Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 170804
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 AM EDT TUE OCT 17 2017

VALID 12Z TUE OCT 17 2017 - 12Z FRI OCT 20 2017

DAYS 1 THROUGH 3...

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

SEVERAL SHORT WAVES IN THE MID LEVEL FLOW WILL CROSS THE PACIFIC
NORTHWEST DURING DAYS 1 THROUGH 3.

FOR THE MOST PART...SNOW LEVELS WILL BE FAIRLY HIGH OVER THE
AREA...WITH SNOW ACCUMULATIONS GENERALLY RELEGATED TO THE HIGHER
TERRAIN OF THE NORTHERN CASCADES ON DAY 1 WHEN THERE IS A WARM
ADVECTION/ISENTROPIC UPGLIDE PATTERN AHEAD OF THE APPROACHING
WAVE.  SNOW LEVELS DROP TO AROUND 5000 FT ALONG THE NORTHERN TIER
OF COUNTIES IN WA STATE ONCE THE WAVE PASSES. SNOW AMOUNTS ARE NOT
EXPECTED TO BE TOO GREAT CONSIDERING THE HEAVIEST PRECIPITATION
WILL HAVE MOVED OUT OF THE AREA BEFORE HEIGHTS/THICKNESS VALUES
DROP TOO MUCH.

HEIGHTS/THICKNESS/SNOW LEVELS INCREASE AHEAD OF A STRONGER WAVE
FROM DAY 2 INTO EARLY DAY 3...FOLLOWED BY THE NEXT ROUND OF SNOW
AS THE SECOND WAVE ONCE THE COLD ADVECTION SETS IN BEHIND THE
TROUGH.  THE TROUGH WHICH DEVELOPS WILL BE STRONGER THAN BEHIND
THE FIRST WAVE...SO THERE IS AT LEAST A CHANCE OF SOME LIGHT SNOW
MAKING INTO THE HIGHER ELEVATIONS OF THE ORE CASCADES ON DAY 3.

THE THERMAL PORTION OF THE FORECAST WAS BASED ON A MULTI MODEL
BLEND THE QPF PORTION OF THE FORECAST WAS BASED ON THE MOST RECENT
WPC QPF.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

BANN

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