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   FOUS11 KWBC 181926   
   QPFHSD   
      
   Probabilistic Heavy Snow and Icing Discussion   
   NWS Weather Prediction Center College Park MD   
   226 PM EST Tue Nov 18 2025   
      
   Valid 00Z Wed Nov 19 2025 - 00Z Sat Nov 22 2025   
      
   ...California through the Southern Rockies...   
   Days 1-3...   
      
   A series of upper lows tracking into the southwestern U.S. will   
   continue through the remainder of the work-week that will keep   
   mountain snow in the forecast from the Sierra Nevada and the peaks   
   of the Transverse Ranges to as far east as the CO/NM Rockies.   
      
   The current stretch of active weather is due to an upper low over   
   southern CA that is directing a swath of rich subtropical moisture   
   and generating large-scale vertical ascent over the Southwest. A   
   lack of a sub-freezing antecedent air-mass is making the more   
   remote mountains ranges of the southern Sierra Nevada, northern AZ,   
   southern UT, and CO's San Juan Mountains as the favored locations   
   for measurable snow through Wednesday evening. By Wednesday night,   
   the 500mb upper low opens up into a potent shortwave trough that   
   takes on a negative tilt over the Gulf of California, resulting in   
   increased divergence aloft and a healthier influx of moisture into   
   the southern Rockies. While snow levels may dip to as low as 7,000ft   
   in parts of NM and CO, the bulk of the heavier snowfall totals   
   will be confined to elevations above 9,000ft in the San Juans and   
   Sangre De Cristo. The heaviest snowfall transpires in these   
   mountain ranges on Thursday and persists with lighter amounts into   
   Friday morning. WPC probabilistic guidance shows moderate-to-high   
   chances (50-80%) for snowfall totals >8" and low-to-moderate   
   chances (20-40%) for snowfall totals >12" for elevations above   
   9,000ft in southern CO and northern NM, while similar probabilities   
   for snowfall totals >8" also exist for southern UT mountain ranges   
   above 8,000ft.   
      
   At the same time as the current upper-level trough goes negative   
   tilt over northern Mexico early Thursday morning, another upper low   
   off the West Coast tracks south along the CA coast on Thursday. By   
   Friday, the upper low is forecast to reside over the southern CA   
   coast with a near carbon-copy setup to Tuesday's upper-level   
   pattern. Snow will start to unfold in Salmon/Trinity/Siskiyou of   
   northern CA early Thursday morning, followed by the Sierra Nevada   
   throughout the daytime hours on Thursday. Snow levels may dip as   
   low as 5,000ft, but only minor snowfall accumulations are   
   anticipated below 6,000ft. The heavier snowfall totals are most   
   likely to unfold at elevations above 7,000ft in the Sierra Nevada   
   through Friday morning. This new upper-low will perform a similar   
   synoptic-scale evolution to Tuesday's low, but this time it will   
   track a little farther south and west, resulting in lesser   
   concerns for snow in the higher mountain ranges of southern NV,   
   northern AZ, and southern UT. WPC probabilities depict moderate   
   chances (40-60%) for snowfall totals >4" along the Sierra Nevada   
   above 7,000ft with low chances (10-30%) for elevations >9,000ft in   
   the southern Sierra Nevada receiving >8" of snow. The peaks of the   
   San Gabriel and San Bernadino Mountains (above 7,000ft) also have   
   moderate chances (40-60%) for snowfall totals >4" late Thursday   
   night and into Friday.   
      
      
   Mullinax   
      
      
      
   $$   
      
   = = =   
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