Quantitative Precipitation Forecast
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FOUS11 KWBC 122247
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
547 PM EST FRI FEB 12 2016

VALID 00Z SAT FEB 13 2016 - 00Z TUE FEB 16 2016

...PACIFIC NORTHWEST/NORTHERN ROCKIES...

SHORTWAVE ENERGY WILL MARCH EASTWARD REACHING COASTAL WA BY LATER
TONIGHT. COLD AIR ACCOMPANYING THE SYSTEM WILL SUFFICIENTLY LOWER
SNOW LEVELS ACROSS THE REGION. DURING THE HEIGHT OF THE
EVENT...LIGHT/MODERATE SNOWS WILL SPREAD OVER THE HIGHER TERRAIN
OF THE PACIFIC NORTHWEST/UPPER INTERMOUNTAIN WEST/NORTHERN ROCKIES
REGION. IN THE WAKE OF THE SHORTWAVE PASSAGE...PERSISTENT
NORTHWESTERLY FLOW OVER THE EASTERN PACIFIC WILL FUNNEL IN A
SERIES OF ADDITIONAL IMPULSES THROUGH THE REGION. MODELS SHOW
FAVORABLE LEFT EXIT REGION JET DYNAMICS IN PLACE WHICH WILL WORK
IN CONJUNCTION WITH STEADY PERIODS OF UPSLOPE FLOW TO SUPPORT
ADDITIONAL SNOW ACCUMULATIONS. MODELS AS A WHOLE GENERALLY AGREE
ON THE SYNOPTIC EVOLUTION SO FAVORED A MULTI-MODEL CONSENSUS WITH
MORE FOCUS ON HIGHER-RESOLUTION OUTPUT FOR THE COMPLEX TERRAIN.


...NORTHERN PLAINS/UPPER TO MIDDLE MISSISSIPPI VALLEY TO THE
OHIO/TENNESSEE VALLEYS EASTWARD TO THE SOUTHERN/CENTRAL
APPALACHIANS INTO THE MID-ATLANTIC...

AS THE PACIFIC SYSTEM FROM THE NORTHWESTERN U.S. ADVANCES
EASTWARD...A SURFACE CYCLONE WILL DIP DOWN FROM SOUTHERN ALBERTA
EVENTUALLY TRACKING THROUGH THE DAKOTAS AND MIDDLE MS VALLEY.
THERE IS GENERAL AGREEMENT IN A RISE IN TROPOSPHERIC MOISTURE
AHEAD OF THE SHORTWAVE WITH PWATS REACHING THE 0.50 INCH MARK
ACROSS NORTHERN MO BY 14/1200Z. AS THE SURFACE LOW MOVES FROM THE
ND/SD BORDER TOWARD IA...EXPECT A PERIOD OF WARM ADVECTION SNOWS
WITH DEFORMATION ZONE ACTIVITY NORTH/WEST OF THE CYCLONE CENTER.
SOLUTION SPREAD HAS DIMINISHED DURING THE 12Z CYCLE AS THE 12Z GFS
TRENDED A BIT WETTER AND TOWARD THE SOUTH/WEST WITH THE 12Z ECMWF
SHOWING A SIMILAR TREND. THIS LED TO FAIRLY HIGH CONFIDENCE IN
PLACING MODERATE TO HEAVY SNOWFALL ACROSS NORTHEASTERN SD WITH A
HIGH RISK OF 4 INCHES ON DAY 2 ALONG THE ND/SD/MN BORDER.

THE AFOREMENTIONED SYSTEM GRADUALLY ELONGATES AND SHEARS A BIT
WHILE MOVING THROUGH THE UPPER GREAT LAKES. ROUNDING THE BASE OF
THE UPPER TROUGH WILL BE AN EVEN MORE IMPRESSIVE SHORTWAVE WHICH
BEGINS TO DIG THROUGH THE OZARKS AND ADJACENT LOCATIONS BY MIDDAY
MONDAY DEPENDING ON THE MODEL. STRONG ISENTROPIC LIFT IS FORECAST
TO TAKE SHAPE DOWNSTREAM SPREADING A BROAD SWATH OF PRECIPITATION
UP ACROSS THE TN VALLEY/CAROLINAS/APPALACHIANS/MID-ATLANTIC
REGION. MUCH OF THIS REGION WILL BE UNDER THE INFLUENCE OF A
POWERFUL ARCTIC HIGH WHICH IS EXPECTED TO KEEP TEMPERATURES WELL
BELOW NORMAL THIS WEEKEND. WHILE EXITING INTO THE WESTERN ATLANTIC
EARLY MONDAY...MODELS SHOW SURFACE RIDGING EXTENDING SOUTHWARD
ALONG THE ENTIRE SPINE OF THE APPALACHIANS. NOTORIOUSLY GUIDANCE
TENDS TO ERODE CAD EVENTS TOO QUICKLY SO LEANED TOWARD THERMAL
PROFILES WHICH HELD THE COLD AIR IN LONGER. THIS SUPPORTS A BROAD
SWATH OF SNOW FROM THE TN VALLEY EASTWARD TO THE MID-ATLANTIC
STATES. STRONG 850-MB WAA OVERRIDING THIS FRIGID AIR MASS WILL
GRADUALLY LEAD TO P-TYPE CHANGES TO SOME SORT OF FREEZING
RAIN/SLEET MIXTURE BY LATE IN THE DAY 3 PERIOD. STAYED AWAY FROM
THE MORE ROBUST ICE ACCUMULATIONS SEEN IN THE 12Z NAM AND LEANED
ON THE 12Z GFS/ECMWF WHILE DISPLACING THE ICING TOWARD THE TERRAIN
WHERE COLDER AIR WILL STAY IN PLACE LONGER. THIS SUPPORTED A
SLIGHT RISK FOR 0.25 INCHES OF ICE ON DAY 3 ACROSS INTERIOR NC.
MODELS STILL ARE UNCERTAIN WITH THE SURFACE LOW TRACK WITH A SMALL
DIFFERENCE HAVING LARGE RAMIFICATIONS FOR P-TYPES OVER THE
AFFECTED REGION.


...GREAT LAKES...

DEEP CYCLONIC FLOW ANCHORING THE GREAT LAKES REGION WILL SUPPORT
HEALTHY SNOWFALL ACCUMULATIONS ON DAY 1. MODELS DEPICT
DEEP-LAYERED NORTHWESTERLY FLOW ACCOMPANIED BY RATHER STEEP
1000-800 MB LAPSE RATES. 850-MB TEMPERATURES WILL BE IN THE -24C
TO -30C RANGE TRAVELING OVER WATERS WHICH REMAIN SLIGHTLY ABOVE
FREEZING FOR THE MOST PART. THESE SUPERADIABATIC LAPSE RATES WILL
SUPPORT BURSTS OF SNOW SHOWERS DOWNWIND OF ALL THE MAJOR GREAT
LAKES WITH THE GUIDANCE DEPICTING MANY OF THE BANDS CROSSING
MULTIPLE LAKE SURFACES...I.E. SUPERIOR/MICHIGAN. AS THE CORE OF
LOWER HEIGHTS ADVANCES EASTWARD...MUCH OF THE SNOWFALL SHOULD
BECOME MORE DISORGANIZED IN NATURE DURING THE DAY 2/3 PERIOD. THE
FORECAST WAS DRIVEN BY HIGHER RESOLUTION OUTPUT WHICH INCLUDED THE
12Z NAM/09Z SREF MEAN AND 12Z NAM-CONUS NEST.


...MAINE...

A PAIR OF FEATURES WILL AFFECT MUCH OF MAINE DURING THE DAY 1
PERIOD. MODELS SHOW A SYSTEM WHICH WILL EXIT THE CAROLINAS THIS
EVENING ADVANCING QUICKLY TOWARD THE NORTHEAST CROSSING JUST EAST
OF NOVA SCOTIA BY SATURDAY MORNING. THERE IS STRONG SUPPORT FOR A
LOW-LEVEL WEST/EAST ORIENTED BOUNDARY WHICH WILL EXTEND BACK
TOWARD COASTAL SECTIONS OF MAINE. FORECAST SOUNDINGS DEPICT QUITE
A BIT OF INSTABILITY ALONG THIS AXIS WITH 850-500 MB LAPSE RATES
APPROACHING 8 C/KM DURING THE EVENT. THIS ENHANCED REGION OF
BUOYANCY APPEARS TO LINGER OVER COASTAL MAINE FOR SEVERAL HOURS
WHICH WILL AID IN HEFTY SNOWFALL ACCUMULATIONS. ADDITIONALLY...THE
PASSAGE OF THE CLOSED UPPER LOW WILL STEEPEN MID-LEVEL LAPSE RATES
WHICH SHOULD DRIVE A ROUND OF SNOW SHOWERS BEFORE THE SYSTEM EXITS
THE COAST. OVERALL OUTPUT FROM RECENT GUIDANCE ARE GENERALLY WELL
CLUSTERED WITH SOME NORTH/SOUTH VARIANCE FROM RUN-TO-RUN.
REGARDLESS...EXPECT AT LEAST A SLIGHT/MODERATE RISK FOR OVER A
FOOT OF SNOW ON DAY 1 PER THE LATEST WPC PROBABILITIES.



RUBIN-OSTER

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