Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 211940
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
340 PM EDT TUE OCT 21 2014

VALID 00Z WED OCT 22 2014 - 00Z SAT OCT 25 2014

...DAYS 1 -3...

...NORTHERN CASCADES...

A WELL-DEFINED SHORTWAVE TROUGH WILL BRING ANOTHER PERIOD OF
SNOW...THIS TIME THE BEST SUPPORT LOOKS TO BE IN THE NORTHERN
CASCADES OF WA DURING THE DAYS 1-2 PERIODS.

WHILE WIDESPREAD HEAVY PRECIPITATION IS EXPECTED...AFFORDED IN
PART BY STRONG UPPER DIVERGENCE ALONG THE LEFT-EXIT REGION OF
TRANS-PACIFIC JET INTERACTING WITH A SUBTROPICAL MOISTURE
PLUME...DEEP-LAYER SOUTHWEST FLOW IS FORECAST TO CONTINUE ACROSS
THE PACIFIC NORTHWEST.  THEREFORE...COLD ADVECTION WILL BE SLOW TO
DEVELOP AS HEIGHTS ONLY GRADUALLY DECREASE...WHICH IS WHY WE STILL
EXPECT THE PRIMARY THREAT FOR MODERATE TO HEAVY SNOW IN THE U.S.
TO BE CONFINED TO THE NORTHERN CASCADES IN WA.

ONCE AGAIN...WPC WAS USED FOR QPF GUIDANCE WITH A BLEND OF THE
GFS..NAM AND ECMWF USED FOR THE THERMAL FIELDS.

EXPECT THE SNOW THREAT TO WANE BY DAY THREE AS THE SHORTWAVE MOVES
DOWNSTREAM...REPLACED BY A BUILDING RIDGE AHEAD OF A NEW LOW
DEVELOPING OFFSHORE.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA





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