Area Forecast Discussion
Issued by NWS

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000 FXUS61 KPBZ 290800 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 400 AM EDT FRI MAY 29 2015 .SYNOPSIS...
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MULTIPLE DISTURBANCES WILL BRING UNSETTLED WEATHER TODAY THROUGH THE WEEKEND...ALONG WITH WARM AND HUMID CONDITIONS.
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&& .NEAR TERM /THROUGH TONIGHT/...
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DRY AIRMASS IN PLACE AT PRESENT...BUT THIS WILL START CHANGING SHORTLY. WITH H500 RIDGE AXIS PULLING EAST AND SURFACE HIGH TRACKING INTO UPSTATE NEW YORK...RETURN FLOW WILL BEGIN TO PUSH DEWPOINTS BACK INTO THE 60S BY MIDDAY. THIS HAPPENS IN OHIO FIRST...WHERE SLIGHT CHANCE POPS ARE INTRODUCED BY LATE MORNING AS THE LOWER AND MID LEVELS QUICKLY MOISTEN UP ON BUFKIT SOUNDINGS. A MID-LEVEL IMPULSE RIDING UP THE BACK OF THE DEPARTING RIDGE WILL HELP TO PROVIDE A TRIGGER DESPITE WARM TEMPERATURES ALOFT KEEPING CAPE PROFILES FROM BECOMING VERY DEEP. THUS...SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP AREAWIDE DURING THE AFTERNOON. ALONG WITH THE RELATIVELY MODEST CAPE...SHEAR IS UNIMPRESSIVE...SO SEVERE STORMS ARE NOT A THREAT. BRIEF HEAVY RAIN IS A POSSIBILITY WITH PWAT BETWEEN 1.5 AND 1.75 INCHES...BUT WARM CLOUD DEPTHS SHOULD REMAIN BELOW 10K FEET DURING THE DAY WHICH WILL PUT A LID ON RAIN POTENTIAL. WAVE DEPARTS BY EVENING...AND EXPECT THAT STORM COVERAGE WILL DROP OFF BY 06Z AS INSTABILITY AND TRIGGER IS LOST. NEXT FRONTAL BOUNDARY WILL BE MAKING A PUSH FROM THE GREAT LAKES BY 12Z THOUGH...AND ELECTED TO BRING CHANCE POPS BACK INTO THE NORTHWEST COUNTIES BY THAT TIME. TEMPERATURES NUDGED UP SLIGHTLY TOWARDS MODEL CONSENSUS FOR DAYTIME HIGHS. LITTLE CHANGE TO VALUES FOR TONIGHT. CL
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY/...
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WARM SOUTHERLY FLOW WILL CONTINUE INTO SATURDAY WITH THE COLD FRONT STILL WELL TO OUR WEST AND A BROAD ATLANTIC HIGH TO THE EAST. STRONG SURFACE HEATING WILL BOLSTER LOW-LEVEL LAPSE RATES...COMBINING WITH THE MOIST AIRMASS WILL GENERATE PRE-FRONTAL SHOWERS AND THUNDERSTORMS. STRONGER MID- AND UPPER-LEVEL FLOW REMAINS WELL TO OUR NORTH...CLOSER TO THE DEEPER WAVE. STILL...ENOUGH INSTABILITY AND SHEAR EXISTS FOR THUNDERSTORM DEVELOPMENT...ESPECIALLY IN THE LATE EVENING HOURS AS THE BOUNDARY NEARS OUR NORTHWEST AND UPSTREAM THUNDERSTORMS CAN PROGRESS EASTWARD. DEEP UPPER-LOW ADVANCES TO NEAR JAMES BAY CANADA LATE SATURDAY WITH AN ELONGATED DEEP MOISTURE FIELD EXTENDING FROM THE MISSISSIPPI DELTA THROUGH EASTERN QUEBEC. BIGGEST QUESTION REMAINS HOW FAR EAST THAT DEEP MOISTURE PROGRESSES SATURDAY NIGHT INTO SUNDAY. 00Z GFS IS FAST AS IT HAS MODERATE PERPENDICULAR MID-LEVEL FLOW DRIVING THE BOUNDARY AND ASSOCIATED MOISTURE THROUGH PGH BY MIDDAY SUNDAY. THE 00Z NAM AND ECMWF DAMPEN THE MID-LEVEL FLOW AND STALL THE BOUNDARY OVERHEAD...KEEPING AMPLE MOISTURE IN THE AREA. THINKING THE LATTER SOLUTION IS MORE PLAUSIBLE GIVEN THAT THE DRIVER TO THE FRONTS EASTWARD PROGRESSION EXITS WELL TO OUR NORTH AND EAST. WITH THIS IN MIND...WILL KEEP HIGH CHANCE AND LIKELY POPS IN THE FORECAST FOR SUNDAY AFTERNOON AND AGAIN MONDAY AS ANOTHER UPPER-LEVEL WAVE APPROACHES. TEMPERATURES WILL BE WELL-ABOVE AVERAGE SATURDAY AND SATURDAY NIGHT WITH THE WARM SOUTHERLY FLOW. SUNDAYS TEMPS WILL BE SOMEWHAT DEPENDENT ON THE PLACEMENT OF THE FRONT...BUT WITH INCREASED CLOUD COVER...SHOULD BE HELD IN CHECK AND CLOSER TO THE AVERAGE. TAX
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&& .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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UPPER-LEVEL WAVE APPROACHING THE GREAT LAKES MONDAY NIGHT WILL EFFECTIVELY SWEEP THE DEEPER MOISTURE OUT OF THE AREA. MODEL GUIDANCE A LOT MORE OPTIMISTIC THAN 24HRS AGO WITH RE-BUILDING THE SURFACE HIGH OVER PENNSYLVANIA MIDDLE OF NEXT WEEK. THIS LEADS TO A DRYING TREND WITH DECREASED CLOUDINESS. THE NEAR AVERAGE TEMPERATURES THAT START THE WEEK WILL INCREASE THROUGH THE LATTER PART OF THE WEEK AS THE HIGH PRESSURE SHIFTS EAST AND SOUTHERLY FLOW IS RE-ESTABLISHED. TAX
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... MOST OF THE PERIOD WILL FEATURE VFR CONDITIONS. FEW CLOUDS WILL BE SEEN OVERNIGHT...AND THE AIRMASS IS TOO DRY FOR FOG. MOISTURE DOES START CREEPING BACK NORTHWARD FRIDAY MORNING...WITH A SCT-BKN CU DECK DEVELOPING BY MIDDAY. INSTABILITY WILL BUILD DURING THE AFTERNOON...AND AN APPROACHING SHORTWAVE WILL HELP TO FIRE OFF SCATTERED SHRA/TSRA DURING THE AFTERNOON AND EVENING HOURS. VCTS WILL CONTINUE TO BE USED AT ALL SITES...GIVEN THAT ANY RESTRICTIONS SHOULD BE FAIRLY BRIEF OVERALL. ACTIVITY WILL BEGIN TO TAPER OFF TOWARDS THE END OF THE TAF PERIOD. .OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/... RESTRICTIONS ARE LIKELY THROUGH THE WEEKEND WITH A SLOW MOVING COLD FRONT...AND COULD CONTINUE ESPECIALLY S OF PIT INTO EARLY NEXT WEEK AS THE FRONT STALLS. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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