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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2056Z Mar 03, 2015)
 
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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
356 PM EST TUE MAR 03 2015

VALID 00Z WED MAR 04 2015 - 00Z SAT MAR 07 2015


DAY 1...


...NORTHEAST...

A SHORTWAVE SYSTEM LIFTING RAPIDLY NORTHEASTWARD INTO SOUTHERN
CANADA IS INDUCING STRONG WARM AIR ADVECTION IN THE TUNE OF
MAXIMUM WINDS OF 50 TO 60 KTS AT 850 MB...PRODUCING SNOW CHANGING
TO SLEET/FREEZING RAIN/RAIN ACROSS MUCH OF SOUTHEASTERN AND
CENTRAL NEW YORK AND SOUTHERN AND CENTRAL NEW ENGLAND.  FARTHER
NORTH...PRECIPITATION IS LIKELY TO REMAIN AS MOSTLY SNOW.  WHILE
SNOWFALL AMOUNTS WILL BE CURTAILED ACROSS SOUTHERN NEW
ENGLAND...NORTHERN NEW ENGLAND IS IN LINE TO RECEIVE AT LEAST 3 TO
6 INCHES...ESPECIALLY ACROSS MAINE. ACROSS INTERIOR
PENNSYLVANIA/SOUTHEAST NEW YORK AND PORTIONS OF NEW
ENGLAND...FREEZING RAIN COULD BUILD TO GREATER THAN A TENTH OF AN
INCH...ESPECIALLY ACROSS NORTHEAST PENNSYLVANIA/SOUTHEAST NEW YORK
AND THE HILLS OF NORTHWEST CONNECTICUT AND WESTERN MASSACHUSETTS.
A MULTI MODEL BLEND WAS USED SINCE THIS IS A VERY SHORT RANGE
FORECAST AND THERE WERE ONLY FEW REAL DIFFERENCES BETWEEN MOST
MODELS.


DAYS 1 THROUGH 3...


...CENTRAL ROCKIES/SOUTHERN PLAINS/LOWER AND MID MISSISSIPPI
VALLEY/OHIO AND TENNESSEE VALLEYS/MID ATLANTIC AND NORTHEAST...

THERE HAS BEEN INCREASING MODEL AGREEMENT FOR THE GENERAL LOCATION
AND AMOUNTS OF FREEZING RAIN/SLEET AND SNOW FOR A COMPLEX AND
WIDESPREAD SYSTEM EXTENDING ACROSS A WIDE SECTION OF THE NATION. 
BECAUSE OF THE NATURE OF THIS SYSTEM IN WHICH A LARGE BAND OF
MOISTURE ENCOUNTERS AN INTRUSION OF MUCH COLDER AIR...THERE IS
ALSO THE COMPLEXITY OF RAIN CHANGING TO SLEET/FREEZING RAIN AND
SNOW FOR MUCH OF THIS AREA.  IN ADDITION...THERE APPEARS TO BE A
VERY DRAMATIC GRADIENT DEVELOPING BETWEEN THE AXIS FOR HEAVIEST
SNOW TO THE NORTHERN EDGE OF SNOWFALL OVER FAIRLY SMALL
DIFFERENCES.  BOTH SITUATIONS ARE DIFFICULT TO FORECAST BECAUSE
VERY SMALL DIFFERENCES IN MODEL AGREEMENT AND CHANGES IN THE
FORECAST THEMSELVES HAVE LARGE CONSEQUENCES FOR CHANGES IN THE
FORECASTS.

THE MAIN DRIVERS FOR THIS EVENT ARE THE COMBINATION OF A LIFTING
TROUGH OVER THE SOUTHWESTERN UNITED STATES THAT CAN PROVIDE A
SIGNIFICANT SOURCE OF MOISTURE INITIALLY FROM THE EASTERN PACIFIC
AND THEN FROM THE GULF OF MEXICO AS WELL AS A SERIES OF SHORTWAVE
TROUGHS ASSOCIATED WITH SOME VERY COLD AIR RETURNING ACROSS A GOOD
CHUNK OF THE EASTERN TWO THIRDS OF THE COUNTRY.  TO SOME...PERHAPS
THE ONLY GOOD NEWS IS THAT ONCE THIS SYSTEM MOVES PAST THE UNITED
STATES ON FRIDAY...A MUCH MORE TRANQUIL WEATHER PATTERN APPEARS TO
FOLLOW FOR AT LEAST SEVERAL DAYS.

ON DAY 1/TUESDAY EVENING INTO WEDNESDAY...THE EJECTING SOUTHWEST
TROUGH WILL BEGIN TO COMBINE WITH THE SOUTHWARD MOVING COLD AIR
MASS TO PRODUCE SOME MODERATE SNOW IN THE COLORADO ROCKIES WHILE
DEVELOPING UPSLOPE FLOW WILL SPREAD MOSTLY LIGHT TO MODERATE SNOW
ACROSS EASTERN COLORADO ACROSS PORTIONS OF THE SOUTHERN PLAINS
FROM THE PANHANDLE OF TEXAS ACROSS OKLAHOMA INTO KANSAS...WITH A
LOW PROBABILITY THAT SNOWFALL WILL EXCEED 4 INCHES.

AS THE ENTIRE TROUGH COMPLEX MOVES EASTWARD...A POWERFUL UPPER JET
WITH MAXIMUM WINDS EXCEEDING 175 KTS WILL SPREAD ACROSS THE
NORTHERN TIER OF STATES WITHIN A BROAD CONFLUENT ZONE COVERING THE
ENTIRE EASTERN HALF OF THE US.  AS THE LEADING EDGE OF THE MUCH
COLDER AIR SLIPS SOUTH AND EASTWARD ACROSS THE SOUTHERN PLAINS AND
ACROSS THE MID MISSISSIPPI VALLEY AND OHIO VALLEY...A LARGE AREA
OF RAINFALL WILL DEVELOP ALONG AND NORTH OF THE FRONT.  COLDER AIR
WILL CONTINUE TO MOVE SOUTHWARD AND RAIN WILL GRADUALLY TURN TO
MOSTLY SLEET AND SNOW.  THE CHANCES FOR FREEZING RAIN WILL
INCREASE AS THE COLDER AIR CONTINUES TO MOVE FURTHER
SOUTHWARD...BUT IN A MUCH MORE SHALLOW LAYER.  SNOW WILL BECOME
HEAVY AT TIMES...WITH A MODERATE PROBABILITY OF GREATER THAN 4
INCHES FROM SOUTHERN MISSOURI/NORTHERN ARKANSAS
UP ALONG THE OHIO RIVER SPANNING SOUTHERN ILLINOIS/INDIANA AND
OHIO...AS WELL AS NORTHERN KENTUCKY/NORTHERN WEST VIRGINIA AND
SOUTHWESTERN PENNSYLVANIA. 

FARTHER SOUTH...THE SAME PATTERN OF RAIN CHANGING TO
SLEET/FREEZING RAIN TO SNOW WILL CONTINUE SLOWLY SOUTHWARD WITH
THE GREATEST CHANCE OF SIGNIFICANT FREEZING FROM NORTHEAST TEXAS
ACROSS A GOOD PORTION OF CENTRAL ARKANSAS INTO NORTHWEST
MISSISSIPPI INTO WESTERN TENNESSEE.  THERE MAY BE PERIODS WHERE
SLEET VERSUS FREEZING RAIN ALTERNATES.  THERE IS A MODERATE CHANCE
OF GREATER THAN .25 INCHES OF FREEZING RAIN ACROSS ARKANSAS AND
WESTERN TENNESSEE.

BY DAY 2/WEDNESDAY EVENING INTO THURSDAY...THE JOINT TROUGHS
CONTINUE TO LIFT NORTHEASTWARD WITH ONLY GENERATING WEAK LOW
PRESSURE ALONG THE COLD FRONT.  SIGNIFICANT SNOW WILL FALL FROM
THE LOWER MISSISSIPPI VALLEY ACROSS LOWER OHIO VALLEY/NORTHERN
TENNESSEE VALLEY AND SPREAD NORTHEASTWARD ACROSS THE MIDDLE
ATLANTIC STATES AND POSSIBLY INTO EXTREME SOUTHERN NEW ENGLAND. 
HEAVIEST SNOW COMBINED FROM DAYS 1 TO 2 WILL FALL FROM SOUTHEAST
MISSOURI ACROSS NORTHEAST ARKANSAS/NORTHWEST TENNESSEE ALONG AND
JUST SOUTH OF THE OHIO RIVER...INCLUDING MUCH OF KENTUCKY AND WEST
VIRGINIA.  THE SIGNIFICANT SNOW WILL THEN EXTEND EASTWARD FROM
NORTHERN VIRGINIA TO NEAR NEW YORK CITY WHERE THIS IS A MODERATE
TO HIGH LIKELIHOOD OF 4 TO 8 INCHES OF SNOW AND EVEN A LOW TO
MODERATE PROBABILITY OF GREATER THAN 8 INCHES. SOME
AREAS...ESPECIALLY ACROSS KENTUCKY AND WEST VIRGINIA INTO NORTHERN
MARYLAND/SOUTHERN PENNSYLVANIA COULD SEE A FOOT OR MORE.

WHILE MUCH OF THE PRECIPITATION IN THE EAST WILL BE A RAIN TO
SLEET TO SNOW TRANSITION WITH THE BETTER CHANCES OF PRECIPITATION
ENDING AS SLEET OR FREEZING RAIN OCCURS FROM CENTRAL AND SOUTHERN
VIRGINIA INTO NORTHERN NORTH CAROLINA.  THERE IS STILL A LOW
PROBABILITY OF GREATER THAN .25 INCHES OF FREEZING RAIN FROM
NORTHERN LOUISIANA AND NORTHERN MISSISSIPPI ACROSS SOUTHERN
TENNESSEE AND NORTHERN ALABAMA.  THERE EVEN IS A CHANCE THAT
FREEZING RAIN CONTINUES FARTHER SOUTHWARD INTO SOUTH CAROLINA ON
DAY 3.

SLEET AND FREEZING RAIN WILL BE THE MAIN PROBLEM ACROSS MUCH OF
CENTRAL AND EASTERN TEXAS/LOUISIANA/NORTHERN AND CENTRAL
MISSISSIPPI INTO NORTHERN ALABAMA.  THERE IS A LOW PROBABILITY
THAT GREATER THAN A QUARTER INCH OF FREEZING RAIN MAY FALL IN THIS
REGION. ON DAY 3...SOME LIGHT FREEZING RAIN MAY MAKE IT ALL THE
WAY TO THE GULF OF MEXICO FROM SOUTHERN LOUISIANA TO SOUTHERN
ALABAMA.

KOCIN