AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 153 AM EDT FRI JUL 8 2011 .SYNOPSIS... A WEAK FRONT OVER OUR AREA WILL CONTINUE TO BRING UNSETTLED WEATHER ACROSS THE REGION THROUGH FRIDAY EVENING. HIGH PRESSURE WILL BUILD INTO OUR AREA SATURDAY AND BE OVER THE REGION SUNDAY AND INTO MONDAY. ANOTHER FRONT MAY BRING MORE UNSETTLED CONDITIONS TO THE REGION LATER MONDAY INTO TUESDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... A FEW WIDELY SEPARATED BUT STRONG CONVECTIVE CELLS CONTINUE OVER THE REGION AT LATE EVENING. EVEN THOUGH THE ATMOSPHERE APPEARS TO HAVE BEEN WORKED OVER BY PREVIOUS CONVECTION IN SEVERAL AREAS... SLIGHT CHANCE TO CHANCE THUNDERSTORM PROBABILITIES WILL CONTINUE EVERYWHERE OVERNIGHT DUE TO THE PRESENCE OF THE QUASI-STATIONARY FRONT, STRONG INSTABILITY, AND DEEP MOISTURE. PATCHY FOG WILL ALSO BE ADDED TO THE WEATHER GRIDS DUE TO THE HIGH LEVELS OF LOW LEVEL MOISTURE...AS WELL AS THE COPIOUS RAIN IN SEVERAL AREAS THIS AFTERNOON AND THIS EVENING. OVERNIGHT LOWS WILL BE VERY WARM AND IT WILL REMAIN VERY HUMID TONIGHT. A FEW ADJUSTMENTS WERE MADE TO OVERNIGHT MINIMUMS BASED ON 18Z MOS GUIDANCE AND 02Z READINGS. && .SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY/... FRIDAY AND FRIDAY NIGHT SHOULD BE CONVECTIVELY ACTIVE WITH THE HOT AND HUMID AIRMASS FINALLY GIVING WAY TO AN APPROACHING UPPER TROUGH/SFC COLD FRONT. THE SPC IS INDICATING A SLGT CHC FOR CONVECTION ACROSS THE SRN AREAS WITH AMPLE CAPE AND DECENT SHEAR IMPOSED OVER THE SAME AREAS. GUSTY WINDS/HEAVY RAINS WILL ACCOMPANY TSTMS. TEMPERATURES FRI WILL BE LESS THAN TODAY WITH MORE CLOUDS AND SHOWERS IN PLACE. SAT THRU SUN WILL FEATURE FAIR WEATHER AS HIGH PRESSURE BUILDS IN TO THE MIDDLE ATLANTIC. A VERY SMALL CHC FOR SHOWERS WILL REMAIN IN THE GRIDS FOR SAT MORNING...IN CASE ANY LINGERING ACTIVITY WITH THE FRONT FROM FRI NIGHT LASTS INTO SAT. THE BEST CHC FOR THIS HAPPENING WILL BE OVER THE DELMARVA AREA. IT WILL STILL BE VERY WARM THIS WEEKEND...BUT THE LOWER DEW POINTS WILL MAKE THE AIR MUCH MORE COMFORTABLE THAN RECENT DAYS. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... NOT TOO MANY CHANGES IN THE LONG TERM FROM THE LATEST SUITE OF MODEL RUNS. THE CAN GGEM WAS NOT USED AS NONE OF THE OTHER MODELS HAD AS STRONG A LOW EXITING NORTH CAROLINA AND THIS AFFECTED THE CAN FOR THE REST OF THE LONG TERM. THIS PACKAGE LEANED TOWARD THE ECMWF. THE LONG TERM WILL BEGIN WITH HOTTER AND INCREASINGLY MORE HUMID WEATHER EXPECTED. A DECAYING FRONTAL BOUNDARY MIGHT ACT AS A FOCUS FOR AFTERNOON CONVECTION. ALTHOUGH CONFIDENCE IS NOT HIGH AND THUS POPS WERE KEPT NORTHWEST OF THE I95 CORRIDOR CLOSER TO THE APPROACHING COLD FRONT. PENDING SKY COVER AND FRONTAL POSITION ON TUESDAY, MONDAY SHOULD BE THE HOTTEST DAY OF THE LONG TERM WITH SOME MID 90S POSSIBLE. THE APPROACHING COLD FRONT SHOULD THEN ACT AS A TRIGGER FOR MORE ORGANIZED SHOWERS AND THUNDERSTORMS. WE KEPT POPS RELATIVELY LOW DUE TO THE CONSENSUS TIMING IN WHICH IT LOOKS TO BE TOO FAR TO THE NORTHWEST ON MONDAY AND POSSIBLY TOO DEEP INTO OUR CWA ON TUESDAY. THE GFS IS MORE AGGRESSIVE WITH MOVING THE COLD FRONT THROUGH WHICH WE TEMPERED SOMEWHAT GIVEN JULY CLIMO. THUS OUR MAX TEMPS ON TUE AS THE FRONT IS MOVING THROUGH AND ON WED AS THE RELATIVELY COOLER AIR IS ARRIVING IS ABOVE MEX MOS GUIDANCE. AT THIS POINT THERE IS FAIRLY GOOD MODEL CONSENSUS FOR OUR CWA TO BE NEAR THE CANADIAN HIGH PRESSURE SYSTEM WITH THE RELATIVELY DRIEST AND COOLEST DAY OF THE LONG TERM PERIOD. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THE STATIONARY FRONT STRETCHED FROM NORTHEAST NEW JERSEY THROUGH EAST CENTRAL PENNSYLVANIA INTO NORTHERN MARYLAND CONTINUES TO BE A FOCUS FOR CONVECTION EARLY THIS MORNING. SOME OF THIS ACTIVITY COULD COME CLOSE TO KRDG...KILG AND KPHL BEFORE 1100 UTC. AN MVFR MENTION OF PRECIPITATION WAS INCLUDED...BUT FOR NOW NO THUNDER WAS INSERTED INTO THE FORECAST. AMENDED FORECASTS WILL BE ISSUED AS THE CONVECTION THREATENS. OTHERWISE...VFR CEILINGS COULD CONTINUE THROUGH 1200 UTC. THE EXCEPTION HERE COULD BE KACY. STATISTICAL GUIDANCE IS SUGGESTING THAT IFR CEILINGS ARE POSSIBLE THIS MORNING WITH THE FLOW PARALLEL TO THE COAST. MVFR VISIBILITIES ARE POSSIBLE WITH PATCHY FOG IN MOST PLACES. THE MAIN FORECAST PROBLEM TODAY WILL BE CONVECTION. THE STATIONARY FRONT WILL START TO OOZE SOUTH TODAY AS HIGH PRESSURE BUILDS IN FROM THE NORTHWEST. THE FRONT SHOULD REMAIN THE FOCUS FOR CONVECTION. FOR NOW...BASED ON TIMING ISSUES...VFR CONDITIONS WITH CB REMARKS WERE INCLUDED IN THE FORECAST THROUGH ABOUT 1800 UTC. AFTER THIS...MOST TERMINALS WERE GIVEN MVFR VISIBILITIES IN RAIN...BUT THIS IS IN ALL LIKELIHOOD JUST AN INDICATION OF WHAT MAY BE. THE BEST CHANCE OF GUSTY WINDS MAY END UP BEING FROM KRDG-KPHL-KILG SOUTH...WITH THE BEST TIMING BETWEEN 2000 UTC AND 0200 UTC. DURING THIS TIME...LOCAL IFR CONDITIONS WILL BE POSSIBLE IN THE CONVECTION. FURTHER NORTH...LACK OF HEATING MAY BE SOMETHING OF AN INHIBITION... BUT GUSTY STORMS ARE POSSIBLE HERE AS WELL. AS THE FRONT SINKS SOUTH THIS EVENING...THE BEST THREAT OF CONVECTION FOLLOWS IT. FURTHER NORTH...AS WINDS BECOME EAST NORTHEAST...THE LOW LEVEL INVERSION COULD MEAN SOME STRATUS FOR AREAS NORTH OF A KILG-KPHL-KACY LINE. THIS HAS BEEN INCLUDED IN THE TERMINALS FORECASTS FOR THIS EVENING. HOWEVER...SINCE THERE IS SOME MODEL SPREAD CONCERNING THE TIMING OF THE FRONT...CONFIDENCE IN THIS OCCURRING IS LOW. LATE TONIGHT...LOW PRESSURE FORMING ON THE FRONT WILL ALLOW ALL TERMINALS TO GO NORTH ON THE WINDS. THIS IS ALSO TH BEST CHANCE FOR IFR CEILINGS. OUTLOOK... IFR STRATUS IS POSSIBLE ALONG AND SOUTH OF A KILG-KACY LINE THROUGH ABOUT 1400 UTC. AFTER THE SURFACE LOW PULLS AWAY...THE LOW LEVEL INVERSION SHOULD BREAK...AND VFR CONDITIONS ARE EXPECTED EVERYWHERE FOR THE REMAINDER OF THE DAY. CONVECTIVE TEMPERATURES COULD BE MET IN THE AFTERNOON...WHICH SHOULD RESULT IN SCATTERED CUMULUS. HOWEVER...INCREASING STABILITY SHOULD LIMITED ANY CONVECTIVE POTENTIAL. WEAK HIGH PRESSURE BUILDING INTO THE REGION SHOULD RESULT IN VFR CONDITIONS CONTINUING SATURDAY NIGHT INTO SUNDAY NIGHT. WARM AIR ADVECTION AHEAD OF A FRONTAL BOUNDARY COULD MEAN SCATTERED THUNDERSTORMS MONDAY...BUT OVERALL VFR CONDITIONS ARE EXPECTED. && .MARINE... NO HEADLINES ATTM. LOW PROB WE WILL NEED AN SCA FRI NIGHT IN THE ATLC WATERS OFF DEL. CONVECTIVE GUSTS AND LIGHTNING ARE THE BIG PROBLEM THIS AFTERNOON AND AGAIN FRIDAY INTO FRIDAY EVENING IN ASSN WITH QSTNRY FRONT FM NYC TO JUST N OF PHL. THAT FRONT SAGS SOUTHEAST OF OUR AREA TOMORROW NIGHT AND THE CONVECTION MOVES OUT TO SEA. A DRY NICE WEEKEND IS ENVISIONED AS HIGH PRESSURE SETTLES IN WITH A DRIER AIRMASS AND LIGHT WIND. NEXT MONDAY...SW FLOW GUSTING 15 KTS AND POSSIBLE TSTMS AT NIGHT. && .HYDROLOGY... WHILE THERE IS AMPLE MOISTURE TO CREATE DOWNPOURS AND LOCALIZED FLOODING CONCERNS LATE THIS EVENING AND INTO THE EARLY OVERNIGHT PERIOD...CELLS WILL BE WIDELY SCATTERED AND WILL BE HANDLED WITH LOCAL ADVISORIES OR WARNINGS IF NEEDED. ALSO...THE SPEED OF MOVEMENT IS PROBABLY ENOUGH TO PREVENT ANY WIDESPREAD PROBLEMS. THIS DEEP MOISTURE WILL CONTINUE THROUGH FRIDAY EVENING WITH RENEWED THUNDERSTORM FORMATION EXPECTED BY AFTERNOON. THE FLASH FLOOD GUIDANCE IS LOWER ACROSS THE NORTH...SO LATER SHIFTS MAY CONSIDER A WATCH FOR THESE AREAS. THERE IS ENOUGH UNCERTAINTY AT THIS TIME TO PRECLUDE A WATCH FOR NOW. THE HEAVY RAIN WORDING WILL BE KEPT IN THE GRIDS AND ZONES FOR NOW. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$