Area Forecast Discussion
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000 FXUS61 KPBZ 200948 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 548 AM EDT WED AUG 20 2014 .SYNOPSIS... A SERIES OF DISTURBANCES WILL KEEP OCCASIONAL SHOWER AND THUNDERSTORM CHANCES IN THE FORECAST THROUGH THE REST OF THE WEEK. && .NEAR TERM /THROUGH THURSDAY/... 545 AM UPDATE...UPPED POPS A BIT AS SHRA/TSRA HAVE CONGEALED SOMEWHAT. WARM FRONT CONTINUES TO GENERATE LIFT AND FURTHER DEVELOPMENT. ISSUED FFW FOR TUSCARAWAS/CARROLL DUE TO EARLIER 2-3 INCH RAINS PLUS APPROACHING STORMS. STILL MAY GET A BRIEF BREAK DURING THE LATE MORNING BEFORE INSTABILITY STORMS DEVELOP THIS AFTERNOON. PREVIOUS DISCUSSION... SURFACE LOW SPINNING OVER MICHIGAN CURRENTLY...PUSHING A WARM FRONT NORTHWARD ACROSS PBZ CWA. FRONT HAS AIDED REDEVELOPMENT OF TSRA BEHIND INITIAL COMPLEX WHICH HAS WEAKENED. HEAVY RAINFALL TOTALS IN A FEW SPOTS IN OHIO...ON THE ORDER OF 1 TO 2 INCHES. HANGING ON TO LIKELY POPS DURING THE NEXT SEVERAL HOURS. THIS BOUNDARY WILL BE THE FOCUS OF PRECIPITATION OVER THE NEXT 24 HOURS. DEVELOPMENT WILL CONTINUE TO BE AIDED BY A MIDLEVEL SHORTWAVE THIS MORNING...WHICH WILL ROTATE THROUGH BY AFTERNOON. A RELATIVE LULL IN PRECIPITATION MAY BE SEEN DURING THE LATE MORNING. HOWEVER...INSTABILITY AND UPPER LEVEL DIVERGENCE WILL COMBINE WITH THE BOUNDARY TO TRIGGER ADDITIONAL SHOWERS AND THUNDERSTORMS THIS AFTERNOON...WITH LIKELY POPS AREAWIDE. PWAT VALUES OF 1.5 TO 1.8 INCHES WILL CONTINUE TO SUPPORT HEAVY RAINFALL. TOUGH TO PINPOINT AREAS THAT HAVE THE BEST CHANCE OF SEEING WATER PROBLEMS. WILL HIGHLIGHT THREAT IN HWO BUT HOLD OFF ON ANY WATCHES AT THIS TIME. NOT EXPECTING MUCH OF A SEVERE THREAT GIVEN THE UNIMPRESSIVE SHEAR PROFILE. TRIED TO KEEP HIGH TEMPS ON THE LOWER SIDE OF GUIDANCE. ACTIVITY DECREASES SOMEWHAT THIS EVENING WITH THE LOSS OF HEATING AND DEPARTURE OF BETTER UPPER SUPPORT. WE MAY BE ABLE TO SQUEEZE IN A SHORT DRY PERIOD DURING THE PREDAWN HOURS BEFORE ACTIVITY RAMPS UP AGAIN SHORTLY AFTER 12Z. && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... A RELATIVELY STATIONARY BOUNDARY STRETCHING SOUTH FROM A WEAK SFC LOW WILL REMAIN IN THE AREA THURS THROUGH FRI WITH SEVERAL DISTURBANCES PROGGED TO TRAVERSE ALONG IT. SHOWERS AND THUNDERSTORMS SHOULD QUICKLY DEVELOP THURS AS THE BOUNDARY LAYER DESTABILIZES AROUND MIDDAY. WHILE THE BEST INSTABILITY AND SHEAR APPEAR TO STAY SOUTH OF THE BOUNDARY THURS...OVER SRN OH...WHERE SPC HAS INCLUDED A SEE TEXT PORTION OF THE DAY TWO OUTLOOK. MEANWHILE...THE 00Z NAM SHOWS AROUND 1500J/KG SFC CAPE AND 30-40KTS 0-6KM BULK SHEAR IN OUR AREA. THE CORE OF THE H5 JET REMAINS OVER SWRN OH. COULD EXPECT A FEW STRONG TO SEVERE THUNDERSTORMS THURS AFTERNOON/EVENING. EXPECTING TO SEE A DIURNAL LULL LATER THURS INTO EARLY FRI...BUT WITH ENOUGH MOISTURE PRESENT ALONG THE BOUNDARY...SHOWER CHANCES WILL EXIST...MAINLY INTO ERN OH. FRIDAY AS THE UPPER RIDGE TRIES TO BUILD OVER THE MS VALLEY...A SFC LOW LIFTS THE BOUNDARY NORTH AS A WARM FRONT SERVING AS A FOCUS FOR ADDITIONAL SHOWERS AND THUNDERSTORMS. A WAVE AT H7 WILL MOVE ALONG THE BOUNDARY AGAIN FRI...BUT TIMING DIFFERENCES EXIST AMONG THE MODEL GUIDANCE. AT THIS POINT WILL CONTINUE TO CARRY HIGH CHC POPS FOCUSED ON THE EARLY EVENING TIMING OF THE 00Z NAM/ECMWF. PWAT VALUES MAX OUT AROUND 2" FRIDAY THROUGH ERN OH AND NRN WV ALONG THE CORRIDOR WHERE SHOWERS AND THUNDERSTORMS ARE EXPECTED. STORM MOTIONS FROM THE 00Z NAM BUFR SOUNDINGS ARE IN THE 20-30KT RANGE...BUT SHOWERS SHOULD BE HIGHLY EFFICIENT AND ANY TRAINING COULD LEAD TO WATER PROBLEMS THROUGH FRI NIGHT. TAX && .LONG TERM /SATURDAY THROUGH TUESDAY/... WITH ACTIVE WEATHER IN THE NEAR TERM...GENERALLY STAYED CLOSE TO THE PREVIOUS FORECAST BLENDING WITH WPC THINKING FOR THE EXTENDED PERIOD. MODELS CONTINUE TO SHOW A RIDGE BUILDING IN THE SRN PLAINS THROUGH THE WEEKEND...SLOWLY SHIFTING THE AXIS INTO OUR REGION BY EARLY NEXT WEEK. THE WEEKEND WILL REMAIN WARM AND MUGGY WITH DAILY RAIN CHANCES AS WE SIT ON THE ERN PERIPHERY OF THE RIDGE. A GRADUAL EASTWARD SHIFT IN THE UPPER TROF AXIS WOULD MEAN A CONTINUATION OF AT LEAST NEAR NORMAL TEMPS THROUGH MIDDLE OF NEXT WEEK WITH A DRYING TREND. TAX && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/... SHOWERS/STORMS HAVE LOST A LITTLE BIT OF PUNCH BUT CONTINUE TO WORK THEIR WAY ACROSS THE AREA. OUTFLOW BOUNDARY OUT AHEAD OF RAIN IS PRODUCING A 20-30 KNOT GUST AS IT MOVES THROUGH...AND HAVE TRIED TO HANDLE THIS FOR THE NEXT COUPLE OF HOURS. MVFR/SPOTTY IFR CAN BE EXPECTED WITH THIS RAIN BATCH AS IT ACCOMPANIES A SHORTWAVE. KEPT VCSH BEHIND THE MAIN BATCH WITH REDEVELOPMENT ACROSS OHIO. A BRIEF BREAK IN RAINFALL IS POSSIBLE BETWEEN 12Z AND 16Z OR SO LATER THIS MORNING. THEN...DIURNAL INSTABILITY BUILDUP WILL ALLOW SHRA/TSRA TO FIRE THIS AFTERNOON. KEPT VCTS MENTION AS IT IS STILL DIFFICULT TO PINPOINT LOCATION AND TIMING...ALTHOUGH BRIEF IFR RESTRICTIONS ARE POSSIBLE ANYWHERE. ACTIVITY STARTS TO CALM DOWN A BIT AFTER SUNSET. OUTLOOK.../WEDNESDAY NIGHT THROUGH SUNDAY/... SEVERAL CROSSING DISTURBANCES WILL CAUSE PERIODIC RESTRICTIONS INTO THE WEEKEND. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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