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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0805Z Jan 24, 2015)
 
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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
305 AM EST SAT JAN 24 2015

VALID 12Z SAT JAN 24 2015 - 12Z TUE JAN 27 2015

DAYS 1 TO 3...

...NEW YORK/NEW ENGLAND DAY 1...

INTENSIFYING SURFACE LOW PRESSURE IS FORECAST TO MOVE EAST OF CAPE
COD SATURDAY EVENING AND THEN INTO THE CANADIAN MARITIMES SUNDAY
MORNING. HEAVY BANDED SNOWFALL IS EXPECTED AS STRENGTHENING
FRONTOGENETIC FORCING...INCREASING ATLANTIC MOISTURE TRANSPORT AND
STRONG JET DYNAMICS ALOFT COME TOGETHER OVER NEW ENGLAND.
THERE IS POTENTIAL LOCALLY FOR AMOUNTS REACHING 1 FOOT UP ACROSS
EASTERN ME.

THE SNOWFALL FORECAST FOR THIS STORM CONTINUES TO BE PROBLEMATIC
DUE TO A RELATIVE LACK OF COLD AIR SINCE HIGH PRESSURE MOVING
OFFSHORE.
THERE IS EXPECTED TO BE JUST ENOUGH COLD AIR THROUGH THE COLUMN
FOR SNOW AND SLEET ACROSS SOUTHEAST NEW YORK AND INTERIOR CT AND
MA AND COASTAL NH AND DOWNEAST MAINE.

FURTHER SOUTH IN SOUTHERN NEW ENGLAND...THE TEMPERATURE PROFILES
STRADDLING THE FREEZING ISOTHERM SFC AND ALOFT LEAD TO THE
LIKELIHOOD OF MULTIPLE PRECIPITATION TYPES. THERE IS A THREAT FOR
FREEZING RAIN/LIGHT ICING IN SOUTHEAST NY/SOUTHERN NEW ENGLAND AS
THE MODELS SUGGESTS ENOUGH WARMING ALOFT FOR PERIODS OF LIQUID
PRECIP WHILE SURFACE TEMPERATURES REMAIN NEAR OR JUST BELOW
FREEZING.

MANUAL PROGS BLENDED CONTINUITY WITH THE NAM/GFS/21Z SREF MEAN/12Z
ECMWF/00Z GEFS MEAN QPF AND TEMPERATURE PROFILES.

...UPPER MS VALLEY/UPPER GREAT LAKES TO THE OHIO VALLEY/CENTRAL
APPALACHIANS AND MID-ATLANTIC/EASTERN NEW ENGLAND...

A SHORTWAVE TROUGH AND ASSOCIATED AREA OF LOW PRESSURE OVER THE
CANADIAN PRAIRIES WILL DIVE SOUTHEAST LATER SATURDAY INTO THE
UPPER MS VALLEY...AND REACH THE OH VALLEY BY LATE SUNDAY. THIS
SYSTEM WILL CROSS THE CENTRAL APPALACHIANS AND MID-ATLANTIC REGION
SUNDAY NIGHT AND MONDAY. THE MODELS SHOW A BAND OF LOW TO MID
LEVEL FRONTOGENESIS JUST NORTH OF THE SURFACE LOW TRACK. THIS WILL
RESULT IN A SWATH OF SNOW. A CLOSED 850-700 MB LOW MAY DEVELOP TO
ENHANCE LOW LEVEL CONVERGENCE AND SNOW AMOUNTS...SO SNOW IS
EXPECTED TO BE DEEPER OVER THE OH VALLEY DAY 2 AND MID ATLANTIC
DAY 3 AND LIGHTER IN THE UPPER MS VALLEY DAY 1.

WPC GENERALLY FAVORED A BLEND OF THE 00Z GFS AND 12Z ECMWF WHICH
FOCUSES SEVERAL INCHES OF SNOW NORTH OF THE LOW TRACK ACROSS THE
OH VALLEY INTO THE ADJACENT CENTRAL APPALACHIANS OF SOUTHWEST
PA/NEARBY WV.  THE 00Z ECMWF WAS ON THE WESTERN EDGE OF THE
ENVELOPE OF SOLUTIONS WITH THE LOW TRACK OFF THE MID ATLANTIC/NEW
ENGLAND COASTS MON NIGHT SO WE WILL WAIT TO SEE IF IT CAN MAINTAIN
CONTINUITY ON SUCCEEDING RUNS.


...NORTHERN ROCKIES...

MID LEVEL MOISTURE AND ENERGY ALOFT RIDING OVER THE TOP OF THE
MEAN RIDGE OVER THE WESTERN U.S. WILL TRAVERSE THE NORTHERN
ROCKIES SATURDAY AND EARLY SUNDAY. A COMBINATION OF UPSLOPE FLOW
AND FORCING ALOFT ALONG WITH A FEED OF MID LEVEL MOISTURE SUPPORTS
SNOW SHOWERS FOR THE HIGHER TERRAIN OF THE RANGES OF NORTHWEST MT
AND NORTHERN ID. A LOW TO MODERATE RISK OF 4 INCH SNOWFALL AMOUNTS
IS DEPICTED.


...UPPER MIDWEST/UPPER GREAT LAKES DAY 3...

ANOTHER IN A SERIES OF SHORTWAVES WILL ADVANCE SOUTHEAST OUT OF
CANADA AND INTO THE UPPER MIDWEST SUNDAY NIGHT AND MONDAY. A NEW
STREAK OF WARM ADVECTION AND FRONTOGENETIC FORCING WILL FAVOR A
STRIPE OF ACCUMULATING SNOWFALL. THE LACK OF MOISTURE TRANSPORT
INTO THE SYSTEM SHOULD RESULT IN MODEST ACCUMULATIONS...WITH A FEW
INCHES EXPECTED FOR NORTHERN MN AND MUCH OF NORTHWEST TO CENTRAL
WI TO THE NEARBY UPPER PENINSULA OF MI.

PETERSEN