Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 261432 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1032 AM EDT TUE APR 26 2016 .SYNOPSIS... A FRONTAL BOUNDARY LOCATED TO OUR NORTH WILL SLOWLY PUSH SOUTHWARD ACROSS THE AREA TODAY AS AN AREA OF LOW PRESSURE MOVES ALONG THE BOUNDARY. THE FRONT WILL PUSH SOUTH OF THE AREA OVERNIGHT INTO WEDNESDAY MORNING AND STALL TO OUR SOUTH. ANOTHER AREA OF LOW PRESSURE WILL MOVE ALONG THIS BOUNDARY TO OUR SOUTH LATE THURSDAY INTO THURSDAY NIGHT. OUR AREA WILL REMAIN ON THE SOUTHERN EDGE OF HIGH PRESSURE CENTERED ACROSS CENTRAL CANADA OVER THE WEEKEND. AN AREA OF LOW PRESSURE AND ASSOCIATED FRONTAL BOUNDARIES MAY AFFECT THE AREA EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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13Z SURFACE ANALYSIS SHOWS A QUASI-STATIONARY FRONT ALONG THE NY- PA, ARCING E-SEWD INTO THE NRN NJ. A WEAK AREA OF LOW PRESSURE WAS NOTED ALONG THIS BOUNDARY NEAR BGM. LOOKING ALOFT, WATER VAPOR SATELLITE IMAGERY SHOWS A SHORTWAVE TROUGH ASSOCIATED WITH THE REMNANTS OF A MIDWEST MCS IS MOVING INTO E PA MID MORNING. WEAKENING TRENDS WITH REGARDS TO THE CONVECTION CONTINUE TO BE NOTED IN THE IR SATELLITE/ MOSAIC RADAR LOOP AS THIS SYSTEM MOVES EASTWARD INTO OUR AREA THIS MORNING. THESE SHOWERS WILL MOVE THRU THE SRN POCONOS AND NW NJ OVER OVER THE NEXT 1-2 HOURS. ELSEWHERE, VIRTUALLY REMOVED THE MENTION OF PRECIP FROM THE FORECAST THRU MIDDAY (THOUGH ISO SHOWERS WERE KEPT IN A FEW LOCATIONS AREAS). LEFTOVER DEBRIS CLOUDS FROM THE REMNANT MCS WILL SWEEP THRU THE AREA WHICH WILL DELAY STRONG SOLAR HEATING BY 2 OR 3 HOURS. MADE ONLY SLIGHT MODIFICATIONS TO MAX TEMPS TODAY, TRYING TO SHOW A TIGHT N-S TEMPERATURE GRADIENT ALONG THE I-80 CORRIDOR SINCE THIS IS WHERE THE FRONT HAS STALLED. WE WERE CONSERVATIVE IN MAKING UPWARD ADJUSTMENTS FOR HIGHS IN THE WARM SECTOR DUE TO THE MORNING CLOUDS BUT HIGHS IN THE MID TO UPPER 80S ARE NOT OUT OF THE QUESTION FROM PHILA SOUTHWARD IF WE CAN SEE AN EXTENDED PERIOD OF SUNSHINE DURING PEAK HEATING THIS AFTERNOON. BASED ON THE LATEST HI-RES CONVECTIVE-ALLOWING MODELS, HOURLY POPS/WX WERE UPDATED FOR THIS AFTERNOON TO BETTER TIME THE CONVECTION THAT IS EXPECTED TO DEVELOP ALONG THE FRONT AS IT PROGRESSES SWD THRU THE AREA. FORECAST SOUNDINGS FROM THE NAM 4KM, RAP AND HRRR SHOW MODEST INSTABILITY WITH ABOUT 600-1000 J/KG OF MLCAPE DEVELOPING FROM SE PA-C NJ AND POINTS SWD BY MID TO LATE AFTERNOON. FORECAST BULK SHEAR PROFILES INCREASE TO NEAR 50 KT LATE THIS AFTERNOON AS A 65 KT MID-LEVEL JET STREAK SHIFTS OVERHEAD. LARGER-SCALE LIFT DOES NOT LOOK QUITE AS FAVORABLE AS IT ONCE DID IN EARLIER MODEL RUNS WITH THE DEEPEST LIFT FROM AN APPROACHING MID-LEVEL SHORTWAVE TROUGH AND UPPER-LEVEL JET STREAK SLIGHTLY REMOVED NORTH (ACROSS FAR NORTHERN PARTS OF THE CWA) FROM WHERE THE STRONGEST DESTABILIZATION IS EXPECTED TO OCCUR THIS AFTERNOON (ACROSS THE SOUTHERN HALF OF THE CWA). NONETHELESS, THERE IS STILL ENOUGH INGREDIENTS AVAILABLE FOR AT LEAST SEVERAL SEVERE THUNDERSTORMS TO DEVELOP. THE MAIN THREAT IS DAMAGING WINDS BUT ISOLATED LARGE HAIL IS POSSIBLE. THE LATEST SPC D1 FORECAST EXPANDED THE SLIGHT RISK INTO MOST OF THE FORECAST AREA. THE GREATEST RISK FOR SEVERE STORMS APPEARS TO BE FROM ABOUT 2-5 PM IN NE PA/NW NJ, 4-7 PM IN SE PA AND S NJ, 5-9 PM IN THE DELMARVA.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... THE COLD FRONT IS EXPECTED TO EXTEND THROUGH THE PHILADELPHIA METROPOLITAN AREA AROUND 800 PM AND IT SHOULD REACH SOUTHERN DELAWARE AND ITS ADJACENT COASTAL WATERS BY MIDNIGHT. THE ARRIVAL OF THE FRONT SHOULD BRING AN END TO THE PRECIPITATION. HOWEVER, CLOUDS ARE ANTICIPATED TO LINGER THROUGH MUCH OF THE NIGHT. THE WIND SHOULD SETTLE INTO THE NORTH AND NORTHEAST BEHIND THE COLD FRONT. TEMPERATURES ARE FORECAST TO DROP INTO THE 40S AND 50S. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... THE COLD FRONT WILL BECOME STATIONARY NEAR THE NC-VA BORDER WEDNESDAY. DRIER AND COOLER AIR WILL WORKS ITS WAY INTO THE REGION AS CANADIAN HIGH PRESSURE CENTERED NEAR THE NORTHWEST PASSAGES RIDGES DOWN TOWARD US. HOWEVER, THE DRIER AIR MAY STRUGGLE TO MAKE IT INTO OUR FAR SOUTHERN ZONES, RESULTING IN CLOUDY SKIES THAT PERSIST INTO MOST OF WEDNESDAY ACROSS THE DELMARVA. LEE CYCLOGENESIS IS CURRENTLY TAKING PLACE IN THE CO FRONT RANGE OF THE ROCKIES. THIS SURFACE LOW WILL MEANDER OVER THE CENTRAL PLAINS FOR THE NEXT FEW DAYS AS THE UPPER TROUGH TIED TO THE SURFACE LOW REMAINS CUTS OFF. THE CUTOFF LOW IS FORECAST TO EVENTUALLY WEAKEN AND BECOME AN OPEN WAVE BY THURSDAY. IN RESPONSE TO THE EVOLVING UPPER PATTERN, THE SURFACE LOW WILL PROGRESS EASTWARD ALONG THE STATIONARY BOUNDARY TO OUR SOUTH ON THURSDAY. A SECONDARY WAVE OF LOW PRESSURE MAY DEVELOP AND RIDE THE FRONT ON FRIDAY. OVERRUNNING PRECIP SHOULD EXPAND NORTHWARD LATE WEDNESDAY NIGHT INTO THURSDAY AS THE FLOW BACKS MORE OUT OF THE SOUTH AHEAD OF THE LOW AND ISENTROPIC LIFT STRENGTHENS ALONG AND ON THE COOL SIDE OF THE BOUNDARY. THERE IS STILL UNCERTAINTY REGARDING HOW FAR NORTH THE FRONT AND PRECIP ADVANCES WITH DRIER AIR BEING REINFORCED BY HIGH PRESSURE ANCHORED TO OUR NORTH. THERE IS SOME EVIDENCE FROM GUIDANCE THAT EVAPORATIVE COOLING AT THE ONSET COULD LEAD TO A COLD AIR DAMMING PATTERN IF THERE IS ENOUGH LOW-LEVEL DRY AIR IN PLACE WHEN THE OVERRUNNING PRECIP MOVES IN. THIS WOULD KEEP THE FORECAST AREA ON THE COLD SIDE OF THE BOUNDARY. WE WILL CONTINUE TO SHOW THE HIGHEST POPS ACROSS OUR SOUTHERN AREAS DUE TO THE PROXIMITY OF THE FRONT. THERE COULD CONTINUE TO BE SOME SHOWERS DURING THE DAY FRIDAY AS A SHORT WAVE PUSHES ACROSS THE AREA AND THE FRONT CONTINUES TO PUSH FURTHER TO OUR SOUTH. SATURDAY LOOKS DRY AS HIGH PRESSURE BRIEFLY BUILDS BACK INTO THE MID ATLANTIC. SHOWERS MAY RETURN SUNDAY INTO MONDAY AS YET ANOTHER WAVE OF LOW PRESSURE IS EXPECTED TO ORGANIZE OVER THE GREAT PLAINS AND TRACK EASTWARD ALONG THE STATIONARY FRONT. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR THRU AT LEAST 18Z FOR THE TERMINALS. THE WIND ARE STILL RATHER LIGHT SO FAR MORNING FROM PHL NORTHWARD. FARTHER SOUTH IN THE WARM SECTOR, SW WINDS ARE GUSTING 20-25 KT. EXPECT WIND GUSTS OF SIMILAR MAGNITUDE TO DEVELOP FARTHER NORTH LATE THIS MORNING AND EARLY AFTERNOON. THE AFTERNOON IS EXPECTED TO BEGIN WITH VFR CONDITIONS ALONG WITH A CONTINUATION OF THE GUSTY WEST SOUTHWEST WIND. HOWEVER, A COLD FRONT APPROACHING FROM THE NORTH SHOULD BRING SHOWERS AND THUNDERSTORMS. THE THUNDERSTORMS WILL BE ACCOMPANIED BY BRIEFLY MODERATE TO HEAVY RAINFALL, LOW CEILING AND VISIBILITY VALUES, AND PERHAPS WIND GUSTS IN EXCESS OF 35 KNOTS. THE FRONT IS ANTICIPATED TO PASS THROUGH KABE, KRDG AND KTTN BETWEEN ABOUT 2200 AND 2300Z BRINGING AND END TO THE POTENTIAL FOR SHOWERS AND THUNDERSTORMS. THE FRONT IS EXPECTED TO ARRIVE AT KPNE AND KPHL AROUND 0000Z, AND AT KILG, KACY AND KMIV ABOUT 0100Z. THE WIND IS FORECAST TO SHIFT TO THE NORTHWEST, THEN TO THE NORTH AND NORTHEAST AND SPEEDS SHOULD DECREASE TO AROUND 8 TO 12 KNOTS. OUTLOOK... WEDNESDAY...MVFR CIGS POSSIBLE FOR THE SOUTHERN TWO-THIRDS OF THE AREA, WITH VFR POSSIBLE NORTHERN AREAS. WEDNESDAY NIGHT...VFR EXPECTED. THURSDAY-THURSDAY NIGHT...VFR EARLY, BECOMING MVFR OR IFR LATE IN THE DAY AND OVERNIGHT WITH RAIN POSSIBLE. FRIDAY-FRIDAY NIGHT...MVFR CIGS POSSIBLE WITH SCATTERED SHOWERS. SATURDAY...VFR CIGS, WITH PERIODS OF MVFR POSSIBLE.
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&& .MARINE... THE SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR OUR OCEAN WATERS FOR TODAY AND TONIGHT. THE ADVISORY IS MAINLY IN EFFECT FOR WAVE HEIGHTS AROUND 5 FEET. HOWEVER, LOCALIZED GUSTS NEAR 25 KNOTS ARE POSSIBLE. A SMALL CRAFT ADVISORY HAS BEEN ISSUED FOR DELAWARE BAY AND IT IS IN EFFECT UNTIL 600 PM. THE WIND DIRECTION IS FORECAST TO FAVOR THE SOUTHWEST FOR TODAY. A COLD FRONT FROM THE NORTH WILL DROP THROUGH THE REGION THIS EVENING AND THE WIND DIRECTION IS EXPECTED TO SHIFT TO THE NORTHWEST TO NORTHEAST QUADRANT. OUTLOOK... WEDNESDAY-SATURDAY...SUB-SMALL CRAFT ADVISORY CONDITIONS EXPECTED TO CONTINUE. WINDS COULD PERIODICALLY GUST AROUND 20 KNOTS, ESPECIALLY THURSDAY AND THURSDAY NIGHT WHEN GUSTS COULD APPROACH ADVISORY LEVELS. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR ANZ450>455. SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ430- 431. && $$ SYNOPSIS...ROBERTSON NEAR TERM...KLEIN SHORT TERM...IOVINO LONG TERM...KLEIN/ROBERTSON AVIATION...IOVINO/KLEIN/ROBERTSON MARINE...IOVINO/ROBERTSON

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