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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 2008Z Apr 22, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
407 PM EDT TUE APR 22 2014

VALID 00Z WED APR 23 2014 - 00Z SAT APR 26 2014

DAYS 1 THROUGH 3...

...PACIFIC NORTHWEST/NORTHERN INTER-MOUNTAIN WEST... 
 
THE OPERATIONAL MODEL GUIDANCE IS IN RATHER GOOD AGREEMENT ON A
LARGE SCALE AMPLIFIED AND ANOMALOUS UPPER TROUGH WILL SWEEP
THROUGH THE WRN STATES TONIGHT AND WED BEFORE ANOTHER DYNAMIC
UPPER JET STREAK ARRIVES INTO THE PAC NW FOR THURS. 
 
THE COMBINATION OF THESE IMPRESSIVE HEIGHT FALLS AND 500MB COLD
ADVECTION WITH POST-FRONTAL WRLY 30 TO 40 KT 700MB MOIST ONSHORE
FLOW SHOULD RESULT IN A LATE SEASON HEAVY MTN SNOWFALL.  THE
ACTIVITY ON TUES SHOULD OCCUR MAINLY FROM THE WA/OR CASCADES AND
PERHAPS THE NRN CA SIERRA EASTWARD INTO THE MTNS OF OR/ID/MT.  THE
SNOWFALL ACTION THIS DAY SHOULD LINGER ACROSS THE CASCADES AND IT
SHOULD GRADUALLY BECOME MORE ISOLATED AS THE FOCUS FOR SNOW BY DAY
3 SHIFTS TO THE CENTRAL U.S..
 
...NERN MN TO THE WESTERN GREAT LAKES... 
 
THE THREAT FOR A MIXTURE OF PRECIPITATION TYPES ACROSS THE
ARROWHEAD OF MN IS BECOMING INCREASINGLY MORE LIKELY ON THURS...
AS AN UPPER TROUGH FROM THE WEST PROGRESSES INTO THE PLAINS/MS
VALLEY. LARGE SCALE WARM ADVECTION/ISENTROPIC LIFT REGIME WILL
COMMENCE ACROSS THE UPPER MS VALLEY WITH GFS AND ECMWF THERMAL
PROFILES SUGGESTING THE ONSET OF SOME FREEZING RAIN OR SLEET IN
ADDITION TO RAIN/SNOW. TENDED TO UNDERCUT THE AMOUNTS OF SNOW
BASED ON THE THINKING THAT WARM ADVECTION ALOFT IN A REGION WHERE
THE ATMOSPHERE IS ALREADY MARGINALLY COLD WOULD INITIALLY RESULT
IN LOW SNOW TO WATER RATIOS.  THINK THAT THE BETTER RISK OF
ACCUMULATING SNOWS FROM THE MN ARROWHEAD INTO THE U.P. WOULD NOT
BE UNTIL LATE THURSDAY NIGHT OR FRIDAY WHEN THE MID LOW GOES BY
AND COLD ADVECTION KICKS IN AS ARCTIC HIGH PRESSURE SETTLES OUT OF
CANADA. 

WHILE SOME FREEZING PCPN IS POSSIBLE WITH THE CENTRAL U.S.
SYSTEM...PRESENT INDICATIONS ARE THAT THE AMOUNTS WILL GENERALLY
BE LIGHT. 

THE PROBABILITY FOR SIGNIFICANT ICING IS LESS THAN 10 PERCENT.
 
BANN