Quantitative Precipitation Forecast
Issued by NWS

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FOUS11 KWBC 250850
QPFHSD

PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
349 AM EST SUN JAN 25 2015

VALID 12Z SUN JAN 25 2015 - 12Z WED JAN 28 2015

DAYS 1 TO 3...

...OHIO VALLEY/CENTRAL APPALACHIANS/MID-ATLANTIC/NEW YORK/NEW
ENGLAND...

A SHORTWAVE TROUGH AND ASSOCIATED AREA OF LOW PRESSURE IS FORECAST
TO MOVE EAST THROUGH THE MID-UPPER MS VALLEY AND OH VALLEY DAY 1.
THIS SYSTEM WILL BE AMPLIFYING THROUGH THE PERIOD...WITH CYCLONE
REDEVELOPMENT OFF THE MID ATLANTIC COAST MONDAY.
THIS STORM TURNS NORTH IN THE DIRECTION OF THE 40N 70W BENCHMARK
AND JUST EAST OF CAPE COD AND ONWARD TOWARDS EITHER MAINE OR THE
CANADIAN MARITIMES.

THE MODELS SHOW A BAND OF LOW TO MID LEVEL FRONTOGENESIS JUST
NORTH OF THE SURFACE LOW TRACK SUNDAY...AND THIS WILL RESULT IN A
SWATH OF SEVERAL INCHES OF SNOWFALL ACROSS CENTRAL OH TO THE
MOUNTAINS OF SOUTHWEST PA AND ADJACENT WV ON DAY 1...WHERE AN
UPSLOPE FLOW COMPONENT AIDS ASCENT AND SNOWFALL.

THE LATEST MODELS ARE FORECASTING A HIGH IMPACT WINTER STORM
AFFECTING THE MID ATLANTIC TO LONG ISLAND...EASTERN NEW YORK AND
MUCH OF NEW ENGLAND MONDAY NIGHT THROUGH TUESDAY NIGHT.  POWERFUL
DEFORMATION AND UPPER DIVERGENCE/LOWER CONVERGENCE MAXIMA SPREAD
ACROSS NORTHERN NJ TO SOUTHEAST NY...SOUTHERN AND EASTERN NEW
ENGLAND.
STRONG FRONTOGENETIC FORCING...ATLANTIC MOISTURE TRANSPORT AND
COUPLED JET DYNAMICS ALL SUPPORT A SWATH OF VERY HEAVY SNOWFALL.
ADDITIONALLY THERE IS POTENTIAL FOR BLIZZARD CONDITIONS TO OCCUR
IN THE AREAS OF HEAVY SNOW.  SEE THE RELATED WATCHES AND WARNINGS
ISSUED BY THE FORECAST OFFICES.

THERE IS SIGNIFICANT SPREAD THOUGH WITH RESPECT TO TIMING AND
PLACEMENT OF THE LOW CENTER THROUGH TUESDAY...BUT ALL OPERATIONAL
MODELS NOW HAVE THE FORECAST OF A MAJOR SNOW STORM/BLIZZARD.  THE
MODELS SHOW A LARGE SPREAD REGARDING WHERE THE HEAVIEST SNOW IN
RESPONSE TO TIMING AND PHASING DIFFERENCES...WITH SLOWER SOLUTIONS
INTRODUCING HEAVY SNOW POTENTIAL FURTHER SOUTH IN THE DELMARVA AND
NJ AND FURTHER INLAND INTO WESTERN NEW ENGLAND AND EASTERN NEW
YORK. SOLUTIONS WITH A FASTER LOW TRACK KEEP THE SNOW THREAT
ACROSS LONG ISLAND AND EASTERN NEW ENGLAND.

MANUAL PROGS GAVE MORE WEIGHTING TO THE 00Z GFS/GEFS MEAN/21Z SREF
MEAN/00Z ECMWF QPF AND TEMPERATURE PROFILES.

...UPPER GREAT LAKES DAY 2...

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 LOW LEVEL CONVERGENCE OVER LK
SUPERIOR AND ADJACENT LAND AREAS INCLUDING THE UP OF MI  WILL
FAVOR A BAND OF ACCUMULATING SNOWFALL. THE LACK OF AVAILABLE
MOISTURE AND BRIEF UPPER DIVERGENCE/LOWER CONVERGENCE MAXIMA LEADS
TO LOW AMOUNTS..WITH A FEW INCHES EXPECTED IN THESE AREAS. MANUAL
PROGS BLENDED THE 00Z GFS/21Z SREF MEAN/12Z ECMWF QPF FOR SNOW
AMOUNTS.


...SIERRA-NEVADA DAYS 2-3...

AN UPPER LOW THAT IS CURRENTLY SITUATED JUST WEST OF THE BAJA
PENINSULA IS FORECAST TO GRADUALLY LIFT NORTH ON MONDAY IN
RESPONSE TO AN UPSTREAM TROUGH DIGGING ACROSS THE EASTERN PACIFIC.
AS THE UPPER TROUGH MOVES NORTH ACROSS SOUTHERN CALIFORNIA
DIFLUENT FLOW ALOFT SUPPORTS EMBEDDED DIVERGENCE MAXIMA CROSSING
SOUTHERN CA INTO THE SOUTHERN SIERRA RANGE.  LOW LEVEL SOUTHEAST
WINDS TRANSPORT MOISTURE INTO THE MOUNTAINS
THERE SHOULD BE SEVERAL INCHES OF SNOW FOR THE HIGHER ELEVATIONS
OF THE SOUTHERN TO CENTRAL SIERRA- NEVADA. THE UPPER TROUGH SHEARS
OUT ON DAY 3 AND MOVES OUR OF THE AREA...SO ASCENT AND MOISTURE
TRANSPORT WEAKENS AND SNOW AMOUNTS DECREASE WITH TIME.

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

PETERSEN

$$




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