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Winter Weather Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2109Z Jan 27, 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
409 PM EST TUE JAN 27 2015

VALID 00Z WED JAN 28 2015 - 00Z SAT JAN 31 2015


DAYS 1 THROUGH 3...

...NEW ENGLAND...

THE FIRST NOR'EASTER OF THE SEASON WILL WRAP UP ON WED... AS THE
WRAPPED UP AREA OF LOW PRESSURE OFF THE NORTHEAST COAST WILL
GRADUALLY LIFT NORTH AND EAST TOWARD THE CANADIAN MARITIMES. THE
IMPRESSIVE AND ELONGATED TROWAL/DEFORMATION ZONE ON THE BACKSIDE
OF THE DEEP SURFACE LOW WILL CONTINUE OVERNIGHT BUT SHOULD BEGIN
TO WEAKEN THROUGHOUT WED. THE GUIDANCE SUGGESTS THE 90 PERCENT
MEAN LAYER RH PRESSING WEST BY THIS EVENING OR CURVING FROM WRN
MAINE TO RI/SERN MA... THEN POSITIONING ACROSS MUCH OF MAINE INTO
NRN NH BY 12Z BEFORE WEAKENING. OVERALL WPC FOLLOWED A BLEND OF
THE GUIDANCE... WHICH STILL SUGGESTS ANOTHER .25 TO .50 INCH
LIQUID QPF... FOR A LOW AND MDT PROB OF 4 INCHES OR GREATER ACROSS
MUCH OF MAINE INTO NRN NH.

...GREAT LAKES INTO NEW ENGLAND...

THE OPEN WAVE TROUGH LIFTING NORTH THROUGH CA TODAY WILL STREAK
ACROSS THE CENTER OF THE INTER-MOUNTAIN WEST ON WED TO SPUR HEAVY
OROGRAPHIC SNOWS IN THE TETONS BEFORE EMERGING OUT INTO THE
CENTRAL PLAINS. THIS FEATURE WILL EVENTUALLY BEGIN TO TEAM UP WITH
MULTIPLE STREAMS... UPPER DYNAMICS FROM THE NRN AND ARCTIC JETS...
TO INDUCE A COUPLE OF SURFACE WAVES WITH THE MAIN WAVE STREAKING
FROM THE CENTRAL PLAINS TO NRN NEW ENGLAND BY EARLY FRI BEFORE
POSSIBLY RE-FORM OFF THE COAST OF NEW ENGLAND BY FRI EVENING. THE
GUIDANCE INDICATING NARROW SPREAD WITH THIS SCENARIO CASTS A 50KT
LOW LEVEL JET FUNNELING NORTH VERY MODEST .50 TO AOA 1 INCH PWS
INTO THE OH VALLEY/GREAT LAKES ON THURS AND NORTHEAST ON FRI. THIS
WILL RESULT IN WARM ADVECTION AND OVERRUNNING 70 TO 90 PERCENT
MEAN LAYER RH SLIDING THROUGH THE REGION FOR A COMBINATION OF
LIGHT TO MDT SNOW WITH PERHAPS AT THE START OF EACH DAY SOME LIGHT
FREEZING DRIZZLE. THE MAIN THREAT ON THURS WILL BE 1 TO 2 INCHES
OF SNOW WITH LOCALLY HIGHER AMOUNTS FROM MI INTO NERN OH/WRN PA
AND WRN NY WITH PERHAPS LIGHT ICING FROM SRN WI TO NWRN OH. THEN
THE ENTIRE PRECIP SHIELD SURGES INTO NEW ENGLAND FOR FRI WITH 2-4
INCH AMOUNTS ACROSS MUCH OF NY STATE INTO NRN/CENTRAL NEW ENGLAND
BEFORE BETTER ATLANTIC INFLOW ALONG AN INVERTED TROUGH POSITIONS
OVER MAINE BY FRI AFTN/EVENING. WPC WENT WITH LOW AND MDT PROBS OF
4 INCHES EACH DAY.

...FOUR CORNERS REGION...

A RATHER AMPLIFIED WEAKNESS OFF THE WEST COAST... MAINLY CA...
WILL BEGIN TO ADVANCE EASTWARD TO BECOME A BIT MORE CONSOLIDATED
OVER CA ON THURS AND PERHAPS CLOSE OFF A MID TO UPPER LOW OVER THE
DESERT SW COME FRI. THIS WILL RESULT IN A STEADY INCREASE OF SRN
STREAM AND SUBTROPICAL MOISTURE SPREADING NORTH AND EAST OVER TIME
AND BY FRI A POTENTIALLY LARGE SYNOPTIC SCALE RAIN/MTN SNOW EVENT.
FOR THE MOST PART... THE GUIDANCE SHOWS THIS SCENARIO WITH A FEW
WRINKLES IN THE FCST BUT MOST INDICATE IDEAL SWRLY UPPER DIFLUENT
UPPER FLOW SETTING UP FOR IDEAL OROGRAPHICS FOR HEAVY SNOWFALL FOR
PARTS OF THE FOUR CORNERS TERRAIN. THE FOCUS POINT APPEARS TO BE
NM AND SWRN CO... AS A MAMMOTH COLD SURFACE RIDGE DOWNSTREAM
WEDGES IN FROM THE MIDWEST. WPC WENT AHEAD AND INTRODUCED 4 TO 12
INCH HEAVY SNOW PROBS BASED ON A BLEND OF THE GUIDANCE... FOCUSING
IN ON THE NM TERRAIN AND SAN JUANS OF SWRN CO.


THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER