Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 271934 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 334 PM EDT SUN JUL 27 2014 .SYNOPSIS... AN AREA OF LOW PRESSURE WILL MOVE OUT OF PENNSYLVANIA TONIGHT AND LIFT INTO NEW ENGLAND MONDAY, PULLING A COLD FRONT ACROSS THE AREA. HIGH PRESSURE WILL BEGIN MOVING INTO THE AREA LATER TUESDAY, AND REMAIN IN CONTROL OF THE WEATHER FOR THROUGH THE END OF THE UPCOMING WEEK. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... THE GFS INITIALIZATION CONTINUES TO LOOK SLIGHTLY BETTER AT 500MB BUT ITS CONVECTIVE FEEDBACK OF VORT MAXES WHILE ON ONE LEVEL CORRECT CONTINUE TO MAKE IT DIFFICULT TO FOLLOW THE MODEL. NEAR AND SHORT TERM SOLUTION ARE AN ECMWF/HI RES ARW BLEND AS THE FORMER HAS VERIFIED THE SYNOPTIC SCALE SHORT WAVES BETTER AND THE LATTER WAS USED FOR CONVECTIVE ADJUSTMENTS AS ITS VERIFYING WELL AT 18Z. COSPA VERIFYING TOO SLOW WITH CONVECTION LEAVING OHIO AND TOO NORTH WITH WV CONVECTION. IT...RAP AND HRRR ALL DEVELOP CONVECTION OVER THE ALLEGHENIES AND ADVECT IT EAST AHEAD OF ONGOING CONVECTION OVER OH/PA BORDER ASSOCIATED WITH THE STRONG SHORT WAVE. SPC ANALYSIS IS SHOWING 2000J ML CAPE IN THAT AREA AND THE STABILITY OF WAVE CLOUDS ON VIS SATL OVER THAT AREA IS NOW GONE. SO WE WILL CONT TO START GRIDS WITH LOW POPS THAT WILL INCREASE WITH TIME THIS EVENING. POPS ARE TIED CLOSE TO THE ARW AND ALSO THE DEEPER LAYER MASS OMEGA FIELDS BY THE MODELS. IN SPITE OF QPF TIMING DIFFERENCES, THE OMEGA FIELDS TIMING ARE CLUSTERED CLOSER. THIS REMAINS A DYNAMIC SCENARIO WITH A NEGATIVE TILT TROF AND EVEN A JET COUPLET OVER OUR CWA FOR A WHILE OVERNIGHT. EVENTUALLY THE MLCAPE WILL DECREASE, EVEN THOUGH THERE WILL BE NO END TO THE PREDICTED BULK SHEAR AVERAGING AROUND 40KTS. SO THE STRONGER (SEVERE?) POTENTIAL WITH THE THUNDER MAY LINGER LONGER INTO THE NIGHT. LAST COUPLE OF COSPAS DONT CORROBORATE THIS. FOR NOW, WE CARRIED SOME ENHANCED WORDING PAST MIDNIGHT. GIVEN THE NEGATIVE TILT FLAVOR OF THE TROF, WHILE RAIN WILL BE HEAVY, IT SHOULD BE PROGRESSIVE. WITH FFG VALUES RUNNING AT TYPICALLY HIGH SUMMER LEVELS, SEVERE THREAT REMAINS OUR MORE FOCUSED CONCERN. WE WERE SLOW WITH DROPPING TEMPS THIS EVENING AND TRIED TO TIME THE DROP TO THE ONSET OF HEAVIER RAIN. MIN TEMPS NOT THAT FAR FROM STAT GUIDANCE. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... SHORT WAVES ROTATING AROUND THE ANOMALOUS STRONG 500MB TROF WILL PASS ACROSS OUR CWA ON MONDAY. CONVECTIVE TEMPS (SELF DESTRUCT SUNSHINE) WILL BE REACHED EASY AND EARLY. THE OVERALL FCST CAPE AND INSTAB ALOFT ON THE BIG THREE MODELS ARE NOT UNSTABLE ENOUGH FOR THUNDER. OTHER THAN SOME EARLY THUNDER NORTHEAST CWA, WE KEPT IT AS SHOWERS WITH HIGHEST POPS NORTHWEST THE REST OF THE DAY. STAT GUIDANCE FOR MAX TEMPS APPEARS TOO HIGH IN THE SERN CWA UNLESS THE COLD FRONT IS 2-4HRS SLOWER THAN PROGGED. WE WERE LOWER THAN GFS MOS THERE AND CLOSE TO A STAT GUIDANCE BLEND ELSEWHERE. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... A MOSTLY DRY START TO THE LONG TERM FORECAST, WITH PRECIPITATION CHANCES INCREASING LATER IN THE WEEK INTO THE WEEKEND. THERE MAY BE SOME LINGERING SHOWERS MONDAY EVENING AS THE FRONT CONTINUES TO PUSH OFFSHORE AND THE MID-LEVEL TROUGH LIFTS OUT, BUT ANY PRECIPITATION IS EXPECTED TO END BY MIDNIGHT. MUCH OF THE UPCOMING WEEK IS EXPECTED TO REMAIN MOSTLY DRY AS PW VALUES DROP TO AN INCH OR LOWER FOR TUESDAY AND WEDNESDAY, BUT MAY RETURN TO 1-1.25 INCHES FOR THURSDAY AND NEAR 1.5 INCHES FOR FRIDAY. HIGH PRESSURE AT THE SURFACE WILL BUILD ACROSS THE REGION, WHILE THE BROAD MID/UPPER TROUGH REMAINS IN PLACE ACROSS MUCH OF THE EASTERN HALF OF THE COUNTRY. THERE AREA NO SIGNIFICANT SHORT WAVE/VORTICITY IMPULSES THAT ARE FORECAST TO MOVE THROUGH FOR MUCH OF THE WEEK, BUT WITH THE TROUGH IN PLACE AND DAYTIME HEATING, THERE COULD BE ENOUGH DAYTIME INSTABILITY TO CREATE ISOLATED SHOWERS OR THUNDERSHOWERS FOR THE LATTER HALF OF THE WEEK. EACH DAY THE CHANCES INCREASE SLIGHTLY AND EXPAND IN COVERAGE. HOWEVER, WE DO NOT HAVE MORE THAN A SLIGHT CHANCE PROBABILITY THROUGH FRIDAY AT THIS TIME. AS WE MOVE INTO NEXT WEEKEND, WE GET A MORE SOLID RETURN OF MOISTURE ACROSS THE AREA AS PW VALUES REBOUND O 1.25-1.5 INCHES. WE ALSO HAVE A BETTER CHANCE OF VORTICITY IMPULSES AFFECTING OUR AREA WITHIN THE SOUTHWEST FLOW ALOFT, AND WITH THE COASTAL FRONT TRYING TO PUSH BACK CLOSER TO SHOWER, WE MAY HAVE A FOCUS FOR PRECIPITATION TO FORM. THEREFORE THE PRECIPITATION CHANCES INCREASE INTO NEXT WEEKEND. TEMPERATURES THROUGH THE EXTENDED ARE FORECAST TO BE CLOSE TO OR SLIGHTLY BELOW NORMAL. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. 18Z TAFS HAVE A HIGH CONVECTIVE IMPACT DURING THIS EVENING INTO THE EARLY OVERNIGHT ACROSS THE TERMINALS AND AIRPORTS. REST OF THIS AFTERNOON. VFR WITH CUMULUS CLOUDS EXPANDING AND SOME CIRRUS ABOVE THEM SOUTH. NO THUNDER MENTIONED ALTHOUGH SOME ISOLATED THUNDER MIGHT FORM BEFORE THE ORGANIZED SYSTEM. LOWEST CONFIDENCE ABOUT NO THUNDER IN PA. PLEASE WATCH FOR POSSIBLE AMENDMENTS. WINDS ARE SLOWLY BACKING TO THE SOUTHWEST AND MAY EVEN GO SOUTH AT SPEEDS OF AROUND 10 KTS. THIS EVENING, EXPECTING A LINE OF STRONG TSTMS TO MOVE THROUGH THE AREA. HIGHEST CONFID AT KABE AND KRDG. LOWEST AT KMIV AND KACY. A EARLY TIMING HEDGE WAS MAINTAINED (MOST LIKELY TIME IS TOWARD THE MIDDLE OF THE TEMPO GROUP). MVFR TO BRIEFLY IFR (BECAUSE OF BREVITY NOT INCLUDED) CONDITIONS LIKELY ALONG WITH GUSTY WEST WINDS. OVERNIGHT PREVAILING MVFR CONDITIONS EXPECTED TO CONTINUE DURING SHOWERS. ISOLATED THUNDER POSSIBLE, BUT CONFIDENCE TOO LOW AS TO WHERE OR WHEN TO INCLUDE. WINDS WILL BE LIGHTER, GENERALLY FROM THE SOUTH. IMPROVEMENT TOWARD MORNING AS PCPN ENDS. THINKING TOO MUCH WIND FOR SGFCNT FOG TO FORM. MONDAY MORNING, VFR CONDITIONS WITH A CUMULUS BASED CIG OCCURRING. GUSTY WEST WINDS, ESPECIALLY FOR JULY, WITH SUSTAINED SPEEDS AROUND 15 KTS AND GUSTS TO AROUND 25 KTS. SOME WIDELY SCATTERED SHOWERS SHOULD START DEVELOPING TOWARD THE END OF THE CURRENT TAF FCST PERIOD. GREATEST CONFIDENCE NORTH, REASON FOR NOW LEFT OUT OF KPHL TAF. OUTLOOK... MONDAY NIGHT-WEDNESDAY NIGHT...MAINLY VFR THURSDAY-FRIDAY...MAINLY VFR. ISOLATED SHOWERS/THUNDERSTORMS POSSIBLE BOTH AFTERNOONS, ESPECIALLY FRIDAY. && .MARINE... A SMALL CRAFT ADVISORY WILL BE ISSUED FOR TONIGHT AND MONDAY FOR THE OCEAN WATERS. ONE WILL BE ISSUED FOR DELAWARE BAY FOR MONDAY. FIRST FOR THE LIKELIHOOD THAT SEAS REACH 5 FEET THIS EVENING AND THEN THE LIKELIHOOD OF NON CONVECTIVE WEST WIND GUSTS REACHING THE CRITERIA ON DELAWARE BAY AS WELL AS THE OCEAN WATERS DURING THE DAY ON MONDAY. WAVE WATCH GUIDANCE BRINGS SIX FOOT SEAS AS IS INTO OUR COASTAL WATERS, SHAVING A FOOT OR SO OFF WOULD STILL GET US THERE TONIGHT. TOUGH NIGHT AS IT IS WITH THUNDERSTORMS EXPECTED. ON MONDAY MORE OF THE GUSTINESS MAY BE CONCENTRATED AROUND THE INLETS AND IN DELAWARE BAY WITH POSSIBLY LESS GUSTINESS FARTHER OFFSHORE. THE GRADIENT AND WINDS SHOULD START RELAXING LATER IN THE DAY ON MONDAY. OUTLOOK... MONDAY NIGHT-FRIDAY...SMALL CRAFT ADVISORY CONDITIONS POSSIBLE EARLY MONDAY NIGHT, SUBSIDING AND REMAINING BELOW ADVISORY LEVELS THROUGH THE PERIOD. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...ROBERTSON NEAR TERM...GIGI SHORT TERM...GIGI LONG TERM...ROBERTSON AVIATION...GIGI/ROBERTSON MARINE...GIGI/ROBERTSON

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