Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 192027
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
427 PM EDT WED APR 19 2017

VALID 00Z THU APR 20 2017 - 00Z SUN APR 23 2017


...PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TO THE
NORTHERN/CENTRAL ROCKIES...

ACCUMULATING SNOW WILL BE POSSIBLE WITH AN UPPER TROUGH
PROGRESSING INLAND OVER THE WESTERN U.S....ESPECIALLY OVER THE
HIGHER ELEVATIONS OF THE NORTHERN/CENTRAL ROCKIES AS THE TROUGH
DIGS SOUTHEASTWARD TOWARDS THE CENTRAL PLAINS AND A STRONG UPPER
JET EXTENDS SOUTH AND EAST OVER THE INTERMOUNTAIN WEST.

THE COMBINATION OF INCREASED ONSHORE FLOW AHEAD OF THE UPPER
TROUGH AND LOWERING TEMPERATURES WITH THE APPROACHING HEIGHT FALLS
SHOULD INITIALLY BRING LIGHT TO LOCALLY MODERATE SNOW TO THE
OLYMPICS...CASCADES...AND HIGHER ELEVATIONS OF NORTHERN CALIFORNIA
WEDNESDAY NIGHT.  THE GREATEST CHANCE FOR SNOW SHOULD THEN SHIFT
TO THE NORTHERN AND CENTRAL ROCKIES THURSDAY INTO FRIDAY WHILE
UPPER RIDGING BUILDS IN ALONG THE WEST COAST AND THE TROUGH SHIFTS
DOWNSTREAM.  PERIODS OF MODERATE TO HEAVY SNOW ARE EXPECTED FROM
THE NORTHERN TETONS/ABSAROKA RANGE INTO THE BIG HORN AND WIND
RIVER RANGES DOWN TO THE LARAMIE RANGE AND NORTHERN COLORADO
ROCKIES AS MOIST UPSLOPE FLOW INCREASES WITH AN INVERTED SURFACE
TROUGH SETTING UP JUST EAST OF THE ROCKIES.


...UPPER GREAT LAKES...

LATE SEASON SNOW WILL BE POSSIBLE ACROSS PORTIONS OF THE UPPER
GREAT LAKES ON THURSDAY AS MID-LEVEL ENERGY CLOSES OFF OVER THE
NORTH CENTRAL U.S. AND A SURFACE LOW LIFTS FROM IOWA TO NORTHERN
MICHIGAN.  MODEL THERMAL PROFILES SUGGESTS CONDITIONS SHOULD
BECOME COLD ENOUGH TO SUPPORT SNOW WITHIN THE NORTHERN EDGE OF THE
DEVELOPING PRECIPITATION SHIELD...BUT THERE ARE STILL
DISCREPANCIES WITH EXACTLY HOW MUCH SNOW CAN ACCUMULATE.  THE
LATEST WPC PROBABILITIES ARE ADVERTISING A SLIGHT RISK (AT LEAST
10% PROBABILITY) OF SNOWFALL ACCUMULATIONS EXCEEDING 4 INCHES
EXTENDING FROM NORTHERN MINNESOTA TO THE U.P. OF MICHIGAN...WITH A
MODERATE RISK (AT LEAST 40% PROBABILITY) OF SNOWFALL EXCEEDING 4
INCHES OVER THE MINNESOTA ARROWHEAD.


...MAINE...

SNOW RETURNS TO THE FORECAST FOR PORTIONS OF WESTERN AND NORTHERN
MAINE WEDNESDAY NIGHT AND THEN AGAIN ON FRIDAY NIGHT.  OVERRUNNING
MOISTURE AND DYNAMIC FORCING AHEAD OF A LOW PRESSURE SYSTEM
LIFTING THROUGH SOUTHERN QUEBEC WEDNESDAY NIGHT SHOULD PRODUCE
ACCUMULATING SNOW ACROSS NORTHERN MAINE INTO NOVA SCOTIA.  THEN ON
FRIDAY NIGHT...THE CLOSED MID-LEVEL ENERGY AND ASSOCIATED SURFACE
LOW IMPACTING THE UPPER GREAT LAKES ON THURSDAY WILL REACH THE
NORTHEASTERN QUADRANT OF THE NATION...RESULTING IN A BROAD
OVERRUNNING SHIELD OF PRECIPITATION WITH SURFACE HIGH PRESSURE
WEDGING IN.  THERMAL PROFILES ARE STILL SOMEWHAT IN QUESTION THREE
DAYS OUT...BUT MODEL CONSENSUS IS FOR PARTS OF WESTERN AND
NORTHERN MAINE TO RECEIVE ADDITIONAL ACCUMULATIONS.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


GERHARDT

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