Quantitative Precipitation Forecast
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FOUS11 KWBC 110841
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
341 AM EST MON DEC 11 2017

VALID 12Z MON DEC 11 2017 - 12Z THU DEC 14 2017


DAYS 1 THROUGH 3...

THE SYNOPTIC SCALE PATTERN ACROSS THE CONTINENTAL U.S. WILL REMAIN
AMPLIFIED THROUGH THE MIDDLE OF THE WEEK, WITH A LARGE RIDGE OVER
THE WEST AND A LARGE-SCALE TROUGH OVER THE EAST.  MULTIPLE
SHORTWAVE IMPULSES AND SURFACE LOWS WILL BE EMBEDDED WITHIN THE
FLOW AROUND THE TROUGH, AND THESE WILL PRODUCE ROUNDS OF WINTRY
WEATHER OVER THE NEXT FEW DAYS, ALONG WITH PERIODS OF LAKE EFFECT
SNOW.  THE ONLY PARTS OF THE U.S. THAT ARE EXPECTED TO HAVE WINTRY
PRECIPITATION THROUGH WEDNESDAY ARE THE GREAT LAKES REGION,
CENTRAL AND NORTHERN APPALACHIANS, AND NEW ENGLAND.  THE WEST IS
EXPECTED TO BE VOID OF ANY NOTEWORTHY SNOW OWING TO THE EXPANSE OF
THE AFOREMENTIONED RIDGE.

WITH THE APPROACH OF AN ALBERTA CLIPPER FROM THE UPPER MIDWEST ON
MONDAY, THERE SHOULD BE AN ABATEMENT IN THE HEAVY LAKE EFFECT SNOW
FOR THE DAY 1 PERIOD FROM LAKES ERIE AND ONTARIO.  ALTHOUGH UPPER
LEVEL FORCING WITH THE APPROACHING SHORTWAVE TROUGH IS STRONG, THE
AMOUNT OF MOISTURE AVAILABLE IS LIMITED, RESULTING IN GENERAL 1 TO
3 INCH AMOUNTS FROM MICHIGAN TO UPSTATE NEW YORK.  THERE MAY BE
SOME 4+ INCH AMOUNTS EAST OF LAKE MICHIGAN OWING TO SOME LAKE
ENHANCEMENT IN THE WAKE OF THIS LOW.

BY EARLY TUESDAY MORNING, A NEW SURFACE LOW IS PROGGED TO DEVELOP
NEAR EASTERN LAKE SUPERIOR IN RESPONSE TO A POTENT ARCTIC
SHORTWAVE DROPPING SOUTHWARD FROM NORTHERN CANADA.  THIS LOW
SHOULD TRACK EASTWARD AND THEN LEAD TO THE DEVELOPMENT OF AN
OCCLUDED LOW OVER NEW ENGLAND BY TUESDAY NIGHT.  THESE TWO LOWS
WILL LEAD TO THE MAJORITY OF THE WIDESPREAD SNOW (OUTSIDE OF
LAKE-EFFECT) DURING THIS FORECAST PERIOD ACROSS INTERIOR PORTIONS
OF THE NORTHEAST U.S., MAINLY DURING DAY 2.  WIDESPREAD 4 TO 8
INCH AMOUNTS APPEAR LIKELY FROM UPSTATE NEW YORK TO MAINE, AND
LOCALLY HIGHER AMOUNTS EAST OF LAKES ERIE AND ONTARIO OWING TO
LAKE ENHANCEMENT BEHIND THE COLD FRONT.  THERE MAY BE A PERIOD OF
MIXED PRECIPITATION JUST INLAND FROM THE NEW ENGLAND COAST BASED
ON RECENT MODEL FORECAST SOUNDINGS.  GIVEN MODEL PROJECTIONS OF
925-850MB TEMPERATURES, THE MAJOR METROPOLITAN AREAS ALONG
INTERSTATE 95 ARE EXPECTED TO REMAIN MOSTLY RAIN FOR THIS EVENT.
SOME OF THE ENSEMBLE MEAN THERMAL PROFILES WERE INCORPORATED INTO
THE FORECAST TO ACCOUNT FOR THE DIFFERENCES NOTED IN THE
DETERMINISTIC GUIDANCE.

THE MATURING SURFACE LOW IS FORECAST TO LIFT NORTHWARD OVER
EASTERN QUEBEC BY WEDNESDAY, ALLOWING PART OF THE DEFORMATION ZONE
TO LINGER ACROSS NORTHERN MAINE DURING THE DAY 3 PERIOD.  THE
CYCLONIC WEST TO NORTHWEST FLOW OFF LAKES ONTARIO AND ERIE WILL
PROVIDE ADDITIONAL ROUNDS OF LAKE EFFECT SNOW AND ANOTHER ALBERTA
CLIPPER TYPE LOW UPSTREAM WILL POSSIBLY YIELD SOME LIGHT SNOWFALL
ACROSS PARTS OF THE UPPER MIDWEST.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT
NATIONWIDE.

D. HAMRICK

$$





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