Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 190908
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
408 AM EST SUN NOV 19 2017

VALID 12Z SUN NOV 19 2017 - 12Z WED NOV 22 2017


DAYS 1-3...

...GREAT LAKES/NORTHEAST...

A STRONG SURFACE LOW ASSOCIATED WITH A WELL-DEFINED UPPER LEVEL
SHORTWAVE TROUGH IS FORECAST TO CONTINUE DEEPENING AS IT TRACKS TO
THE NORTHEAST FROM THE LOWER GREAT LAKES REGION INTO SOUTHEAST
CANADA SUN MORNING.  STRONG WARM ADVECTION AHEAD OF THE LOW WILL
SUPPORT MAINLY RAIN ACROSS THE NORTHEAST...HOWEVER SHALLOW LOW
LEVEL COLD AIR OVER NORTHERN NEW HAMPSHIRE AND MAINE MAY REMAIN IN
PLACE LONG ENOUGH TO SUPPORT A WINTRY MIX WITH SOME MINOR SNOW/ICE
ACCUMULATIONS EARLY IN THE PERIOD BEFORE CHANGING OVER RAIN LATER
IN THE MORNING.  AFTER A PERIOD OF RAIN...STRONG COLD AIR
ADVECTION ON THE BACKSIDE OF THE SYSTEM MAY SUPPORT A BRIEF
CHANGEOVER BACK TO SNOW BEFORE PRECIPITATION ENDS SUN
AFTERNOON-EVENING.  THE HEAVIEST SNOWS HOWEVER ARE EXPECTED TO
OCCUR WELL IN THE WAKE OF THE LOW AS WEST-NORTHWESTERLY
FLOW...WITH EMBEDDED SHORTWAVE ENERGY ALOFT...IS FORECAST TO
PRODUCE LAKE EFFECT SNOW SHOWERS...WITH THE POTENTIAL FOR SEVERAL
INCHES OF ACCUMULATION OCCURRING IN THE LEES OF LAKES ERIE AND
ONTARIO SUN INTO MON.

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

A VIGOROUS FRONT ASSOCIATED WITH A POSITIVELY TILTED UPPER TROUGH
WILL BRING HEAVY PRECIPITATION...INCLUDING HEAVY MOUNTAIN SNOWS TO
THE NORTHERN CASCADES ON SUN...WITH WPC DAY 1 PROBABILITIES
(ENDING 12 UTC MON) CONTINUING TO INDICATE A SIGNIFICANT THREAT
FOR ACCUMULATIONS OF A FOOT OR MORE OVER THE HIGHER REACHES OF THE
NORTHERN WASHINGTON CASCADES.  THIS SYSTEM IS EXPECTED TO
WEAKEN...WITH REMNANT SHORTWAVE ENERGY SPILLING SOUTHEAST ACROSS
THE TOP OF AN AMPLIFYING RIDGE MON NIGHT INTO TUE...PRODUCING SNOW
SHOWERS ACROSS THE NORTHERN ROCKIES.  SNOW LEVELS WILL BE ON THE
INCREASE AS A STRONG RIDGE CONTINUES TO BUILD ACROSS THE WESTERN
U.S.  BY DAY 3 (ENDING 12 UTC WED)...WPC PROBABILITIES SHOW LITTLE
POTENTIAL FOR WIDESPREAD HEAVY ACCUMULATIONS ACROSS THE WESTERN
U.S.

FOR DAYS 1-3...THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN
10 PERCENT.

PEREIRA

$$




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