Area Forecast Discussion
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000 FXUS61 KPBZ 012211 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 611 PM EDT SAT AUG 1 2015 .SYNOPSIS... DRY WEATHER AND SEASONAL TEMPERATURES WILL CONTINUE THROUGH SUNDAY BEFORE A COLD FRONT BRINGS A CHANCE OF SHOWERS ON MONDAY. && .NEAR TERM /THROUGH SUNDAY/...
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THE CUMULUS FIELD IS ALREADY FADING EARLY THIS EVENING...EXCEPT IN A CORRIDOR THAT BASICALLY RUNS DOWN THE TURNPIKE. THIS IS A CORRIDOR ALONG WHICH OUTFLOW FROM EARLIER SPRINKLES/SHOWERS IN THE NORTHERN CWA HAVE PUSHED A WEAK BOUNDARY THAT IS EVIDENT ON RADAR IMAGERY. THIS BOUNDARY HAS BEEN SUFFICIENT TO ALLOW FOR CONTINUED CONVERGENCE IN THE CORRIDOR...WHICH IS MANIFEST AS A LOCAL MAXIMIZING CORRIDOR FOR CUMULUS DEVELOPMENT EVEN AFTER PEAK HEATING. HOWEVER...AS THE SHOWERS CONTINUE TO FADE INTO OBLIVION...THIS BOUNDARY WILL WEAKEN AND DISSIPATE...AND THE CUMULUS WILL DO LIKEWISE WITHIN THE NEXT SEVERAL HOURS. THIS WILL YIELD A CLEAR OVERNIGHT ACROSS THE CWA. RECENT NIGHTS HAVE INDICATED A VERY STARK DIFFERENTIATION BETWEEN THE URBAN AREAS AND RURAL AREAS IN OVERNIGHT TEMPERATURES. IT HAS BEEN NOTED THE PAST TWO NIGHTS THAT THE IMMEDIATE ENVIRONS OF PITTSBURGH CITY HAVE BEEN HELD UP ROUGHLY 6-8 DEGREES HIGHER THAN THE AIRPORT. BECAUSE OF ALL THE CONCRETE...AMPLE DAYTIME SUN...AND LACK OF COOLING RAINFALL...IT WOULD SEEM THIS DIFFERENTIAL IS LIKELY TO HOLD TONIGHT. SO WHILE OUTLYING AREAS ACROSS MOST OF THE CWA WILL DROP INTO THE 50S TONIGHT...URBAN AREAS MAY WELL STICK IN THE MID 60S. SOUTHWESTERLY FLOW INCREASES GOING INTO SUNDAY. THIS MEANS WARM ADVECTION WILL BE RETURNING. TEMPERATURES AT 850 MB RUN UP TOWARD ABOUT +17C ON ALL GUIDANCE. STRONG MIXING SHOULD ALLOW FOR WIDESPREAD MID 80S UNDER AMPLE SUN YET AGAIN. FRIES
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... ALTHOUGH THE CHANCE FOR SHOWERS WILL INCREASE SUNDAY NIGHT...COLD FRONT SHOULD MAKE ITS PASSAGE ACROSS THE REGION SOMETIME MONDAY MORNING. DID NOT FEEL COMFORTABLE ENOUGH TO BUMP UP POPS TO LIKELY OVER A WIDESPREAD AREA WITH MOISTURE AS A POSSIBLE LIMITING FACTOR...ALTHOUGH DYNAMICS ALONG THE FRONT ARE FAVORABLE. FOR NOW HAVE SIMPLY ADDED LIKELY POPS NORTH OF THE INTERSTATE 80 CORRIDOR. SPC HAS A MARGINAL RISK FOR SEVERE WEATHER ON MONDAY. TWO CRITICAL FACTORS WILL BE TIMING OF PRECIPITATION ALONG THE FRONT ALONG WITH INSTABILITY VALUES (NAM HAS ABOUT 3 TIMES AS MUCH INSTABILITY AS GFS...LIKELY DUE TO WET BIAS OF SURFACE DEWPOINTS). ACCOMPANYING THE SURFACE COLD FRONT WILL BE AN UPPER LEVEL LOW OVER SOUTHERN ONTARIO. WITH THE PROXIMITY OF THE LOW...SHORTWAVES WILL BEGIN TO CRANK AROUND THE LOW. NAM/SREF BRING A SHORTWAVE ON TUESDAY ACROSS THE REGION FROM THE NORTH...WHILE THE GFS/ECMWF KEEP THE SHORTWAVE TO THE NORTH. BETWEEN THE SHORTWAVES AND THE COLD FRONT EVENTUALLY STALLING OUT SOUTH OF THE AREA...HAVE GONE WITH A BLANKET LOW CHANCE OF SHOWERS IN THE FORECAST. DIURNAL SPREAD IN TEMPERATURES WILL SHRINK BY A FEW DEGREES DUE TO CLOUD COVER THROUGH THE PERIOD. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... UPPER TROUGH WILL REMAIN SITUATED OVER THE EASTERN US THROUGH THE LONG TERM WITH SEVERAL SHORTWAVES PROGGED TO HELP DEEPEN IT THROUGH THE PERIOD. THIS WILL LIKELY KEEP TEMPERATURES JUST SLIGHTLY COOLER THAN SEASONAL AVERAGES. BY LATE IN THE WEEK...MODEL GUIDANCE SUGGESTS A SURFACE WAVE COULD DEVELOP AND LIFT ACROSS THE OHIO VALLEY LATE. BUT...WITH RUN TO RUN INCONSISTENCY OPTED TO STAY CLOSER TO WPC GUIDANCE VALUES...WHICH KEEP CHANCE POPS THROUGH THE BEGINNING OF NEXT WEEKEND. && .AVIATION /22Z SATURDAY THROUGH THURSDAY/... GENERAL VFR WILL CONTINUE INTO SUNDAY WITH DRY SURFACE HIGH PRESSURE SUPPRESSING PRECIP UNDER NW FLOW ALOFT. OUTLOOK...SUNDAY NIGHT THROUGH THURSDAY... RESTRICTION POTENTIAL WILL INCREASE WITH THE APPROACH AND PASSAGE OF A MONDAY COLD FRONT. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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