Quantitative Precipitation Forecast
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FOUS11 KWBC 240804
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 AM EDT FRI MAR 24 2017

VALID 12Z FRI MAR 24 2017 - 12Z MON MAR 27 2017


DAYS 1 THROUGH 3...

...WESTERN U.S....

ON FRIDAY SNOW IS EXPECTED WITH A LONGWAVE TROUGH AND ASSOCIATED
COLD FRONT EXPECTED TO MOVE INLAND OVER THE PACIFIC NORTHWEST AND
NORTHERN CALIFORNIA. WITH MODERATE TO HEAVY SNOW IS FORECAST
ACROSS THE WA/OR CASCADES AND THE RANGES OF NORTHERN TO CENTRAL
CA...AND THEN AS THE TROUGH COMES INTO THE NORTHERN ROCKIES SNOW
FALLS IN THE RANGES OF ID AND ADJACENT NORTHWEST MT.

ON FRIDAY...THE MODELS INDICATE COOLING OCCURS ACROSS THE CO
PALMER RIDGE AND NEARBY HIGH PLAINS...WHERE RAIN CHANGES TO SNOW.
WITH THE UPPER LOW DRIFTING EAST NORTHEAST FROM CO INTO KS...A
PERIOD OF UPPER DIVERGENCE MAXIMA CONTINUES SNOW UNTIL THE LOW
PULLS FAR ENOUGH EAST THAT THE UPPER DIVERGENCE MOVES AWAY INTO KS
AND SNOW COMES TO AN END. THE NAM INDICATES HEAVIER AMOUNTS AFTER
THE SNOW TRANSITION WITH MUCH LOWER AMOUNTS IN THE SREF AND GEFS
MEANS....ECMWF AND GFS.

ON SATURDAY...THE DEPARTURE OF THE UPPER TROUGH LEAD TO A BREAK IN
THE PACIFIC NORTHWEST.  THE PRIMARY AREA OF SNOW MOVES INTO THE
RANGES OF WY AND NORTHERN UT...CONTINUING EAST INTO WESTERN CO AS
THE UPPER TROUGH MOVES ACROSS UT SAT NIGHT.

ON SUNDAY...THE MODELS SHOW THE GRADUAL APPROACH OF THE NEXT UPPER
TROUGH FROM THE NORTHEAST PACIFIC.  PRECIP PICKS AS THE UPPER JET
STREAMS ONSHORE INTO OR...WITH ATTENDANT UPPER DIVERGENCE MAXIMA
TARGETING VALLEY RAINS AND MOUNTAIN SNOW IN THE OR/WA CASCADES
DOWN INTO NORTHWEST CA.  THE GFS INDICATES THE STRONGER DIVERGENCE
MAXIMA AND HEAVIER QPF IN THE OR CASCADES/AND SHASTAS/SISKIYOUS OF
NORTHERN CA...SO PROBABILITIES FOR HEAVY SNOW ARE HIGHEST THERE.
AS THE UPPER TROUGH COMES ONSHORE THE JET FORWARD PROPAGATES
INLAND INTO NV WITH THE UPPER DIVERGENCE MAXIMA IN THE LEFT JET
EXIT REGION INITIATING SNOWS IN THE RANGES OF SOUTHERN ID.


...UPPER GREAT LAKES TO THE NORTHEAST...

AREAS OF SNOW...SLEET...AND FREEZING RAIN WILL BE POSSIBLE WITHIN
THE NORTHERN EDGE OF PRECIPITATION DEVELOPING TO THE NORTH OF A
FRONTAL BOUNDARY EXPECTED TO STRETCH FROM THE UPPER GREAT LAKES TO
THE NORTHEAST FRIDAY THROUGH SUNDAY...WITH AN ARCTIC AIRMASS
SLIDING SOUTHEASTWARD OUT OF CANADA INTO THE  NORTHEAST THIS
WEEKEND SUPPLYING THE LOW-LEVEL COLD AIR.

THE PRIMARY THREAT FOR LIGHT FREEZING RAIN ACCUMULATIONS IS
CENTERED OVER NORTHERN WI/NORTHERN MI...AND THEN THE HIGHER
ELEVATIONS OF NORTHEAST PA TO THE CATSKILLS OF NY ON
FRI...CONTINUING IN THE CATSKILLS/HELDEBERGS OF NY AND SOUTHERN
GREEN MNTNS/ADIRONDACKS SAT...AND EXPANDING INTO PORTIONS OF THE
BERKSHIRES AND SOUTHERN GREEN MNTNS OF VT SAT NIGHT/SUN AS HIGH
PRESSURE IN QUEBEC AND THEN MAINE REINFORCES COLD AIR IN THE
REGION. A FEW ENSEMBLE MEMBERS AND OPERATIONAL NAM PRODUCE
ISOLATED MAXIMA OF A QUARTER INCH OF ICING.

THE INITIAL PRECIP PRODUCES A STRIPE OF LIGHT SNOW IN NORTHEAST NY
TO NORTHERN VT AND NH...WITH 3 TO 5 INCHES OF SNOW EXPECTED IN TH
NORTHERN GREEN AND WHITE MNTNS ON DAY ONE.

THE PROBABILITY OF RECEIVING A QUARTER INCH OF FREEZING RAIN IS
LESS THAN 10 PERCENT DAYS 1 AND 2.


PETERSEN


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