AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 935 AM EDT FRI JUL 8 2011 .SYNOPSIS... A STATIONARY FRONT OVER SOUTHERN PORTIONS OF OUR AREA WILL CONTINUE TO BRING UNSETTLED WEATHER ACROSS THE REGION TODAY AND INTO TONIGHT. LOW PRESSURE WILL APPROACH FROM THE SOUTHWEST ALONG THE FRONT THIS AFTERNOON AND PASS THROUGH THE AREA TONIGHT. HIGH PRESSURE WILL BUILD INTO OUR AREA DURING 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 PM THIS EVENING/... CONDITIONS ARE SHAPING UP FOR THE POTENTIAL FOR HEAVY RAIN...AND POSSIBLE FLASH FLOODING...FOR AT LEAST PART OF OUR AREA. A STATIONARY FRONT OVER THE SOUTHERN HALF OF THE REGION WILL COMBINE WITH ANOMALOUSLY HIGH PRECIPITABLE WATER VALUES AND RATHER SLOW 700 HPA WIND SPEEDS TO PRODUCE THE POSSIBILITY OF FLASH FLOODING MAINLY THIS AFTERNOON AND EARLY TONIGHT FOR THE CENTRAL AND SOUTHERN PORTIONS OF OUR AREA. IRONICALLY...THE FLASH FLOOD GUIDANCE VALUES ARE PRETTY HIGH IN THESE AREAS...AND ONE WOULD THINK THAT WE COULD ACCEPT LESSER AMOUNTS OF PRECIPITATION WITHOUT THE NEED FOR A FLASH FLOOD WATCH. IN FACT...NORTHERN AREAS ARE MUCH LOWER IN GUIDANCE VALUES...LESS THAN 2 INCHES IN SOME AREAS. SO MAYBE THE NORTHERN AREAS SHOULD HAVE THE WATCH AND SOUTHERN AREAS NOT? WELL...THE CONCEPTUAL MODEL IS THAT FLASH FLOODING WOULD BE NEARER TO WHERE THE STATIONARY FRONT IS AND WHERE THE PRECIPITABLE WATER VALUES ARE HIGHEST. PRECIPITABLE WATER VALUES ARE OVER 2 INCHES OVER THE SOUTHERN HALF...AND THIS IS THE AREA WHERE THE LOW APPROACHING FROM THE WEST-SOUTHWEST WILL TRAVERSE LATE THIS AFTERNOON AND EARLY TONIGHT. INITIALLY...CELLS WILL MOVE THROUGH THE NORTHWESTERN AREAS EARLY THIS MORNING...BUT THEY WILL MOVE INTO SLIGHTLY LESS UNSTABLE AIR AND WERE WEAKENING AS THEY MOVED INTO THE LEHIGH VALLEY. MORE ACTIVITY WILL FORM LATER THIS MORNING FOR WESTERN AND NORTHERN AREAS...THEN ACTIVITY IS PROGGED TO FORM FURTHER SOUTH THIS AFTERNOON AND TONIGHT IN VIEW OF UPWARD VERTICAL MOTION FIELDS. THIS IS WHEN THE LARGEST POTENTIAL FOR FLASH FLOODING IS THOUGHT TO EXIST. SO...A FLASH FLOOD WATCH WILL BE ISSUED FOR THE CENTRAL AND SOUTHERN PORTIONS OF OUR AREA FROM 16Z TODAY THROUGH 08Z TONIGHT. CONFIDENCE IS RATHER LOW FOR FLASH FLOODING...BUT URBAN CONCERNS IN THE I-95 CORRIDOR ALSO ENTERED THE EQUATION. BASICALLY...2/3 TO 1 INCH NORTH UP TO 1.5 TO 2 INCHES SOUTH IS FORECAST TODAY AND TONIGHT. HEAVY RAIN WAS USED IN ALL THE WEATHER GRIDS TODAY INTO TONIGHT. LOCAL AMOUNTS WILL BE MUCH HIGHER...PERHAPS 3.5 INCHES IN 3 HOURS CENTRAL AND SOUTH...IF ANY TRAINING OF CELLS OR BOUNDARY INTERACTIONS OCCUR. IN ADDITION...THE SOUTHERN TWO-THIRDS OF OUR AREA HAS BEEN CONTINUED IN THE SLIGHT RISK FOR TODAY...AND ENHANCED WORDING FOR WINDS HAIL AND LIGHTNING WAS USED FOR THIS AFTERNOON EVERYWHERE...AND EARLY TONIGHT CENTRAL AND SOUTH. SPC WAS PRIMARILY CONCERNED WITH WET MICROBURSTS. WITH GOOD DIRECTIONAL SHEAR DEVELOPING ACCORDING TO MODEL SOUNDINGS...IT IS WONDERED IF THERE COULD BE SOME SUPERCELLS WHICH COULD SPAWN A TORNADO TOO. AN ACTIVE DAY IS IN STORE ON THE RADAR IMAGERY. CLOUDS AND CONVECTION SHOULD KEEP TEMPERATURES FROM REACHING LEVELS OF THE PAST FEW DAYS. A BLEND OF MAV AND MET MOS WAS USED...HEDGED SLIGHTLY TOWARD THE WARMER MAVS. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/... ONGOING CONVECTION IS EXPECTED ESPECIALLY CENTRAL AND SOUTH THIS EVENING BUT CONDITIONS SHOULD EASE UP OVERNIGHT AS THE FORCING ERODES...WITH ONLY A SLIGHT CHANCE EARLY SATURDAY MORNING. CLEARING SHOULD COMMENCE OVERNIGHT NORTH AND SPREAD SOUTHEAST SATURDAY MORNING. HIGH PRESSURE AND DRIER AIR WILL BUILD DURING SATURDAY...AND BE OVER THE AREA SUNDAY SO FAIR WEATHER IS GENERALLY EXPECTED. 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 /14Z FRIDAY THROUGH TUESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. REST OF TODAY...AN E-W BAND OF IFR/MVFR CONDS IN S NJ SE PA AND FAR N DEL SHOULD LIFT BY 15Z TO VFR CIGS WITH VFR CONDS ELSEWHERE. THIS BAND OF IFR/MVFR CIGS IN S NJ N DE MAY REFORM VCNTY KABE NWD INTO NW NJ AND NE PA MIDDAY/EARLY AFTN....ALONG AND N OF THE SLOWLY SOUTHWARD SAGGING COOL FRONT. THUNDERSTORMS...SHOULD FIRST DEVELOP BETWEEN 16Z AND 18Z NEAR THE COOL FRONT IN NNJ AND NE PA. OTHER CLUSTERS OF STORMS WILL DEVELOP TO OUR SW AND MOVE INTO OUR AREA DURING MID OR LATE AFTERNOON IN THE HOT/UNSTABLE AIRMASS. SEVERAL STORMS ARE EXPECTED TO PRODUCE BRIEF IFR/LIFR CONDS IN 1/2SM +T+SHRA WLY G50 KT WITH SREF RELATIVELY HIGH PROBS FOR SVR/SUPERCELLS AND POSSIBLY A TOR IN OUR CWA THIS AFTN. WHETHER THEY GO OVER THE TAF LOCATIONS IS UNKNOWN. THE CONVECTION IN SE VA THIS MORNING SHOULD PASS OFF TO THE SE OF THE FA. 12Z IAD AND APG ARE RELATIVELY DRY WITH 90-93MAX TEMP. SOUNDINGS MODIFIED FOR 85/73 AND LOOK RIPE FOR STORMS...EL 42 AND UP TO 2000J CAPE WITH SUPERCELL POTENTIAL. PLS SEE NEW 13Z SWODY1 FROM SPC. TONIGHT...MVFR OR IFR CIGS SPREAD S BEHIND THE FRONT WITH HEAVY CONVECTION BECOMING CONCENTRATED FROM KPHL-KACY SOUTHWARD AND EVENTUALLY DRIFTING OFFSHORE TOWARD DAWN. OUTLOOK... SATURDAY...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. SAT NIGHT AND SUNDAY...WEAK HIGH PRESSURE BUILDING INTO THE REGION SHOULD RESULT IN VFR CONDITIONS. SUN NIGHT...VFR TO START BUT WAA MVFR CIGS MAY DEVELOP IN E PA LATE. MONDAY...WARM AIR ADVECTION AHEAD OF A FRONTAL BOUNDARY COULD MEAN SCATTERED THUNDERSTORMS LATE MONDAY OR MONDAY NIGHT...BUT OVERALL VFR CONDITIONS ARE EXPECTED. && .MARINE... NO HEADLINES. THE STATIONARY FRONT STRETCHED ACROSS THE NORTHERN OCEAN WATERS THIS MORNING...WITH THE REMAINDER OF THE WATERS REMAINS IN THE SOUTH SOUTHWEST FLOW ON THE WARM SIDE OF THE FRONT. FOR THE MOST PART A 3 FOOT SOUTHERLY SHORT PERIOD SWELL CONTINUES ON THE WATERS. AS THE FRONT OOZES SOUTH TODAY...MORE OF THE OCEAN WATERS ADJACENT TO THE NEW JERSEY COAST WILL SEE WINDS BECOMES POST FRONTAL...AND SHOULD REMAIN BELOW 15 KNOTS. SOUTH OF THE FRONT...THE SOUTH SOUTHWEST FLOW SHOULD GENERALLY REMAIN BELOW 15 KNOTS INTO THIS EVENING. THE MAIN FORECAST PROBLEM COMES LATER TONIGHT AND SATURDAY MORNING. ALL SHORT RANGE MODELS SHOW A WAVE DEVELOPING ON THE FRONT LATE TONIGHT AND MOVING OFF THE NEW JERSEY AND DELAWARE COASTS SATURDAY MORNING. THE 0000 UTC NAM CONTINUES THE TREND THE NAM HAS SHOWN FOR THREE DAYS...AND DEEPENS THE SYSTEM SATURDAY. THE 0000 UTC NAM SOLUTION WOULD RESULT IN STRONG SMALL CRAFT NORTHEAST WINDS (WITH NEAR GALE GUSTS) FOR THE SOUTHERN OCEAN WATERS. THE MODEL CONSENSUS (EXCLUDING THE 0000 UTC NAM) SHOWS A MUCH WEAKER SOLUTION...AND THIS SEEMS TO BE MORE IN LINE WITH LOCAL EXPECTATIONS. WITH THAT IN MIND...WHILE IT WOULD APPEAR AS THOUGH GUSTS TO 20 KNOTS ARE POSSIBLE LATER TONIGHT AND SATURDAY MORNING ACROSS THE SOUTHERN OCEAN WATERS...SMALL CRAFT WINDS APPEAR UNLIKELY. HOWEVER...THE SEAS COULD BE A DIFFERENT MATTER. THE LATEST WNAWAVE GUIDANCE HAS BACKED OFF A TAD WITH REGARD TO SEAS...AND WOULD KEEP ALL OF OUR OCEAN WATERS BELOW 5 FEET LATE TONIGHT AND SATURDAY MORNING. FOR NOW...THIS SOLUTION IS ACCEPTED...AND WE WILL HOLD OFF ON ISSUING A SMALL CRAFT ADVISORY. IF LATER GUIDANCE SUGGEST SEAS WILL BE HIGHER...A SMALL CRAFT ADVISORY FOR THE OCEAN FOR SEAS COULD BE ISSUED LATER TODAY. AFTER THE LOW PULLS AWAY LATE SATURDAY MORNING...WINDS SHOULD DROP BELOW 15 KNOTS. AS WEAK HIGH PRESSURE BUILDS IN FROM THE WEST...THE GRADIENT COULD DROP OFF ENOUGH TO ALLOW LOCAL SEA AND BAY BREEZES TO DEVELOP IN THE MID TO LATE AFTERNOON. AS THE HIGH BUILDS OFF THE MID ATLANTIC COAST SATURDAY NIGHT INTO SUNDAY NIGHT...WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT LEVELS. THE RETURN FLOW AROUND THE HIGH COULD RESULT IN WINDS AND SEAS INCREASING MONDAY INTO TUESDAY. THERE IS A CHANCE FOR WINDS TO GUST TO 25 KNOTS DURING THIS TIME...BUT CONFIDENCE IN THIS IS LOW FOR NOW. && .EQUIPMENT... NWR LEWES CONTS OTS. RTS IS UNKNOWN. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR PAZ067>071. NJ...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR NJZ009-010-012>027. DE...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR DEZ001>004. MD...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR MDZ008-012-015-019- 020. MARINE...NONE. && $$ SYNOPSIS...O`HARA