Quantitative Precipitation Forecast
Issued by NWS

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792
FOUS11 KWBC 270808
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
408 AM EDT MON MAR 27 2017

VALID 12Z MON MAR 27 2017 - 12Z THU MAR 30 2017

DAYS 1 THROUGH 3...

...WESTERN U.S....

MOUNTAIN SNOWS WILL CONTINUE MON-WED...WITH THE
CASCADES...UINTA/WASATCH RANGES IN UTAH...AND COLORADO ROCKIES
EXPECTED TO SEE THE GREATEST CHANCE FOR SNOWFALL ACCUMULATIONS IN
EXCESS OF A FOOT.

AN UPPER TROUGH AND ASSOCIATED COLD FRONT PRESSING INLAND OVER THE
GREAT BASIN MONDAY WILL BE THE INITIAL FOCUS FOR SNOWFALL.  THE
COMBINATION OF LOWERING SNOW LEVELS AND MOIST FLOW INTO THE
TERRAIN SHOULD BRING MODERATE TO LOCALLY HEAVY SNOW TO THE HIGHER
ELEVATIONS OF THE WASATCH AND UINTAS OF UT WITH SECONDARY MAXIMA
NEAR THE FRONT AS IT CROSSES THE BOISE/SALMON RIVER MOUNTAINS AND
TETONS OF WESTERN WY.

ON TUESDAY...THE UPPER TROUGH IS EXPECTED TO AMPLIFY WHILE
CONTINUING TO DIG SOUTHEASTWARD AND EVENTUALLY CLOSE OFF AN UPPER
LOW NEAR THE SOUTHWEST/FOUR CORNERS REGION.  THE SHARPENING UPPER
TROUGH SHOULD HELP TRIGGER PERIODS OF MODERATE TO HEAVY SNOW OVER
THE THE COLORADO ROCKIES...ESPECIALLY ALONG THE FRONT RANGE ONCE A
SURFACE LOW DEEPENS OVER THE SOUTHERN HIGH PLAINS AND UPSLOPE FLOW
INCREASES ACROSS THE REGION TUESDAY NIGHT INTO WEDNESDAY.
SECONDARY MAXIMA OCCUR ALONG THE FRONT RANGE IN WYOMING AND SANGRE
DE CRISTO RANGE IN NORTHERN NM.  ON WED...THE UNCERTAINTY REGARDS
HOW FAST THE LOW DEPARTS ON TO THE PLAINS.  THE SLOWER SREF MEAN
PRODUCES MORE SNOW IN EASTERN CO/NORTHEAST NM THAN THE
GFS/ECMWF/UKMET DUE TO THE OTHER MODELS MOVING THE LOW EAST
FASTER. GREATER WEIGHTING WAS GIVEN TO THE FASTER MOVING MAJORITY.

LONGER DURATION SNOW IS EXPECTED MON NIGHT-WED AS LARGE AREAS OF
700 MB THETA-E ADVECTION AND CONVERGENCE DEVELOP UNDER QUASI-ZONAL
FLOW SETTING UP OVER THE PACIFIC NORTHWEST MON NIGHT-TUE.  ON WED
THE APPROACH AND ARRIVAL OF THE 700 MB TROUGH AND ASSOCIATED FRONT
LEADS TO A SURGE IN THE LOW LEVEL JET AND PRE-FRONTAL CONVERGENCE
FOCUSES AN ADDITIONAL ROUND OF SNOW OVER THE OLYMPICS AND
WASHINGTON CASCADES...WITH SNOW BECOMING POTENTIALLY HEAVY ALONG
THE CASCADES.  THE MOISTURE SURGE EXTENDS INLAND AS THE WAVE MOVES
ONSHORE WED WITH A PERIOD OF SNOW EXPECTED IN THE RANGES OF
SOUTHERN TO CENTRAL ID.

THE PROBABILITY OF RECEIVING A QUARTER INCH OF FREEZING RAIN IS
LESS THAN 10 PERCENT ACROSS THE WESTERN US.

...NORTHERN NEW ENGLAND...

FREEZING RAIN IS EXPECTED FOR INTERIOR NH AND ME ON MONDAY AS
RESIDUAL COLD AIR IS IN PLACE AT THE SURFACE.  LOW-MID LEVEL WARM
ADVECTION BOTH RAISES TEMPERATURES ABOVE FREEZING ALOFT AND
RESULTS IN PRECIPITATION DEVELOPING AHEAD OF THE WEAKENING UPPER
LOW. THE PRIMARY THREAT REGION IS THE WHITE MNTNS OF NH AND RANGES
OF SOUTHWEST ME.

WPC PROBABILISTIC GUIDANCE CONTINUES TO SHOW A SLIGHT RISK (AT
LEAST 10% PROBABILITY) OF ICE ACCUMULATIONS EXCEEDING 0.25" OVER
PORTIONS OF NORTHERN NEW HAMPSHIRE AND WESTERN MAINE.

SNOW IS EXPECTED ON MONDAY...WITH 4-6 INCHES  EXPECTED OVER
NORTHERN MAINE.
THE PRIMARY UNCERTAINTY IS WHERE MULTIPLE PRECIP TYPES OCCUR OVER
CENTRAL MAINE...WITH THE UNCERTAINTIES OF THE DURATION OF EACH
TYPE DRIVING DIFFERENCES IN AMOUNTS.

SECONDARY LOW PRESSURE DEVELOPS SOUTHEAST OF NEW ENGLAND TUE
NIGHT...FAR ENOUGH AWAY FROM MAINE TO LIMIT ANY ADDITIONAL SNOW
TUE NIGHT INTO WED.

THE PROBABILITY OF A QUARTER INCH OF FREEZING RAIN IS LESS THAN 10
PERCENT DAYS 2 AND 3 IN THE EASTERN US.

PETERSEN


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