Quantitative Precipitation Forecast
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FOUS11 KWBC 272116
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
415 PM EST SAT DEC 27 2014

VALID 00Z SUN DEC 28 2014 - 00Z WED DEC 31 2014


DAYS 1 THROUGH 3...

...PACIFIC NORTHWEST/NORTHERN GREAT BASIN/NORTHERN TO CENTRAL
ROCKIES...

ON DAY 1...LATE SAT-LATE SUN...THE MODELS ARE IN OVERALL GOOD
AGREEMENT WITH A WELL-DEFINED SHORTWAVE TROUGH FORECAST TO DIG
SOUTH FROM BRITISH COLUMBIA THROUGH THE PACIFIC NORTHWEST-NORTHERN
ROCKIES AND INTO THE CENTRAL GREAT BASIN.  WHILE THE MODELS ARE
ADVERTISING FAIRLY MODEST PWS...PERSISTENT NORTHWESTERLY-WESTERLY
FLOW IS EXPECTED TO PROMOTE MODERATE TO HEAVY PRECIPITATION IN THE
FAVORED TERRAIN ACROSS WESTERN WA..OREGON AND THE NORTHERN ROCKIES
WEST OF THE DIVIDE.  UPSLOPE FLOW IN THE WAKE OF A SURFACE-LOW
LEVEL CENTER MOVING OUT INTO THE NORTHERN HIGH PLAINS MAY AFFORD
SOME HEAVY SNOWS EAST OF THE DIVIDE AS WELL ACROSS WESTERN MT AND
NORTHWESTERN WY.  SNOW ACCUMULATIONS ARE EXPECTED TO BE WIDESPREAD
IN THE NORTH AS SNOW LEVELS DROP TO AS LOW AS 1500 FT IN SOME
LOCATIONS.  HOWEVER ACCUMULATIONS OF A FOOT OR MORE WILL MOST
LIKELY CENTER OVER THE HIGHER REACHES OF THE NORTHERN
CASCADES...BLUES AND NORTHERN ROCKIES.

ON DAY 2...LATE SUN-LATE MON...LEADING ENERGY FROM THE
AFOREMENTIONED SHORTWAVE IS FORECAST TO CONTINUE TO SQUEEZE OUT
WHAT LITTLE MOISTURE THERE IS AVAILABLE AS IT DROPS FURTHER TO THE
SOUTH EARLY IN THE PERIOD BEFORE BEGINNING TO SHEAR
EAST...PRODUCING MAINLY LIGHT-MODERATE SNOWS ACROSS THE CENTRAL
ROCKIES INTO THE ADJACENT HIGH PLAINS.  MEANWHILE...PERSISTENT
ONSHORE FLOW AND A SECOND BATCH OF SHORTWAVE ENERGY WILL CONTINUE
TO FUEL THE POTENTIAL FOR MODERATE TO HEAVY SNOWS ACROSS THE
SOUTHERN WA-OREGON CASCADES.

BY DAY 3...LATE MON-LATE TUE...THE POTENTIAL FOR HEAVY SNOW IS
FORECAST TO DIMINISH FURTHER ACROSS MUCH OF THE REGION AS DEEP
NORTHEASTERLY FLOW DEVELOPS TO THE NORTH OF MID-UPPER CENTER
CLOSING OFF NEAR THE CA-NV BORDER ON TUE.

THE WPC FORECAST RELIED ON WPC QPF AND A BLEND OF THE GFS..ECMWF
THERMAL FIELDS THROUGH MUCH OF THE PERIOD.  THE NAM WAS LARGELY
DISCOUNTED...ESPECIALLY BEYOND THE DAY 1 PERIOD AS IT MOVES TO THE
AMPLIFIED SIDE OF THE GUIDANCE WITH RESPECT TO THE LEADING
SHORTWAVE AS IT DIGS OUT OF THE PACIFIC NORTHWEST.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA


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