Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 202108
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
507 PM EDT SUN APR 20 2014

VALID 00Z MON APR 21 2014 - 00Z THU APR 24 2014

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

MODELS REMAIN IN GOOD AGREEMENT REGARDING A 700 MB TROUGH AND
FRONT MOVING EAST ACROSS THE PACIFIC NORTHWEST FROM LATE DAY 1 BUT
MAINLY ON DAY 2 AND INTO DAY 3.  SNOW SHOWERS ARE EXPECTED AT
HIGHER ELEVATIONS OF THE OR/WA CASCADES WITH THE FRONTAL PASSAGE.
AS COLD ADVECTION OCCURS BEHIND THE FRONT... SNOW LEVELS DECREASE
AND LAPSE RATES STEEPEN TO 7-8 DEG C/KM.  MEAN LAYER RH STILL
LOOKS TO BE IN THE 80 TO 90 PCT RANGE AT THE SAME TIME AN UPPER
LEVEL DIVERGENCE MAXIMA IN THE LEFT EXIT REGION SUPPORT POST
FRONTAL SHOWERS UNTIL THE UPPER TROUGH PASSES.

AS THE UPPER TROUGH APPROACHES THE NORTHERN ROCKIES TUE
NIGHT...SNOW SHOWERS DEVELOP UNDER THE UPPER DIVERGENCE MAXIMA/MID
LEVEL DEFORMATION IN THE RANGES OF ID AND SOUTHWESTERN MT AND
ADJACENT NORTHWEST WY.

GIVEN GOOD MODEL AGREEMENT...PAID MOST ATTENTION TO THE ECMWF
SINCE IT HAD GOTTEN INTO BETTER AGREEMENT WITH OTHER MODELS ON THE
SPEED TO THE TROF.  ALSO INCLUDED THE GFS AND SOME CONTRIBUTION ON
DAY 2 BY THE NAM TO AID PLACEMENT OF BEST PCPN IN COMPLEX TERRAIN.

THE PROBABILITY FOR SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

BANN


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