AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1058 PM EDT THU JUL 7 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 FRIDAY 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 FRIDAY 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 /03Z FRIDAY THROUGH TUESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THE 00Z TAFS WILL CONTINUE THE TSRA THREAT FOR THE NEXT COUPLE OF HOURS FOR KACY AND KMIV AS A POCKET OF GREATEST INSTABILITY REMAINS JUST TO THE SOUTH IN DELAWARE. THE REST OF THE TAF SITES THE SHOWERS AND TSRAS ARE TOO ISOLATED TO INCLUDE AND WILL AMEND ACCORDINGLY. THERE ARE OTHER SHOWERS AND TSRAS TO OUR WEST WHICH AT THE LEAST SHOULD BRING SOME MID AND HIGH LEVEL CLOUDS OVERNIGHT. COVERAGE AND CONFIDENCE ABOUT ACTUAL PRECIPITATION OCCURRING IS TOO LOW TO INCLUDE WITH THIS ISSUANCE. WE EXPECT SOME MVFR (IFR AT KMIV) CONDITIONS TO FORM DUE TO FOG TOWARD MORNING. THEN ON FRIDAY AN ORGANIZED AREA OF SHOWERS AND TSRAS SHOULD DEVELOP AND MOVE ACROSS THE AREA. THE FAVORED TIMING IS DURING THE AFTERNOON AND EARLY EVENING WHERE SHOWERS WERE FORECAST AS THE PREVAILING GROUP. WE SHOULD HAVE SOME TSRAS ALSO WHICH WE WILL HOPEFULLY BETTER TIME AS THE EVENT COMES CLOSER. OUTLOOK... FRIDAY NIGHT...MVFR CONDS PROBABLY SPREADING SEWD TO MOST TAF LOCATIONS IN THE WAKE OF THE DEPARTING COLD FRONT AND ASSTD CONVECTION. THIS WEEKEND...WEAK HIGH PRESSURE BUILDING EAST FROM THE GREAT LAKES SHOULD PROVIDE VFR CONDITIONS. THE ONLY EXCEPTION HERE COULD BE SATURDAY EVENING...AS WIDELY SCATTERED THUNDERSTORMS COULD AFFECT NORTHERN AREAS. LIGHT WIND. NEXT MONDAY...VFR EXCEPT PATCHY MVFR FOG NEAR DAWN MAY SEE TSTMS LATE AT NIGHT IN WARM AIR ADVECTION ASSOCIATED WITH A WARM FRONTAL PASSAGE. SW WIND MAY GUST 15-20 KTS IN THE AFTN. && .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. && $$ SYNOPSIS.../O`HARA