Quantitative Precipitation Forecast
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FOUS11 KWBC 102039
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
338 PM EST SAT DEC 10 2016

VALID 00Z SUN DEC 11 2016 - 00Z WED DEC 14 2016

WEST COAST/INTERMOUNTAIN WEST/ROCKIES...

THE PROCESS OF THE UPPER TROUGH SPLITTING WHILE PROGRESSING ACROSS
THE NORTHERN ROCKIES CREATES BOTH FAVORABLE CONDITIONS FOR SNOW
ACROSS A LARGE PORTION OF THE HIGHER TERRAIN IN THIS REGION
THROUGH MONDAY AS WELL AS HIGHER UNCERTAINTY FOR SNOW POSSIBLY
CONFINING ITSELF TO NORTHERN CALIFORNIA AND PARTS OF THE
INTERMOUNTAIN WEST WITH RISING SNOW LEVELS BY TUESDAY. THE
UNCERTAINTY DEVELOPS IN RESPONSE TO DIFFERENT TIMING AND AMOUNTS
OF SPLITTING...WITH THE SREF ARW CORE MEMBERS GENERALLY THE ODD
MODELING SYSTEM OUT WITH WEAKER SPLITTING AND STRONGER HEIGHT
FALLS OVER THE ROCKIES ON TUESDAY...WHILE ALL OTHER ENSEMBLE
SYSTEMS SPLIT THE TROUGH SOONER AND MORE STRONGLY THUS FORMING A
STRONGER MID LEVEL LOW OFFSHORE...WHICH IS MORE LIKE THE
DETERMINISTIC SOLUTIONS AND WPC PREFERENCES. THUS...THE SREF ARW
MEMBERS ARE GENERALLY LESS AND FARTHER SOUTH WITH SNOW
PROBABILITIES BY TUESDAY. IF THIS CORE WERE REMOVED OR MORE LIKE
THE OTHER ENSEMBLES...PROBABILITIES WOULD BE HIGHER. AS IT
STANDS...LOW AND MODERATE PROBABILITIES OF 8 AND 12 INCHES OF SNOW
ARE DEPICTED FOR THE CASCADES/BITTERROOTS/WASATCH/COLORADO ROCKIES
THROUGH SUNDAY...WITH LOW AND MODERATE PROBABILITIES OF 4 AND 8
INCHES ACROSS THE CASCADES/BITTERROOTS/TETONS BY MONDAY...AND LOW
PROBABILITIES OF 12 INCHES FOR THE SIERRAS BY TUESDAY...WITH LOW
PROBABILITIES OF 4 INCHES OVER THE WASATCH AND CENTRAL ROCKIES.

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

GREAT LAKES/NORTHEAST/NEW ENGLAND...

CONFIDENCE AND ASSOCIATED UNCERTAINTY WITH THIS EVENT ARE ABOUT
AVERAGE BASED ON THE LATEST ENSEMBLE MEMBER SPREAD. THE GFS AND
ECMWF ENSEMBLE MEMBERS ARE GENERALLY WEAKER...FLATTER...AND FASTER
WITH THE SURFACE LOW REACHING THE WESTERN GREAT LAKES BY
SUNDAY...WITH THE SREF MEMBERS PARTICULARLY THE ARW CORE STRONGER
AND FARTHER NORTH THUS ALLOWING THE FINAL SNOW PROBABILITIES FOR
DAY 1 TO EXTEND MORE INTO NORTHERN WISCONSIN AND NORTHERN MICHIGAN
THAN WOULD BE SUGGESTED FROM THE DETERMINISTIC FORECAST ALONE. THE
WPC FORECAST FAVORS THE FLATTER AND WEAKER SCENARIO WHICH IS MORE
LIKE THE LATEST OPERATIONAL RUNS OF THE GFS AND ECMWF. FACTORING
IN THE MOST PREFERRED SIDE OF THE SOLUTION ENVELOPE FAVORS THE
HIGHEST CHANCE OF 4 AND 8 INCHES OF SNOW ACROSS NORTHERN INDIANA
INTO SOUTHERN MICHIGAN. BY MONDAY...THE STRONGER SREF ARW MEMBERS
PULL THE RAIN/SNOW LINE FARTHER NORTH ACROSS INTERIOR NEW
ENGLAND...WHILE MOST OF THE ECMWF ENSEMBLE MEMBERS ARE CLOSER TO
THE NEW ENGLAND COAST DUE IN LARGE PART TO A WEAKER AND FASTER LOW
REFORMING OFFSHORE. COMPLETING THE SOLUTION ENVELOPE ARE THE SREF
NMMB AND GEFS MEMBERS WHICH ARE ABOUT MIDWAY BETWEEN...WITH WPC
LEANING TOWARD THE FASTER/WEAKER CAMP OF SOLUTIONS. THUS...THE
FINAL SNOW PROBABILITIES FOR TUESDAY DEPICT LOW PROBABILITIES OF 4
AND 8 INCHES ACROSS A BROAD REGION TO ACCOUNT FOR THE MODEL
SPREAD.

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

JAMES

$$





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