Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 231540 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1140 AM EDT WED JUL 23 2014 .SYNOPSIS... A COLD FRONT WILL APPROACH OUR AREA FROM THE NORTHWEST TODAY AND CROSS THE REGION TONIGHT INTO THURSDAY MORNING. HIGH PRESSURE WILL BUILD IN BEHIND THE DEPARTING FRONT FOR THE END OF THE WEEK INTO THE FIRST PART OF THE WEEKEND. A COMPLEX SYSTEM WILL THEN AFFECT THE REGION FOR SUNDAY INTO MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AN UPPER-LEVEL TROUGH AMPLIFYING INTO THE NORTHEAST WILL RESULT IN GRADUAL HEIGHT FALLS THIS AFTERNOON. THIS IS MOST NOTED HOWEVER TO OUR NORTH AND NORTHWEST ALONG WITH A STRENGTHENING FLOW. THIS FEATURE WILL ALSO DRIVE A COLD FRONT TOWARD OUR AREA FROM THE NORTHWEST. A VERY WARM/HOT AND HUMID AIRMASS IS IN PLACE WITH DEW POINTS AROUND 70 DEGREES. IT WILL BE COOLER ALONG THE IMMEDIATE SHORE THOUGH GIVEN A SOUTHERLY WIND. BASED ON SOME DRIER AIR FROM ALOFT BEING MIXED TO THE SURFACE WITH AMPLE HEATING THE DEW POINTS SHOULD LOWER A LITTLE, AND THEREFORE THE HEAT INDEX DURING PEAK HEATING SHOULD TOP OUT IN THE UPPER 90S IN THE WILMINGTON TO PHILADELPHIA TO TRENTON METROS. THEREFORE, NO HEAT ADVISORY ISSUED ATTM. THE AFOREMENTIONED AMPLIFYING UPPER-LEVEL TROUGH AND ARRIVING COLD FRONT WILL TRIGGER SHOWERS AND THUNDERSTORMS TO OUR WEST. A FEW ISOLATED CELLS CANNOT BE RULED OUT MAINLY WELL INLAND THIS AFTERNOON WITH THE HOT AIRMASS, AS A LEE SIDE TROUGH IS PRESENT FROM ABOUT CENTRAL PENNSYLVANIA SOUTHWARD. MOST OF OUR CONVECTION HOWEVER LOOKS TO WAIT FOR THE COLD FRONT TO ARRIVE LATER THIS AFTERNOON AND THIS EVENING. THE 12Z STERLING, VA RAOB SHOWED A CAP BETWEEN 700 MB AND 600 MB. THE SEVERE WEATHER THREAT LOOKS RATHER LOW /NOT ZERO/ THIS AFTERNOON GIVEN A LACK OF BULK SHEAR /500 MB WINDS LESS THAN 30 KNOTS/ DESPITE PLENTY OF INSTABILITY. AS A RESULT, ANY STORM ORGANIZATION SHOULD BE HELD TO NEAR AND ALONG THE COLD FRONT AND/OR THE LEE SIDE TROUGH. AN ISOLATED DOWNBURST DAMAGING WIND GUST /DRY AIR ALOFT/ CANNOT BE RULED OUT HOWEVER ACROSS THE FAR WESTERN ZONES LATE THIS AFTERNOON IF CONVECTION FIRES GIVEN THE HOT AIRMASS IN PLACE. SOME TWEAKS TO THE POPS WERE MADE, BUT NOTHING SIGNIFICANT ATTM. WE DID SHAVE BACK THE ENHANCED WORDING SOME ESPECIALLY WITH THE LOW POPS. THE HOURLY GRIDS WERE TWEAKED BASED ON THE LATEST OBSERVATIONS, AND THE LAMP/LAV GUIDANCE WAS BLENDED IN TO HELP ASSIST WITH TRENDS. OVERALL, NO MAJOR CHANGES MADE ATTM TO THE HIGH TEMPERATURES. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... SLOW SEWD PROGRESS OF THE COLD FRONT INTO THE UNSTABLE AIRMASS SHOULD YIELD BANDS OF TSTMS INTO THE NIGHT BUT NOT NECESSARILY WIDESPREAD. ONE OR 2 TSTMS COULD BE SVR BUT BULK SHEAR FOR SVR IS MARGINAL AT WORST AND ONLY THE TT AND SOME CAPE ALLOW FOR MODEST ISOLATED SVR POTENTIAL. PWAT 1.8 INCHES OFFERS A CHANCE OF NARROW PATHS OF 2 INCH RAINS BENEATH THE BIGGEST STORMS. LIGHTNING STRIKES MIGHT BE THE BIG PROBLEM? FCST BASIS; 50 50 BLEND OF THE 00Z/23 GFS/NAM GUIDANCE IN THIS 330 AM ISSUANCE EXCEPT MOSTLY NAM METMOS TEMPS. && .LONG TERM /THURSDAY THROUGH TUESDAY/... THE CDFNT WILL BE EXITING THE AREA ERLY THU, BUT LINGERING SHWRS AND TSTMS ARE STILL EXPECTED WITH ANY INSTABILITY STILL AROUND. THE BEST CHCS ARE ERLY. THEN, HIGH PRESSURE WILL BUILD IN FROM THE W AND DOMINATE THE WX PATN THRU THE ERLY PART OF THE WEEKEND. DRY WX IS THEN EXPECTED THRU SAT. AS THE HIGH SLOWLY MOVES EWD, THE FLOW WILL BECOME MORE SLY AND SWLY AND EXPECT A RISE IN TEMPS AND HUMIDITY BY THE WEEKEND. THEN, BY SUN, AN AREA OF LOW PRESSURE NR THE GRTLKS WILL BE MOVG EWD. WHILE ITS EXACT TRACK IS STILL A MATTER OF DEBATE BTWN THE MDLS, THEY DO AGREE THAT THERE WILL BE SOME KIND OF DOUBLE BARRELED-LOW STRUCTURE BY SUN NIGHT. THERE COULD BE A WK CFP WITH THE FIRST LOW SUN NIGHT OR MON, THE MAIN CFP WILL BE MON NIGHT OR TUE WITH THE SECOND LOW. AGAIN, THE DETAILS WILL STILL NEED TO BE RESOLVED AT THIS TIME SCALE, BUT THE SUN INTO MON TIME FRAME COULD BE STORMY DEPENDING ON HOW THINGS ULTIMATELY PLAY OUT. HIGH PRES WILL BUILD IN BEHIND THIS DEPARTING CDFNT FOR TUE. TEMPS LOOK TO BE AT OR SLIGHTLY ABOVE NRML THRU THE PD, UNTIL THE CFP ON TUE WHEN TEMPS WILL BE BELOW NRML. EXPECT COMFORTABLE HUMIDITY ERLY IN THE PD, THEN INCREASING HUMIDITY IN ADVANCE OF THE CFP ERLY NEXT WEEK. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THIS AFTERNOON...VFR WITH CLOUD BASES AROUND 5000 FEET. SOME THUNDERSTORMS ARE EXPECTED TO DEVELOP WEST OF KABE AND KRDG THIS AFTERNOON, HOWEVER PROBABLY NOT ARRIVING AT THESE TERMINALS UNTIL AFTER 21Z. THERE IS THE POTENTIAL FOR SOME BRIEF GUSTY WEST WINDS WITH THE THUNDERSTORMS. SOUTHWESTERLY SURFACE WINDS MAINLY 10-15 KNOTS. TONIGHT...VFR CEILINGS. A BAND OF SHOWERS AND THUNDERSTORMS MOVING THROUGH THE AREA IN THE EVENING, BEFORE WEAKENING TOWARD THE COAST. A TIME OF MVFR/IFR CONDITIONS SHOULD ACCOMPANY THIS ACTIVITY, ESPECIALLY THE VISIBILITIES. SOUTHWEST WINDS AROUND 5 KNOTS, SHIFTING TO THE NORTH-NORTHWEST LATE. GUSTY WESTERLY SURFACE WINDS IN A THUNDERSTORM ARE POSSIBLE IN THE EVENING. THURSDAY...VFR CEILINGS SHOULD THIN OUT FROM NORTHWEST TO SOUTHEAST THROUGH THE DAY. HOWEVER, SOME MVFR/IFR CONDITIONS MAY LINGER WITH A FEW SHOWERS OR A THUNDERSTORM THROUGH EARLY AFTERNOON ESPECIALLY FROM NEAR THE KPHL METRO ON SOUTH AND EAST. LOCALIZED MVFR FOG POSSIBLE EARLY. NORTH-NORTHWEST WINDS AROUND 10 KNOTS. OUTLOOK... THU NIGHT THROUGH SAT...MAINLY VFR UNDER HIGH PRESSURE. HIGH CONFIDENCE. SUN...SUB-VFR POSSIBLE IN SCATTERED SHOWERS AND THUNDERSTORMS. MODERATE CONFIDENCE. && .MARINE... NO HEADLINES THROUGH TONIGHT. MAINLY S-SW WIND G UNDER 20 KT SHIFT TO NORTH TOWARD DAWN THURSDAY. WAVE HEIGHTS ON OUR OCEAN WATERS SHOULD BE 2 TO 4 FEET. WAVES ON DELAWARE BAY ARE EXPECTED TO BE 2 FEET OR LESS. SCATTERED THUNDERSTORMS TONIGHT. OUTLOOK... THU THROUGH SAT...NO MARINE HEADLINE EXPECTED WITH HIGH PRES OVERHEAD. SUN...INCREASING SEAS AHEAD OF NEXT SYS MAY YIELD SCA, ESPECIALLY N BY LATER IN THE DAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...NIERENBERG NEAR TERM...GORSE SHORT TERM...DRAG LONG TERM...NIERENBERG AVIATION...GORSE/NIERENBERG MARINE...DRAG/NIERENBERG

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