Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 131017
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
516 AM EST SAT FEB 13 2016

VALID 12Z SAT FEB 13 2016 - 12Z TUE FEB 16 2016

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

SNOW LEVELS WILL CONTINUE TO DROP BEHIND AN UPPER TROUGH AND
ASSOCIATED COLD FRONT PROGRESSING THROUGH THE NORTHWESTERN CORNER
OF THE NATION EARLY SATURDAY...ALLOWING FOR ACCUMULATING SNOW
ALONG THE OLYMPICS..WASHINGTON CASCADES...AND NORTHERN ROCKIES.
AS THE UPPER TROUGH PROGRESSES DOWNSTREAM...PERSISTENT ONSHORE
FLOW...COMBINED WITH WEAK IMPULSES OF ENERGY ALOFT...SHOULD
CONTINUE TO SUPPORT MODERATE TO HEAVY SNOW OVER THE WINDWARD SIDE
OF THE TERRAIN THROUGH SUNDAY AND MONDAY.  GUIDANCE WAS IN FAIRLY
GOOD AGREEMENT ACROSS THE REGION...SO THE FORECAST WAS BASED ON A
MULTI-MODEL CONSENSUS.


...NORTHERN PLAINS/MIDWEST...

WAA/MOISTURE ADVECTION AHEAD OF AN UPPER TROUGH EJECTING OUT OF
THE NORTHERN ROCKIES WILL SUPPORT A SWATH OF LIGHT TO MODERATE
SNOWS OVER THE NORTHERN PLAINS SATURDAY EVENING...WHICH SHOULD
SPREAD SOUTHEASTWARD INTO THE MIDWEST ON SUNDAY.  THE WPC FORECAST
STARTED WITH A NON-NAM COMPROMISE SINCE IT WAS A SOUTHWESTERN
OUTLIER WITH THE HEAVIEST SNOW AXIS STRETCHING FROM THE EASTERN
DAKOTAS INTO SOUTHERN MINNESOTA AND NORTHERN IOWA.


...OHIO/TENNESSEE VALLEYS TO THE MID-ATLANTIC/NORTHEAST...

INGREDIENTS ARE POTENTIALLY COMING TOGETHER FOR A HIGH-IMPACT
WINTER WEATHER EVENT ACROSS THE EASTERN U.S. EARLY NEXT WEEK...BUT
THE DETAILS OF THE FORECAST REMAIN VERY UNCERTAIN.

STRONG ISENTROPIC LIFT AHEAD OF AN UPPER TROUGH CROSSING THE
PLAINS WILL FOCUS PRECIPITATION ACROSS THE TENNESSEE VALLEY AND
LOWER OHIO VALLEY SUNDAY NIGHT...WHICH SHOULD INTENSIFY AND SPREAD
NORTH AND EAST INTO THE MID-ATLANTIC AND NORTHEAST ON MONDAY AS
THE UPPER TROUGH SHARPENS AND A SURFACE LOW BEGINS TO DEEPEN WHILE
TRACKING TOWARDS THE APPALACHIANS.  SEVERAL LOCATIONS COULD
TRANSITION FROM HEAVY SNOW...TO FREEZING RAIN...TO HEAVY RAIN AS
WARM MOIST AIR OVERRUNS A STRONG ARCTIC AIRMASS IN PLACE ACROSS
THE EASTERN U.S..  THE MAJORITY OF MODEL GUIDANCE CONTINUES TO
MAKE FAIRLY SIGNIFICANT FLUCTUATIONS WITH THE LARGE SCALE
EVOLUTION OF THE UPPER TROUGH AND DEEPENING SURFACE LOW...MAKING
IT EXTREMELY CHALLENGING TO NARROW IN ON THE DETAILS OF THE
FORECAST...WHICH ARE ALREADY HIGHLY SENSITIVE TO THE SLIGHTEST
SHIFT IN GUIDANCE.  FOR NOW...THE WPC FORECAST TRIED TO STAY IN
THE MIDDLE OF THE LARGE MODEL SPREAD...BUT THE FORECAST WILL NEED
TO BE MONITORED CLOSELY FOR UPDATES.

PLEASE REFER TO THE PMDHMD FOR MORE DETAILS ON MODEL DIFFERENCES
AND THE QPFPFD FOR DETAILS ON THE HEAVY RAIN THREAT WITH THIS
EVENT.


...GREAT LAKES...

DEEP CYCLONIC FLOW WILL CONTINUE TO FOSTER SNOW SHOWERS DOWNWIND
OF THE GREAT LAKES ON SATURDAY.  HOWEVER...ACTIVITY SHOULD BEGIN
TO WIND DOWN SATURDAY NIGHT INTO SUNDAY AS A STRONG SURFACE HIGH
SLIDES EASTWARD OVER THE REGION.  DETERMINISTIC GUIDANCE REMAINED
IN GOOD AGREEMENT AND MINIMAL ADJUSTMENTS WERE MADE TO CONTINUITY.


...MAINE...

AN AXIS OF MODERATE TO HEAVY SNOW FOCUSED ALONG AN INVERTED
SURFACE TROUGH COULD CLIP THE COAST OF MAINE BEFORE THE ANCHORING
SURFACE LOW RACES INTO THE CANADIAN MARITIMES ON SATURDAY.  THE
LATEST MODEL GUIDANCE HAS SHIFTED TOWARDS KEEPING THE HEAVIEST
SNOW OFFSHORE...SO THE LATEST WPC FORECAST REFLECTS THIS TREND.


GERHARDT

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