048  
FOUS11 KWBC 240901  
QPFHSD  
 
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
501 AM EDT MON APR 24 2017  
 
VALID 12Z MON APR 24 2017 - 12Z THU APR 27 2017  
 
   
..PACIFIC NORTHWEST/NORTHERN CA/NORTHERN AND CENTRAL ROCKIES
 
 
A SERIES OF SHORTWAVES WILL CONTINUE TO MOVE THROUGH A BROAD UPPER  
TROUGH...PRODUCING WIDESPREAD MOUNTAIN SNOW SHOWERS...WITH LOCALLY  
HEAVY ACCUMULATIONS...FROM THE CASCADES AND NORTHERN SIERRA TO THE  
NORTHERN AND CENTRAL ROCKIES ON MON. SOME OF THE HEAVIEST  
ACCUMULATIONS ARE EXPECTED TO CENTER ALONG THE SOUTHWESTERN  
MT...NORTHWESTERN AND CENTRAL WY RANGES. ENHANCED MID-UPPER LEVEL  
LIFT...AFFORDED BY A WELL-DEFINED MID LEVEL SHORTWAVE AND  
LEFT-EXIT REGION UPPER JET DYNAMICS...ALONG WITH A LOW LEVEL  
CENTER DEVELOPING OVER CENTRAL WY...IS EXPECTED TO RAISE THE  
THREAT FOR LOCALLY HEAVY ACCUMULATIONS. WPC PROBABILISTIC  
GUIDANCE INDICATES AT LEAST A SLIGHT RISK FOR 8-INCHES OR MORE  
ACROSS MUCH OF THIS REGION ON DAY 1 (ENDING 12 UTC TUE)...WITH A  
SLIGHT RISK FOR 12-INCHES ACROSS SOME OF THE HIGHER PEAKS. THERE  
IS ALSO A SIGNIFICANT CHANCE FOR HEAVY SNOWS ALONG PORTIONS OF THE  
OREGON ROCKIES ON MON...WHERE FAVORABLE UPPER JET DYNAMICS AND A  
STRONG MID LEVEL SHORTWAVE WILL PLAY A ROLE AS WELL.  
 
BY EARLY TUE...AS THE UPPER TROUGH AXIS SHIFTS EAST AND A  
SHORTWAVE RIDGE BUILDS...SHOWERS ARE EXPECTED TO BRIEFLY DIMINISH  
ACROSS THE NORTHWEST. SNOW SHOWERS WILL CONTINUE FURTHER EAST  
HOWEVER ACROSS THE NORTHERN AND CENTRAL ROCKIES...WITH  
PROBABILISTIC GUIDANCE CONTINUING TO SHOW THE POTENTIAL FOR  
LOCALLY HEAVY AMOUNTS ACROSS SOME OF THE HIGHER PEAKS.  
 
AS SHOWERS WANE ACROSS THE ROCKIES LATE TUE INTO EARLY  
WED...PRECIPITATION IS EXPECTED TO RETURN TO THE NORTHWEST AS THE  
RIDGE QUICKLY GIVES WAY TO A SHORTWAVE TROUGH ON THE NOSE OF A  
POWERFUL JET THAT IS FORECAST TO EXTEND SOUTHEAST FROM EASTERN  
PACIFIC ACROSS THE PACIFIC NORTHWEST AND INTO THE GREAT BASIN BY  
EARLY THU. THIS WILL BRING A RENEWED CHANCE FOR LOCALLY HEAVY  
SNOW ACCUMULATIONS TO PORTIONS OF THE NORTHERN/CENTRAL CASCADES  
AND THE NORTHERN ROCKIES.  
 
THE PROBABILITY OF SIGNIFICANT IS LESS THAN 10 PERCENT.  
   
..NORTHERN PLAINS/UPPER MIDWEST
 
 
LOW TO MID LEVEL FRONTOGENESIS IS EXPECTED TO SUPPORT SOME LIGHT  
SNOW ACCUMULATIONS ACROSS NORTHERN ND INTO NORTHWESTERN MN...NORTH  
AND WEST OF AN AREA LOW PRESSURE THAT IS FORECAST TO TRACK ACROSS  
SD MON BEFORE LIFTING NORTHEAST ACROSS MN MON NIGHT INTO TUE.  
OVERALL GUIDANCE CONTINUES TO AGREE THAT THE HEAVIEST  
ACCUMULATIONS ASSOCIATED WITH THIS SYSTEM WILL CENTER ACROSS  
SOUTHERN MANITOBA INTO WESTERN ONTARIO. THIS SYSTEM IS EXPECTED  
TO SHEAR INTO WESTERN ONTARIO ON TUE. HOWEVER...LOW PRESSURE AND  
HEAVIER PRECIPITATION IS EXPECTED TO DEVELOP AND LIFT NORTHEAST  
ALONG ITS TRAILING BOUNDARY AS THE NEXT OF THE WESTERN U.S.  
SHORTWAVES MOVES OUT INTO THE CENTRAL U.S. LOW LEVEL COLD AIR  
SUPPORTED BY A STRONG LOW LEVEL RIDGE EXTENDING SOUTH FROM CENTRAL  
CANADA IS EXPECTED TO REMAIN IN PLACE...PRODUCING MIXED  
PRECIPITATION NORTH OF THE ASSOCIATED LOW...WITH SEVERAL GUIDANCE  
MEMBERS INDICATING SEVERAL HOURS OF FREEZING RAIN...RESULTING IN  
SIGNIFICANT ICE ACCUMULATIONS FROM THE ARROWHEAD REGION OF MN TO  
THE WESTERN U.P. OF MI. WPC PROBABILISTIC GUIDANCE SHOWS A SLIGHT  
RISK FOR ICE ACCUMULATIONS OF A 0.25 INCH OR MORE IN THE ARROWHEAD  
OF DAY 2 (ENDING 12 UTC WED)...SHIFTING SOUTHEAST INTO  
NORTHWESTERN WI AND THE WESTERN U.P. ON DAY 3 (ENDING 12 UTC THU).  
 
PEREIRA  
 

 
 
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