Area Forecast Discussion
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000 FXUS61 KPBZ 301345 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 945 AM EDT TUE SEP 30 2014 .SYNOPSIS... WEAK LOW PRESSURE WILL CROSS THE REGION TODAY. WARM AND DRY CONDITIONS WILL FOLLOW UNTIL THE PASSAGE OF A FRIDAY COLD FRONT. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WITH 945AM UPDATE...HAVE CONTINUED TO EXPAND COVERAGE OF LIKELY AND CATEGORICAL POPS. REGARDLESS OF WHAT THE HRRR AND RAP ARE CURRENTLY DEPICTING...LINE OF SHOWERS AND ISOLATED THUNDERSTORMS CONTINUES TO HOLD TOGETHER. HOWEVER...12Z PIT SOUNDING SHOWS A LOT OF DRY AIR...WHICH IS LIKELY THE REASON THAT MODELS SHOW A WEAKENING TREND IN SHOWERS LATER TODAY AS THE AIR MASS MOVES FARTHER EAST. IN ADDITION...THE STORM PREDICTION CENTER HAS EXPANDED ITS AREA FOR A MARGINAL HAIL THREAT...AND HAVE LIKEWISE EXPANDED THE AREA IN THE FORECAST THAT MENTIONS A SMALL HAIL THREAT. 4AM DISCUSSION FOLLOWS. WEAK BOUNDARY WITH STRONG UPPER LEVEL SUPPORT WILL SLOWLY CROSS THE AREA TODAY. STILL HAVING A TOUGH TIME GETTING A HANDLE ON HOW MUCH PRECIPITATION THIS SYSTEM WILL PRODUCE. THE BEST UPPER LEVEL SUPPORT WILL BE WITH THE MAIN 50H LOW WHICH WILL TRAIL BEHIND THE FRONT AND MOVE INTO NE OHIO LATE THIS AFTERNOON. THE ATMOSPHERIC MOISTURE NEVER REALLY GETS LINED UP AS THE MID AND UPPER LEVEL MOISTURE MOVES IN AHEAD OF THE 50H LOW...BUT THE LOW LEVEL MOISTURE HANGS BACK WITH THE MAIN SHORTWAVE ROTATING AROUND THE UPPER LEVEL SYSTEM. FORECAST SOUNDINGS ARE SHOWING A DRY LAYER UP TO AROUND 5000 FT THROUGH THE ENTIRE DAY...MAKING IT DIFFICULT FOR SHOWERS TO REACH THE GROUND. WILL LEAVE IN CHANCE POPS FOR TODAY WITH THE HIGHEST PROBABILITY FOR MEASURABLE RAIN ACROSS THE NORTH CLOSER TO THE UPPER LEVEL LOW. IF THE LOW LEVELS ARE ABLE TO SATURATE TODAY THEN MORE WIDESPREAD SHOWER ACTIVITY IS POSSIBLE. IN ADDITION...COLD POOL ALOFT...WITH PASSING 50H...LOW MAY PROVIDE ENOUGH ELEVATED INSTABILITY THAT AN ISOLATED STORM COULD DEVELOP THIS AFTERNOON. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/... THE ENTIRE SYSTEM WEAKENS THIS EVENING. THE 50H LOW OPENS UP AND WHATS LEFT OF THE SURFACE BOUNDARY DRIFTS INTO EASTERN PA. UPPER LEVEL WAVES OF ENERGY WILL SWING AROUND THE BACKSIDE OF THE EXITING 50H LOW SO WILL LEAVE IN SLIGHT CHANCE/LOW CHANCE POPS IN THE FAR EAST FOR A PORTION OF THE EVENING HOURS. UPPER LEVEL RIDGE WILL MOVE IN BEHIND THE LOW ON THURSDAY... PROVIDING SUNSHINE AND WARM TEMPERATURES. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... STILL SEEING SOME MINOR TIMING ISSUES WITH FRONTAL PASSAGE ON FRIDAY. LATEST NAM IS SLOWING EVERYTHING DOWN...GFS IS THE MOST PROGRESSIVE AND THE 12Z ECMWF IS SOMEWHERE IN BETWEEN. FRIDAY DOES APPEAR LIKE A GOOD CHANCE FOR SOME MUCH NEEDED WIDESPREAD RAIN. MUCH COLDER AIR WILL SETTLE IN FOR THE WEEKEND. OVERALL THE PATTERN WILL SHIFT FROM THE QUIET WE HAVE EXPERIENCED OVER THE LAST TWO OR SO WEEKS...TO A MORE ACTIVE AND COOLER PATTERN. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... CLOSED LOW ALOFT WILL ROTATE SOUTHEAST TOWARD LAKE ERIE THIS AFTERNOON WITH A WEAK COLD FRONT TO FOLLOW. BAND OF SHOWERS ACROSS OHIO THIS MORNING CLOSER TO UPPER LEVEL SUPPORT. MODELS SHOWING RATHER WIDESPREAD COVERAGE FOR SHOWERS THIS AFTERNOON BUT NOT WHOLLY CONVINCED OF THIS BASED ON MODEL SOUNDINGS WITH AVAILABLE MOISTURE. VCSH REMAINS MOST PORTS THIS AFTERNOON WITH RESTRICTIONS POSSIBLE MAINLY AT KFKL AND KDUJ. OUTLOOK.../WEDNESDAY THROUGH SATURDAY/... THE NXT CHC FOR WIDESPREAD RESTRICTIONS WL COME WITH A FRIDAY CDFNT. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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