850  
FOUS11 KWBC 051826  
QPFHSD  
 
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
126 PM EST SUN FEB 05 2023  
 
VALID 00Z MON FEB 06 2023 - 00Z THU FEB 09 2023  
 
   
..WESTERN U.S.
 
 
DAYS 1-3...  
 
TWO DISTINCT TROUGHS MOVING INTO THE WEST THROUGH THE MIDDLE OF  
THE UPCOMING WEEK WILL SPREAD DUAL ATMOSPHERIC RIVERS (AR) ONSHORE  
TO RESULT IN WAVES OF HEAVY SNOW, ESPECIALLY ACROSS THE HIGHER  
TERRAIN.  
 
THE FIRST OF THESE IMPULSES IS MOVING ONSHORE CA THIS MORNING AS A  
SHARPENING LONGWAVE TROUGH, WITH ITS AXIS SURGING INTO THE GREAT  
BASIN TONIGHT. THIS FEATURE WILL BECOME INCREASINGLY SHEARED OUT  
TO THE NORTHEAST IN RESPONSE TO NORTHERN STREAM ENERGY SURGING  
INTO THE UPPER MIDWEST TO SPLIT THE TROUGH, BUT MAINTAIN A LONG SW  
TO NE ORIENTED AXIS FROM THE FOUR CORNERS INTO THE GREAT LAKES BY  
D2. THE SOUTHERN END OF THIS TROUGH IS THEN PROGGED TO DEEP INTO A  
CLOSED LOW OVER THE FOUR CORNERS, PROVIDING ADDITIONAL ASCENT INTO  
THE SOUTHERN ROCKIES AND SOUTHERN HIGH PLAINS. CONFLUENT FLOW  
SOUTH AND DOWNSTREAM OF THIS TROUGH COMBINED WITH THE INTENSIFYING  
SUB-TROPICAL JET STREAK WILL DRIVE HIGH PWS AND AN AR FROM CA INTO  
THE SOUTHWEST, CHARACTERIZED BY IVT OF AROUND 250 KG/M/S. WHILE  
THE MOST INTENSE ASCENT ACROSS CA WILL WEAKEN DURING D1, BROAD,  
LARGE SCALE LIFT WILL OVERSPREAD MUCH OF THE REGION FROM THE  
CASCADES THROUGH THE CO ROCKIES, RESULTING IN MODERATE TO HEAVY  
SNOW ABOVE GENERALLY 2500-4000 FT ACROSS THE WEST, WITH SOME  
ENHANCED SNOWFALL RATES OF 1-2"/HR LIKELY AT TIMES EARLY ON D1 IN  
THE CASCADES, BLUE MOUNTAINS, AND WASATCH WHERE UPSLOPE FLOW AND  
SOME MID-LEVEL FGEN WILL OVERLAP. WPC PROBABILITIES FOR MORE THAN  
6 INCHES OF SNOW ARE MODERATE TO HIGH FOR A SMATTERING OF TERRAIN  
FROM THE WA CASCADES THROUGH THE CO ROCKIES. IN GENERAL, THE  
HEAVIEST SNOW WILL BE ABOVE 4000 FT AND FOCUSED IN UPSLOPE TERRAIN.  
 
A SECOND IMPULSE WILL THEN APPROACH THE PACIFIC NORTHWEST COAST  
TUESDAY AFTN /D2/, AND WHILE THIS FEATURE IS PROGGED TO RACE  
EASTWARD THANKS TO CONFLUENT AND PROGRESSIVE 500MB FLOW SURGING  
INTO THE COAST, IT WILL PROVIDE ROBUST ASCENT THROUGH HEIGHT FALLS  
AND PVA, IN A REGION OF IMPRESSIVE MOISTURE, WHICH WILL PERSIST  
EVEN BEYOND THE MOST INTENSE FORCING AS THE CONFLUENT FLOW  
PERSISTS BEHIND THE SHORTWAVE. IVT IS PROGGED BY BOTH THE ECENS  
AND GEFS TO EXCEED 500 KG/M/S INTO WA/OR DURING THIS PERIOD, AND  
THE GUIDANCE HAS BECOME INCREASINGLY ROBUST WITH ITS SNOWFALL  
POTENTIAL TUESDAY AND WEDNESDAY BEFORE RIDGING BLOSSOMS ACROSS THE  
PACIFIC COAST LATE IN THE FORECAST PERIOD. STRONG WAA ASSOCIATED  
WITH THE WARM FRONT WILL DRIVE SNOW LEVELS TO AROUND 5000 FT ALONG  
AND WEST OF THE CASCADES TUESDAY, COINCIDENT WITH THE HEAVIEST  
PRECIPITATION, BUT THE SUBSEQUENT COLD FRONT AND CAA WILL DRIVE  
SNOW LEVELS DOWN BELOW 2000 FT WEDNESDAY WITH CONTINUED AT LEAST  
MODERATE SNOWFALL. THIS COULD PRODUCE SIGNIFICANT PASS LEVEL  
IMPACTS WHICH IS SUPPORTED BY HIGH PWSSI PROBABILITIES FOR  
MODERATE IMPACTS DUE TO SNOW RATE NEAR SNOQUALMIE, STEVENS, AND  
LOOKOUT PASSES. WPC PROBABILITIES FOR 6+ INCHES OF SNOW ARE ABOVE  
80% IN THE NORTHERN WA CASCADES AND OLYMPICS ON D2, WITH 50-80%  
PROBABILITIES EXTENDING INTO THE OR CASCADES, NORTHERN ROCKIES,  
AND BITTERROOTS BY D3.  
 
THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.  
 
WEISS  
 

 
 
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