Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS11 KWBC 201957
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
357 PM EDT THU APR 20 2017

VALID 00Z FRI APR 21 2017 - 00Z MON APR 24 2017


...NORTHERN AND CENTRAL ROCKIES...

PRECIPITATION ACROSS ID IS FORECAST TO MOVE EAST INTO THE ROCKIES
OF MT AND WY AS A WELL-DEFINED SHORTWAVE SLIDING SOUTHEAST INTO
THE BASE OF A NEGATIVELY TILTED TROUGH  SHIFTS EAST ACROSS THE
ROCKIES TO SUPPORT WIDESPREAD MOUNTAINS SNOWS FROM THE RANGES OF
WESTERN AND SOUTH CENTRAL MT ACROSS THE RANGES OF WY AND NORTHERN
CO.

LOCALLY HEAVY ACCUMULATIONS ARE POSSIBLE...WITH THE GREATEST
THREAT CENTERING ALONG THE ABSAROKA...WIND RIVER AND BIG HORNS OF
WY.  MODELS SHOW A LOW LEVEL CENTER DEVELOPING AND THEN LINGERING
OVER CENTRAL-EASTERN WY LATE THU INTO FRI...RESULTING IN A PERIOD
OF PRONOUNCED AND PROLONGED LOW LEVEL INFLOW/UPSLOPE
FLOW...SUPPORTING HIGHER AMOUNTS IN THE RANGES OF WY DUE TO THE
FORECAST LONGER DURATION SNOWS.

...NORTHERN NEW ENGLAND...

A MID-UPPER LEVEL SHORTWAVE IS EXPECTED TO CROSS QUEBEC AND
NORTHERN NEW ENGLAND.  AS THE WAVE APPROACHES...LOW TO MID LEVEL
WARM AND MOIST ADVECTION PRODUCES PRECIPITATION.  A COMBINATION OF
DYNAMIC AND WET BULB COOLING IS EXPECTED TO SUPPORT RAIN CHANGING
TO SNOW.  THE PARENT SURFACE LOW WEAKENS AS IT MOVES INTO NORTHERN
NEW ENGLAND AS A SECONDARY LOW DEVELOPS OFF THE LONG
ISLAND/SOUTHERN NEW ENGLAND COAST FRI NIGHT-SAT MORNING.  SNOW IS
EXPECTED ACROSS NORTHERN MAINE FRI NIGHT...WITH ACCUMULATING SNOW
POSSIBLE...ESPECIALLY ACROSS THE HIGHER ELEVATIONS BEFORE
PRECIPITATION COMES TO AN END ON SAT.  TIMING OF THE WAVE PRODUCES
DIFFERING AMOUNTS...WITH THE 06Z AND 12Z GEFS FORECASTING HIGHER
AMOUNTS FOLLOWING SLOWER TIMING OF THE WAVE AND LONGER DURATION OF
SNOW.  GIVEN AN UPSTREAM WAVE IN HUDSON`S BAY TO ACT TO EJECT THE
WAVE ACROSS THE REGION..THE SLOWER SOLUTIONS ARE LEAST
PREFERRED...SO LESS WEIGHT WAS GIVEN TO THE 06Z RUN OF THE GEFS.

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

PETERSEN


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