Quantitative Precipitation Forecast
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FOUS11 KWBC 242112
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
412 PM EST WED DEC 24 2014

VALID 00Z THU DEC 25 2014 - 00Z SUN DEC 28 2014

WEST COAST/INTERMOUNTAIN WEST/ROCKIES...

MODEL AGREEMENT CONCERNING THE SPEED AND INTENSITY OF THE
SHORTWAVE TROUGH REACHING THE PACIFIC NORTHWEST LATER TODAY IS
QUITE GOOD AS IT MOVES INTO THE INTERMOUNTAIN WEST BY THURSDAY.

BEYOND THURSDAY THOUGH...THE FORECAST OF LIQUID EQUIVALENT AMOUNTS
AND THERMAL PROFILES BEGINS TO SHIFT TOWARD A BLEND OF THE 24/12Z
ECMWF AND 24/12Z GFS DUE TO THE FACT THAT THE MODELS HAVE
DIFFERING WAYS THAT THEY HANDLE SOME SHORTWAVE ENERGY OUT AHEAD OF
THE MAIN TROF.  THIS IN TURNS LED TO A CONSIDERABLE SPREAD OF
POSSIBLE SOLNS MAINLY IN TERMS OF SNOWFALL OVER THE PLAINS WHILE
THE AMOUNT OF SNOW IN THE MOUNTAINS WAS FAIRLY CONSISTENT BETWEEN
THE MODELS.

THINKING WAS THAT THE NAM WAS TOO SLOW WHILE THE GFS WAS TOO FAST.
 THE 24/12Z ECMWF WAS A BIT MORE PROGRESSIVE THAN ITS PREVIOUS RUN
WHILE /12Z ECMWF ENSEMBLE MEAN...WHICH ACCOUNTS FOR THE SLOWING
TREND AS THE TROUGH REACHES THE SOUTHERN ROCKIES AND BEGINS TO
INFLUENCE THE HIGH PLAINS.

THE PROBABILITIES FOR HEAVY SNOW GRADUALLY SHIFT EAST THROUGH
FRIDAY...STARTING OVER THE WESTERN STATES AND THEN SPREADING
ACROSS THE INTERMOUNTAIN WEST...AND EVENTUALLY CROSSING THE
ROCKIES AND OUT ONTO THE ADJACENT PLAINS.

A NARROW RIBBON OF ICE MAY ALSO DEVELOP OVER THE WESTERN HIGH
PLAINS OF TEXAS OR OKLAHOMA BEHIND A COLD FRONT LATE FRIDAY OR
SATURDAY...ALTHOUGH PROBABILITIES OF 0.25 INCHES ARE PRESENTLY
LESS THAN 10 PERCENT.

WESTERN OH VALLEY INTO MICHIGAN...

OVERALL...THE MODELS HAVE CONVERGED ON THE IDEA OF A MORE EASTERLY
TRACK THAN WAS SHOWN 24 HOURS AGO AND IN FAIRLY GOOD AGREEMENT
WITH THE IDEAS FROM THE OVERNIGHT SHIFT OF A WARMER BOUNDARY LAYER
AND EASTERLY TRACK.  ABOUT THE ONLY AREA LEFT IN THE LOWER 48
WHERE A RISK OF 4 INCHES OR MORE IS DEPICTED IS THE FAR NORTHERN
PORTION OF LOWER MI.  WHILE SNOW MAY MIX IN WITH RAIN...OR CHANGE
ENTIRELY TO SNOW...ELSEWHERE WARM TEMPS SHOULD PRECLUDE MUCH IN
THE WAY OF ACCUMULATIONS.  ALSO WORKING AGAINST A BIGGER AREA OF
SIGNIFICANT ACCUMULATION IS THE FAIRLY LIMITED AMOUNT OF TIME
BEFORE THE ENTIRE SYSTEM LIFTS NORTH OF THE BORDER.

THE PROBABILITY OF 0.25 INCHES OF ICE IS LESS THAN 10 PERCENT.

BANN

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