Quantitative Precipitation Forecast
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FOUS11 KWBC 150803
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
302 AM EST WED FEB 15 2017

VALID 12Z WED FEB 15 2017 - 12Z SAT FEB 18 2017


NORTHEAST/NEW ENGLAND...

THERE IS A HIGH PROBABILITY OF 12 INCHES OF SNOW ALONG A SMALL
PORTION OF NEW HAMPSHIRE/MAINE BORDER TODAY AND TONIGHT...WITH LOW
TO MODERATE PROBABILITIES OF 4 AND 8 INCHES OF SNOW EXTENDING
SOUTHWESTWARD TO AREAS DOWNWIND OF LAKES ERIE AND ONTARIO. MODELS
CONTINUE TO ADVERTISE A SMALL, YET HIGH-END, IMPACTFUL
EVENT...WITH MODELS TRENDING SOUTHWESTWARD WITH THE LOW REFORMING
IN THE GULF OF MAINE. THUS...THE PROBABILITIES REFLECT A
SOUTHWESTWARD SHIFT FROM THE PREVIOUS FORECAST...WITH 2 MAIN CAMPS
OF SOLUTIONS...THE SREF ARW AND GEFS MEMBERS WHICH ARE MORE INLAND
WITH THEIR HEAVY SNOW...AND THE SREF NMMB AND ECMWF MEMBERS WHICH
ARE SOUTHWESTWARD WITH THEIR HEAVY SNOW. GIVEN RECENT
DETERMINISTIC MODEL TRENDS AND ACCOMPANYING SOUTHWESTWARD
ADJUSTMENTS TO THE MODE...THE SREF NMMB AND ECMWF MEMBERS LIKELY
REPRESENT THE MORE PROBABLE SIDE OF THE SOLUTION ENVELOPE.

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

NORTHWEST/N ROCKIES/CALIFORNIA/INTERMOUNTAIN WEST...

THERE IS A LOW PROBABILITY OF REACHING OR EXCEEDING 0.25 OF ICE
ACROSS INTERIOR WASHINGTON TODAY AND TONIGHT...WITH THE GREATEST
SUPPORT OFFERED FROM THE SREF NMMB MEMBERS WHICH ARE WETTER THAN
THE SREF ARW/GEFS/ECMWF ENSEMBLE MEMBERS...WITH THE AVERAGE OF ALL
MEMBERS SLIGHTLY HIGHER THAN 10 PERCENT.

REGARDING SNOW...LOW TO MODERATE PROBABILITIES OF 8 AND 12 INCHES
OF SNOW WILL AFFECT THE CASCADES/BITTERROOTS/SIERRAS THURSDAY AND
THURSDAY NIGHT BEFORE MOVING SOUTHWARD TO AFFECT THE SIERRAS SOME
MORE FRIDAY AND FRIDAY NIGHT...AS WELL AS SUPPORTING LOW TO
MODERATE PROBABILITIES OF 4 AND 8 INCHES FOR THE HIGHER ELEVATIONS
OF SOUTHERN NEVADA INTO THE WASATCH DEPENDING ON VARIOUS ENSEMBLE
SYSTEMS. GIVEN THE SLOW MOVING AND HIGH AMPLITUDE SPLITTING
LONGWAVE TROUGH...SNOW LEVELS WILL BE RATHER HIGHER FOR MUCH OF
THIS EVENT. CONCERNING THE MODELS...THE SPREAD CONTAINS LITTLE OR
MANAGEABLE SPREAD THROUGH THURSDAY NIGHT...WITH ALL ENSEMBLE
MEMBERS EQUALLY DISPERSED. BY FRIDAY AND FRIDAY NIGHT
HOWEVER...THE SPREAD BECOMES QUITE HIGH...WITH THE GEFS MEMBERS
PRIMARILY THE ONLY ENSEMBLE SOLUTIONS SUPPORTING HEAVY SNOW FOR
THE WA/OR CASCADES. MEANWHILE...THE SREF NMMB MEMBERS ARE THE MOST
PROGRESSIVE IN MOVING HEAVY SNOW INTO NEVADA AND WASATCH...WHILE
THE SREF ARW MEMBERS AND ECMWF ENSEMBLE MEMBERS ARE THE SLOWEST
AND MOST SOUTHWESTWARD...FAVORING THE SIERRAS PRIMARILY. THE WPC
MODE AND GENERAL PREFERENCES LEAN ABOUT 70 PERCENT TOWARD THE
SLOWER/SOUTHWESTWARD SREF ARW AND ECMWF ENSEMBLE
MEMBERS...ACCOMPANIED BY JUST AVERAGE CONFIDENCE GIVEN THE SPREAD
AND COMPLICATED STRUCTURE TO THE LONGWAVE PATTERN.

JAMES

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