Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 011021 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 621 AM EDT MON SEP 1 2014 .SYNOPSIS... HIGH PRESSURE WELL OFF THE EAST COAST WILL MAINTAIN A SOUTHWESTERLY FLOW OVER THE REGION THROUGH TUESDAY. A COLD FRONT IS THEN EXPECTED TO MOVE ACROSS THE AREA LATE TUESDAY AND EARLY WEDNESDAY. HIGH PRESSURE WILL BUILD IN BEHIND THIS FRONT BEGINNING WEDNESDAY AFTERNOON. ANOTHER COLD FRONT COULD APPROACH FROM THE WEST FRIDAY NIGHT BEFORE STALLING TO OUR SOUTH NEXT WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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AN UPPER-LEVEL RIDGE REMAINS PARKED TO OUR SOUTH AND SOUTHEAST ALONG WITH SURFACE HIGH PRESSURE. THIS WILL MAINTAIN A RATHER WARM AND HUMID FLOW OF AIR ACROSS OUR AREA. THE DEEP SOUTHWESTERLY FLOW ON THE WESTERN PERIPHERY OF THE RIDGE FEATURES SOME ADDITIONAL SHORT WAVES. THE WATER VAPOR IMAGERY AT 10Z SHOWS A SHORT WAVE NEAR WEST VIRGINIA, WITH SOME CONVECTIVE DEVELOPMENT OUT AHEAD OF IT. THE POPS WERE ADJUSTED UPWARD SOME EARLY THIS MORNING ESPECIALLY ACROSS PORTIONS OF MARYLAND AND DELAWARE AS A CLUSTER OF SHOWERS AND EMBEDDED THUNDER IS APPROACHING FROM THE SOUTHWEST. WHILE THE ADDITIONAL SHORT WAVES ARE TENDING TO SHEAR NORTHEASTWARD WITH TIME THIS AFTERNOON, THERE SHOULD BE ENOUGH LIFT ASSOCIATED WITH THEM IN COMBINATION WITH A RATHER BUOYANT AIRMASS ALREADY IN PLACE. THE DAY SHOULD START OUT WITH A DECENT AMOUNT OF CLOUDS AT VARYING LEVELS. ANY LOWER BASES SHOULD LIFT SOME WITH HEATING AND SOME MIXING, HOWEVER OWING TO THE RATHER MOIST AND WARM ENVIRONMENT THIS WILL PROMOTE THE DEVELOPMENT OF MORE CLOUDS. IT IS NOT REAL CLEAR WHAT WILL ACTUALLY FOCUS THE CONVECTION ESPECIALLY THIS AFTERNOON, HOWEVER DIFFERENTIAL HEATING BOUNDARIES IN ADDITION TO AREAS OF LOW-LEVEL CONVERGENCE SHOULD ALLOW FOR SOME CONVECTIVE DEVELOPMENT. WHERE BREAKS IN THE CLOUDS OCCUR, ADDITIONAL HEATING WILL RESULT IN MORE INSTABILITY. THE MID LEVEL FLOW HOWEVER IS FORECAST TO BE LESS COMPARED TO YESTERDAY, AND THIS WILL TEND TO KEEP THE SHEAR AND THEREFORE STORM ORGANIZATION ON THE LOWER SIDE. DESPITE THIS, ENOUGH FOCUS COULD OCCUR TO PERHAPS GET SOME SHORT LINES OR A SMALL CLUSTER OF CONVECTION GOING THROUGH THE DAY. WHERE THIS OCCURS, IF IT DOES, CARRIES LOWER CONFIDENCE, HOWEVER PERHAPS THE FARTHER SOUTH AND EAST ONE GOES ACROSS THE CWA BASED ON THE SHEARING SHORT WAVE ENERGY. SINCE THE OVERALL COVERAGE IS A BIT UNCERTAIN, WE CARRIED CHC POPS FOR AT LEAST SCATTERED CONVECTION AND STARTED THE THUNDER MENTION MAINLY AT NOON. OVERALL, WE ARE NOT EXPECTING TODAY TO BE A WASHOUT AND CONVECTIVE COVERAGE SHOULD BE LESS THAN YESTERDAY. THE PW VALUES ARE STILL FORECAST TO BE NEAR 2 INCHES TODAY, THEREFORE LOCALIZED HEAVY RAIN FOR A BRIEF TIME SHOULD OCCUR. IF CONVECTIVE CORES CAN BE ROBUST ENOUGH AND PULSE THEN WATER LOADED DOWNDRAFTS COULD RESULT IN LOCALIZED/BRIEF GUSTY SURFACE WINDS. AS FOR HIGH TEMPERATURES, WE USED AN EVEN BLEND OF THE NAM/GFS MOS BUT THEN ADJUSTED THESE UP SOME MAINLY INLAND. THIS IS A RATHER WARM AIRMASS AND ANY ADDITIONAL HEATING CAN CAUSE HIGHER TEMPERATURES /AS WHAT WAS OBSERVED YESTERDAY FOR MANY LOCALES/.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... AS THE UPPER-LEVEL RIDGE STARTS TO SHIFT A BIT WESTWARD, THE FLOW ALOFT ACROSS THE MID ATLANTIC MAY START TO TURN FROM SOUTHWEST TO WESTERLY AHEAD OF AN AMPLIFYING UPPER-LEVEL TROUGH DIVING ACROSS THE GREAT LAKES REGION. WHILE THERE ARE SOME SHORT WAVES STILL EMBEDDED IN THIS FLOW, THE STRONGER ONES APPEAR TO HAVE SHIFTED EAST WITH PERHAPS EVEN SOME NVA OVERSPREADING THE AREA. AS A RESULT, ANY LINGERING CONVECTION SHOULD WEAKEN AND DISSIPATE DURING THE EVENING AS THE INSTABILITY WANES AND ANY APPRECIABLE FORCING EXITS THE AREA. WE SHOULD THEN THIN OUT THE CLOUDINESS, WHICH COMBINED WITH LIGHT WINDS AND A HUMID AIRMASS WILL PROBABLY RESULT IN SOME FOG. AT THIS POINT, WE ADDED PATCHY FOG TOWARD MORNING. THE WESTERN ZONES COULD HAVE SOME INCREASE IN CLOUDS LATE AS AN UPPER-LEVEL TROUGH STARTS TO APPROACH FROM THE WEST. AS FOR LOW TEMPERATURES, WE USED AN EVEN BLEND OF THE NAM/GFS MOS OVERALL ALTHOUGH SOME MINOR TWEAKS WERE THEN MADE. A WARM AND MUGGY NIGHT IS EXPECTED FOR THE AREA. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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TUESDAY...AFTER SOME PATCHY MORNING FOG...SKIES SHOULD BECOME PARTLY TO MOSTLY SUNNY WITH HIGHS IN THE UPPER 80S AND LOW 90S, AND HEAT INDEX VALUES WILL BE EVEN HIGHER GIVEN DEWPOINTS ARE EXPECTED TO HOVER IN THE LOW 70S THANKS TO THE CONTINUING SOUTHWEST FLOW. CLOUDINESS WILL BE ON THE INCREASE LATE IN THE DAY, AS WILL BE THE POPS, AS A COLD FRONT APPROACHES FROM THE WEST. TUESDAY NIGHT...MODELS STILL INDICATE A COLD FRONT ARRIVING DURING THE EVENING HOURS, THEN CROSSING THE COASTAL WATERS BY MORNING. WHILE TEMPERATURES BEHIND THIS FRONT WON`T BE DRAMATICALLY COOLER, THE DEWPOINTS WILL BE LOWER, SO THE AIR WILL BEGIN TO FEEL MORE COMFORTABLE. THERE WILL BE A CHANCE OF SHOWERS AND STORMS AHEAD OF AND WITH THE FRONT, HOWEVER WITH A ZONAL FLOW EXPECTED IN THE MID LEVELS OF THE ATMOSPHERE, AND MODEST DRY AIR ADVECTION OCCURRING AHEAD OF THE FRONT, MOISTURE AVAILABILITY WILL BE SOMEWHAT QUESTIONABLE. WEDNESDAY THROUGH FRIDAY...HIGH PRESSURE BUILDS OVER THE REGION IN THE WAKE OF THE COLD FRONT. AS A RESULT EXPECT A FEW, NICE, SUMMER- LIKE DAYS WITH HIGHS IN THE 80S. SATURDAY THROUGH SUNDAY...THE NEXT COLD FRONT IS SET TO ARRIVE OVER THE WEEKEND. THOUGH THERE IS SOME QUESTION WITH THE CONTINUED ZONAL FLOW HOW FAR SOUTH THE FRONT WILL DIG, BOTH THE GFS AND ECMWF HAVE BEEN CONSISTENT IN SHOWING THE FRONT MOVING SOUTH OF OUR REGION THROUGH THIS PERIOD.
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&& .AVIATION /10Z MONDAY THROUGH FRIDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...LOCAL AREAS OF MVFR/IFR CEILINGS EARLY, OTHERWISE MOSTLY VFR. IT APPEARS THAT FOG EARLY WILL BE LOCALIZED. SOME SHOWERS AND THUNDERSTORMS ARE ANTICIPATED ESPECIALLY FROM MIDDAY ON, HOWEVER THESE MAY TEND TO BE SCATTERED. AS A RESULT, WE INDICATED LIGHT SHOWERS WITH NO THUNDER MENTIONED FOR NOW. THIS WILL BE REVISITED LATER THIS MORNING. LIGHT WINDS, BECOMING SOUTHWESTERLY AND INCREASING TO AROUND 10 KNOTS. TONIGHT...SOME SHOWERS AND THUNDERSTORMS TO START, HOWEVER THESE SHOULD DISSIPATE DURING THE EVENING. OTHERWISE, VFR MUCH OF THE NIGHT WITH CLOUDS TENDING TO THIN OUT. THERE SHOULD BE SOME FOG OVERNIGHT, RESULTING IN LOCAL MVFR/IFR VISIBILITIES. SOUTHWEST WINDS NEAR 5 KNOTS, BECOMING LIGHT AND VARIABLE OR EVEN CALM. OUTLOOK... TUESDAY AND TUESDAY NIGHT...CONDITIONS IMPROVING TO VFR EARLY IN THE DAY. SOME SHOWERS AND THUNDERSTORMS POSSIBLE LATE TUESDAY AFTERNOON AND TUESDAY EVENING, ALONG WITH AN ABRUPT WIND SHIFT AS A COLD FRONT MOVES THROUGH THE REGION. WEDNESDAY THROUGH FRIDAY...GENERALLY VFR CONDITIONS EXPECTED. FRIDAY NIGHT AND SATURDAY...ANOTHER COLD FRONT IS EXPECTED TO APPROACH FROM THE WEST. IFR CONDITIONS POSSIBLE.
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&& .MARINE... HIGH PRESSURE LOCATED TO OUR EAST WILL MAINTAIN A SOUTHWESTERLY FLOW OF WARM AND HUMID AIR ACROSS THE REGION THROUGH TONIGHT. WHILE THE FLOW IS FORECAST TO BE LESS TODAY COMPARED TO YESTERDAY, THE SOUTHERLY COMPONENT WILL KEEP THE SEAS UP SOME. THESE HAVE APPROACHED 5 FEET EARLY THIS MORNING TOWARD 20NM, HOWEVER OVERALL THEY ARE EXPECTED TO BE 4 FEET OR LESS. AS A RESULT, THE CONDITIONS WERE KEPT BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH TONIGHT. SOME SHOWERS AND THUNDERSTORMS WILL BE AROUND TODAY AND THIS EVENING, HOWEVER THESE MAY BE MORE EVIDENT ACROSS THE LAND AREAS. OUTLOOK... TUESDAY THROUGH SATURDAY...SEAS AND WINDS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA. SOME GUSTY WINDS WILL BE POSSIBLE IN THE VICINITY OF THUNDERSTORMS MONDAY EVENING AND TUESDAY NIGHT, AND AGAIN FRIDAY NIGHT AND SATURDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...MIKETTA NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...MIKETTA AVIATION...GORSE/MIKETTA MARINE...GORSE/MIKETTA

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