Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 270127 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 927 PM EDT SUN JUL 26 2015 .SYNOPSIS... A COLD FRONT WILL APPROACH THE REGION TONIGHT FROM THE NORTHWEST. BY MONDAY, THIS FRONT WILL DISSIPATE INTO A TROUGH OF LOW PRESSURE. HIGH PRESSURE WILL THEN BUILD EASTWARD INTO THE REGION FOR THE MIDDLE OF THE WEEK BEFORE ANOTHER COLD FRONT COMES THROUGH THE REGION THURSDAY NIGHT. ANOTHER AREA OF HIGH PRESSURE WILL BUILD EASTWARD FOR THE END OF NEXT WEEK WITH A FRONTAL BOUNDARY LOCATED TO OUR SOUTH. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 930 PM EDT UPDATE... MAIN CHANGE WAS TO ADJUST POPS TO REFLECT CURRENT RADAR TRENDS. UPPER LEVEL SHORT WAVE TROUGH REMAINS TO OUR WEST, SO CONVECTION COULD CONTINUE THROUGH THE OVERNIGHT HOURS. HOWEVER, GIVEN THE LOSS OF DIURNAL HEATING AND A STILL MARGINAL LOW LEVEL SHEAR PROFILE, THINK COVERAGE WILL BE SOMEWHAT LIMITED OVERNIGHT. SO HAVE SLIGHTLY LOWERED POPS THROUGH 12Z. PREVIOUS NEAR TERM DISCUSSION...THE WEAKENING COLD FRONT/WIND SHIFT ACROSS THE CENTRAL PART OF PENNSYLVANIA WILL SLOWLY DRIFT TOWARDS THE EAST- SOUTHEAST TONIGHT. SCATTERED SHOWERS AND THUNDERSTORMS WILL TRY TO PENETRATE OUR NORTHERN ZONES LATER THIS EVENING AHEAD OF THE FRONT, OR WHAT EVER IS LEFT OF IT. THERE IS NEARLY 1000J/KG OF DCAPE AS THE AIRMASS CONTINUES TO MODIFY ON THE MOISTER SIDE. MID- LEVEL LAPSE RATES ARE RATHER VANILLA THOUGH WITH THE STRONGER HEATING OF THE DAY THE LOW- LEVEL LAPSE RATES HAVE INCREASED CLOSER TO DRY ADIABATIC IN THE 0- 3KM LAYER. THE STORMS ARE MORE PULSEY WITH SHEAR BEING ON THE WEAKER SIDE...15 KNOTS MAYBE, THOUGH PRECIP LOADING IN THE COLUMN COULD PRODUCE AN ISOLATED STRONGER WIND GUST ALONG WITH HEAVY RAIN. THE MEAN FLOW ALOFT TOO IS WEAK SO THE STORMS MAY SIT AND CYCLE FOR A WHILE OVER THE SAME AREA CAUSING LOCALIZED POOR DRAINAGE FLOODING ISSUES. AS THE EVENING AND NIGHT WEAR ON THE AMOUNT OF SURFACE BASED INSTABILITY LESSENS AND WHATS LEFT OF THE LOW-LEVEL JET MOVES FARTHER TOWARDS THE NORTHEAST. THERE IS NOT A LOT OF SURFACE SYNOPTIC LIFTING LEFT TONIGHT BUT WEAK MID-LEVEL COLD POOL INTERACTION WITH A FEW PASSING SHORTWAVES MAY KEEP THE SHOWERY ACTIVITY GOING THROUGH THE OVERNIGHT HOURS...THE CHANCES INCREASE FROM NORTHWEST TO SOUTHEAST LATE TONIGHT. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... ALMOST A WASH-RINSE-REPEAT KIND OF DAY ON MONDAY. WIND SHIFT LINE STILL HANGING AROUND THE REGION THOUGH EVEN MORE DIFFUSE THAN ON SUNDAY. AMPLE LOW-LEVEL MOISTURE WITH TOTAL COLUMN PWATS CONTINUING TO CLIMB ABOVE 1.5 INCHES. A FEW PASSING SHORTWAVES ALOFT RIDING ALONG ANY SURFACE CONVERGENCE BOUNDARY WILL HELP TO INITIATE AFTERNOON CONVECTION, BUT AGAIN THE HIGHER TERRAIN/RIDGE TOPS MAY BE THE FOCUS AGAIN. OVERALL WE MAINTAIN THE CHANCE POPS FOR SCATTERED SHOWERS AND THUNDERSTORMS. TEMPERATURES WERE BUMPED UP SEVERAL DEGREES FROM MOS WITH THE THINKING THAT MOS IS TRYING TO WASH US OUT TOO MUCH TOMORROW AFTERNOON. SURFACE FLOW DOESN`T CHANGE ALL THAT MUCH FROM DAY TO DAY AND THE LOW-LEVEL THERMAL PROFILE DOES COOL EVER SO SLIGHTLY, BUT WE FEEL WE`LL HAVE ANOTHER CHANCE AT REACHING 90F MONDAY AFTERNOON...TOO MUCH MIXING FROM ALOFT ADIABATICALLY. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... MONDAY NIGHT THROUGH WEDNESDAY NIGHT: A GRADUAL CONTINUED UPTICK IN HEAT AND HUMIDITY WITH A STRONG RIDGE ACROSS THE SOUTHERN PLAINS MAKING ANOTHER CHARGE INTO THE REGION WITH RISING HEIGHTS. THIS WILL RESULT IN A MAINLY DRY PERIOD (POSSIBLE EXCEPTION OF AN ISOLATED THUNDERSTORM SOUTH TUESDAY AFTERNOON). FOR ACTUAL HIGH TEMPERATURES, MODELED 925 MB TEMPERATURES RISE FROM AROUND 23C ON TUESDAY TO 25C FOR WEDNESDAY. THIS EQUATES TO HIGH TEMPERATURES STARTING OFF AROUND 90 ON TUESDAY THEN RISING INTO THE MID 90`S FOR WEDNESDAY, STARTING ANOTHER POTENTIAL MODELED HEAT WAVE FOR MOST OF THE REGION. LESS SPREAD IN PRESENT IN THE OPERATIONAL MODELS AND THE ENSEMBLES IN THIS PERIOD COMPARED TO YESTERDAY AS THE GFS HAS TRENDED COOLER WITH TEMPERATURES. FORTUNATELY MODELED DEWPOINTS ARE IN THE LOW/MID 60`S DURING THE PEAK HEATING HOURS BOTH TUESDAY AND WEDNESDAY. THIS WOULD LIMIT THE MAXIMUM HEAT INDEX TO BETWEEN 95 AND 100 DEGREES. THURSDAY THROUGH SUNDAY: THE COLD FRONTAL BOUNDARY APPROACHING THE REGION TO START THIS PERIOD WILL LIKELY BE THE TRIGGER FOR AN INCREASE IN CLOUDS AND SOME SCATTERED AFTERNOON/EVENING SHOWERS AND STORMS ON THURSDAY. ONCE AGAIN, THE LACK OF SHEAR LOOKS TO BE A LIMITATION IN THE WAY OF ANY SEVERE WEATHER. HOWEVER, AN ISOLATED STRONG WIND GUST CAN NOT BE RULED OUT. THE 12Z (DAYTIME) RUNS OF THE GFS CONTINUE TO RUN WARMER AND DRIER ON THURSDAY THAN OTHER MODELS AND GFS RUNS, CURRENT THINKING IS THIS AN ANOMALY RATHER THAN THE RULE AND THE FORECAST WILL GO MORE TOWARD THE ECMWF WITH TEMPERATURES ON THURSDAY. HIGHER HUMIDITY THOUGH GIVES THE REGION A HIGHER CHANCE FOR THE HEAT INDEX TO REACH 100 DEGREES IN PARTS OF THE REGION. SOME DRIER AND PERHAPS SLIGHTLY COOLER AIR IS LIKELY TO END THE POTENTIAL HEAT WAVE BEHIND THE FRONT ON FRIDAY. COMPARED TO JUST YESTERDAY, THE OPERATIONAL MODELS AND THE RESPECTIVE ENSEMBLES ARE FARTHER OFFSHORE WITH THE FRONT AND ARE SHOWING A MUCH LOWER THREAT FOR WAVES OF LOW PRESSURE DEVELOP ALONG THE BOUNDARY. THE FORECAST REFLECTS A DRY BUT STILL HOT CONDITIONS NEXT WEEKEND WITH EVEN WARM AIR ADVECTION AGAIN BY NEXT SUNDAY WITH A FRONTAL PASSAGE TO OUR NORTH. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TONIGHT...MOSTLY VFR CONDITIONS EXPECTED. ISOLATED THUNDERSTORMS AND SCATTERED SHOWERS ARE POSSIBLE THROUGH THE OVERNIGHT HOURS. HOWEVER, WITH LIMITED COVERAGE, DON`T HAVE ENOUGH CONFIDENCE TO INCLUDE MENTION IN ANY TAFS EXCEPT KRDG AND KABE. IF ANY OF THE OTHER TAF SITES ARE AFFECTED, IT WILL LIKELY BE 06Z OR LATER. PATCHY BR IS POSSIBLE ESPECIALLY FOR ANY TAF SITES THAT DO RECEIVE RAIN OVERNIGHT, OR IF FLOW STAYS MORE OF AN ON SHORE DIRECTION FOR OUR COASTAL/NEAR COASTAL SITES (KILG, KMIV, AND KACY). MONDAY...MOSTLY VFR. MORE SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE IN THE AFTERNOON HOURS BUT TOO HARD TO PINPOINT AT THIS TIME. WINDS REMAIN MOSTLY OUT OF THE SOUTH, SLIGHTLY SOUTHEAST. OUTLOOK... MONDAY NIGHT: VFR, ISOLATED TO SCATTERED SHOWERS THUNDERSTORMS, MAY BRIEFLY REDUCE VISIBILITIES AND CEILINGS. WINDS AT OR UNDER UNDER 10 KNOTS OUTSIDE OF THUNDERSTORMS. TUESDAY THROUGH WEDNESDAY NIGHT: VFR. WINDS AT OR UNDER 10 KNOTS THROUGH MOST OF THE PERIOD, WITH SOME SOUTHWESTERLY WIND GUSTS AROUND 15 KNOTS WEDNESDAY AFTERNOON. THURSDAY AND THURSDAY NIGHT: VFR, ISOLATED TO SCATTERED SHOWERS THUNDERSTORMS, MAY BRIEFLY REDUCE VISIBILITIES AND CEILINGS. WEST- SOUTHWEST WIND GUSTS AROUND 15 KNOTS POSSIBLE THURSDAY AND EVENING, LOCALLY HIGHER GUSTS IN THUNDERSTORMS. FRIDAY AND FRIDAY NIGHT: VFR. WINDS AT OR UNDER 10 KNOTS. && .MARINE... SUB-SCA CONDITIONS EXPECTED TONIGHT AND TOMORROW AS A WEAK SURFACE FRONT TRIES TO PUSH THROUGH. SOUTHERLY WINDS AROUND 10 TO 15 KNOTS WITH SOME GUSTS UPWARDS OF 20 KNOTS STILL POSSIBLE TONIGHT AND TOMORROW. SEAS DO INCH UP UNDER THE SOUTHERLY FLOW TONIGHT AND TOMORROW BUT SHOULD REMAIN 4 FEET OR LESS. OUTLOOK... SEAS AND WINDS LOOK TO REMAIN BELOW SCA CRITERIA THROUGH FRIDAY. ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS ARE POSSIBLE MONDAY NIGHT AND THURSDAY AFTERNOON/EVENING WITH THE POTENTIAL FOR LIGHTNING A STRONG WIND GUST OR TWO. SEAS OVERALL FOUR FEET OR LESS WITH WIND GUSTS 20 KNOTS OR LESS THROUGH THURSDAY. SEAS BUILDING TO AROUND FIVE FEET WITH SOME ISOLATED 25 KNOT FOR A PERIOD THURSDAY NIGHT BEFORE DECREASING ON FRIDAY. && .RIP CURRENTS... WITH THE LONG PERIOD (11-12 SECOND) 2 FOOT EASTERLY SWELL CONTINUING...EXPECT THE MODERATE RISK OF DANGEROUS RIP CURRENTS TO CONTINUE THROUGH MONDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GAINES NEAR TERM...HEAVENER/JOHNSON SHORT TERM...HEAVENER LONG TERM...GAINES AVIATION...GAINES/HEAVENER/JOHNSON MARINE...GAINES/HEAVENER RIP CURRENTS...JOHNSON

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