Area Forecast Discussion
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000 FXUS61 KPBZ 070020 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 820 PM EDT MON JUL 6 2015 .SYNOPSIS... WHILE SHOWERS WILL DIMINISH IN COVERAGE THIS EVENING...UNSETTLED WEATHER WILL CONTINUE THROUGH MUCH OF THE WEEK AS A COLD FRONT CROSSES THE REGION TUESDAY NIGHT AND THEN STALLS ACROSS THE REGION. && .NEAR TERM /THROUGH TUESDAY/...
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A WEAKENING UPPER LOW CONTINUES TO FILL OVERHEAD AND EVER-SO- SLOWLY LIFT NORTHEASTWARD. THIS HAS ALLOWED FOR A FAIRLY PRIME ENVIRONMENT TO DEVELOP THAT FACILITATES HEAVY RAINFALL LATE THIS AFTERNOON. PWAT VALUES PER THE NAM HAVE RUN UP TOWARD 1.8 INCHES THIS AFTERNOON...AND GIVEN SURFACE DEWPOINTS RUNNING IN THE MID 60S TO LOWER 70S ACROSS THE AREA...THESE TYPES OF PWATS ARE NOT AT ALL SURPRISING. MODEST INSTABILITY OF A FEW HUNDRED J/KG CAN BE NOTED ON MODEL SOUNDINGS...HOWEVER LAYER SHEAR IS EXCEEDINGLY WEAK. THIS HAS ALLOWED FOR SOME RATHER COPIOUS RAIN PRODUCERS TO FORM THIS AFTERNOON...AND MOVE RIDICULOUSLY SLOWLY. THIS IS PARTICULARLY TRUE WHERE LOW LEVEL CONVERGENCE SEEMS TO BE MAXIMIZED IN THE DECAYING DEFORMATION ZONE AROUND THE FILLING 850 MB LOW. AS SUCH...WEAK NORTHEASTERLY FLOW HAS ALLOWED FOR A RATHER STATIONARY BAND OF CONVERGENCE IN THE LOW LEVELS THAT HAS FORCED RATHER CONTINUOUS CONVECTIVE INITIATION OVER EASTERN OHIO THROUGH THE AFTERNOON. HOWEVER...AS THIS CONVERGENCE WEAKENS PROGRESSIVELY INTO THIS EVENING...THE HEAVY RAIN THREAT SHOULD GRADUALLY SUBSIDE. HIGH RESOLUTIONS MODELS INDICATE A STRONG DOWNWARD TURN IN ACTIVITY AFTER 00Z...AND THAT SEEMS TO BE OCCURING AS WE SPEAK ON THE REGIONAL RADAR MOSAIC. OTHERWISE...SOMEWHAT LOWER PWATS AND LEANER 700 MB RH VALUES MOVE INTO THE REGION OVERNIGHT...WHICH SHOULD SLOWLY WIND DOWN THE RAIN CHANCES FROM WEST TO EAST. HOWEVER...HIGH BOUNDARY LAYER RH VALUES MEAN LOW TEMPERATURES ARE LIKELY TO STAY UP WITH HUMID CONDITIONS CONTINUINGAND PATCHY FOG BECOMING AN ISSUE. FRIES PREVIOUS DISCUSSION FOR TUESDAY...A COLD FRONT WILL APPROACH FROM THE WEST DURING THE DAY. EFFECTIVE SHEAR APPEARS TO BE QUITE WEAK WITH ONLY MODEST INSTABILITY PRESENT...AND SPC HAS PUT NEARLY ALL LOCATIONS IN A MARGINAL RISK FOR SEVERE WEATHER. COMPARED TO RECENT DAYS...TOMORROW WILL BE ON THE WARM SIDE. THE PROJECTED HIGH IN PITTSBURGH IS 86 DEGREES...WHICH HAS NOT BEEN REACHED IN ABOUT 3 WEEKS...EVEN THOUGH THE NORMAL HIGH FOR THIS DATE IS 83 DEGREES.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... THE FRONT WILL CROSS THE REGION TOMORROW NIGHT...BRINGING WIDESPREAD RAINFALL. AS HAS BEEN THE CASE RECENTLY...THE FRONT APPEARS LIKELY TO STALL OUT ACROSS THE REGION. LATEST MODELS SHOW FAIRLY GOOD AGREEMENT THAT THE FRONT WILL STALL ACROSS SOUTHERN PORTIONS OF THE FORECAST AREA WEDNESDAY INTO WEDNESDAY...BUT HAVE A BIT MORE DISAGREEMENT ON THURSDAY. 12Z NAM HAS THE BULK OF THE RAINFALL FROM PITTSBURGH NORTH INTO NEW YORK...WHILE THE 12Z ECMWF SHOWS RAINFALL PRIMARILY SOUTH OF PITTSBURGH INTO KENTUCKY. UNTIL MODELS COME INTO BETTER AGREEMENT...WILL SIMPLY KEEP CHANCE POPS FOR THURSDAY. WITH CONSIDERABLE CLOUD COVER EXPECTED THROUGH THE PERIOD...TEMPERATURES SHOULD DROP A FEW DEGREES BELOW NORMAL VALUES. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... FRONTAL BOUNDARY WILL WAVER ACROSS THE REGION THROUGH THE PERIOD AS SHORTWAVES MOVE EAST IN RELATIVELY ZONAL MID LEVEL FLOW. WITH INDIVIDUAL SHORTWAVES HARD TO TIME HAVE KEPT CHANCE POPS THROUGH THE PERIOD. TEMPERATURES CLOSE TO WPC PROGS WHICH SEEMED A GOOD COMPROMISE. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... SCATTERED SHOWERS AND THUNDERSTORMS CONTINUE TO DIMINISH LATE THIS EVENING...WITH ALL TERMINALS VFR. SHOULD KEEP SOME OF THE MID- LEVEL CLOUDS OVERNIGHT...BUT SOME CLEARING COULD LEAD TO SOME MVFR FOG IN THE PRE-DAWN HOURS TUESDAY. HIGH CLOUDS WILL BEGIN TO MOVE IN BY DAYBREAK TUESDAY IN ADVANCE OF THE FRONT THAT WILL SLOWLY APPROACH FROM THE WEST. UNSTABLE CONDITIONS AHEAD OF THE FRONT MEANS THAT RESTRICTIONS ARE AGAIN POSSIBLE IN SHOWERS AND THUNDERSTORMS THAT DEVELOP TUESDAY AFTERNOON. TAX .OUTLOOK.../TUESDAY THROUGH SATURDAY/... A STALLED BOUNDARY ACROSS THE AREA WILL LEAD TO PERIODIC RESTRICTIONS THROUGH THE LATTER PART OF THE WEEK. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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