Area Forecast Discussion
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000 FXUS61 KPBZ 241625 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1225 PM EDT SUN MAY 24 2015 .SYNOPSIS... WARMTH AND HUMIDITY WILL RETURN TO THE REGION...BUT SO WILL SHOWER AND THUNDERSTORM CHANCES AS THE HOLIDAY WEEKEND DRAWS TO A CLOSE. && .NEAR TERM /THROUGH TONIGHT/...
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DRY WEATHER WILL CONTINUE FOR THE NEAR TERM PERIOD AS UPPER HIGH PRESSURE BUILDS OVER THE UPPER OHIO AND GREAT LAKES REGIONS. A GRADUAL INCREASE IN HUMIDITY CAN ALSO BE EXPECTED WITH INCREASING HIGH CLOUDINESS AS SOUTHERLY FLOW INTENSIFIES WITH THE EASTWARD SHIFTING SURFACE HIGH. THE RESULTING WARM ADVECTION REGIME WILL SUPPORT TEMPERATURES APPROXIMATELY 5 DEGREES ABOVE THE AVERAGES...FORECAST FOR WHICH WAS CHANGED LITTLE FROM PREVIOUS ISSUANCE.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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RECURRING SHORTWAVE IMPULSES ARE FORECAST TO ERODE THE RIDGE OVER THE REGION THROUGH MID WEEK WITH MOISTURE DEPTH INCREASING IN THE DEVELOPING WARM SOUTHWEST FLOW. SHOWER AND THUNDERSTORM PROBABILITIES WILL THUS BE ON THE INCREASE BEGINNING ALONG A ZANESVILLE TO FRANKLIN LINE LATE ON MONDAY. GIVEN THE LACK OF CONFIDENCE IN MODEL BOUNDARY LAYER MOISTURE MAGNITUDE AND RESULTING INSTABILITY UNDER WARM ADVECTION ALOFT...ALONG WITH POORLY RESOLVED CONVECTION TENDENCIES...HAVE RESERVED LIKELY POPS FOR THE WEDNESDAY TIME FRAME GIVEN THE NAM AND GFS PROPENSITY FOR A STRONGER SHORTWAVE EMERGING FROM THE PARENT TROUGH...WHICH IS PROJECTED OVER THE MISSISSIPPI VALLEY BY THEN. AS FOR SEVERE POTENTIAL...MID LEVEL WARMTH WILL LIMIT INSTABILITY AND NAM/GFS DEEP LAYER SHEAR PROJECTIONS ARE MARGINAL AT BEST...AT LEAST UNTIL THE UPPER TROUGH APPROACH ON WEDNESDAY. THAT SAME WARMTH WOULD SUPPORT HEAVY RAINFALL VIA WARM CLOUD PROCESSES...AND PRECIPITAL WATER VALUES WILL BE APPRECIABLY HIGHER UNDER THIS TRAIN SUPPORT PATTERN...BUT CONVECTION POTENTIAL IS EXPECTED TO BE DIURNALLY DEPENDANT AND SUSTAINED MOISTURE CONVERGENCE ABSENT UNTIL THE AFOREMENTIONED SHORTWAVE CROSSES AND A COLD FRONT SLIDES OUT OF THE MIDWEST ON WEDNESDAY. THE BOTTOM LINE IS THAT A HAZARDOUS WEATHER OUTLOOK IS NOT NEEDED AT THIS TIME...ALTHOUGH PRECURSOR RAINFALL AND TIMING OF THE APPROACHING MID/UPPER SUPPORT MAY ALTER THAT DIAGNOSIS AS MID WEEK APPROACHES.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... THE LATEST MODEL RUNS AGREE ON SCENARIO OF EASTERN CONUS RIDGE EROSION...WITH A WEAK COLD FRONT ENCROACHING ON THE UPPER OHIO REGION ON THURSDAY. CHANCE POPS WERE MAINTAINED WITH THAT TIMING...BUT ELIMINATED FOR FRIDAY GIVEN EXPECTATIONS OF SHORTWAVE RIDGING. A DEEPER SHORTWAVE TROUGH WITH A STRONGER COLD FRONT ACCOMPANIED BY INCREASING PRECIP CHANCES ARE PROJECTED FOR THE WEEKEND. TEMPERATURES ARE EXPECTED TO AVERAGE AROUND THE NORMALS FOR THE PERIOD. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/... HIGH PRESSURE WILL SUPPORT VFR WITH LIGHT SOUTHERLY WIND INTO MONDAY. .OUTLOOK.../SUNDAY THROUGH THURSDAY/... ABUNDANT MOISTURE AND DISTURBANCES IN SOUTHWEST FLOW ARE LIKELY TO SPAWN PERIODIC RESTRICTIONS THROUGH THURSDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$ 15

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