Area Forecast Discussion
Issued by NWS

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000
FXUS61 KPBZ 262321
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
621 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 TO LINGER 850-600 MB DEFORMATION
FIELD OVER WESTERN PENNSYLVANIA THROUGH MUCH OF THE EVENING...AND
REALLY ONLY START TO EDGE IT SUBSTANTIALLY EASTWARD OVERNIGHT
TOWARD MORNING. AS THIS OCCURS...HOWEVER...COLD ADVECTION SHOULD
BEGIN TO START IN EARNEST...AND BRING 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. HOWEVER...GIVEN THAT QPF SHOULD
BECOME MUCH LIGHTER OTHER THAN IN THE UPSLOPE AREAS SUCH AS THE
RIDGES...ACCUMULATIONS SHOULD SLOW DOWN TREMENDOUSLY BY THE
OVERNIGHT HOURS.

DUE TO THE FACT THAT FLOW REMAINS FAIRLY WELL ALIGNED AND SOME
INSTABILITY REMAINS IN THE BOUNDARY LAYER...SNOW SHOWERS AND
FLURRIES SEEM LIKELY TO CONTINUE IN THE RIDGES INTO THE DAYTIME ON
TUESDAY...HOWEVER WEAKER SATURATION AND LOWER DEWPOINTS WILL
LIKELY BEING TO TAKE A TOLL EVEN ON THIS ACTIVITY BY THAT
JUNCTURE. THIS SHOULD ALLOW FOR POPS TO BE ROLLED BACK BY THE
DAYTIME TUESDAY A BIT.

ALL THAT SAID...DUE TO THE SLOW MIGRATION OF THE WESTERN EDGE OF
THE DEFORMATION FIELD THIS EVENING...WINTER WEATHER ADVISORIES FOR
THE PITTSBURGH METRO AREA WERE EXTENDED UNTIL 10 PM...ALL OTHER
ADVISORIES REMAIN IN EFFECT THROUGH THE NIGHT.

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 /00Z TUESDAY THROUGH SATURDAY/...
AS WESTERN EDGE OF STORM MOVES TO THE EAST...IFR VISIBILITIES IN
WIDESPREAD SNOW SHOULD COME TO AN END BY THE EVENING. MVFR SNOW
SHOWERS WILL CONTINUE INTO THE EVENING...WITH COVERAGE DIMINISHING
ENOUGH AT TERMINALS TO ONLY INCLUDE A FLURRY MENTION AFTER
MIDNIGHT. WHILE MOST MODEL GUIDANCE THINKS THAT WIDESPREAD IFR
CIGS WILL PERSIST OVERNIGHT...THINK THIS IS TOO PESSIMISTIC...AND
HAVE GONE WITH GENERAL MVFR CIGS. EXCEPTION TO THIS IS
FKL/DUJ...WHERE IFR CIGS SHOULD CONTINUE OVERNIGHT.

.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 PAZ007>009-
     013>016-022-023-073-074-076.
     WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
     PAZ020-021-029.
WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST TUESDAY FOR WVZ023-041.

&&

$$






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