Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 231902 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 302 PM 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 AM THURSDAY MORNING/...
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AN UPPER-LEVEL TROUGH WILL CONTINUE TO AMPLIFY ACROSS THE NORTHEAST AND NORTHERN MID ATLANTIC REGIONS THROUGH THIS EVENING. AS THIS OCCURS, GRADUAL HEIGHT FALLS WILL OVERSPREAD OUR REGION AND A COLD FRONT WILL ARRIVE. THE MOST NOTED HEIGHT FALLS AND STRENGTHENING CYCLONIC MID TO UPPER-LEVEL FLOW IS FOCUSED MORE TO OUR NORTH AND SOME OF THIS EVEN LAGS BEHIND THE COLD FRONT. DESPITE THIS, AMPLE INSTABILITY DUE TO A VERY WARM/HOT AND HUMID AIRMASS IS IN PLACE AND SOME CONVECTION WILL CONTINUE TO DEVELOP FROM THE WEST. SOME SPOTS THIS AFTERNOON WILL HAVE A HEAT INDEX VERY NEAR 100 DEGREES. THE INITIAL CONVECTION APPEARS TO BE TIED MAINLY TO NEAR A LEE SIDE TROUGH AND ALSO TERRAIN INFLUENCE, AND WILL BE SLOW MOVING GIVEN THE INITIAL WEAKER WIND FIELDS. AS THE COLD FRONT ARRIVES, ADDITIONAL SHOWERS AND THUNDERSTORMS ARE EXPECTED TO ARRIVE FROM THE WEST. IT APPEARS THAT ANY ORGANIZED CONVECTION IS MORE TIED TO THE COLD FRONT AND/OR THE LEE SIDE TROUGH THROUGH THIS EVENING. THIS IS WHEN ANY ORGANIZED CONVECTION SHOULD OCCUR, WITH THE GREATER CHC ACROSS OUR WESTERN ZONES. THERE SHOULD BE AT LEAST A BROKEN BAND OF CONVECTION PROPAGATING EASTWARD ACROSS THE CWA THROUGH THIS EVENING, ALTHOUGH IT MAY TEND TO WEAKEN TOWARD THE COAST AS IT ENCOUNTERS SOME LOWER INSTABILITY BEYOND SUNSET. GIVEN STEEP LOW-LEVEL LAPSE RATES PRIOR TO THE ONSET OF BOUNDARY LAYER COOLING, A LOCALIZED DOWNBURST DAMAGING WIND GUST COULD OCCUR GIVEN THE INSTABILITY AND SOME DRIER AIR ALOFT. THE SEVERE WEATHER THREAT STILL LOOKS RATHER LOW GIVEN WEAK SHEAR FOR STORM ORGANIZATION, HOWEVER ISOLATED SEVERE WEATHER IS POSSIBLE. THE CONVECTION WILL ALSO BE CAPABLE OF PRODUCING VERY HEAVY RAIN AND FREQUENT LIGHTNING GIVEN THE MOIST LOWER LEVEL ENVIRONMENT IN PLACE. WE CONTINUED WITH LOW LIKELY POPS FROM WEST TO EAST, ALTHOUGH THESE FADE TO CHC POPS TOWARD THE COAST AND SOUTHERN AREAS ASSUMING THE CONVECTION WEAKENS AT LEAST SOME. WE ALSO CONTINUED SOME ENHANCED WORDING /NON-SEVERE/ FOR THE AREAS ESPECIALLY WITH THE LIKELY POPS THROUGH THIS EVENING. ONCE THE CONVECTION WEAKENS WITH AN EASTWARD EXTENT, SOME SHOWERS OR A THUNDERSTORM MAY CONTINUE THROUGH THE NIGHT ESPECIALLY FARTHER EAST AS THE FRONT GRADUALLY SHIFTS EASTWARD AND ENOUGH INSTABILITY IS FORECAST TO HANG ON. AS FOR LOW TEMPERATURES, WE USED AN EVEN BLEND OF THE NAM/GFS MOS WITH SOME TWEAKS. IT WILL BE A WARM AND HUMID NIGHT, AND SOME LOCAL FOG IS POSSIBLE ESPECIALLY WHERE IT RAINS A DECENT AMOUNT AND IF SOME CLEARING IS ABLE TO OCCUR. OVERALL, THIS DOES NOT APPEAR TO BE WIDESPREAD THEREFORE IT WAS NOT INCLUDED ATTM.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
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AN UPPER-LEVEL TROUGH WILL BE ACROSS THE NORTHEAST, HOWEVER ITS AXIS IS FORECAST TO HANG BACK TO THE WEST UNTIL LATE IN THE DAY. THIS MAY ALLOW THE COLD FRONT TO SLOWLY CLEAR OUR EASTERN AND SOUTHERN ZONES. THE COMBINATION OF THE COLD FRONT, INSTABILITY AND ENOUGH FORCING SHOULD SUSTAIN OR ALLOW FOR THE REDEVELOPMENT OF SOME SHOWERS AND THUNDERSTORMS. THIS LOOKS PRIMARILY FOCUSED ACROSS THE EASTERN AND SOUTHERN PORTIONS OF THE CWA. THE NORTHWESTERN AREAS SHOULD SEE A DRYING TREND, WITH EVEN A DROP IN THE DEW POINTS THROUGH THE DAY. THE CLOUD COVER COULD BE PROBLEMATIC AS CONVECTION ALONG WITH THE SOUTHWESTERLY FLOW ALOFT COULD MAINTAIN MID TO HIGH CLOUDS ACROSS A GOOD PART OF THE AREA FOR AWHILE. OVERALL, ANY SHOWERS AND STORMS CAN PRODUCE LOCALLY HEAVY RAIN GIVEN THE HIGH PW VALUES BEING SQUEEZED TO THE SOUTH AND EAST. AS OF NOW WHILE A GUSTY THUNDERSTORM CANNOT BE RULED OUT, SEVERE THUNDERSTORMS ARE NOT ANTICIPATED DUE TO WEAKER MID LEVEL LAPSE RATES AND LOW-LEVEL FLOW. WE CONFINED THE HIGHEST POPS /CHC/ SOUTH AND EAST OF INTERSTATE 95, WITH THESE LOWERING WITH TIME THROUGH THE AFTERNOON. HIGH TEMPERATURES WERE BASED ON AN EVEN BLEND OF THE NAM/GFS MOS, THEN SOME TWEAKS WERE MADE BASED ON THE IDEA OF MORE CLOUDS ACROSS THE SOUTHERN AREAS.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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HIGH PRESSURE BUILDS IN FROM THE W AND DOMINATES 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.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF THIS AFTERNOON...VFR WITH CLOUD BASES AROUND 5000 FEET. SOME THUNDERSTORMS NORTH AND WEST OF KABE AND KRDG SHOULD ORGANIZE SOME WITH A BROKEN LINE ARRIVING AT THESE TERMINALS AROUND 22Z, THEN CONTINUE EASTWARD THEREAFTER. THERE IS THE POTENTIAL FOR SOME BRIEF GUSTY WEST WINDS AND VERY HEAVY RAIN WITH THE THUNDERSTORMS. SOUTHWESTERLY SURFACE WINDS MAINLY AROUND 10 KNOTS. TONIGHT...VFR CEILINGS OVERALL. A BROKEN 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 WITH A THUNDERSTORM ARE POSSIBLE IN THE EVENING. LOCALIZED MVFR FOG IS POSSIBLE LATE. 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 MID 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.
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&& .MARINE...
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NO HEADLINES ANTICIPATED THROUGH THURSDAY. A COLD FRONT WILL APPROACH FROM THE WEST THROUGH THIS EVENING, THEN GRADUALLY SETTLE SOUTH AND EAST OF THE AREA OVERNIGHT AND THURSDAY MORNING. A SOUTHERLY FLOW WILL BE MAINTAINED AHEAD OF THE FRONT, WITH SOME ENHANCEMENT NEARSHORE INTO THIS EVENING DUE TO A SEA BREEZE. THE WINDS WILL THEN SHIFT TO THE NORTHWEST AND NORTH OVERNIGHT AND THURSDAY BEHIND THE FRONT, AS DRIER AIR GRADUALLY SEEPS SOUTHEASTWARD. THE FLOW OVERALL IS FORECAST TO BE WEAK ENOUGH TO KEEP WINDS BELOW ADVISORY CRITERIA. HOWEVER, A FEW GUSTY THUNDERSTORMS ARE POSSIBLE THIS EVENING FOR ALL THE ZONES AND THEN MAINLY THE SOUTHERN ZONES THURSDAY. OUTLOOK... THU NIGHT 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.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...NIERENBERG NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...NIERENBERG AVIATION...GORSE/NIERENBERG MARINE...GORSE/NIERENBERG

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