Area Forecast Discussion
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000 FXUS61 KPBZ 201827 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 227 PM EDT SAT SEP 20 2014 .SYNOPSIS...
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A COLD FRONT CROSSES SUNDAY BRINGING SHOWERS AND A FEW THUNDERSTORMS. MUCH COOLER WEATHER MONDAY BEFORE HIGH PRESSURE TAKES CONTROL...YIELDING A WARMING TREND BACK ABOVE NORMAL BY WEEKS END.
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&& .NEAR TERM /THROUGH SUNDAY/...
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WATER VAPOR IMAGERY PORTRAYS INVASION OF MID AND UPPER LEVEL MOISTURE OVER THE OHIO VALLEY. CIRRUS CLOUDS WILL PROVIDE A NEAR CANOPY FOR MUCH OF THE AFTERNOON INTO THE OVERNIGHT HOURS. NAM12 HAS DONE A GOOD JOB IDENTIFY AREAS OF MOISTURE CONVERGENCE BETWEEN 3-6KFT THAT SHOWS UP NICELY ON VISIBLE SATELLITE AS PATCHES OF BKN-OVC CU FROM ZZV TO CLARION. THIS WILL BE SHORT LIVED AS DRIER ADVECTS IN FROM THE SW. OVERALL NOT MUCH CHANGE WITH THE ONLY RAIN PRODUCING WEATHER SYSTEM OF THE ENTIRE FORECAST. 12Z NCEP CHAIN AND 9Z SREF HAVE A GOOD HANDLE ON COLD FRONT TIMING DURING THE MID TO LATE MORNING HOURS WEST OF I-79 THEN EARLY AFTERNOON POINTS EAST. HIGH RES CONVECTIVE ALLOWING MODELS SUGGEST TWO WAVES OF PCPN. THE FIRST AHEAD OF THE COLD FRONT THEN A BREAK BEFORE YET ANOTHER ROUND ARRIVES ASSOCIATED WITH THE COLD POOL ALOFT. DO NOT FORESEE AN ALL DAY RAIN AND GIVEN THE FACT THE LINE OF SHOWERS WILL BE BROKEN...SOME LOCATIONS MAY NOT SEE MEASURABLE PCPN AT ALL. THE CYCLONE DEEPENS AS IT CROSSES SOUTHERN CANADA THUS PRESSURE GRADIENT PICKS UP CREATING A HEALTHY WIND FIELD. WITH BAROCLINIC ZONE CROSSING EASTERN AREAS DURING THE AFTERNOON...THERE IS A POTENTIAL FOR A GUSTY SHOWER OR STORM. LAPSE RATES ARE BELOW 5CKM-1 AND MOISTURE DEPTH IS CONFINED BELOW 10KFT... SO ITS HARD TO SEE A LINE OF SEVERE THUNDERSTORMS DEVELOPING. THAT SAID...WILL MAINTAIN HWO MENTION OF GUSTY WINDS FOR PA...NRN WV...AND WRN MD...BUT THREAT IS GONE FOR OHIO GIVEN EARLIER FROPA. POPS WERE INCREASED CLOSER TO LAKE ERIE WHERE BETTER UPPER LEVEL FORCING EXISTS PER PROXIMITY TO CYCLONE...OTHERWISE CHC TO LKLY POPS WILL COVER THE REMAINDER OF THE AREA.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
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STRONG CAA ENSUES SUNDAY NIGHT AS THE MID LEVEL TROUGH AXIS SWEEPS THROUGH. OVERNIGHT LOWS WILL BOTTOM OUT IN THE MID TO UPPER 40S...BUT WITH H8 TEMPS 12-13C COOLER THAN 24 HOURS AGO DAYTIME HIGHS WON/T CLIMB MUCH MONDAY...AS 50S WILL BE THE BEST WE CAN DO. ANY MEASURABLE QPF WILL RESIDE EAST OF THE NRN WV PANHANDLE SUN NGT WITH LKLY NUMBERS OVER FAR EASTERN AREAS. NW WINDS WILL CREATE POTENTIAL FOR LAKE ENHANCED SHOWERS AND CLOUDS MUCH OF MONDAY NORTH OF I-76. ANTICYCLONIC FLOW DRIES OUT THE COLUMN FROM WEST TO EAST MON NIGHT. THE POTENTIAL FOR PATCHY FOG EXISTS AS PLACEMENT OF HIGH WILL BE CONDUCIVE FOR CALM WINDS AND A CLEAR SKY.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... 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. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... 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. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$ 98

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