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Winter Weather Forecast Discussion
 
(Latest Discussion - Issued 2147Z Jan 26, 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
447 PM EST MON JAN 26 2015

VALID 00Z TUE JAN 27 2015 - 00Z FRI JAN 30 2015

DAYS 1 TO 3...

...NORTHEAST...

A MAJOR WINTER COASTAL STORM/NOR-EASTER IS BEGINNING TO TAKE SHAPE
THIS AFTN AND THE RESULTANT WILL BE POSSIBLE HISTORIC SNOWFALL
TOTALS ACROSS PARTS OF THE NORTHEAST.

MULTIPLE UPPER STREAMS OF SHORT WAVE DYNAMICS... INCLUDING A
VIGOROUS IMPULSE ARRIVING NEAR THE NORTH CAROLINA COAST... WILL
COMBINE AND PHASE JUST OFFSHORE OF THE NRN MID-ATL AND SRN NEW
ENGLAND COAST. THIS WILL HELP INDUCE AN AREA OF LOW PRESSURE...
WHICH WILL DEEPEN AND GO THROUGH RAPID CYCLOGENESIS OVERNIGHT INTO
TUES MORNING... BASICALLY DEEPENING BY 10-15 MB. THIS INTENSE LOW
WILL SLOWLY LIFT UP THE COAST... AS A DOWNSTREAM RIDGE SLOWS ITS
PROGRESSION ALONG WITH A RATHER DRAMATIC NEG TILT TO THE LONG WAVE
UPPER TROUGH. THIS WILL ALLOW AN ANOMALOUS PLUME OF ATLANTIC AND
EVEN GULF MOISTURE TO SURGE INTO THE COLD SECTOR AND SET UP AN
EXTENSIVE COMMA HEAD/DEFORMATION ZONE OF BANDING HEAVY SNOWS.

THERE REMAINS SOME NARROW SPREAD ON THE SURFACE LOW TRACK AND
PROGRESSION THROUGH WED EVENING... BASICALLY TWO CAMPS. THE SLOWER
NAM/ECMWF AND EC MEAN VERSUS THE MORE PROGRESSIVE GFS/CANADIAN AND
UKMET. GIVEN THE PHASING OF STREAMS... SEMI-BLOCKING RIDGE
DOWNSTREAM AND POSSIBLE BETTER MICRO-PHYSICS IN PLAY FOR A DAY 1
FORECAST... WPC WENT WITH A BLEND OF THE ECMWF/NAM AND INTERNAL
QPF/PRECIP TYPE FOR THE FCST. THIS ALLOWS FOR A MORE SYNOPTIC AND
EVEN PARTIAL MESOSCALE FCST OF TWO POSSIBLE STRIPES OF SIGNIFICANT
ACCUMULATIONS. THE ONE AREA FROM WRN LONG ISLAND/NYC METRO AREA
NORTH AND EAST INTO WRN CT AND CENTRAL MA/SERN NH FROM STRONG
850-650MB FRONTOGENESIS AND THE DRAPED FRONTAL ZONE. THE OTHER
AREA FROM ERN LONG ISLAND/COASTAL RI INTO ERN MA INCLUDING THE BOS
METRO AREA OR TO THE LEFT OF THE DEEP SURFACE LOW TRACK. NOW IF
THE FASTER PROGRESSION COMES TRUE... THE NYC AREA PERHAPS WILL BE
SPARED BY HALF THE AMOUNTS BUT BOS STILL IMPACTED GREATLY. WPC
BLANKETED THE ENTIRE REGION IN HEAVY SNOW PROBS THROUGH TUES AND
LINGERING FOR PARTS OF NRN/ERN NEW ENGLAND ON WED. WHEN ALL IS
SAID AND DONE... POSSIBLE TWO FEET OR GREATER AMOUNTS WILL BE
POSSIBLE WITHIN THE MESOSCALE BANDING THAT ULTIMATELY SETS UP. FOR
MORE SPECIFICS ON WARNINGS AND TOTAL ACCUMULATION AMOUNTS...
PLEASE REFER TO YOUR LOCAL NWS FORECAST OFFICE

...SIERRA-NEVADA/GREAT BASIN/ROCKIES...

AN UPPER LOW OFFSHORE OF SRN CA WILL LIFT UP INTO CA ON TUES AS AN
OPEN WAVE TROUGH AND THEN PROCEED BY SHEARING-OUT DOWNSTREAM ON
WED THROUGH PARTS OF THE INTER-MOUNTAIN WEST. DECENT FORCING AND
MOISTURE ADVECTION SHOULD RESULT IN FAVORABLE OROGRAPHICS INVOF
THE CENTRAL/SRN SIERRAS ON TUES AND TETONS/NRN WASATCH ON WED.

...GREAT LAKES...

THE COMBINATION OF UPPER DYNAMICS SHEARING-OUT OF THE
INTER-MOUNTAIN WEST AND A NRN STREAM SHORT WAVE TROUGH WILL
ATTEMPT TO PHASE OVER THE UPPER MS VALLEY/WRN GREAT LAKES.
HOWEVER... DESPITE THE MERGING... THE MOISTURE AVAILABILITY WILL
BE SCARCE AND WILL RESULT IN ANOTHER CLIPPER LIKE FEATURE. THIS
MEANS MINIMAL ACCUMULATIONS AND WINDY CONDITIONS WITH THE HEAVIEST
AMOUNTS LIKELY NORTH OF THE SURFACE LOW TRACK. THUS WPC INTRODUCED
HEAVY SNOW PROBS NEAR THE MN/CANADIAN BORDER ON WED AND ON THURS
ACROSS PARTS OF MI TOWARDS THE ERN LAKES BASED ON A
BLEND/COMPROMISE OF THE ECMWF/GFS.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

MUSHER