Area Forecast Discussion
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000 FXUS61 KPBZ 301856 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 256 PM EDT TUE SEP 30 2014 .SYNOPSIS... AFTER WIDESPREAD RAIN DEPARTS THE REGION THIS EVENING...TEMPERATURES WILL BE ON THE REBOUND AGAIN FOR THE REST OF THE WORK WEEK. A COLD FRONT WILL BRINGS WIDESPREAD RAIN FRIDAY AND FRIDAY NIGHT BEFORE MUCH COLDER AIR ARRIVES THIS WEEKEND. && .NEAR TERM /THROUGH WEDNESDAY/... BIG TEMPERATURE CONTRAST ACROSS THE FORECAST REGION WITH UPPER 50S IN THE NORTHWEST BEHIND THE FRONTAL BAND OF SHOWERS AND 80 DEGREES AHEAD OF THE BAND. NORTHERN PORTION OF THE BAND IS BEGINNING TO FALL APART WITH SOME CONVECTIVE CELLS DEVELOPING IN ADVANCE OF THE LINE...WHILE THE SOUTHERN PORTION HAS DONE A BETTER JOB HOLDING TOGETHER...WITH SOME CONVECTIVE ELEMENTS DEVELOPING ALONG THE LINE ITSELF. SHOULD NOT BE ANY THREAT OF THUNDERSTORMS BEHIND THE BAND. HOWEVER...WITH UPPER LEVEL LOW DROPPING SOUTHEAST FROM LAKE ERIE INTO WESTERN PENNSYLVANIA...HAVE KEPT SOME POPS INTO THE FORECAST THROUGH MUCH OF THE NIGHT. SOME ISOLATED ECHOES ARE BEGINNING TO APPEAR ACROSS NORTH CENTRAL OHIO. WITH THE PROXIMITY OF THE UPPER LOW...HAVE KEPT MOSTLY CLOUDY SKIES IN THE FORECAST THROUGH WEDNESDAY MORNING...WITH DIMINISHING TRENDS IN THE AFTERNOON. AS A RESULT...THINK THAT STRATUS SHOULD PREVENT FOG DEVELOPMENT IN THE MORNING. HAVE ADDED SLIGHT CHANCE POPS FOR MUCH OF THE FORECAST AREA WEDNESDAY AS WELL DUE TO PROXIMITY OF UPPER LOW. ALTHOUGH TEMPERATURES HAVE DROPPED SIGNIFICANTLY BEHIND THE FRONT...EXPECT THAT TEMPERATURES WILL REBOUND TO NEAR SEASONAL LEVELS TOMORROW. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... LARGE SCALE RIDGING QUICKLY BUILDS BACK INTO THE AREA WEDNESDAY NIGHT INTO THURSDAY. IN FACT...THE MODEL CONSENSUS DOES FAVOR SOME SORT OF A WEAK WARM FRONTAL PASSAGE WEDNESDAY NIGHT INTO THURSDAY MORNING WHICH DOES MANAGE TO BRIEFLY INCREASE MOISTURE POOLING ALONG IT. THIS MAY YIELD AN INCREASE IN CLOUDS WEDNESDAY NIGHT INTO THURSDAY...HOWEVER GIVEN THE WEAKNESS OF THE BOUNDARY AND WEAK SATURATION...PARTLY CLOUDY SKIES WILL BE FEATURED IN THE FORECAST. DEEP SOUTHWESTERLY FLOW BECOMES ESTABLISHED ON THURSDAY AND CONTINUES RIGHT INTO EARLY FRIDAY AS THE NEXT SYSTEM BEARS DOWN ON THE AREA. THE 12Z GUIDANCE HAS LARGELY SLOWED RELATIVE TO THE 00Z GUIDANCE AND FAVORS A LATE AFTERNOON/EVENING COLD FRONTAL PASSAGE ON FRIDAY. POPS WERE SLOWED TO ACCOUNT FOR THIS. WHAT IS ALSO NOTABLE IS THE INCREASE IN TEMPERATURES FOR FRIDAY ACROSS THE EASTERN CWA ON THE GFS/ECMWF. BOTH DEPICT LOWER 80S IN THE EASTERN REACHES OF THE CWA UNDER A VERY WELL MIXED LOWER ATMOSPHERE IN THE DRY PRE-FRONTAL ENVIRONMENT. THIS WILL BE IN STARK CONTRAST TO THE WESTERN CWA...WHERE DRASTICALLY INCREASED LAYER MOISTURE...500-700 J/KG OF CAPE AND STRONG SHEAR WILL BE RESULTING IN VERY STRONG CHANCES OF RAIN SHOWERS WITH A FEW THUNDERSTORMS CHARGING EASTWARD INTO THE CWA ALONG WITH MUCH COLDER CONDITIONS TO START THE EXTENDED FORECAST. FRIES && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... THE COLD FRONT WILL LIKELY BE SLICING THROUGH THE AREA FRIDAY EVENING...WITH SHOWERS AND THUNDERSTORMS WINDING DOWN FROM WEST TO EAST AS IT DOES SO. STRONG WINDS WILL BE LIKELY ALONG THE FRONT AS IT DOES SO OWING TO ROUGHLY 30-35 KTS OF MOMENTUM OFF THE SURFACE TO MIX DOWN WITH THE FRONTAL PASSAGE. THIS COMBINED WITH A DRASTIC AIR MASS DENSITY DISCONTINUITY SHOULD YIELD A FAIRLY WINDY PERIOD FROM FRIDAY AFTERNOON INTO FRIDAY NIGHT. MUCH COLDER AND STILL UNSTABLE CONDITIONS WILL DOMINATE THE REGION THROUGH THE WEEKEND AS AN UPPER LOW SETTLES IN OVERHEAD BY SATURDAY. MODEL SOUNDINGS SUGGEST STRONG LOW LEVEL LAPSE RATES WITH CONTINUED COLD ADVECTION SHOULD ALLOW FOR A DIURNAL INCREASE IN SHOWERS UNDER THE UPPER LOW ON SATURDAY. WITH WET BULB ZERO HEIGHTS FALLING LIKE A ROCK...THERE MAY BE SOME P-TYPE CONSIDERATIONS...POSSIBLY SOME GRAUPEL OR SOMETHING OF THAT NATURE...HOWEVER THE GENERAL STORY WILL BE THE TRANSITION TO MUCH COLDER CONDITIONS INTO THE WEEKEND. BEYOND THE WEEKEND...A GENERAL CONTINUATION OF AN EASTERN TROUGH AND WESTERN FLAT/BROAD RIDGING SCENARIO SEEMS TO PLAY OUT. THIS SHOULD YIELD WEAKER AND FASTER MOVING SYSTEMS OVER THE TOP OF THE RIDGE AND INTO THE EASTERN U.S. WITH GENERALLY COOL CONDITIONS REMAINING. FRIES && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... MODEL FORECASTS INDICATED THAT THE FRONTAL BAND WOULD PASS THROUGH WITH VFR CONDITIONS...WHILE OBSERVATIONS AT MOST SITES HAVE DROPPED TO IFR. WITH MODELS NOT HANDLING THE PASSAGE WELL...HAVE GENERALLY USED UPSTREAM OBSERVATIONS AND TRENDS FOR CREATING 18Z TAFS. THINK THAT ANY SORT OF THUNDERSTORM THREAT SHOULD BE CONTAINED TO DUJ/LBE/MGW AT THIS POINT. BEHIND THE BAND...EXPECT THAT SITES SHOULD DROP TO IFR FOR A FEW HOURS. HOWEVER...ONE CONCERN IS THAT IFR CONDITIONS OBSERVED UPSTREAM MAY BE DUE TO LAKE ERIE INFLUENCE...WHICH WOULD NOT BE AS STRONG AT LOCAL TERMINALS. IN THAT CASE...WIDESPREAD IFR CONDITIONS MAY NOT OCCUR. BY EVENING...EXPECT THAT CLOUDS WILL REMAIN WIDESPREAD DUE TO UPPER LEVEL LOW. WITH MVFR STRATUS EXPECTED OVERNIGHT...HAVE NOT ADDED FOG AT ANY TERMINALS. AS STRATUS SCATTERS OUT WEDNESDAY MORNING...REMAINING CLOUDS SHOULD LIFT TO VFR CONDITIONS. OUTLOOK.../WEDNESDAY THROUGH SUNDAY/... THE NXT CHC FOR WIDESPREAD RESTRICTIONS WL COME WITH A FRIDAY/FRIDAY NIGHT CDFNT. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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