Area Forecast Discussion
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000 FXUS61 KPBZ 201652 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1252 PM EDT SAT SEP 20 2014 .SYNOPSIS... DRY AND WARM FOR ONE MORE DAY UNTIL A COLD FRONT BRINGS BRIEF ROUNDS OF SHOWERS AND THUNDERSTORMS SUNDAY. MUCH COOLER MONDAY...HOWEVER A WARMING TREND WILL ENSUE EACH DAY NEXT WEEK WITH HIGH PRESSURE CAMPED OUT OVER THE REGION. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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NO CHANGES NEEDED FOR THE MIDDAY UPDATE. ONE LAST WARM DAY BEFORE A COLD FRONT APPROACHING FROM THE WEST TAKES THE WEATHER AND TEMPERATURES DOWNHILL. THE LATEST 12Z PIT RAOB ILLUSTRATES LOTS OF DRY AIR FROM H7 THROUGH H4 WHICH WILL MIX OUT MOST OF THE LOW LEVEL MOISTURE NOTED NEAR THE SURFACE. NONETHELESS STILL EXPECT CUMULUS DEVELOPMENT DURING THE AFTERNOON AS TEMPERATURES CLIMB INTO THE MID 70S. THE MAIN WEATHER STORY THIS AFTERNOON WILL BE GUSTY WINDS. PRESSURE GRADIENT INCREASES WITH LOW PRESSURE ENCROACHING FROM THE MIDWEST AND A FAIRLY DEEP MIXING LAYER. AFTERNOON MIXING HEIGHTS WILL BE AROUND 5-6KFT EQUATING TO GUSTS AROUND 30 MPH. NAM IS GENERATING ISOLD STORMS OVER THE HIGHER TERRAIN THIS AFTERNOON...HOWEVER DUE TO THE INFLATED LLVL MOISTURE THAT ITS PREDICTING...IGNORED IT AND CONTINUE WITH A DRY FCST AREA WIDE.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY/... ATMOSPHERIC MOISTURE WILL BE INCREASING SATURDAY NIGHT AHEAD OF A COLD FRONT THAT WILL SLOWLY MOVE THROUGH THE MIDWEST. PRE-FRONTAL SHORTWAVE TROUGH WILL SWING THROUGH SATURDAY NIGHT. THE UPPER LEVEL ENERGY WEAKENS AS IT MOVES THROUGH AND IT WILL BE ENCOUNTERING A RATHER STABLE ATMOSPHERE. WILL KEEP POPS LOW SATURDAY NIGHT AS SHORTWAVE MAY PROVIDE MORE CLOUDS THAN PRECIPITATION. FRONT REACHES WESTERN ZONES BY LATE SUNDAY MORNING. MODELS CONTINUE TO SHOW A DESTABILIZING ATMOSPHERE AND AN IMPRESSIVE WIND FIELD AHEAD OF THE SURFACE BOUNDARY...BUT CONTINUE TO SEE A LACK OF UPPER LEVEL SUPPORT. THE CLOUD COVER FROM SATURDAY NIGHTS SHORTWAVE WILL LIMIT THE AMOUNT OF SUNSHINE SUNDAY MAKING IT DIFFICULT TO REACH CONVECTIVE TEMPS. A SIGNIFICANT LINE OF LOW LEVEL FORCING DEVELOPS ALONG THE BOUNDARY SUNDAY AFTERNOON AS MOISTURE CONVERGENCE IN THE LOWEST LAYERS INCREASES. 0-6 KM BULK SHEAR VALUES ARE STILL IMPRESSIVE...BUT MUCH WILL DEPEND ON THE CLOUD COVER AND HOW THIS LIMITS SURFACE TEMPS. ADDITIONALLY...ANY SHOWERS THAT FALL WITH THE PRE-FRONTAL SHORTWAVE WILL COOL THE ATMOSPHERE...FURTHER DECREASING THE THREAT FOR STRONGER STORMS. SUNDAY`S FRONT WILL NEED TO BE WATCHED AS THE POTENTIAL IS THERE FOR A STRONGER EVENT...BUT SO ARE THE LIMITING FACTORS. IF A LINE OF STRONGER STORMS DEVELOPS IT WILL BE DIRECTLY AHEAD OF THE BOUNDARY. FRONT PICKS UP SPEED SUNDAY EVENING AS STRONG SHORTWAVE DIGS INTO THE UPPER OHIO VALLEY. STRONG CAA AND NORTHWEST FLOW WILL FOLLOW THE SHORTWAVE. WOULD EXPECT A LARGE STRATOCU DECK TO MOVE OVER THE REGION LATE SUNDAY NIGHT AND THROUGH A LARGE PART OF MONDAY. ITS POSSIBLE THAT A COUPLE OF ROUNDS OF SHOWERS WILL DEVELOP...SUNDAY NIGHT WITH THE SHORTWAVE...AND AGAIN MONDAY AFTERNOON WITH THE MAIN COLD POOL. WILL GO BELOW GUIDANCE FOR TEMPS ON MONDAY WITH THE CAA AND CLOUD COVER. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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ECMWF AND GFS ENSEMBLES REMAIN IN GOOD AGREEMENT WITH SUBSIDENCE THROUGH THE EXTENDED FORECAST. H5 HEIGHTS CLIMB TO AROUND 588DM AND REMAIN THERE THROUGH THE WORK WEEK. WITH ANTICYCLONES STACKED ON TOP OF THEMSELVES...LITTLE IN THE WAY OF CLOUD IS FORESEEN UNTIL FRIDAY WHEN RETURN FLOW ON THE BACK SIDE OF THE RIDGE ALLOWS MID AND UPPER LEVEL CLOUDS TO ADVECT EASTWARD. H8 TEMPS REBOUND QUICKLY TUESDAY ALLOWING FOR A WARMER AFTERNOON AS TEMPERATURES RECOVER BACK TO SEASONAL NORMS. SW FLOW AND BETTER MIXING PROMOTE EVEN WARMER AFTERNOONS THUR - SAT WITH LOW TO MID 70S COMMON SAVE FOR THE HIGHER ELEVATIONS. OVERALL DAYTIME TEMPERATURES WERE A BLEND OF THE PREVIOUS FORECAST AND WPC...WHILE NIGHT TIME LOWS BIAS CORRECTED ECMWF GRIDS ALONG WITH INHERITED FORECAST WERE USED.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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VFR WEATHER HOLDS UNTIL SUNDAY MORNING WHEN A COLD FRONT APPROACHES FROM THE WEST. CIGS WILL TEETER ON THE FRINGE OF MVFR/VFR SUN MORNING...HOWEVER EXPECT MORE VFR THAN MVFR OUTSIDE FKL AND DUJ. TWO ROUNDS OF SHOWERS WITH EMBEDDED THUNDERSTORMS ARE FORECAST. THE FIRST ARRIVES AHEAD OF THE FRONT MID SUN MORNING...WHILE THE SECOND IS ASSOCIATED WITH THE UPPER AIR DISTURBANCE IN THE AFTERNOON. COULD NOT RULE OUT A VERY SHORT WINDOW OF IFR VSBYS...BUT THE TEMPORAL WINDOW AND PROB IS TOO LOW FOR TERMINAL FCST. OUTLOOK.../18Z SUNDAY THROUGH THURSDAY/... BRIEF MVFR RESTRICTIONS ARE POSSIBLE SUNDAY AFTERNOON WHEN A COLD FRONT CROSSES. ANY SHOWER OR THUNDERSTORM COULD PRODUCE WINDS IN EXCESS OF 35 KTS.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$ SYNOPSIS...98 NEAR TERM...98 SHORT TERM...22 LONG TERM...98 AVIATION...98

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