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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0857Z Jan 30, 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
357 AM EST FRI JAN 30 2015

VALID 12Z FRI JAN 30 2015 - 12Z MON FEB 02 2015


DAYS 1 AND 2...

...NORTHEAST...

AN AMPLIFYING TROUGH MOVING THROUGH THE EASTERN U.S. FRI MORNING
IS EXPECTED TO ASSUME A NEGATIVE TILT AS IT MOVES OFF OF THE MID
ATLANTIC/NORTHEAST COAST FRI AFTERNOON-EVENING. A RELATIVELY WEAK
AREA OF LOW PRESSURE CROSSING THE GREAT LAKES WILL FEATURE A
REDEVELOPING AREA OF LOW PRESSURE NEAR THE COAST OF SOUTHEAST NEW
ENGLAND THAT WILL THEN INTENSIFY INTO ANOTHER SIGNIFICANT
SNOWSTORM FOR PORTIONS OF NORTHERN AND NORTHEAST NEW ENGLAND. IN
PARTICULAR...MAINE WILL BE THE PRIMARY FOCUS WITH ACCUMULATIONS OF
A FOOT OR LIKELY ACROSS PORTIONS OF THE STATE.

THE FORECAST WAS BASED PRIMARILY OFF A COMBINATION OF THE
GFS..NAM..ECMWF AND SREF MEAN..WHICH IN THEIR LATEST RUNS HAVE ALL
SHOWN AN EASTWARD SHIFT WITH THE LOW TRACK AND ASSOCIATED
PRECIPITATION AXIS. 

...SOUTHWEST/SOUTHERN ROCKIES...

A LONGWAVE TROUGH WILL BECOME BETTER ORGANIZED AS IT MOVES
EASTWARD ACROSS THE CALIFORNIA COAST AND OVER THE SOUTHWEST ON
FRIDAY INTO SATURDAY BEFORE RETREATING SOUTHWARD INTO NORTHERN
MEXICO ON SUNDAY. SEVERAL SHORTWAVE FEATURES CAN BE SEEN ROTATING
ABOUT THE DEVELOPING NEAR CUTOFF SYSTEM BEFORE THE MAIN TROUGH
BEGINS TO EDGE SOUTHWARD SOUTH OF THE BORDER.  A BLEND OF THE
NAM..GFS..ECMWF AND SREF MEAN WAS USED TO HELP FINETUNE SNOWFALL
AMOUNTS ACROSS THE DIVERSE TOPOGRAPHY OF THE REGION. HEAVIEST SNOW
IS EXPECTED TO AFFECT THE HIGHER ELEVATIONS OF NEW MEXICO AND THE
SAN JUAN/SANGRE DE CRISTO PEAKS ACROSS SOUTHERN COLORADO. PORTIONS
OF THE SOUTHERN WASATCH IN UTAH CAN EXPECT SOME SIGNIFICANT
SNOWFALL AS WELL.

FOR DAY 1..FRIDAY MORNING INTO SATURDAY MORNING...THERE IS A
MODERATE TO HIGH PROBABILITY OF 4 TO 8 INCHES OF SNOW ESPECIALLY
ACROSS NORTHEAST NEW MEXICO AS WELL AS ACROSS THE SOUTHERN
WASATCH.  TWO DAY TOTALS OF 12 OR MORE INCHES ACROSS THE HIGHER
PEAKS OF NORTHERN NEW MEXICO AND SOUTHERN CO ARE POSSIBLE.

DAYS 2 AND 3...

...CENTRAL PLAINS/MID MISSISSIPPI VALLEY/OHIO VALLEY/LOWER GREAT
LAKES/NORTHERN MID ATLANTIC/NORTHEAST...

WHILE THE SOUTHWEST TROUGH HEADS SOUTHWARD INTO MEXICO...ENERGY
AND MOISTURE EJECTING EASTWARD ACROSS THE PLAINS AND MISSISSIPPI
VALLEY WILL COMBINE WITH A SHARPLY AMPLIFYING TROUGH MOVING
SOUTHEASTWARD ACROSS THE NORTHERN ROCKIES ON SATURDAY NIGHT AND
BECOME A SIGNIFICANT TROUGH OVER THE MISSISSIPPI VALLEY BY SUNDAY.
THE CONSOLIDATION OF THESE SYSTEMS APPEAR TO PRODUCE AN EXPANDING
AREA OF SIGNIFICANT SNOW WITH MODERATE TO HIGH PROBABILITIES OF
GREATER THAN 4 INCHES OF SNOW FROM EASTERN NEB TO CENTRAL IL ON
DAY 2... SATURDAY MORNING INTO SUNDAY MORNING...WITH A LOW
PROBABILITY OF GREATER THAN 8 INCHES CENTERED ACROSS SOUTHERN
IA/NORTHERN MO INTO CENTRAL IL.  AS THIS STORM DEVELOPS...MUCH
COLDER AIR WILL BUILD NOT ONLY BEHIND THE SYSTEM AS A LARGE ARCTIC
ANTICYCLONE HEADS SOUTHWARD INTO THE NORTHERN PLAINS...BUT COLDER
AIR WILL ALSO BLEED EASTWARD AS PRESSURES RISE OVER SOUTHEASTERN
CANADA AND NORTHERN NEW ENGLAND IN ASSOCIATION WITH A PRONOUNCED
UPPER CONFLUENCE ZONE.  THE COMBINATION OF THESE TWO SYSTEMS WILL
HELP GENERATE A INCREASINGLY BAROCLINIC ZONE UPON WHICH THE
DEVELOPING SURFACE WILL MOVE ALONG.  ON DAY 3...SUN MORNING INTO
MON MORNING...A MODERATE TO HIGH RISK FOR 4-INCHES OR MORE OF SNOW
IS FORECAST TO EXTEND FROM CENTRAL IL TO EASTERN PA...WITH A
SLIGHT RISK FOR 8-INCHES EXTENDING FROM IND TO WESTERN MD/PA AND
EASTERN WV.

THE PREVAILING SHIFT IN THE 00Z MODELS WAS FOR A MORE NORTHERLY
TRACK WITH THIS SYSTEM...WHICH IS REFLECTED IN THE WPC
FORECAST...PARTICULARLY FROM LATE DAY 2 ONWARD.  HOWEVER FORECAST
CONFIDENCE WAS TEMPERED BY THE RUN-TO-RUN INCONSISTENCIES THE
MODELS HAVE SHOWN ALONG THE WITH DISTINCT POSSIBILITY THAT THE
MODELS MAY REVERSE TRENDS IN SUBSEQUENT RUNS. 

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

PEREIRA