Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 301430 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1030 AM EDT TUE JUN 30 2015 .SYNOPSIS... A WARM FRONT OVER THE OHIO VALLEY IS PREDICTED TO LIFT SLOWLY NORTHEAST INTO AND THROUGH THE FORECAST AREA TONIGHT. IT WILL BE FOLLOWED BY A SLOW MOVING COLD FRONT LATE WEDNESDAY OR THURSDAY. THAT FRONT IS EXPECTED TO STALL JUST SOUTH OF OUR REGION FOR THE REMAINDER OF THE WORK WEEK. ANOTHER COLD FRONT SHOULD PASS THROUGH OUR REGION ON INDEPENDENCE DAY. A WEAK HIGH PRESSURE SYSTEM SHOULD FOLLOW ON SUNDAY AND MOVE OFFSHORE AS A WARM FRONT APPROACHES FROM THE OHIO VALLEY ON MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... LATEST RADAR TRENDS INDICATE -SHRA WITH AN OCCASIONAL RUMBLE OF THUNDER MOVING THRU THE POCONOS AND LEHIGH VALLEY AS ISENTROPIC LIFT AND ELEVATED INSTABILITY PRECEDE A WARM FRONT INVOF DE BAY ATTM. AS MID-LEVEL FLOW BECOMES MORE MERIDIONAL IN RESPONSE TO S/WV TROUGH APPROACHING FROM THE WEST...THE WM FRONT WILL MAKE SLOW PROGRESS NORTH THRU THE DAY. THE MAIN CONCERN FOR TODAY`S FORECAST IS THE POTENTIAL FOR CONVECTION. THERE IS STILL A LOT OF UNCERTAINTY WITH REGARD TO CONVECTIVE POTENTIAL. APPROACHING S/WV WILL PROVIDE A SOURCE OF LIFT...AS BEST FORCING OCCURS NEAR THE WARM FRONTAL BOUNDARY. AMPLE LOW- LEVEL MOISTURE IS IN PLACE...AS DRIER MID-LEVEL AIR ADVECTS IN ALOFT. THE MAIN UNCERTAINTY IS INSTABILITY...AS LAPSE RATES ARE LESS THAN IDEAL...WITH PERHAPS EVEN SOME CAPPING. SAT TRENDS ALSO INDICATE CONSIDERABLE CLOUDINESS. THEREFORE ML CAPE MAY HAVE A TOUGH TIME REACHING 1 KJ. ALTHOUGH INSTABILITY IS LIMITED...BULK SHEAR IS 40 KNOTS NW OF I-95 ALONG W/ AMPLE LOW-LEVEL HELICITY...AS 0-1 KM SHEAR REACHES 20 KNOTS. SO THERE IS SVR POTENTIAL TODAY MAINLY NW OF I-95...ESP THE POCONOS AND LEHIGH VALLEY...W/ THE MAIN THREAT BEING DAMAGING WINDS AND SMALL HAIL GIVEN INVERTED-V PROFILES AND FAVORABLE WBZ HEIGHTS. WILL ALSO HAVE TO WATCH ACTIVITY NEAR THE WARM FRONT... WHERE A SUPERCELL CANNOT BE RULED OUT...PARTICULARLY IF GREATER INSTABILITY IS REALIZED. FLASH FLOODING IS ALSO A CONCERN MAINLY NW OF I-95...WHERE CELLS WILL HAVE A TENDANCY TO TRAIN. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... A CHANCE OF SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE THROUGH TONIGHT AS THE WARM FRONT TO OUR SOUTH LIFTS ACROSS THE AREA AND ADDITIONAL SHORT WAVES/VORTICITY IMPULSES MOVE ACROSS THE AREA. IT IS POSSIBLE THAT THERE COULD BE A BREAK IN SHOWER ACTIVITY FOR SOME AREAS DURING A PORTION OF THE OVERNIGHT IN BETWEEN SHORT WAVES. HOWEVER, WE EXPECT ACTIVITY TO INCREASE AGAIN TOWARD THE VERY EARLY MORNING HOURS WEDNESDAY. THERE REMAINS SOME INSTABILITY THROUGH THE NIGHT AND BULK SHEAR MAY ACTUALLY INCREASE OVERNIGHT, SO THERE REMAINS THE POTENTIAL FOR SOME STRONG STORMS. LOWS TONIGHT ARE A BLEND OF MAV/MET MOS AND MOSGUIDE. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... THERE WAS ABOUT A 50/50 SPLIT BETWEEN THE GFS AND WRF-NMMB INITIALIZATION AT 500MB. FARTHER DOWNWARD, THE WRF-NMMB LOOKED BETTER. DP/DTING THE WESTERN CONUS RIDGE LOOKS STRONGER, WHILE THE ERN NOAM TROF IS BROADER. WHILE THE MODELS AGREE ON A CONTINUATION OF THIS OVERALL SYNOPTIC PATTERN, THEY VARY ON DETAILS AND CONTINUE TO FIND THEMSELVES IN ODD POSITIONS WITH THE NORMALLY SLOWER ECMWF AND WRF-NMMB CONSIDERABLY FASTER THAN THE OTHER MEDIUM RANGE MODELS. AS PER PMDHMD WE ARE LEANING AWAY FROM THESE FASTER RESULTS AND GOING MORE TOWARD CONTINUITY. REGARDLESS WITH THE CURRENT PATTERN REMAINING IN PLACE IT IS TOUGH TO CONFIDENTLY PREDICT MUCH PROLONGED DRY WEATHER. THE START OF THE LONG TERM DOES HAVE DECENT MODELING CONSENSUS. WHILE THE WARM FRONT SHOULD BE LIFTING NORTHEAST OF OUR CWA, SHORT WAVES INTERACTING WITH THE WARM SECTOR SHOULD RE-GENERATE MORE SHOWERS AND TSTMS RATHER QUICKLY ON WEDNESDAY MORNING. COLD POCKET ALOFT COUPLED WITH NEAR NEUTRAL LOWER LEVEL THERMAL FIELDS KEEP PREDICTED TOTAL TOTALS AT OR AROUND 50C. APPROPRIATELY MIXED LAYER CAPES (ABOVE 1000J IN DELMARVA) PEAK DURING THE MORNING AND DECREASE AS THE AFTERNOON PROGRESSES AS THE COLD POCKET GETS SHEARED. HIGHEST POPS ARE IN THE MORNING WITH A TRAIL OFF AS THE DAY CONTINUES. STRONGER SHEAR AND CAPE ARE DECOUPLED AND (CAPE) MAY NOT RAMP UP FAST ENOUGH GIVEN TIMING OF FEATURES FOR SEVERE WHICH LOOKS BETTER NORTHEAST OF OUR CWA. AIR MASS SUPPORTIVE OF MID TO UPPER 80S FOR MAX TEMPS MOST OF OUR CWA. GIVEN THE BRIEF FLATTENING OF THE TROF ALOFT, WE DID NOT CARRY MUCH OF A CHANCE OF THUNDER INTO THE NIGHT AND NO POPS ANYWHERE OVERNIGHT. STAT GUIDANCE MINS LOOK REASONABLE. ON THURSDAY THE FRONTAL BOUNDARY IS EXPECTED TO STALL JUST SOUTH OF OUR CWA. FROM HERE THE TIMING OF IMPULSES ON THE FRONT START TO DIVERGE. REGARDLESS, THE BOUNDARY IS CLOSE ENOUGH TO ACT AS A TRIGGER WITH HIGHER CONFIDENCE (THUS HIGHER POPS) IN THE SOUTHEASTERN PART OF UR CWA. MIXED LAYER CAPES IN DELMARVA REACH THE LOWER 1000S, BUT ARE RELATIVELY LOW FARTHER TO THE NORTHWEST. THUNDER CHANCES MAY BE OVERSTATED. THERMAL FIELDS SUGGEST A 2-3F DROP OFF IN MAX TEMPS FROM WED. NOW THE MODELS REALLY START DIVERGING FOR THURSDAY NIGHT AND FRIDAY WITH THE GFS AND CAN GGEM EMPHASIZING FRIDAY WITH THE ECMWF AND WRF THURSDAY NIGHT. WHERE MODELS AGREE IS THAT INSTABILITY IN OUR CWA IS MODEST AND THERE ARE HIGHER CHANCES SOUTH THAN NORTH. TIMING RESOLUTION IS TOO UNCERTAIN TO FORECAST DRY WEATHER FOR EITHER PERIOD. WE DID STEER HIGHER POPS INTO THURSDAY NIGHT AS THE GEFS IS SLIGHTLY FASTER THAN THE OP GFS. IT DOES NOT BECOME MUCH CLEARER FOR INDEPENDENCE DAY WITH THE ECMWF FORECASTING A DRY DAY AND THE CAN GGEM HAVING A TOTAL WASHOUT. MOST MODELS ARE NOT INDICATING A SFC LOW ON THE LEVEL OF LAST SATURDAY, SO FOR NOW WE KEPT THE FORECAST FOR INDEPENDENCE DAY CLOSE TO CONTINUITY AND SUMMER CLIMO AND NOT SOUND LIKE A TOTAL LOSS. SUNDAY/MONDAY REMAIN CLOSE TO CONTINUITY. WITH BOTH THE GFS AND EC DRY WE HAVE SUNDAY PREDICTED TO BE THE BETTER OF THE TWO WEEKEND DAYS AND KEPT THE CHANCE FOR THUNDERSTORMS IN FOR MONDAY AS THE WARM FRONT IS PREDICTED TO RETURN. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. GENERAL VFR CONDITIONS WILL PERSIST ACROSS THE TAF SITES TODAY, ALTHOUGH CLOUD COVER WILL CONTINUE TO INCREASE AND LOWER THROUGH THE DAY. SHOWERS WILL BE ON THE INCREASE THROUGH THE MORNING AND INTO THE AFTERNOON. WITH INSTABILITY INCREASING TODAY, THERE WILL BE A CHANCE OF THUNDERSTORMS. ANY SHOWERS OR THUNDERSTORMS HAVE THE POTENTIAL TO TEMPORARILY REDUCE VSBYS AND/OR CIGS. WINDS WILL GENERALLY BE SOUTH TO SOUTHEAST, AND COULD GUST AROUND 15-20 KNOTS LATER THIS MORNING INTO THIS AFTERNOON. A CHANCE OF SHOWERS WILL CONTINUE TONIGHT, ALONG WITH THE CHANCE FOR SCATTERED THUNDERSTORMS. ANY SHOWERS OR THUNDERSTORMS HAVE THE POTENTIAL TO TEMPORARILY REDUCE VSBYS AND/OR CIGS. THERE IS A BETTER POTENTIAL FOR LOWER VSBYS OVERNIGHT AS A WARM FRONT LIFTS ACROSS THE AREA. WIND GUSTS WILL DROP OFF BY SUNSET, WITH A SOUTHERLY FLOW REMAINING THROUGH THE NIGHT. OUTLOOK... WEDNESDAY...MAINLY VFR EXCEPT MVFR OR IFR CONDITIONS WITH SCATTERED SHOWERS AND THUNDERSTORMS. WEDNESDAY NIGHT...MOSTLY VFR WITH ANY PCPN CHANCES DECREASING QUICKLY. THURSDAY THROUGH SATURDAY...PREDOMINATELY VFR, BUT SOME MVFR OR IFR CONDITIONS DURING SCATTERED SHOWERS AND THUNDERSTORMS. IMPACT OUTLOOKED TO BE GREATER FOR SOUTHERN AIRPORTS AND TERMINALS. && .MARINE... SUB-SMALL CRAFT ADVISORY CONDITIONS WILL REMAIN ACROSS THE WATERS TODAY INTO TONIGHT, ALTHOUGH WINDS MAY GUST AROUND 20 KNOTS AT TIMES. SEAS WILL REMAIN AROUND 3-4 FEET. THERE IS A CHANCE OF SHOWERS AND THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT. HIGHER WINDS AND WAVES COULD OCCUR WITH ANY SHOWERS OR THUNDERSTORMS. OUTLOOK... WEDNESDAY AND WEDNESDAY NIGHT...SEAS ON THE OCEAN MAY APPROACH SMALL CRAFT ADVISORY CRITERIA IN PRE FRONTAL SOUTHERLY FLOW, BUT THERE IS CONSIDERABLE UNCERTAINTY. THURSDAY AND THURSDAY NIGHT...WINDS AND SEAS SHOULD REMAIN BELOW SCA CRITERIA. FRIDAY THROUGH SATURDAY...SEAS ON THE SOUTHERN OCEAN WATERS MIGHT REACH SMALL CRAFT ADVISORY LEVELS PENDING THE STRENGTH OF THE LOW PRESSURE SYSTEM ON THE FRONTAL BOUNDARY. CONFIDENCE IS LESS THAN AVERAGE. && .RIP CURRENTS... BASED ON OUR LOCAL FORECAST APPLICATION USING A 3 FOOT WAVES/8 SECOND PERIOD AND SOUTHEAST WIND AROUND 12 KNOTS, WE WILL CONTINUE WITH A MODERATE RISK OF RIP CURRENTS FOR NEW JERSEY AND LOW FOR DELAWARE. && .CLIMATE... THE CHART BELOW SHOWS RAINFALL STATISTICS AT OUR FOUR BIG CLIMATE SITES THRU 6/29. THE COLUMNS ARE BROKEN DOWN BY SITE, "POR" (HOW FAR RECORDS DATE BACK), JUNE 2015 RAINFALL, NORMAL JUNE RAINFALL, JUNE 2015 RAINFALL RANKING, AS WELL AS THE WETTEST JUNE ON RECORD. SITE POR JUNE NORMAL RANK WETTEST ILG 1894 12.46 3.50 2ND 13.66 (2013) ACY 1874 8.04 2.81 2ND 8.45 (1920) ABE 1922 7.02 3.86 6TH 10.51 (1938) PHL 1872 7.23 3.08 10TH 10.56 (2013) AT THIS TIME, IT HAS BEEN THE SECOND WETTEST JUNE ON RECORD IN BOTH WILMINGTON AND ATLANTIC CITY. WITH TODAY BEING THE LAST DAY IN THE MONTH, CURRENT FORECASTS DO NOT FAVOR EITHER SITE BREAKING THEIR ALL-TIME JUNE RAINFALL RECORD. HOWEVER, IT WOULD ONLY TAKE A HEAVY SHOWER OR THUNDERSTORM TO CLOSE THE GAP, WHICH IS 0.41 INCHES IN ATLANTIC CITY AND 1.2 INCHES IN WILMINGTON. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GIGI NEAR TERM...FRANCK/ROBERTSON SHORT TERM...ROBERTSON LONG TERM...GIGI AVIATION...GIGI/ROBERTSON MARINE...GIGI/ROBERTSON RIP CURRENTS... CLIMATE...FRANCK

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