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Area Forecast Discussion
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000
FXUS61 KPBZ 270215
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
915 PM EST MON JAN 26 2015

.SYNOPSIS...
LIGHT TO OCCASIONALLY MODERATE SNOW WILL SHIFT EASTWARD TONIGHT
AS LOW PRESSURE DEVELOPS TOWARD THE COAST.

&&

.NEAR TERM /THROUGH TUESDAY/...
GFS AND NAM SOLUTIONS CONTINUE START TO EDGE THE 850-600 MB
DEFORMATION FIELD OVER WESTERN PENNSYLVANIA EASTWARD
OVERNIGHT...AND THIS SEEMS TO ALREADY BE MANIFEST IN RADAR AND
SATELLITE ENHANCEMENT SIGNATURES. AS THIS OCCURS...HOWEVER...COLD
ADVECTION LOOKS TO RAPIDLY BE BRINGING THE DENDRITIC GROWTH LAYER
DOWN TOWARD THE BOUNDARY LAYER SATURATION. THIS SHOULD SLOW DOWN
THE EROSION OF RADAR COVERAGE...SO WHILE THE MECHANISM FOR SNOW
GENERATION WILL BE CHANGING FROM MORE LARGE SCALE SYNOPTIC LIFT TO
INSTABILITY DRIVEN SNOW SHOWERS...THE CHANGE IN REALITY IN
COVERAGE MAY NOT BE THAT STARK FROM WHAT WE AR SEEING AT THE
MOMENT. HOWEVER...GIVEN THAT QPF SHOULD BECOME MUCH LIGHTER OTHER
THAN IN THE UPSLOPE AREAS SUCH AS THE RIDGES...ACCUMULATIONS
SHOULD SLOW DOWN TREMENDOUSLY OVERNIGHT.

GIVEN THE EROSION OF LARGE SCALE LIFT IN THE NON-UPSLOPE
AREAS...THE WINTER WEATHER ADVISORIES WERE CANCELED FOR ALL BUT
THE EASTERN FRONTIER OF THE CWA. THIS INCLUDES THE RIDGES AS WELL
AS FOREST...JEFFERSON...AND INDIANA COUNTY...WHICH ALL REMAIN ON
THE CUSP OF THE INTERFACE WITH LARGER SCALE LIFT THAT STILL
REMAINS RESIDENT OVER CENTRAL PENNSYLVANIA. ADDITIONALLY...AS
UPSLOPE FLOW INCREASES AND DENDRITIC GROWTH MAXIMIZES
OVERNIGHT...INCREASINGLY EFFICIENT SNOW SHOWERS IN THE RIDGES
SHOULD ALLOW FOR A CONTINUATION OF ACCUMULATION...EVEN AS THE
SATURATED LAYER IS EVISCERATED.

ONE SIDE NOTE...DUE TO THE FACT THAT DAYTIME TEMPERATURES WERE
AROUND FREEZING IN MANY SPOTS SOUTH OF THE TURNPIKE...WITH THE
LOSS OF DAYTIME INSOLATION EVEN THOUGH IT WAS CLOUDY...MANY ROADS
WILL LIKELY START TO BECOME ICY THIS EVENING. A SPECIAL WEATHER
STATEMENT WAS ISSUED FOR THIS THROUGH 9 PM. PLEASE REFER TO
PITSPSPBZ FOR MORE INFORMATION. FRIES

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
SNOW SHWR POTENTIAL WL CONT TO DECLINE THROUGH TUESDAY AS HIGH
PRES BLDS. A COLD WEDNESDAY MRNG WL FOLLOW WITH LOWS IN THE SINGLE
DIGITS TO NR ZERO OVR NRN COUNTIES. READINGS WERE ADJUSTED FOR THE
LATEST DETERMINISTIC TRENDS AND COLLABORATION.

FAST MOVING LOW PRES IS PROJECTED OFF THE GREAT LAKES ON THURSDAY.
CURRENT LOW TRACK ALNG I 76 SUGGESTS SUFFICIENT WARMTH OVR SRN
ZONES TO PRECLUDE AN ACCUMULATING ICE OR SNOW EVENT. PROGRESSION
SHOULD LIMIT ELSEWHERE.  MORE ON THAT SYSTEM IN FUTURE PACKAGES.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
MAIN CONCERN FOR THE EARLY PART OF THE LONG TERM WILL BE THE SPEED 
IN WHICH THE UPPER LEVEL TROUGH/CLIPPER CROSSES THE REGION. THE MOST 
RECENT RUN OF THE GFS SEEMS TO BE THE FASTEST...SO OPTED TO STAY 
CLOSER TO A BLEND OF THE ECMWF AND PREVIOUS RUNS. THIS WOULD KEEP 
PRECIP INTO THE EARLY PART OF FRIDAY WITH NW FLOW AND SNOW SHOWERS 
LINGERING INTO FRIDAY AFTERNOON. BEYOND THIS TIME PERIOD THE MODEL 
SOLUTIONS DIVERGE A BIT MORE AT THE SURFACE...MAKING IT HARD TO PUT 
ANYTHING MORE THAN CHANCE POPS IN THE FORECAST. WILL MAINTAIN AN 
OVERALL COOLING TREND IN TEMPERATURES AS A BROAD TROUGH REMAINS 
OVERHEAD THROUGH TUESDAY...WHICH IS CLOSE TO WPC FORECAST VALUES.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
SLOWLY SEEING IMPROVEMENT FROM IFR THIS EVENING AS THE BACK EDGE
OF THE SNOW GRADUALLY SHIFTS EASTWARD. BACK EDGE...CURRENTLY ON A
LINE FROM NEAR KFKL TO NEAR KPIT WILL TAKE 6-9 HRS TO CLEAR THE
ERN TERMINALS OF DUJ AND LBE. ALL TERMINALS WEST OF THE SNOW WILL
HOLD WITH LOW END MVFR CIGS THROUGH THE OVERNIGHT AND INTO TUES.
WINDS WILL GRADUALLY SHIFT WSW TUES AND REMAIN LIGHT.
TAX

.OUTLOOK.../TUESDAY THROUGH FRIDAY/...
THE NEXT CHANCE FOR WIDESPREAD RESTRICTIONS IS EXPECTED ON
THURSDAY AND FRIDAY WITH CROSSING LOW PRESSURE.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...WINTER WEATHER ADVISORY UNTIL 7 AM EST TUESDAY FOR MDZ001.
OH...NONE.
PA...WINTER WEATHER ADVISORY UNTIL 7 AM EST TUESDAY FOR PAZ009-016-
     023-074-076.
WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST TUESDAY FOR WVZ023-041.

&&

$$






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