Area Forecast Discussion
Issued by NWS

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000
FXUS61 KPBZ 251755
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1255 PM EST TUE NOV 25 2014

.SYNOPSIS...
A STORM SYSTEM MAY BRING SNOW TO PORTIONS OF THE AREA ON
WEDNESDAY WITH COLDER CONDITIONS EXPECTED FOR THE REMAINDER OF THE
WORK WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
VERY LITTLE CHANGE THROUGH THE NEAR TERM AS WE CONTINUE TO BE IN
THE SQUEEZE BETWEEN THE MOISTURE PLUME TO THE EAST-SOUTHEAST AND
THE LIFTING UPPER TROUGH TO THE NORTH. THIS HAS ALLOWED FOR
MOSTLY-PARTLY SUNNY SKIES OVER MUCH OF THE FORECAST AREA...MINUS
THE RIDGES AND A ROW OF COUNTIES NORTH AND WEST OF I-70 AND I-79 IN
OHIO AND NW PA. THIS SHOULD REMAIN THE CASE THROUGH THE EVENING
BEFORE CLOUDS ASSOCIATED WITH THE DEVELOPING COASTAL LOW BEGIN TO
PUSH NORTHWESTWARD.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
AN UPPER LOW CURRENTLY EMERGING FROM THE LEE OF THE ROCKIES AND
DIGGING INTO THE SOUTHERN HIGH PLAINS IS PROJECTED TO ROUND THE
BASE OF THE UPPER TROUGH OVER THE GREAT LAKES AND RAPIDLY DEVELOP
AS IT ENCOUNTERS THE SUBTROPICAL JET FEED UP THE EASTERN SEABOARD.
MODEL SOLUTIONS CONTINUE TO VARY A BIT ON THE EXACT CORRIDOR OF
NORTHEASTWARD EJECTION OF THIS SYSTEM UP THE APPALACHIAN
CHAIN...WHICH HAS DRASTIC RAMIFICATIONS TO OUR FORECAST IN THE
UPPER OHIO VALLEY...HOWEVER MOST MODEL SOLUTIONS NOW FAVOR AT
LEAST SOME SNOWFALL IN ALL POINTS FROM PITTSBURGH EASTWARD ON
WEDNESDAY AT SOME POINT.

AS THIS UPPER WAVE ADVANCES NORTHEASTWARD...THE MOISTURE FEED UP
THE ATLANTIC IS RAPIDLY WRAPPED BACK INTO THE DEVELOPING HIGHLY
TILTED BAROCLINIC CYCLONE. THE PREPONDERANCE OF MODEL SOLUTIONS
SUGGEST AN 850 MB LOW TRACK TO THE EAST OF THE APPALACHIANS ON
WEDNESDAY...WHICH SHOULD LARGELY KEEP OUR AREA ENTRENCHED ON THE
COLDER SIDE OF THE SYSTEM. THIS SHOULD KEEP OUR PRECIPITATION TYPE
AS ALL SNOW EVERYWHERE THAT PRECIPITATION DOES OCCUR...HOWEVER
MARGINAL ONSET TEMPERATURES NEAR FREEZING MAY MAKE ACCUMULATIONS
DIFFICULT TO MUSTER IN SOME OF THE LOWEST ELEVATIONS AROUND
MORGANTOWN. THAT SAID...WHILE THE BULK OF THE LOW LEVEL FORCING
FOR ASCENT AND STRONGEST OMEGAS ARE LIKELY TO REMAIN TO THE EAST
OF THE AREA IN THE DEEPER MOISTURE FEED...SOME INTERESTING DYNAMICS
SEEM LIKELY TO PLAY OUT IN THE MID-LEVELS.

BOTH THE NAM AND GFS HAVE REALLY SEEMINGLY LATCHED ONTO A DEEP AND
IMPRESSIVE LAYER OF FRONTOGENESIS FROM 700-400 MB...WITH THE
UPWARD BRANCH OF THIS AGEOSTROPHIC CIRCULATION LIFTING INTO OUR
SOUTHEASTERN THIRD OR QUARTER OF OUR CWA ROUGHLY 12-18Z ON
WEDNESDAY. COINCIDENT WITH THIS LARGE OF LARGE SCALE LIFT IS THE
DENDRITIC GROWTH ZONE...AND GIVEN THE AMOUNT OF ATLANTIC MOISTURE
BEING THROWN BACK INTO IT...DENDRITE FORMATION SEEMS LIKELY TO BE
FAIRLY ROBUST FOR A SHORT PERIOD ON WEDNESDAY CONCURRENT WITH THE
RATHER SHORT WINDOW OF DEEP MOISTURE AND LIFT. MODEL SOLUTIONS
HAVE LARGELY INCREASED THEIR QPF EXPECTATIONS ALONG THE
SOUTHEASTERN FRINGE OF THE CWA WITH THIS...AND ALL SEEM RATHER
REASONABLE EXCEPT THE NAM...WHICH HAS MASSIVELY UNREALISTIC
NEGATIVE OMEGA VALUES NOTED IN THE UPWARD BRANCH OF THE
FRONTOGENETICAL CIRCULATION. THE MITIGATING FACTORS FOR HIGH RATIO
SNOWFALL WILL LIKELY COME VIA MARGINAL BOUNDARY LAYER AND GROUND
TEMPERATURES. AS A RESULT...WHILE THE COBB NUMBERS WOULD FAVOR
15:1 SNOWS FOR MOST LOCATIONS...THE FORECAST FAVORS MORE ALONG THE
LINES OF 7:1 IN THE LOWER ELEVATIONS AND 12:1 IN THE HIGHER
ELEVATIONS FOR MELTING CONSIDERATIONS. THE END RESULT SEEMS MOST
LIKELY TO BE VERY LIGHT ACCUMULATIONS EVERYWHERE EXCEPT MAYBE A
AN INCH OR TWO INCHES IN MORGANTOWN...LATROBE...AND INDIANA...A
GENERAL 3 TO 6 INCHES IN MOST THE RIDGES...EXCEPT AROUND 6 INCHES
POSSIBLE IN THE SOUTHEASTERN RIDGES OF TUCKER/GARRETT COUNTY. THIS
FORECAST FOLLOWS LARGELY ON PERSISTENCE WITH THE PREVIOUS
FORECASTS...EXCEPT TO EXPAND VERY LIGHT ACCUMULATIONS A BIT DEEPER
IN THE FORECAST AREA. DUE TO A BIT OF CONTINUED FLUX IN THESE
NUMBERS AND A LACK OF CONFIDENCE IN WIDESPREAD WARNING CRITERIA
NUMBERS...WINTER STORM WATCHES REMAIN IN EFFECT FOR WEDNESDAY.

WITH COLDS AND LIGHT NORTHERLY WINDS ALONG WITH DYNAMICAL COOLING
LIKELY TO PLAY A ROLE...HIGHS ON WEDNESDAY WERE ADJUSTED DOWNWARD.
STATISTICAL GUIDANCE LIKELY IS COMPLETELY USELESS IN A PATTERN AS
SUCH...SO TEMPERATURES WERE ADJUSTED HEAVILY TOWARD DIRECT MODEL
OUTPUT FROM THE NAM...ECMWF...AND GFS...WHICH ALL FAVORED NOTHING
MORE THAN LOWER TO MID 30S WHERE SNOW IS EXPECTED. FRIES

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
DEEPER MOISTURE FROM LARGE COASTAL LOW BEGINS PULLING AWAY TO THE
EAST THANKSGIVING MORNING THANKS TO ANOTHER SW TROF MOVING QUICKLY
IN FROM THE WEST. ENOUGH LLVL MOISTURE LINGERS WEDS NIGHT TO KEEP
POPS WARRANTED AREAWIDE. THE SW TROF WILL STREAM WELL TO OUR
SOUTH...ULTIMATELY KEEPING HIGHER POP CHANCES OVER WV...BUT DEEPER
MOISTURE WILL POOL NORTHWARD ALONG THE WRN PERIPHERY OF THE HIGHER
TERRAIN. WITH NW FLOW KICKING IN...SNOW CHANCES WILL INCREASE
THROUGH THANKSGIVING DAY. MOST OF THE FORECAST AREA HAS A DECENT
CHANCE OF SEEING AT LEAST SOME SNOW FLAKES ON THANKSGIVING...BUT
DOWNSTREAM FLOW FROM THE LAKES AND UPSLOPING WILL FAVOR THE TYPICAL
NW FLOW AREAS.

BY THURS EVENING DRIER AIR BEGINS TO WORK IN FROM THE SW LIMITING
THE POTENTIAL OVER ERN OHIO AND THE NRN PANHANDLE OF WV. AT THIS
TIME THE CAA BRINGS H85 TEMPS NEAR -10C ENHANCING LAKE-INDUCED CAPE
AND OVERALL SNOW CRYSTAL GROWTH. FORECASTING LIGHT ACCUMULATIONS FOR
THE RIDGES AND DOWNSTREAM OF THE LAKE...PRIMARILY NORTH OF I-80.

DRIER AIR UNDER SFC HIGH PRESSURE MOVES IN FOR FRI...BUT IT WONT
STAY LONG. A STREAM OF MOISTURE FROM THE CANADIAN ROCKIES WILL KEEP
CLOUDS AND PRECIPITATION CHANCES IN THROUGH THE WEEKEND AS NW FLOW
HOLDS INTO EARLY SUN. HIGH PRESSURE WILL SLIDE SOUTH INTO THE NRN
PLAINS OVER THE LATTER PART OF THE WEEKEND...DISLODGING A WEAK
COLORADO LOW WITH RELATIVELY LOW MOISTURE INTO OUR AREA. WHILE THIS
MEANS MORE LIGHT PRECIPITATION...THE GOOD NEWS IS A TRANSITION TO
SWERLY FLOW AND OVERALL WARMING INTO NEXT WEEK. MODELS HAVE MADE
REMARKABLE PROGRESS IN CONSISTENCY OVER THE LAST 24HRS LENDING TO
HIGHER CONFIDENCE IN THE EXTENDED TRENDS.
TAX

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
GENERAL VFR OVERNIGHT UNTIL CLOUDS AND MOISTURE SPREAD NORTHWEST
FROM COASTAL LOW DEVELOPING TONIGHT. PRECIP SHIELD WILL SPREAD IFR
SNOW FROM PITTSBURGH AND MORGANTOWN EAST MAINLY FROM 12-18Z THEN
IMPROVING LATE DAY. GUSTY WEST WINDS WILL DIMINISH THIS EVENING.
LIGHT NORTH TO NORTHEAST WINDS LATER TONIGHT THROUGH WEDNESDAY.

OUTLOOK.../WEDNESDAY NIGHT THROUGH SUNDAY/...
RESTRICTIONS POSSIBLE THURSDAY IN SNOW SHOWERS. A FRONT WILL BRING
POSSIBLE RESTRICTIONS IN SHOWERS SUNDAY INTO MONDAY.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY
     AFTERNOON FOR MDZ001.
OH...NONE.
PA...NONE.
WV...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY
     AFTERNOON FOR WVZ041.

&&

$$










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