Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 191930
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
330 PM EDT SUN OCT 19 2014

VALID 00Z MON OCT 20 2014 - 00Z THU OCT 23 2014


...DAYS 1-2...

THE PROBABILITY OF HEAVY SNOW AND/OR SIGNIFICANT ICING IS LESS
THAN 10 PERCENT.

...DAY 3...

STRONG WARM ADVECTION DEVELOPS IN THE PACIFIC
NORTHWEST...INCLUDING IN THE CASCADES OF WASHINGTON STATES...AS
SOUTH TO SOUTHWEST FLOW IN LOW-MID LEVELS DEVELOPS.
LAYER RELATIVE HUMIDITY INCREASES TO 90-99 PERCENT AND ASCENT
COMMENCES WITH THE WARM ADVECTION AND UPPER DIVERGENCE MAXIMA NEAR
A 300 MB JET MAXIMA...CAUSING PRECIPITATION TO DEVELOP.  PRECIP
STARTS AS SNOW AT HIGHER ELEVATIONS OF THE CASCADES AND MAY CHANGE
OVER TO RAIN AS WARM AIR MOVING INTO THE REGION CAUSES SNOW LEVELS
TO RISE.
THE PRIMARY UNCERTAINTY IS THE DURATION OF SNOWFALL THE MODELS ARE
IN GOOD AGREEMENT IN MAINTAINING THE MEAN UPPER TROUGH WEST OF THE
PAC NORTHWEST...SO A MODEL CONSENSUS WAS USED FOR QPF AND
TEMPERATURE PROFILES.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PETERSEN



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