Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 212119
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
419 PM EST TUE FEB 21 2017

VALID 00Z WED FEB 22 2017 - 00Z SAT FEB 25 2017


...WESTERN U.S. TO THE UPPER MIDWEST ...

BROAD CYCLONIC FLOW IS EXPECTED TO PERSIST ACROSS THE WESTERN U.S.
EARLY IN THE PERIOD...WITH A POSITIVELY TILTED TROUGH CENTERED
ALONG 130W TUE EVENING.  MOUNTAIN SNOWS ARE EXPECTED TO CONTINUE
FOR PORTIONS OF THE OLYMPICS...CASCADES AND SIERRA TO THE NORTHERN
AND CENTRAL ROCKIES INTO WED.  LIMITED MOISTURE IS EXPECTED TO
HAMPER THE THREAT FOR WIDESPREAD HEAVY ACCUMULATIONS THROUGH LATE
WED.  HOWEVER...A BAROCLINIC ZONE DROPPING SOUTH INTO THE REGION
MAY BOLSTER THE POTENTIAL FOR AT LEAST SOME LOCALLY HEAVY AMOUNTS
ACROSS THE RANGES OF NORTHERN UT WED AFTERNOON/EVENING.

AS A WELL-DEFINED SHORTWAVE DIGS INTO THE BASE OF THE BROADER
SCALE TROUGH AND PIVOTS EAST ACROSS THE GREAT BASIN...SNOWS ARE
EXPECTED TO INCREASE IN COVERAGE AND SPREAD EAST ACROSS THE WY AND
NORTHERN CO RANGES INTO THE ADJACENT HIGH PLAINS ON THU.
INCREASING MOISTURE ADVECTION AFFORDED BY AMPLIFYING EASTERLY FLOW
TO THE NORTH OF A STRENGTHENING LEE SIDE LOW INTERACTING WITH LOW
TO MID LEVEL FRONTOGENESIS AND DIVERGENT FLOW ALOFT IS EXPECTED TO
SUPPORT HEAVY SNOWS ACROSS THE CENTRAL HIGH PLAINS BACK INTO THE
SOUTHEASTERN WY MOUNTAINS.  THE WPC FORECAST REFLECTS THE
NORTHERLY SHIFT IN THE 12 UTC GFS/ECMWF...DISCOUNTING THE NAM
WHICH PRODUCED HEAVIER AMOUNTS FURTHER TO THE SOUTH.

THE AFOREMENTIONED SHORTWAVE TROUGH IS EXPECTED TO EJECT OUT INTO
THE CENTRAL PLAINS THU NIGHT WITH A CLOSED LOW DEVELOPING AS IT
CONTINUES FURTHER TO THE NORTHEAST INTO THE UPPER MS VALLEY ON
FRI.  STRONG LIFT AFFORDED BY LOW TO MID LEVEL FRONTOGENESIS AND
AN UPPER JET COUPLET IS EXPECTED TO SUPPORT A STRIPE OF MODERATE
TO HEAVY SNOWS FROM THE MID MO VALLEY NORTHEASTWARD INTO THE UPPER
GREAT LAKES REGION.  MODEL SPREAD WITH RESPECT TO THE PLACEMENT OF
HEAVIER AMOUNTS IS SIGNIFICANT AND THEREFORE CONFIDENCE IN THE
FORECAST DETAILS IS LOW AT THIS POINT.  THE WPC FORECAST GAVE
SIGNIFICANT WEIGHT TO A GFS AND ECMWF COMPROMISE...AGAIN
DISCOUNTING THE NAM WHICH BECOMES A FAST OUTLIER FROM THU
AFTERNOON ONWARD.

THE PROBABILITY OF ICE ACCUMULATIONS GREATER THAN 0.25 IS LESS
THAN 10 PERCENT.

PEREIRA

$$





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