sawtooths, northern ID/western MT ranges, western WY ranges, the=20   
   higher central NV ranges, and the Wasatch.   
      
   The progression of the cold front is notable with the Day 2.5 snow   
   probs for >8" limited to the Wasatch and 50-80% for northern and=20   
   western CO Ranges.   
      
   Jackson   
      
      
      
   ...Winter Storm Key Messages are in effect for California (1) and   
   the Great Lakes/Northeast (2) as linked below...   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_1.png__;!!DZ3fjg!-g-GW__WozhP2rpufLMN5NvBEkkjdn8JWvmleGJtVDvie=   
   KanJvcNGyGIHQAVOvIb69relAxzfxlMKZa2cZavzv-P0Oo$=20   
      
   https://urldefense.com/v3/__https://www.wpc.ncep.noaa.gov/key_messages/Late=   
   stKeyMessage_2.png__;!!DZ3fjg!-g-GW__WozhP2rpufLMN5NvBEkkjdn8JWvmleGJtVDvie=   
   KanJvcNGyGIHQAVOvIb69relAxzfxlMKZa2cZavVPwJrv8$=20   
      
      
      
   $$   
      
   =3D =3D =3D   
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