THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


PROBABILISTIC HEAVY SNOW AND ICE DISCUSSION




PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
411 PM EST WED MAR 04 2015

VALID 00Z THU MAR 05 2015 - 00Z SUN MAR 08 2015


DAYS 1 AND 2...


...SOUTHERN PLAINS/LOWER AND MID MISSISSIPPI VALLEY/GULF
COAST/OHIO AND TENNESSEE VALLEYS/MID ATLANTIC AND NORTHEAST...

A COMPLEX AND WIDESPREAD WINTER WEATHER SYSTEM IS CURRENTLY
UNDERWAY AND CONTINUE THROUGH THURSDAY.  THIS SYSTEM HAS BEEN
CHARACTERIZED BY VARIOUS PHASE TRANSITIONS MAKING FOR A
CHALLENGING FORECAST OF SNOW/SLEET AND FREEZING RAIN AMOUNTS.  IN
MANY LOCATIONS...THERE ARE COMBINATIONS OF ALL 3. 

THE FORECAST STILL CALLS FOR A DRAMATIC GRADIENT BETWEEN THE
HEAVIEST SNOW AND THE NORTHERN EDGE OF MAIN SNOWBAND...WITH SMALL
DIFFERENCES IN MODEL SOLUTIONS REPRESENTING POTENTIALLY LARGE
DIFFERENCES IN SNOWFALL AMOUNTS.  THERE ALSO IS THE CHALLENGE OF
TIMING THE CHANGEOVERS FROM ONE PHASE TO ANOTHER AND WHAT FORM THE
CHANGEOVER ENTAILS. THE MAIN DRIVERS OF THIS SYSTEM ARE A LIFTING
TROUGH OVER THE SOUTHWEST US AND A COUPLE SHORTWAVES...ONE A
FAIRLY WEAK SYSTEM LIFTING NORTHEASTWARD NEAR THE US CANADIAN
BORDER AND THE OTHER A SHARP SHORTWAVE SYSTEM BOTH ASSOCIATED WITH
AN IMPRESSIVE COLD OUTBREAK FOR EARLY MARCH.  THIS SYSTEM WILL
COMBINE WITH THE SOUTHWESTERN TROUGH AS A POWERFUL UPPER JET
CROSSES THE NORTHERN TIER OF STATES WITH A BROAD CONFLUENT ZONE
WHILE HIGH PRESSURE AND COLDER AIR SLIP FARTHER SOUTHWARD OVER THE
NEXT 36 HOURS.  SOME OF THE MOISTURE WITH THIS SYSTEM ORIGINATES
FAR SOUTHWARD OVER THE TROPICS AS INDICATED BY SATELLITE IMAGERY. 

THE BROAD AREA OF RAIN CHANGING TO FREEZING RAIN/SLEET AND SNOW
WILL CONTINUE TO SAG SOUTHWARD WITH THE HEAVIEST BAND OF SNOWFALL
CONTINUING TO BE INDICATED TO EXTEND EAST NORTHEASTWARD FROM
ARKANSAS ACROSS NW TENNESSEE AND MUCH OF KENTUCKY AND WEST
VIRGINIA.  THIS AXIS WILL MOVE EASTWARD ACROSS NORTHERN
VIRGINIA/DELAWARE/SOUTHEAST PENNSYLVANIA ACROSS NEW JERSEY.  MANY
OF THESE AREAS WILL LIKELY SEE GREATER THAN 4 TO 8 INCHES OF SNOW
WITH A MODERATE CHANCE FOR 8+ INCHES ACROSS KENTUCKY AND WEST
VIRGINIA.  ALL OF THESE LOCATIONS WILL GO THROUGH A SIMILAR
TRANSITION PROCESS FROM RAIN TO FREEZING RAIN/SLEET AND THEN TO
SNOW.  WHILE THE DEEPER COLD AIR RESULTS IN A CHANGE TO SNOW AND
SLEET...MORE SHALLOW COLD AIR WILL MORE LIKELY RESULT IN GREATER
AMOUNTS OF FREEZING RAIN EXTENDING AS FAR SOUTH AS EASTERN
TEXAS...MUCH OF LOUISIANA AND MISSISSIPPI AND CENTRAL AND NORTHERN
ALABAMA.  THERE IS A LOW TO MODERATE LIKELIHOOD OF FREEZING RAIN
AMOUNTS EXCEEDING .25 INCHES FROM EXTREME EASTERN TEXAS ACROSS
NORTHERN LOUISIANA INTO CENTRAL MISSISSIPPI. 

THERE IS STILL THE LIKELIHOOD THAT 4 TO 8 INCHES OF SNOW WILL BE
COMMON FROM WASHINGTON DC TO NEW YORK CITY ALTHOUGH THERE ARE
ISSUES ON THE NORTH END OF LOWER TOTALS AND ON THE SOUTHERN END
WITH CHANGEOVER TIMES.  WHILE THE 12Z NAM/GFS BOTH INDICATED A
POSSIBLE SOUTHWARD SHIFT IN THE QPF AREA...LATER FORECASTS BY THE
18Z NAM/12Z UKMET...CANADIAN AND ECMWF ALL HAD FARTHER NORTH
SOLUTIONS SUGGESTING THAT THE FEWER CHANGES TO PREVIOUS
FORECASTS...THE BETTER.

KOCIN






Last Updated: 411 PM EST WED MAR 04 2015