Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 041338 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 938 AM EDT TUE AUG 4 2015 .SYNOPSIS... A COLD FRONT OVER WESTERN PENNSYLVANIA WILL APPROACH FROM THE WEST THIS MORNING. THE FRONT WILL MOVE THROUGH OUR REGION THIS AFTERNOON AND TONIGHT BEFORE STALLING JUST TO OUR SOUTH WEDNESDAY THROUGH THE END OF THE WEEK. WAVES OF LOW PRESSURE WILL RIDE ALONG THE BOUNDARY WITH THE FINAL WAVE OF LOW PRESSURE TRACKING JUST OFF THE MID-ATLANTIC COAST ON SATURDAY. HIGH PRESSURE BUILDS IN FROM FROM EASTERN CANADA SUNDAY AND MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... ADJUSTED A FEW PARAMETERS IN THE GRIDS THIS MORNING FOR THE UPDATE. QUITE A BIT OF SUN RIGHT NOW AS THE OVERNIGHT CONVECTION HAS MOVED OFFSHORE AND WE AWAIT THE ARRIVAL OF THE COLD FRONT. DEWPOINTS ARE UP FROM YESTERDAY AS PLANNED, ESPECIALLY ACROSS THE COASTAL PLAIN. THIS COMBINED WITH PLENTY OF SOLAR HEATING THIS MORNING WILL SEE THIS AIRMASS HIT CONVECTIVE TEMPS. THE CU WILL POP THIS AFTERNOON...LEADING TO SHOWERS AND THUNDERSTORMS. FOR PRECIP PLACEMENT LATER TODAY, I ELIMINATED POPS FROM OUR NORTHWESTERN ZONES AS THE FOCUS WILL BE FURTHER EAST. STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE LATER TODAY ALONG THE COAST. WITH 850 TEMPS SLATED TO HIT ABOUT 18 DEGREES C, I LOWERED THIS AFTERNOON`S HIGH TEMPS BY 1 DEGREE CWA-WIDE. HEAT INDICES WILL HIT THE LOWER TO MIDDLE 90S ACROSS OUR SOUTHEASTERN ZONES WHERE THE BEST MOISTURE IS POOLING. PREVIOUS DISCUSSION...OVERNIGHT SURFACE ANALYSIS SHOWS A COLD FRONT POSITIONED OVER WESTERN NY AND THE OH VALLEY. MEANWHILE, A SURFACE TROUGH WAS LOCATED JUST EAST OF I-95 IN THE MID-ATLANTIC REGION. WINDS ARE OUT OF THE S-SW (NW) AND DEWPOINTS IN THE LOW 70S (LOW 60S)TO THE EAST (WEST) OF THE TROUGH. UPPER-LEVEL DIVERGENCE IN THE RIGHT ENTRANCE REGION OF AN UPPER- LEVEL JET STREAK OVER THE NORTHEAST STATES AND DPVA FROM A SUBTLE MID-LEVEL SHORTWAVE TROUGH HAS BEEN THE SOURCE OF LIFT FOR NOCTURNAL CONVECTION THAT WAS MOVING ACROSS EASTERN PA AND THE NORTHERN HALF OF NJ. HI-RES CAM GUIDANCE HAD A POOR HANDLE ON THE OVERNIGHT CONVECTION, SO FORECAST THRU EARLY THIS MORNING BASED MORE OFF OF AN EXTRAPOLATION OF CURRENT SATELLITE/RADAR AND FROM MESOANALYSIS TRENDS. THERE IS ENOUGH ELEVATED INSTABILITY TO KEEP THE SHOWERS AND STORMS GOING EARLY MORNING AS THEY MOVE EASTWARD THIS MORNING. WE ARE PARTICULARLY KEEPING AN EYE ON A CLUSTER OF STORMS NEAR THE MASON- DIXON LINE JUST TO OUR WEST AS THEY CURRENTLY HAVE SEVERE THUNDERSTORM WARNINGS WITH IT. AT 07Z, THERE WAS 2000+ J/KG OF ELEVATED CAPE DOWNSTREAM OF THESE STORMS. THE AFOREMENTIONED COLD FRONT WILL ADVANCE EASTWARD THRU THE LEHIGH VALLEY AND NW NJ EARLY THIS AFTERNOON AND I-95 CORRIDOR LATE IN THE DAY. ONCE THE DEBRIS CLOUDS FROM THE CURRENT CONVECTION MOVES OFF THE COAST, STRONG HEATING WILL ALLOW THE ATMOSPHERE TO DESTABILIZE THIS AFTERNOON. A HOT (HIGHS IN THE LOWER 90S) AND HUMID (DEWPOINTS IN THE UPPER 60S/LOW 70S) AIRMASS WILL BE PRESENT AHEAD OF THE FRONT. FORECAST SOUNDINGS FROM THE 00Z NAM AND GFS ARE VASTLY DIFFERENT BUT AFTER ACCOUNTING FOR MOISTURE BIASES FROM BOTH MODELS, MLCAPE WILL RANGE FROM AROUND 1500 J/KG NEAR THE I-95 CORRIDOR TO 3000 J/KG IN THE LOWER DELMARVA DURING PEAK HEATING. THE 00Z HI-RES NCAR ENSEMBLES SUPPORT THESE NUMBERS AS WELL. BULK SHEAR WILL ALSO BE MODERATELY STRONG AS WESTERLY WINDS IN THE MID-LEVELS INCREASE TO 40-50 KT. THE ONE LIMITING FACTOR WILL BE THE ABSENCE OF ORGANIZED LIFT ALOFT. HOWEVER, SURFACE CONVERGENCE NEAR THE FRONTAL BOUNDARY SHOULD PROVIDE JUST ENOUGH LIFT TO INITIATE CONVECTION THIS AFTERNOON. SPC HAS PLACED AREAS EAST OF I-95 IN A SLIGHT RISK FOR SEVERE STORMS. THE ENVIRONMENT WILL SUPPORT DAMAGING STRAIGHT LINE- WINDS FROM WET MICROBURSTS AND LARGE HAIL WITH THE STRONGEST CORES. THE THREAT APPEARS TO BE GREATEST FROM APPROXIMATELY 2-8 PM. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... THE COLD FRONT WILL SLOWLY MOVE EASTWARD THRU THE COASTAL PLAIN THIS EVENING AND EVENTUALLY OFF THE COAST OVERNIGHT. ACCORDINGLY, THE HIGHEST POPS RESIDE THIS EVENING OVER SOUTHERN NJ AND THE DELMARVA. PUT A LITTLE MORE WEIGHT IN THE HI-RES GUIDANCE FOR THIS EVENING`S ROUND OF CONVECTION THAN THE ONGOING ROUND EARLY THIS MORNING AS THE LATTER ROUND OF CONVECTION IS MAINLY FOCUSED/FORCED ALONG THE WELL- DEFINED SYNOPTIC COLD FRONT. POST-FRONTAL NW WINDS WILL BE LIGHT, BUT THERE APPEARS TO BE ENOUGH DRY AIR ADVECTION TO LIMIT THE FOG POTENTIAL OVERNIGHT. IF THE FRONT SLOWS DOWN ENOUGH AND SKIES ARE ABLE TO CLEAR OVERNIGHT, THEN FOG MAY DEVELOP NEAR THE COAST, ESPECIALLY IN AREAS THAT RECEIVE RAIN. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... THE COLD FRONT WILL MOVE OFF THE COAST WEDNESDAY WHILE HIGH PRESSURE BUILDS IN THE MIDWEST. A RELATIVELY TIGHT PRESSURE GRADIENT FOR THIS TIME OF YEAR IS FORECAST OVER OUR AREA, LEADING TO A BREEZY NW WIND. DRY AIR ADVECTION WILL BE MORE PROMINENT THAT COLD AIR ADVECTION BEHIND THE FRONT. MAX TEMPS RANGE FROM THE UPPER 70S IN THE POCONOS TO NEAR 90F IN THE MORE URBAN AREAS ALONG AND EAST OF I-95. HOWEVER, IT WILL FEEL COMFORTABLE WITH DEWPOINTS ONLY EXPECTED TO BE IN THE 50S. THE EXTENDED PART OF THE FORECAST (THURSDAY NIGHT AND BEYOND) REMAINS UNTOUCHED. PREVIOUS DISCUSSION FROM THE DAY SHIFT FOLLOWS... 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. 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 /14Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR THIS MORNING AND EARLY AFTERNOON. SCT SHRA AND TSRA EXPECTED TO DEVELOP AGAIN DURING THE MID AND LATE AFTERNOON. BASED ON TIMING OF A COLD FRONT, THE I-95 (TTN/PNE/PHL/ILG) AND SOUTHERN NJ (MIV/ACY) TERMINALS HAVE THE BEST CHANCE TO SEE STORMS. INCLUDED A PROB30 GROUP IN THE 06Z TAFS FOR THESE TERMINALS. LATER TAF CYCLES WILL LIKELY ADD A TEMPO AND THEN PREVAILING GROUP FOR TSRA WHEN CONFIDENCE IN TIMING AND LOCATIONS INCREASES. OUTLOOK... 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... WITH SOME UPWELLING ENHANCING THE INVERSION OVER THE WATER, I ELIMINATED THE MENTION OF 30 KT OVER THE OCEAN WATERS. PREVIOUS DISCUSSION...EXTENDED THE SCA THAT WAS ALREADY IN EFFECT FOR TODAY INTO TONIGHT. S-SW WINDS WILL GUST TO 25 KT TODAY AND EARLY THIS EVENING. THE SEAS WILL BE ELEVATED TO 4-6 FT DURING THIS TIME. WINDS ARE EXPECTED TO WEAKEN AFTER SUNSET BUT SEAS WILL TAKE SEVERAL MORE HOURS TO SUBSIDE TO BELOW SCA CRITERIA. IN DELAWARE BAY, WE`LL TOP THE WIND GUSTS OUT AT 20 KTS (SUB SMALL CRAFT). OUTLOOK... 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 TODAY 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 5 AM EDT WEDNESDAY FOR ANZ450>455. && $$ SYNOPSIS...KLEIN NEAR TERM...KLEIN/KRUZDLO SHORT TERM...KLEIN LONG TERM...GIGI/KLEIN AVIATION...GIGI/KLEIN MARINE...GIGI/KLEIN/KRUZDLO RIP CURRENTS...

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