Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 170832
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
431 AM EDT FRI APR 17 2015

VALID 12Z FRI APR 17 2015 - 12Z MON APR 20 2015

...CENTRAL ROCKIES...

A SPRING UPSLOPE SNOW EVENT WILL CONTINUE TODAY OVER THE CENTRAL
ROCKIES AS AN UPPER LOW MEANDERS NORTHEAST FROM THE FOUR CORNERS
REGION ACROSS CO AND
AREAS OF UPPER DIVERGENCE/LOWER CONVERGENCE COMBINE WITH UPSLOPE
FLOW IN FAVORED WINDWARD TERRAIN AND PERSISTENT MOISTURE TO
PRODUCE PERIODS OF SNOW.  THE HEAVIEST SNOW FRIDAY IS EXPECTED
OVER THE HIGHER ELEVATIONS OF THE FRONT RANGE OF NORTH CENTRAL
COLORADO AND ADJACENT SOUTHEAST WY IN THE LARAMIE MOUNTAINS.  SOME
OF THE HIGHER PEAKS COULD SEE ANOTHER 1 FOOT OF SNOW...BUT AMOUNTS
WILL DECREASE SHARPLY HEADING EAST INTO THE HIGH PLAINS DUE TO
WARMING TEMPERATURES.   ON SATURDAY...LIGHT SNOW IS SNOW EXPECTED
IN THE RANGES OF EASTERN WY AS UPPER DIVERGENCE MAXIMA PERSIST
EARLY IN THE PERIOD BEFORE WEAKENING AS THE UPPER LOW SHEARS AS IT
DRIFTS NORTHEAST ACROSS THE CENTRAL PLAINS.

MODELS HAVE QPF DIFFERENCES WITH THE GFS SHOWING HIGHER AMOUNTS
DAYS 1-2 IN RESPONSE TO STRONG 700 MB CONVERGENCE MAXIMA.  AMOUNTS
IN THE GFS ENSEMBLE MEAN ARE LIGHTER DAYS 1-2 AND GIVEN MORE
WEIGHTING GIVEN THE GFS LONG TERM BIAS TOWARDS HIGH AMOUNTS ON CO.
 SNOW FALL AMOUNTS MATCHED UP WELL WITH CONTINUITY.


...MAINE...

A SHORTWAVE CROSSING NEW ENGLAND IS EXPECTED TO PRODUCE A BURST OF
WARM ADVECTION PRECIPITATION FOLLOWED BY PRECIP IN THE MID LEVEL
DEFORMATION ZONE WITH THE POTENTIAL FOR HIGHER ELEVATIONS OF
WESTERN MAINE TO SEE A PERIOD OF SNOW.  VALLEY AREAS ARE INITIALLY
TOO WARM FOR SNOW AND POST FRONTAL COOLING MAY RESULT IN A  BRIEF
CHANGE OVER IN INTERIOR SECTIONS BEFORE THE PRECIP ENDS.  THE WPC
FORECAST USED A GFS/ECMWF MODEL COMPROMISE IN ORDER TO ACCOUNT FOR
THE TEMPERATURE AND QPF UNCERTAINTY.

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

PETERSEN


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