Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 220610
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 AM EDT WED OCT 22 2014

VALID 12Z WED OCT 22 2014 - 12Z SAT OCT 25 2014

...DAYS 1 -3...

...NORTHERN WA CASCADES...

A SUSTAINED PERIOD OF MOIST ONSHORE FLOW AND PERIODS OF UPPER
DIVERGENCE AS THE UPPER JET CROSSES SOUTHERN BRITISH COLUMBIA
SHOULD CAUSE SNOW AT HIGHER ELEVATIONS OF THE WA CASCADES ON DAY
1. WIDESPREAD HEAVY PRECIPITATION IS EXPECTED. LOW TO MID LEVEL
SOUTHERLY FLOW PRODUCES WARM ADVECTION AND KEEPS SNOW ELEVATIONS
HIGH.

ON DAY 2 THE FLOW BACK WITH THE JET MAXIMA RETREATING BACK NORTH
OUT OF OREGON NORTH ACROSS WA WITH THE GFS SHOWING AN IMPRESSIVE
130-150 KT 300 MB JET MAXIMA.
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 TO BE CONFINED TO THE NORTHERN CASCADES IN
WA.

EXPECT THE SNOW THREAT TO BE LIMITED ON DAY THREE AS THE NEXT
ROUND OF WARM ADVECTION ENSUES AHEAD OF A NEW LOW DEVELOPING
OFFSHORE.  SNOW LEVELS RISE AGAIN AND SNOW TURNS TO RAIN IN MANY
CASES.  ASCENT IS STRONGER FURTHER WEST IN WA AND OR IN THE GFS
AND ECMWF WITH LOW AMOUNTS WHERE ELEVATIONS ARE HIGH ENOUGH FOR
SNOW IN THE CASCADES.

A BLEND OF THE GFS AND ECMWF WAS USED FOR THE QPF/THERMAL FIELDS.
THE NAM WAS AN OUTLIER WITH THE LOW DEVELOPMENT SOUTH OF THE
PRIMARY CLUSTER SO ITS SOLUTION WAS GIVEN THE LEAST WEIGHT.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN





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