Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 242108
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
407 PM EST SAT JAN 24 2015

VALID 00Z SUN JAN 25 2015 - 00Z WED JAN 28 2015

DAYS 1 TO 2...

...NORTHERN NEW ENGLAND...

THE MID LEVEL DEFORMATION ZONE ASSOCIATED WITH THE DEEPENING LOW
CENTER OFF THE NEW ENGLAND COAST WILL STILL BE CLIPPING PORTIONS
OF DOWN EAST MAINE THROUGH THIS EVENING. A FEW INCHES OF
ADDITIONAL SNOW WILL BE POSSIBLE AS A RESULT BEFORE THE LOW
QUICKLY PULLS AWAY INTO THE CANADIAN MARITIMES OVERNIGHT.

...NORTHERN PLAINS/UPPER MIDWEST TO THE OHIO VALLEY/CENTRAL
APPALACHIANS AND MID-ATLANTIC...

A SHORTWAVE TROUGH AND ASSOCIATED AREA OF LOW PRESSURE OVER THE
CANADIAN PRAIRIES WILL DIVE SOUTHEAST BY THIS EVENING THROUGH THE
UPPER MS VALLEY...AND REACH THE OH VALLEY BY LATE SUNDAY. THIS
SYSTEM WILL BE AMPLIFYING THROUGH THE PERIOD...AND WILL BE
ATTEMPTING TO GO NEGATIVE TILT AS IT CROSSES THE CENTRAL
APPALACHIANS AND MID-ATLANTIC THROUGH MONDAY. THE MODELS SHOW A
BAND OF LOW TO MID LEVEL FRONTOGENESIS JUST NORTH OF THE SURFACE
LOW TRACK...AND THIS WILL RESULT IN A SWATH OF ACCUMULATING
SNOWFALL GIVEN A SUFFICIENTLY DEEP ENOUGH COLUMN OF COLD AIR. A
CLOSED 850 MB TO 700 MB CIRCULATION IS EXPECTED TO PROVIDE FOR
SOME ENHANCED LOW LEVEL FORCING...WHICH WILL FAVOR AT LEAST A
NARROW AXIS OF HEAVIER SNOWFALL. THE SYSTEM AS IT REACHES THE
CENTRAL APPALACHIANS WILL ALSO BE ABLE TO TAKE ADVANTAGE OF
UPSLOPE FLOW WHICH SHOULD FAVOR A DISTINCT MAXIMA IN SNOWFALL OVER
PORTIONS OF NORTHERN WV...WESTERN MD AND WESTERN PA. THIS WILL
ALSO COINCIDE WITH THE ENERGY AMPLIFYING ALOFT AND FAVORING
STRONGER DEEP LAYER ASCENT. A LOW TO MODERATE RISK OF 4 INCH OR
GREATER SNOWFALL AMOUNTS IS INDICATED WITH THE TRACK OF THE
SYSTEM...EXCEPT OVER THE CENTRAL APPALACHIANS WHERE A LOW TO
MODERATE RISK OF 8 INCHES IS FORECAST. WPC GENERALLY FAVORED A
CONSENSUS LED BY THE 12Z GFS AND 00Z ECMWF FOR THIS SYSTEM.

...UPPER MS VALLEY/UPPER GREAT LAKES...

ANOTHER IN A SERIES OF SHORTWAVES/CLIPPERS WILL ADVANCE SOUTHEAST
OUT OF CANADA AND INTO THE UPPER MIDWEST SUNDAY NIGHT AND MONDAY.
A NEW STREAK OF WARM ADVECTION AND FRONTOGENETIC FORCING WILL
FAVOR A STRIP OF ACCUMULATING SNOWFALL. THE LACK OF MOISTURE
TRANSPORT INTO THE SYSTEM SHOULD RESULT IN MODEST
ACCUMULATIONS...WITH A FEW INCHES POSSIBLE LOCALLY FOR NORTHERN
MN...THE U.P. OF MI AND DOWN INTO NORTHERN WI.


THE PROBABILITY OF 0.25 INCH OR GREATER ICING IS LESS THAN 10
PERCENT.


DAY 3...

...SIERRA-NEVADA...

AN UPPER LOW THAT IS CURRENTLY SITUATED JUST WEST OF THE BAJA
PENINSULA IS FORECAST TO GRADUALLY LIFT NORTH BEGINNING MONDAY IN
RESPONSE TO AN UPSTREAM TROUGH DIGGING ACROSS THE EASTERN PACIFIC.
THIS UPPER LOW SHOULD WEAKEN AND CROSS THROUGH CALIFORNIA/NEVADA
ON TUESDAY. SUFFICIENT HEIGHT FALLS ASSOCIATED WITH THE UPPER LOW
SHOULD LOWER SNOW LEVELS...AND COUPLED WITH THE INFLUX OF
SUBTROPICAL MOISTURE THERE SHOULD BE SOME ACCUMULATING SNOW FOR
THE HIGHER ELEVATIONS OF THE CENTRAL SIERRA- NEVADA. SEVERAL
INCHES OF SNOW CAN BE EXPECTED...AND SO A LOW TO MODERATE RISK OF
4 INCH OR GREATER SNOW AMOUNTS IS INDICATED.

...MID-ATLANTIC AND NEW ENGLAND...

THE LATEST MODELS ARE STRONGLY HINTING AT A HIGH IMPACT WINTER
STORM AFFECTING SOUTHERN AND EASTERN NEW ENGLAND AND PERHAPS SOME
PORTION OF THE MID-ATLANTIC MONDAY NIGHT AND TUESDAY. THE
AMPLIFYING TROUGH CROSSING THE CENTRAL APPALACHIANS AND
MID-ATLANTIC ON MONDAY WILL FOSTER CLOSED LOW DEVELOPMENT ALOFT
AND SURFACE CYCLOGENESIS JUST OFF THE DELMARVA. LOW PRESSURE IS
FORECAST TO RAPIDLY INTENSIFY AND LIFT NORTHEAST TO OFFSHORE
SOUTHERN NEW ENGLAND ON TUESDAY WITH A TRACK THAT TAKES THE LOW
FAIRLY CLOSE TO THE 40N 70W BENCH MARK.

THERE IS SIGNIFICANT SPREAD THOUGH WITH RESPECT TO TIMING AND
PLACEMENT OF THE LOW CENTER THROUGH TUESDAY...BUT WHAT IS
IMPORTANT IS THAT EVERY MODEL TODAY TRENDED WEST WITH THE LOW
TRACK AND ALSO SUPPORTS A POWERFUL DEFORMATION ZONE WRAPPING WEST
AND OVERRUNNING SOUTHERN AND EASTERN NEW ENGLAND. THIS IS
ESPECIALLY THE CASE IN TERMS OF THE 12Z NAM...12Z GFS...12Z UKMET
AND 12Z GEM MODEL OUTPUT. THE NAM WAS THE MOST AGGRESSIVE FOR QPF
AND FOR THE TIME BEING IS BEING DISCOUNTED. THE 12Z ECMWF FOCUSES
AN INTENSE LOW CENTER THAT IS SLOWER TO LIFT NORTHEAST OFF THE
EAST COAST...AND THEREFORE HAS A MUCH MORE SIGNIFICANT IMPACT TO
PORTIONS OF THE MID-ATLANTIC COASTAL PLAIN. WPC FAVORED A SOLUTION
MORE CLOSELY ALIGNED WITH THE RELATIVELY FASTER 12Z GFS/12Z UKMET
SOLUTIONS AND INCORPORATING SOME OF THE 00Z ECMWF. THIS SCENARIO
WOULD FAVOR AN INTENSE DEFORMATION ZONE IMPACTING SOUTHERN AND
EASTERN NEW ENGLAND WITH STRONG FRONTOGENETIC FORCING...ATLANTIC
MOISTURE TRANSPORT AND JET DYNAMICS ALL COINCIDING TO SUPPORT A
SWATH OF VERY HEAVY SNOWFALL. A MODERATE TO HIGH RISK OF 1 FOOT OR
GREATER SNOW AMOUNTS IS DEPICTED ACCORDINGLY. A LOW RISK OF 4 INCH
OR GREATER SNOW AMOUNTS IS DEPICTED FOR NOW AS FAR SOUTH AS THE
DELMARVA.


THE PROBABILITY OF 0.25 INCH OR GREATER ICING IS LESS THAN 10
PERCENT.

ORRISON

$$





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