Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 040148 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 948 PM EDT MON AUG 3 2015 .SYNOPSIS... A COLD FRONT FROM THE GREAT LAKES WILL SLOWLY APPROACH FROM THE NORTHWEST OVERNIGHT, EVENTUALLY TRACKING THROUGH OUR REGION ON TUESDAY. THIS FRONT IS FORECAST TO STALL JUST SOUTH OF OUR AREA THROUGH THE END OF THE WEEK WITH WAVES OF LOW PRESSURE MOVING ALONG IT. THE FINAL WAVE OF LOW PRESSURE LOOKS TO PASS OFFSHORE SOUTHEAST OF THE REGION ON SATURDAY. A HIGH PRESSURE SYSTEM FROM EASTERN CANADA SHOULD THEN BUILD SOUTHWARD ON SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... A FRONTAL BOUNDARY WILL CONTINUE TO APPROACH OUR REGION FROM THE NORTHWEST OVERNIGHT. SCATTERED SHOWERS WITH ISOLATED LIGHTNING STRIKES LINGERED IN THE PENNSYLVANIA COUNTIES OF SCHUYLKILL, CARBON AND BERKS, AS WELL AS IN THE LEHIGH VALLEY AROUND 930 PM. AS THE ATMOSPHERE CONTINUES TO BECOME MORE STABLE, THE SHOWERS ARE ANTICIPATED TO DIMINISH, MOST LIKELY BEFORE MIDNIGHT. MEANWHILE, IT WAS APPEARING LESS PROBABLE THAT THE CONVECTION IN WESTERN PENNSYLVANIA THIS EVENING WILL REACH OUR FORECAST AREA WITH CONDITIONS BECOMING INCREASINGLY STABLE OVER THE SUSQUEHANNA RIVER VALLEY, AS WELL. THE SKY COVER SHOULD FAVOR PARTLY CLOUDY DURING THE NIGHT WITH A LIGHT SOUTHWESTERLY SURFACE FLOW. MINIMUM TEMPERATURES ARE FORECAST TO BE MOSTLY IN THE UPPER 60S AND THE LOWER 70S IN OUR REGION. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... FRONT GETS HUNG UP ALONG THE COAST TOMORROW. WITH SOME ADDITIONAL MOISTURE (VS. TODAY) POOLING NEAR THE FRONT AND A SHORTWAVE IN THE AREA, THE THINKING IS THAT SHOWERS AND THUNDERSTORMS COULD BE MORE NUMEROUS TOMORROW ACROSS THE EASTERN ZONES. THERE`S A SIGNIFICANT DIFFERENCE BETWEEN THE NAM AND GFS WITH THE NAM MUCH FURTHER WEST WITH PRECIP. I`VE CHOSEN TO GO CLOSER TO THE GFS WITH SUPPORT FROM STAT GUIDANCE. TEMPS TOMORROW, OVERALL, SHOULD BE A COUPLE DEGREES COOLER THAN TODAY`S HIGH. FORECASTING 90 FOR PHILLY. WINDS WILL BE A BIT MORE WESTERLY TOMORROW AFTERNOON WITH SIMILAR GUSTS VS. TODAY. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... IN A MODEL INITIALIZATION FLIP FROM THE WEEKEND, THE WRF/NAM INITIALIZED THE 500MB PATTERN BETTER THAN THE GFS OR ECMWF IN THE WESTERN CONUS, WHILE IN ERN NOAM THE GFS LOOKED BETTER. THE GFS LOOKED CLOSER AT 850 MB AND 925MB. DP/DTING THE INITIALIZATION OVER THE PAST 24 HOURS, THE RIDGING IN MONTANA AND IDAHO IS STRONGER AND DOWN THE ROAD THIS IS LEADING TO A MORE BIFURCATED SOLUTION TO HOW THE ENERGY ROUNDS THIS RIDGE, THUS THERE IS NO DECREASE IN UNCERTAINTY WITH THIS SOUNDING RUN. THE GFS WAS NOT USED BECAUSE OF ITS WEAKER WESTERN CONUS INITIALIZATION AND POOR RUN TO RUN CONTINUITY. GEFS MEAN WITH THE WAVE OF LOW PRESSURE IS FARTHER SOUTH AND THEN A FASTER EXIT ON SATURDAY. OUR FORECAST IS CLOSEST TO A ECMWF/CAN GGEM/MF-ARPEGE BLEND. IT SHOULD BE NOTED THAT THE UKMET HAS TRENDED SOUTHWARD WITH A MUCH WEAKER LOW WHILE THE NOGAPS AND JMA HAVE GONE BACK TO NOT HAVING ANY PCPN REACH OUR CWA UNTIL SATURDAY. SO THE ACTIVE MIDDLE STRETCH OF THE LONG TERM CONTINUES WITH TEMPERATURES CLOSER TO THE NORMAL. THE POTENTIAL REMAINS FOR A SOAKING RAIN CENTERED AROUND FRIDAY, ALTHOUGH THERE REMAINS UNCERTAINTIES AS TO THE IMPACT WITHIN OUR CWA. LAST NIGHT`S NAEFS ENSEMBLE MEAN CONTINUE TO SHOW AN ANOMALOUSLY STRONG SFC LOW PRESSURE SYSTEM FOR EARLY AUGUST WITH A FIVE YEAR RETURN PERIOD AND SD OF BETWEEN 2 AND 3 AS IT CROSSES THE CENTRAL APPALACHIANS. THE LACK OF THE RUN TO RUN CONTINUITY REMAINS. THE WAY THE MODELS RESOLVE CONVECTIVE SYSTEMS THAT WILL DEVELOP ACROSS THE MIDWEST AND UPPER MISSISSIPPI VALLEY AS THE LOWS MOVES EAST IS MAINLY WHY. THE MORE ROBUST "FEEDBACK" LENDS TO STRONGER AND FARTHER NORTH LOWS, WHILE MODELS WITH LESS MCV BULLSEYES HAVE WEAKER AND MORE SUPPRESSED SOLUTIONS. IT REMAINS HARD TO SEPARATE THE TRUE MCS(S) FROM PROLONGED FEEDBACK HANGOVERS. LIKELY THIS WILL BE THE CASE INTO WEDNESDAY AS THE CONVECTION THAT DAY IS THE CAUSE OF MOST OF THE MODELING HEARTBURN. TUESDAY NIGHT, THE MODEL TIMING HAS SLOWED IN MOVING THE COLD FRONT OFFSHORE AND WE MAINTAIN LOW POPS SOUTHEAST PART OF OUR CWA FOR THUNDERSTORMS. GIVEN HOW DRIER AIR IS MOVING, THE MORE ROBUST STORMS SHOULD BE DONE BY THIS TIME PERIOD. WE ARE EITHER AT OR SLIGHTLY ABOVE STAT GUIDANCE FOR MINS GIVEN THE SLOWER MODELING TREND. WEDNESDAY, REMAINS POPLESS AS HIGH PRESSURE BUILDS INTO THE REGION. THE GFS IS STANDING ALONE WITH STGR CAA AND OVERALL STRONGER SFC WINDS. IT ALSO STANDS ALONE WITH CHANNELIZED VORT MAX PCPN GETTING INTO THE NORTHERN PART OF OUR CWA. GIVEN THE DP/DT TREND, GOING FASTER DOES NOT SEEM TO HAVE MUCH CORROBORATION. WE ARE CLOSER TO A NON-GFS SOLUTION AND NAM MOS FOR HIGH TEMPS. ALSO NO POPS. BUT, CONVECTIVE TEMPS SHOULD BE REACHED NORTH AND SOME POPCORN TO MAYBE EVEN CIG CU LIKELY. WHILE IT WILL BE DRIER, NOT OUT OF THE QUESTION OF A COUPLE OF MORE 90S IN THE EASTERN/COASTAL PART OF OUR CWA. WEDNESDAY NIGHT, DRY, AS THIS IS ONE FORECAST PERIOD ALL OF THE MODELS AGREE UPON. WITH HIGH PRESSURE OVER THE AREA, COMFORTABLE STAT GUIDANCE MINS LOOK REASONABLE. THURSDAY, POPS WERE MOVED BACK APPROXIMATELY 12 HOURS. TOO LATE IN ITS FORECAST CYCLE TO HAVE CONFIDENCE IN THE WRF/NAM TIMING, BUT MANY OF THE MODELS DO NOT HAVE ANY MEASURABLE AT ALL THURSDAY DAY BASED ON THE MORE ROUNDABOUT APPROACH FOR THE SHORT WAVES. BECAUSE OF THE DRIER TRENDING, WE WENT ABOVE STAT GUIDANCE FOR MAX TEMPS. THURSDAY NIGHT THROUGH FRIDAY NIGHT THERE UNFORTUNATELY REMAINS UNCERTAINTY AS TO THE EVOLUTION OF THE SYSTEM, BUT THE SYNOPTIC SCALE SET-UP STILL POINTS TO HEAVY RAIN, EVEN IF IT DOES NOT NECESSARILY OCCUR OR AFFECT OUR CWA THE MOST. THE HEAVY RAIN WILL BE TIED TO CONVECTION AND THUS HOW UNSTABLE ALOFT IT BECOMES WITHIN OUR CWA WILL DETERMINE THE FINAL OUTCOME. HIGHEST POPS ARE THURSDAY NIGHT AND FRIDAY WITH THUNDER EMPHASIZED MORE FOR THE SOUTHERN PART OF OUR CWA. COME FRIDAY NIGHT THE PREDICTED INSTABILITY (REALLY LACK THEREOF) ALOFT DOES NOT SUBSTANTIATE THE ECMWF`S PCPN/QPF SOLUTION AND WAS NOT USED. THIS DOES NOT MEAN HEAVIER RAIN COULD NOT HAPPEN EARLIER. MAX TEMPS MAY VERY WELL BE OVERSTATED ON FRIDAY IF THIS TIMING HOLDS. BECAUSE OF TIMING DISCREPANCIES WE KEPT IN A LOW CHANCE FOR PRECIPITATION ON SATURDAY. AFTER ABOVE, THE END OF THE LONG TERM APPEARS QUIET AS HIGH PRESSURE NOSES ITS WAY SOUTHWARD FROM CANADA AND THE FRONTAL BOUNDARY AND LOW PRESSURE SYSTEMS MOVE OFFSHORE. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. THE SHOWERS AROUND KRDG AND KABE AT 0130Z WILL CONTINUE TO DIMINISH. WE ARE EXPECTING THE SHOWERS AND THUNDERSTORMS THAT WERE IN WESTERN PENNSYLVANIA THIS EVENING TO FALL APART AS WELL BEFORE REACHING OUR TAF SITES. WERE ARE FORECASTING MAINLY VFR CONDITIONS THROUGH THE TAF PERIOD. WE HAVE INDICATED SOME MVFR VISIBILITY RESTRICTIONS AT KRDG AROUND DAYBREAK DUE TO THE MOISTURE THAT WAS INTRODUCED BY THIS EVENING`S RAINFALL IN THAT AREA. ISOLATED SHOWERS AND THUNDERSTORMS REMAIN POSSIBLE FOR TUESDAY AFTERNOON. THE MOST PROBABLE AREA FOR PRECIPITATION IS AROUND KMIV AND KACY SO WE HAVE INCLUDED A PROB30 GROUP IN THOSE TAFS. A LIGHT SOUTHWEST SURFACE FLOW OVERNIGHT SHOULD BEGIN TO FAVOR THE WEST SOUTHWEST ON TUESDAY. WIND SPEEDS ARE FORECAST TO INCREASE AROUND 10 KNOTS ON TUESDAY WITH GUSTS IN THE UPPER TEENS. OUTLOOK... TUESDAY NIGHT...MOSTLY VFR CONDITIONS. ISOLATED TO PERHAPS SCATTERED SHWRS/TSTORMS ARE POSSIBLE VERY EARLY SOUTHEASTERN TERMINALS. WEDNESDAY AND WEDNESDAY NIGHT...MAINLY VFR CONDITIONS. THURSDAY THROUGH FRIDAY NIGHT...MVFR CONDITIONS DURING SHWRS/TSTORMS, WITH SOME IFR CONDITIONS POSSIBLE. WHILE CONFIDENCE OF OCCURRENCE IS INCREASING, TIMING CONFIDENCE REMAINS LOW. SATURDAY...PREDOMINATELY VFR CONDITIONS EXPECTED TO RETURN AS SHOWER FREQUENCY DIMINISHES. && .MARINE... WILL KEEP THE SMALL CRAFT ADVISORY HEADLINES IN PLACE TONIGHT FOR THE OCEAN WATERS AND EXTEND THEM THROUGH TOMORROW. GUSTS TO 25 KTS CAN BE EXPECTED ALONG WITH SEAS IN THE 4 TO 6 FT RANGE. WAVEWATCH NUMBERS WERE HIGHER AND WERE TRIMMED. IN DELAWARE BAY, WE`LL TOP THE WIND GUSTS OUT AT 20 KTS (SUB SMALL CRAFT). OUTLOOK... TUESDAY NIGHT...SMALL CRAFT ADVISORY CONDITIONS FOR SEAS ON THE OCEAN MIGHT LAST INTO THE EVENING. CONFIDENCE TOO LOW TO EXTEND. WEDNESDAY THROUGH THURSDAY...SUB-ADVISORY CONDITIONS ARE EXPECTED. THURSDAY NIGHT THROUGH FRIDAY NIGHT...MOSTLY SUB-SCA CONDITIONS; HOWEVER, A STALLED FRONT AND A WAVE OF LOW PRESSURE MOVING ALONG IT COULD ENHANCE SEAS AND/OR WINDS FOR THE COASTAL WATERS, MAKING SCA CONDITIONS POSSIBLE. SATURDAY...SUB SMALL CRAFT ADVISORY CONDITIONS EXPECTED TO RETURN. THIS IS BASED ON TIMING OF WAVES OF LOW PRESSURE CLOSE, CONFIDENCE AT THIS JUNCTURE IS LESS THAN AVERAGE. && .RIP CURRENTS... THERE IS A MODERATE RISK FOR THE FORMATION OF DANGEROUS RIP CURRENTS ON TUESDAY ALONG THE NEW JERSEY SHORE AND AT THE DELAWARE BEACHES. SEAS HAVE CONTINUED TO BUILD IN THE STIFF SOUTHERLY FLOW. WAVE HEIGHTS IN THE SURF ZONE WILL BE UP TO 4 OR 5 FEET. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT TUESDAY FOR ANZ450>455. && $$ SYNOPSIS...GIGI/KLINE NEAR TERM...IOVINO SHORT TERM...KRUZDLO LONG TERM...GIGI AVIATION...GIGI/IOVINO/KLINE MARINE...GIGI/KLINE/KRUZDLO RIP CURRENTS...IOVINO

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