-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 222147
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
547 PM EDT WED MAY 22 2013

.SYNOPSIS...
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SHOWER AND THUNDERSTORM CHANCES WILL CONTINUE UNTIL A COLD FRONT
PASSES THROUGH THURSDAY EVENING. HIGH PRESSURE RETURNS FOR THE
WEEKEND.
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&&

.NEAR TERM /THROUGH THURSDAY/...
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MESO DATA SHOWS ML CAPES 1500 J/KG OVR WV INTO WRN PA. MESO/NR
TERM MDL DATA SHOWS SHEAR SHOULD INCRS VERY SLIGHTLY INTO THE
EVENING...MAINTAINING SOME RISK FOR A FEW SVR TSTMS. ATM SHOULD
BEGIN TO STABILIZE IN THE FCST AREA AFT SUNSET. ANOTHER SURGE OF
MOISTURE SEEN ON STLT IS EXP TO MOVE NWD KEEPING SHWR CHCS INTO
THE OVRNGT PD. STILL A CHC OF A TSTM WITH SOME ELEVATED INSTAB BUT
SVR THREAT SHOULD END. A CDFNT WL APRCH FM THE WEST THU BRINGING
ADDNL SHWRS/TSTMS. MDL PROGS SHOW INSTAB SHOULD BE MINIMAL AND
THIS SEEMS REASONABLE GIVEN EXPD CLD COVER.
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&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
A RAPID TRANSITION TO MUCH COLDER CONDITIONS TAKES PLACE DURING
THIS PERIOD AS THE CONSENSUS OF THE MORE RELIABLE GLOBAL MODEL
SYSTEMS SUGGESTING THE MID-LEVEL SYSTEM TRACKING THROUGH THE
REGION SHOULD CLOSE OFF AS IT MOVES OVER PITTSBURGH AND SLOWLY
OOZES SOUTHEASTWARD. THE CLOSED SOLUTIONS FAVORED BY THE MORE
RELIABLE MODELS END UP TRENDING TOWARD THE SLOWER END OF THE
GUIDANCE PACK WITH THIS SYSTEM...WHICH MAKES SENSE GIVEN THE
HIGHER LONG WAVE AMPLITUDE. AS SUCH...THE SYSTEMS DEPARTURE WAS
SLOWED IN THE FORECAST WHICH RESULTED IN INCREASING POPS INTO
FRIDAY.

WHILE ITS DEPARTURE IS SLOWER...MUCH DRIER AIR DOES WORK INTO THE
AREA BY FRIDAY NIGHT WITH THE CONSENSUS OFFERING EXTREMELY LEAN
LAYER RH PROFILES AND WEAKENING NORTHWEST COLD ADVECTION. THIS
SETS THE STAGE FOR STELLAR RADIATIONAL COOLING GOING INTO SATURDAY
MORNING. GRIDDED GUIDANCE SUGGESTS WIDESPREAD 30S ACROSS THE
AREA...WHICH WITH 850 MB TEMPERATURES FALLING TOWARD -2C IS NOT TOO
SHOCKING. FROST WAS ADDED TO THE GRID TO ACCOMMODATE LOWS
GENERALLY IN THE MID 30S ACROSS VAST TRACTS OF THE CWA...AND
FROST/FREEZE HEADLINES SEEM POSSIBLE AT THIS POINT. THESE
TEMPERATURES AT 850 MB FAIL TO MODERATE DURING THE DAY SATURDAY
MUCH...SO TEMPERATURES WILL LIKELY ONLY WANDER FOR HIGHS FROM THE
UPPER 50S FRIDAY TOWARD THE LOWER 60S SATURDAY. FRIES

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
SIMILAR CONDITIONS PERSIST THROUGH THE REST OF THE WEEKEND AND
EVEN POSSIBLY INTO MONDAY MORNING WITH VERY DRY CONDITIONS AND
LIGHT WINDS FAVORING SUPERIOR RADIATIONAL COOLING EACH NIGHT. AS
SUCH...LOWS CONTINUE TO LOOK TO HEAD TOWARD THE 30S EACH
NIGHT...WITH A FEW LOCATIONS INEVITABLY DROPPING BELOW FREEZING.
ONCE AGAIN...FROST WAS ADDED TO THE FORECAST INTO THE
OVERNIGHT/EARLY MORNINGS THIS WEEKEND...AND FROST/FREEZE HEADLINES
AGAIN SEEM QUITE POSSIBLE.

OTHERWISE...VERY GRADUAL MODERATION OF LOW LEVEL TEMPERATURES WILL
BE LIKELY AS THE CLOSED SYSTEM DEPARTS EASTWARD BUT DRY CYCLONIC
NORTHWESTERLY FLOW ALOFT REMAINS THE LARGE CONTROLLING FACTOR FOR
OUR WEATHER. THIS IS THANKS IN PART TO THE FACT THAT THE MODEL
CONSENSUS KEEPS THE LARGE SCALE RIDGE AXIS LARGELY TO OUR WEST
THROUGH THE MIDDLE OF NEXT WEEK. AS A RESULT...CONDITIONS SHOULD
REMAIN GENERALLY DRY WITH VERY SLOW MODERATION OF TEMPERATURES
THROUGH THE WEEK. FRIES

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
LOW TO MEDIUM CONFIDENCE FORECAST ON SHOWER AND THUNDERSTORM TIMING.
VFR WEATHER WILL PREVAIL MUCH OF THE FCST PERIOD /AT LEAST INTO
THE OVERNIGHT HOURS/...THE CHALLENGE IS TIMING ON ANY SHRA OR TSRA
IMPACTING THE TERMINALS. MAINTAINED VCTS FOR LATE AFTERNOON AND
EVENING BEFORE TRANSITIONING TO VFR SHRA UNTIL MIDNIGHT. CLOUDS
WILL DEVELOP IN THE PREDAWN HOURS...LATEST GUIDANCE SUGGEST CIGS
IN THE 015-025 WHICH IS HIGHER THAN EARLIER RUNS AND IN LINE WITH
ONGOING FORECAST. STRATOCU WILL LIFT BY MID MRNG INTO A LOW END
VFR DECK. FOR PLACES THAT EXPERIENCE RAINFALL...PATCHY FOG COULD
DEVELOP DURING THE PREDAWN HOURS. 98

.OUTLOOK.../THURSDAY THROUGH SUNDAY/...
THE PROBABILITY OF WIDESPREAD IFR WEATHER IS LOW.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

$$

07