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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0942Z Nov 17, 2014)
 
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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
442 AM EST MON NOV 17 2014

VALID 12Z MON NOV 17 2014 - 12Z THU NOV 20 2014

DAY 1...

...EASTERN U.S. SYSTEM...

SEVERAL STREAMS OF SHORTWAVE ENERGY EMBEDDED WITHIN A
SHARPENING/DEEPENING SYNOPTIC SCALE TROUGH WILL BE THE MAIN PLAYS
MAINLY ON DAY 1 AS THEY AID IN CYCLOGENESIS OVER THE EASTERN
UNITED STATES.  THE RESULTING LOW SHOULD TRACK NORTHEAST INTO
CANADA LATER TONIGHT.  RADAR IMAGERY EARLY THIS MORNING SHOWED
MOISTURE STREAMING NORTHEASTWARD FROM THE GULF INTO THE MID
ATLANTIC REGION AND CONTINUING ON INTO NEW ENGLAND.  A RELATIVELY
SMALL AREA ON THE WESTERN SIDE OF THE SYSTEM SHOULD BE COLD ENOUGH
TO SUPPORT ANY ORGANIZED SNOWFALL...WITH A TRANSITION ZONE OF
RAIN/SNOW MIX IN BETWEEN AIR MASSES. 

WITH ENOUGH WARM AIR BEING DRAWN NORTHWARD AHEAD OF THE
SYSTEM...ENSEMBLE SOLNS AND GLOBAL MODELS POINT TO ONLY A LIMITED
AREA WHERE A LOW END SLIGHT RISK FOR 4 INCHES OF SNOW IS
WARRANTED...AND THAT SHOULD BE IN THE UPSLOPE REGION OF THE
APPALACHIANS.  IN ADDITION...WHILE AREAS TO THE LEE OF THE EASTERN
LAKES SHOULD HAVE A PERIOD WHERE PCPN IS TIED TO THE SYNOPTIC
SCALE CYCLONE TODAY BEFORE COLD AIR STREAMING ACROSS LAKES ERIE
AND ONTARIO STARTS TO REV UP LAKE EFFECT SNOWS LATER TONIGHT.

THERE IS THE POTENTIAL FOR ISOLATED POCKETS OF LIGHT FREEZING PCPN
IN SOME OF THE COLDER VALLEYS IN THE APPALACHIANS WHERE COLD AIR
NEAR THE SFC FAILS TO BE SCOURED OUT WHILE THE WARMER/WETTER
AIRMASS STREAMS OVER HEAD.  THE BETTER RISK FOR FREEZING RAIN
LOOKS TO BE IN PORTIONS OF INTERIOR NEW ENGLAND AS AIR FROM THE
ATLANTIC RIDES UP AND OVER A WARM FRONT.  WHILE THE DURATION OF
FREEZING PCPN SHOULD BE FAIRLY SHORT...THERE WERE ENOUGH SIGNS IN
THE ENSEMBLES TO WARRANT A SLIGHT RISK OF A QUARTER INCH OF
FREEZING PCPN BEFORE ENOUGH COLD AIR COMES IN FROM THE NORTHWEST
TO CHANGE THE PCPN OVER TO ALL SNOW. 


...WESTERN GREAT LAKES...

LAKE EFFECT SNOWS OVER THE WESTERN GREAT LAKES SHOULD BE
DEVELOPING THIS MORNING AS WINDS SHIFT TO THE NORTHWEST AND DRAWS
A VERY COLD AIRMASS OVER THE OPEN WATERS.  CONSIDERING THAT WATER
TEMPERATURES ARE ON THE ORDER OF 5 DEGS C IN LAKE SUPERIOR AND H85
TEMPS DROP TO MINUS 18 C...OVER A FOOT OF SNOW IS QUITE POSSIBLE
IN THE SNOW BELTS OF THE UPPER PENINSULA.  A SIMILAR SCENARIO
SHOULD PLAY OUT TO THE LEE OF LAKE MI A BIT LATER. 

DAYS 2 AND 3...

...GREAT LAKES...

LAKE EFFECT SNOWS SHOULD BE COMMON TO THE LEE OF EACH GREAT
LAKE...ESPECIALLY ON TUE/TUE NIGHT WHEN THE CORE OF THE COLDEST
AIR SPREADS ACROSS THE LAKES.  LARGE HOURLY SNOWFALL RATES WILL BE
A GIVEN WHERE LAKE EFFECT SNOW BANDS SET UP.  THUS THINK SOME
PLACES WILL BE MEASURING SNOW BY THE FOOT FOR THE EVENT.

THE CONDITIONS BECOME LESS FAVORABLE OVER THE UPPER PENINSULA OF
MI BY TUESDAY EVENING AS LOW LEVEL FLOW BECOMES MORE WESTERLY THAN
NORTH OR NORTHWEST.  THAT SHIFT IN WIND DIRECTION SHOULD FAVOR
AREAS TO THE LEE OF LAKE MI AND ESPECIALLY TO THE LEE OF LAKES
ERIE AND ONTARIO.  BY WEDNESDAY...LAKE EFFECT SNOWS SHOULD BE
SCALING BACK ACROSS THE REGION AS LOW LEVEL WINDS BACK TO THE
SOUTH AND H92 AND H85 START WARMING.

WHILE PINPOINTING EXACTLY WERE A SNOW BAND WILL SET UP IS
IMPOSSIBLE THIS FAR OUT...THE HIGHEST PROBABILITIES SHOWN BY THE
ENSEMBLES ROUGHLY PARALLELED THE IDEA THAT THE FOCUS FOR HEAVIEST
SNOWS WILL GRADUALLY SHIFT EAST AND THAT TUESDAY/TUESDAY NIGHT
SHOULD SEE HIGHER SNOWFALL TOTALS. 

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

BANN