Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 140753
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
352 AM EDT MON APR 14 2014

VALID 12Z MON APR 14 2014 - 12Z THU APR 17 2014

...OH VALLEY/EASTERN GREAT LAKES/NORTHEAST

A NARROW SWATH OF SNOW WILL ACCOMPANY THE BACK SIDE OF THE RAPIDLY
EXITING LOW CURRENTLY OVER ILLINOIS AS IT REACHES CANADA LATER
TODAY.  MODEL GUIDANCE IS RELATIVELY CLOSE WITH THE PATH AND SPEED
OF THE LOW AND ALSO AGREE THAT TEMPERATURES PARTICULARLY WITHIN
THE BOUNDARY LAYER AND CLOSEST TO THE GROUND WILL REMAIN ONLY
MARGINALLY SUPPORTIVE OF SIGNIFICANTLY ACCUMULATING SNOW.  USED A
4-WAY MODEL BLEND INVOLVING THE GFS/ECMWF/CANADIAN/UKMET FOR THIS
PARTICULAR SYSTEM...WHICH EMPHASIZED THE WARMER SIDE OF THE
GUIDANCE AND EXCLUDED THE COLDER NAM AND SREF MEAN...RESULTING IN
LOW PROBABILITIES OF 4 INCHES OF SNOW FOR PORTIONS OF MICHIGAN AND
OHIO TODAY AND TONIGHT.

ANOTHER SURFACE LOW WILL DEVELOP OVER THE EASTERN OH VALLEY MONDAY
NIGHT BEFORE ACCELERATING THROUGH CENTRAL NY ON TUESDAY IN
ASSOCIATION WITH APPROACH OF ITS LONGWAVE TROUGH...WITH RAIN
LIKELY MIXING WITH SNOW BEFORE TRANSITIONING TO ALL SNOW AND
EVENTUALLY ENDING BEHIND THE LOW...PARTICULARLY FOR THE HIGHER
ELEVATIONS ACROSS PA/NY/VT/NH/ME...SUPPORTING LOW PROBABILITIES OF
4 INCHES OF SNOW.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

...ROCKIES...

UPSLOPE FLOW ALONG THE NORTHERN AND EASTERN FACING SLOPES OF THE
NORTHERN-CENTRAL ROCKIES WILL BECOME THE PRIMARY MECHANISM FOR
ASCENT TUESDAY AND WEDNESDAY AS THE VIGOROUS SHORTWAVE TROUGH
PRESENTLY NEARING THE PACIFIC NORTHWEST CROSSES THE REGION.
GENERALLY PREFERRED A SOLUTION CLOSE TO THE INTERMEDIATE
ECMWF/UKMET FOR DETERMINING THE LIQUID EQUIVALENT AMOUNTS AND
P-TYPES VERSUS THE MORE AMPLIFIED NAM/GFS WHICH HAD LESS MODEL
SUPPORT.  THE RESULT IS LOW PROBABILITIES OF 8 INCHES OR MORE OF
SNOW FOR THE TETONS AND CENTRAL ROCKIES...WITH PERHAPS A FOOT OR
MORE FOR THE EASTERN FACING SLOPES IN COLORADO.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

...UPPER MIDWEST...

USED THE WEAKER AND FLATTER SOLUTIONS OF THE ECMWF/UKMET OVER THE
STRONGER NAM/GFS FOR THE SHORTWAVE TROUGH PRESENTLY NEARING THE
PACIFIC NORTHWEST THAT REACHES THE PLAINS ON WEDNESDAY WITH BROAD
AND DEEP ASCENT FORMING ALONG THE PATH OF THE SURFACE LOW CROSSING
IOWA INTO WISCONSIN.  THE WEAKER/FLATTER SOLUTIONS SUPPORT LESS
SNOW THAN THE NAM/GFS.  OTHERWISE...THE MODEL SPREAD IS ABOUT
AVERAGE...BUT STILL WITH ONLY LIMITED CONFIDENCE GIVEN THE ROLE OF
A SHORTWAVE TROUGH REACHING SOUTH CENTRAL CANADA BY WEDNESDAY
NIGHT...WHICH MAY INTERACT WITH THE TROUGH ENTERING THE
PLAINS...THUS AFFECTING ITS INFLUENCE.  MIXED PRECIPITATION SEEMS
LIKELY WITH THIS PARTICULARLY EVENT AS WELL GIVEN THE ISENTROPIC
LIFT REGIME NORTH OF THE LOW...WHERE TEMPERATURES WILL LIKELY BE
BELOW FREEZING.  HOWEVER...THE PROBABILITIES FOR 0.25 INCHES OF
ICE WERE TOO LOW TO INCLUDE BASED ON THE SPREAD.  THUS...DEPICTED
MODERATE AND LOW PROBABILITIES OF 4 INCHES AND 8 INCHES OF SNOW
RESPECTIVELY INSTEAD DUE TO SLIGHTLY HIGHER CONFIDENCE.

JAMES



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