Skip Navigation Links weather.gov 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center

 
 

 

Follow the Weather Prediction Center on Facebook Follow the Weather Prediction Center on Twitter
NCEP Quarterly Newsletter
WPC Home
Analyses and Forecasts
   National High & Low
   WPC Discussions
   Surface Analysis
   Days ½-2½ CONUS
   Days 3-7 CONUS
   Days 4-8 Alaska
   QPF
   PQPF
   Flood Outlook
   Winter Weather
   Storm Summaries
   Heat Index
   Air Quality
   Tropical Products
   Daily Weather Map
   GIS Products
Current Watches/
Warnings

Satellite and Radar Imagery
   Satellite Images
   National Radar
Product Archive
WPC Verification
   QPF
   Medium Range
   Model Diagnostics
   Event Reviews
International Desks
Development and Training
   Development
WPC Overview
   About the WPC
   Staff
   WPC History
   Accomplishments
   Other Sites
   FAQs
Meteorological Calculators
Contact Us
   About Our Site
 
USA.gov is the U.S. Government's official web portal to all federal, state, and local government web resources and services.
 
Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0904Z Nov 25, 2014)
 
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
 
Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 AM EST TUE NOV 25 2014

VALID 12Z TUE NOV 25 2014 - 12Z FRI NOV 28 2014


DAYS 1 THROUGH 3...


...APPALACHIANS/MID ATLANTIC/NORTHEAST...

A DEVELOPING LOW PRESSURE SYSTEM IS STILL ON TRACK TO PRODUCE AN
EARLY SEASON SNOWSTORM ON THE BUSY TRAVEL DAY BEFORE THANKSGIVING
ON WEDNESDAY.  WHILE THERE HAS BEEN SOME CONVERGENCE ON THE
GENERAL TRACK/DEVELOPMENT OF THE STORM...THERE IS ENOUGH SPREAD
THAT MAKES SNOWFALL PREDICTION DIFFICULT SINCE THE RAIN/SNOW
TRANSITION WILL BE LOCATED NEAR THE I95 CORRIDOR.

IN AREAS WHERE SNOW IS THE PREDOMINANT FORM OF QPF...THE ENSEMBLE
OF SOLUTIONS SUGGESTS A GENERAL SWATH OF 6 TO 12 INCHES OF SNOW
FROM THE SPINE OF THE APPALACHIANS ACROSS SOUTHERN/NORTHEASTERN
PENNSYLVANIA/SOUTHEAST INTERIOR NEW YORK/INTERIOR SOUTHERN NEW
ENGLAND AND NORTHEAST NEW ENGLAND.  BASED ON THE ENTIRE SUITE OF
MODELS USED TO GENERATE OUR PROBABILITIES...THERE IS A LOW TO
MODERATE CHANCE OF A FOOT OR MORE OF SNOW FROM NORTHEAST
PENNSYLVANIA/NORTHERN NEW JERSEY ACROSS MUCH OF SOUTHERN AND
EASTERN NEW ENGLAND.  THERE ARE HIGH PROBABILITIES OF GREATER THAN
4 TO 8 INCHES OF SNOW FROM NW VIRGINIA/NORTHEAST WEST VIRGINIA
NORTHEASTWARD INTO NEW ENGLAND.

THE MOST HEAVILY POPULATED AREA FROM WASHINGTON DC NORTHEASTWARD
THROUGH PHILADELPHIA, NEW YORK AND BOSTON STILL APPEAR TO RECEIVE
THE BULK OF QPF IN THE FORM OF RAIN BUT WITH A CHANGEOVER TO SNOW
WITH A MODERATE CHANCE THAT AMOUNTS COULD APPROACH 4 INCHES. IN
GENERAL...THE MODELS HAVE TRENDED ON A MORE SIMILAR PATH THAT IS
SLIGHTLY MORE OFFSHORE/FASTER AND LESS INTENSE THAN PREVIOUS
OPERATIONAL ECMWF RUNS. WHILE OLD FASHIONED AND MODESTLY RELIABLE
MEASURES SUCH AS THE 1000/500 MB THICKNESS APPEAR TO RUN HIGH FOR
SNOWFALL IN THE MAJOR CITIES...THERE ARE SOME IMPORTANT CONCERNS
REGARDING BOUNDARY LAYER AND LOWER TROPOSPHERIC TEMPERATURES. 
FIRST OF ALL...COLDER AIR WILL BLEED SLOWLY INTO THE REGION
FOLLOWING NEAR RECORD WARM TEMPERATURES.  HOWEVER...MANY OF THE
MODELS HAVE BEEN QUITE CONSISTENT IN SHOWING THAT 850 MB
TEMPERATURES WILL START OUT ABOVE FREEZING BUT WILL QUICKLY DROP
BELOW FREEZING WEDNESDAY MORNING AS NORTHERLY LOW LEVEL FLOW AND
EVAPORATIVE COOLING DROP TEMPERATURES BENEATH A 175 TO 200 KT JET
EMBEDDED WITHIN HIGHLY CONFLUENT FLOW.

THE SURFACE LOW WILL MOVE FAIRLY RAPIDLY NORTHEASTWARD ALONG A
STRENGTHENING BAROCLINIC ZONE WITH MODEST DEEPENING RATES ALTHOUGH
THE 00Z NAM/UKMET INDICATES MORE SIGNIFICANT DEEPENING RATES. IF
THE ACTUAL STORM INTENSIFIES AT MORE RAPID RATES...SNOWFALL AND
QPF AMOUNTS WOULD LIKELY COMMENSURATELY INCREASE.

FROM A MODEL PERSPECTIVE...THE EURO/SREF AND GEFS MEANS SHOWED
RELATIVELY CONSISTENT QPF DISTRIBUTIONS WITH THE LATEST 2 RUNS OF
THE EURO IN GENERAL AGREEMENT.  WHILE THE 00Z NAM SEEMED TOO FAR
WEST WITH QPF/SNOW OVER THE SOUTHERN APPALACHIANS...IT SEEMED TO
HAVE MORE CONSISTENT FORECAST FOR DAY 2...WHILE THE LATEST GFS
FORECASTS WERE SLIGHTLY MORE DEFICIENT IN QPF THAN IN RECENT DAYS
AND LESS CONSISTENT WITH THE GEFS MEAN.


...GREAT LAKES/NORTHERN PLAINS/MIDWEST...

A MOISTURE DEPRIVED SHORTWAVE WILL DIVE SOUTHEASTWARD ACROSS THE
NORTHERN PLAINS/MISSISSIPPI AND TENNESSEE VALLEY FOLLOWED BY
ANOTHER ROUND OF VERY COLD AIR. A ROUND OF MOSTLY LIGHT SNOW WILL
FALL WITH THIS SYSTEM FROM NORTH DAKOTA ACROSS THE UPPER
MISSISSIPPI VALLEY INTO THE OHIO VALLEY WITH ONLY VERY SMALL ODDS
OF ACCUMULATIONS UP TO 4 INCHES.

COLDER AIR COMES IN BEHIND THIS SYSTEM AND WITH IT...THE POTENTIAL
FOR SOME LAKE EFFECT SNOW BUT IS NOT EXPECTED TO BE ANYWHERE NEAR
THE LENGTH AND MAGNITUDE OF RECENT EVENTS.


...PACIFIC NORTHWEST/NORTHERN ROCKIES...

A SERIES OF SHORT WAVES COMING OVER THE EASTERN PACIFIC RIDGE WILL
IMPACT THE PACIFIC NORTHWEST AND NORTHERN ROCKIES TO VARYING
DEGREES DURING EACH OF THE NEXT THREE DAYS.

THE HEAVIEST AND MOST WIDESPREAD SNOWFALL WILL OCCUR ON DAY 1 AS A
LONG PLUME OF PACIFIC MOISTURE GLIDES SOUTHEASTWARD FROM THE
NORTHWEST INTO THE CENTRAL ROCKIES.  A STRONG LOW LEVEL BAROCLINIC
ZONE OVER THE NORTHERN ROCKIES AND NORTHERN PLAINS WILL FOCUS
UPSLOPE FLOW ACROSS THE NORTHERN ROCKIES AHEAD OF A 150 KNOT JET
STREAK. THIS FAVORS THE HIGHER TERRAIN WHERE SWATHS OF 6 TO 12
INCHES OF SNOW ARE INDICATED OVER THE NORTHERN CASCADES OF
WA...THE BITTERROOTS OF ID...THE ROCKY MOUNTAIN FRONT RANGE IN
MT...AND THE GRAND TETONS IN WY.

KOCIN