Quantitative Precipitation Forecast
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671
FOUS11 KWBC 212047
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
346 PM EST TUE NOV 21 2017

VALID 00Z WED NOV 22 2017 - 00Z SAT NOV 25 2017


DAYS 1-3...

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

A LARGE AMPLIFIED UPPER RIDGE WILL BE THE MAIN THEME ACROSS THE
WEST OVER THE NEXT THREE DAYS. THIS LARGE SCALE FEATURE WILL BUILD
ON WED BUT ANOTHER SET OF HEIGHT FALLS FROM THE NERN PAC WILL MOVE
INTO WA/OR ON THANKSGIVING. ENOUGH PAC MOISTURE TRANSPORT AND THE
PASSAGE OF AN ASSOCIATED SURFACE COLD FRONT SHOULD YIELD SOME SNOW
ACROSS THE WA CASCADES/OLYMPICS. THIS FEATURE ALOFT AND THERMAL
BOUNDARY WILL SLIDE PROGRESSIVELY DOWNSTREAM ON FRI, WHICH MAY
CONTINUE TO YIELD HEAVY SNOW ACROSS THE NORTHERN WA CASCADES BUT
INCLUDE THE NORTHERN ROCKIES/BITTERROOTS AND TETONS.

...EASTERN GREAT LAKES AND NORTHERN NEW ENGLAND...

A DYNAMIC SHORT WAVE TROUGH AND ASSOCIATED STRONG SURFACE COLD
FRONT IS PLOWING THROUGH THE GREAT LAKES REGION/OH VALLEY THIS
AFTERNOON. AN ORGANIZED AND EXPANDING PRECIP SHIELD FROM SOUTHERN
LOWER MI TO IL IS TRACKING ALONG AND JUST BEHIND THIS DRAMATIC
THERMAL BOUNDARY. THE MODEL GUIDANCE INDICATES, THIS AFTERNOON
THROUGH THE OVERNIGHT HRS, A WINDOW OF ENOUGH DYNAMIC FORCING AND
ENHANCED VERTICAL LIFT BUT ENOUGH COOLING OF THE THERMAL COLUMN
FOR POSSIBLE LIGHT SNOWFALL WITH MINIMAL ACCUMULATIONS. THIS
APPEARS MOST LIKELY FROM NERN OH/NWRN PA INTO WESTERN AND UPSTATE
NY THROUGH WED MORNING. ALSO, AS THE COLD FRONT AND UPPER TROUGH
SWEEP TO THE NERN SEABOARD ON WED, POSSIBLE PHASING OF UPPER JETS
MAY ALLOW SURFACE LOW DEVELOPMENT NEAR COASTAL MAINE BEFORE
LIFTING/DEEPENING UP INTO THE CANADIAN MARITIMES. THIS MAY PRODUCE
 A BURST OF HEAVY SNOWFALL ACROSS THE WESTERN/NWRN PORTION OF
MAINE BEFORE SHIFTING INTO EASTERN QUEBEC.

...UPPER MIDWEST...

A WEAK SHORT WAVE IMPULSE CAUGHT IN THE BROAD LARGE SCALE SWRLY
FLOW ALOFT IN THE PAC IS ROUNDING THE BUILDING UPPER WESTERN RIDGE
TODAY. THIS SHORT WAVE WILL SLIDE SOUTHEAST FROM ALBERTA AND REACH
THE UPPER MIDWEST ON WED. THIS SHOULD INDUCE A WEAK SURFACE WAVE
AND PRODUCE ENOUGH LIFT AND FORCING FOR A STREAK OF WARM
ADVECTION/OVERRUNNING LIGHT FREEZING DRIZZLE AND SNOW. A BLEND OF
THE GUIDANCE SUGGESTS THE MAIN CORRIDOR FOR THIS EXTREMELY LIGHT
FROZEN PRECIP FROM NERN ND INTO WEST CENTRAL MN.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER


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