Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 010154 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 954 PM EDT FRI JUL 31 2015 .SYNOPSIS... HIGH PRESSURE ACROSS THE APPALACHIANS WILL GIVE WAY TO A WEAK COLD FRONT, WHICH IS FORECAST TO CROSS OUR AREA LATE SATURDAY INTO SUNDAY. A STRONGER COLD FRONT IS FORECASTED TO CROSS OUR REGION LATE MONDAY INTO EARLY TUESDAY, THEN STALL OFFSHORE ON WEDNESDAY INTO THURSDAY. HIGH PRESSURE MAY ARRIVE ON FRIDAY. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... FEW CHANGES MADE TO THE NEAR TERM. WINDS HAVE ALREADY GENERALLY DROPPED OFF TO 5 KT OR LESS. THUS, EXPECT TEMPS TO FALL INTO THE 60S MOST AREAS...EXCEPT POSSIBLY UPPER 50S IN THE POCONOS AND LOW 70S IN AND NEAR PHILADELPHIA AND NEAR THE OCEAN AND BAYS. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... FOR SATURDAY...THE FLOW ALOFT IS BROADLY CYC BUT WITHOUT NOTEWORTHY DISTURBANCES AND THE AIRMASS CONTINUES RATHER DRY. ONCLY EXPECTED CLOUDS ARE SOME DIURNAL CU SIMILAR TO TODAY. THE SFC PRES PATTERN SHOULD BE SIMILAR TO TODAY AS WELL SO GENLY WLY WIND SHOULD DEVELOP IN THE MORNING AND CONT THROUGH AFTN. THE 850MB WINDS ARE FCST TO BE SMWHT STRONGER SO THERE COULD BE A LITTLE MORE GUSTINESS WITH AFTN MIXING. HAVE INCLUDED A SLGT CHC FOR LATE AFTN T-STORMS OVER NRN NJ AND ADJ PA WITH SOME MARGINAL INSTBY EXPECTED. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... OVERVIEW... DOMINANT MID-LEVEL FEATURE THRU THE LONG-TERM PERIOD IS A CLOSED LOW INVOF HUDSON`S BAY ALONG W/ SEVERAL S/WV DISTURBANCES MOVING THRU IT. THIS FEATURE WILL BE MAINTAINED BY A DEVELOPING RIDGE OVER WESTERN NOAM AND HIGH-LATITUDE BLOCKING OVER DAVIS STRAIT. ALTHOUGH THERE IS UNCERTAINTY IN THE TIMING AND STRENGTH OF THE INDIVIDUAL S/WV IMPULSES...AND HOW THEY AFFECT THE AMPLITUDE OF THE TROUGH...A DEVELOPING OMEGA BLOCK OVER NOAM SHOULD LOCK IN THE OVERALL PATTERN THRU AT LEAST D+7. THE MOST APPARENT MODEL TRENDS ARE TO SPEED THE TIMING OF A PRIMARY COLD FRONT THRU THE AREA ON MON NIGHT /AS OPPOSED TO TUE NIGHT/ ...WITH THE FRONT BECOMING STATIONARY NEAR THE NJ COAST AND DELMARVA THRU THU. THE STALLED FRONT SOLUTION IS PLAUSIBLE...GIVEN THE MID-LEVEL LOW OVER HUDSON`S BAY MOVING SLOWLY NORTHEAST THRU THE PERIOD... WHICH WILL LEAD TO A MORE ZONAL FLOW OVER THE AREA PARALLELING THE FRONT BY MID-WEEK. THIS SOLUTION IS ALSO SUPPORTED BY THE ECENS/GEFS MEANS...WITH OVERALL SUPPORT FROM THE INDIVIDUAL MEMBERS AS WELL. THEREFORE...RELIED MORE HEAVILY ON THE EURO GIVEN ITS RECENT PERFORMANCE AS WELL AS THE MORE STABLE ECENS/ GEFS MEANS...AND DISCOUNTED THE MORE PROGRESSIVE GFS AFTER 00Z THU ESPECIALLY GIVEN THE MORE ROBUST NOAM BLOCKING PATTERN. OVERALL...THE MAIN CONCERNS ARE THE POTENTIAL FOR CONVECTION AND LOCALIZED FLASH FLOODING IN THE MON THRU THU TIME FRAME. TEMPS WILL BE AOA NORMAL THRU AT LEAST WED...WITH ABOVE AVG UNCERTAINTY GOING FORWARD...DUE TO THE QUESTIONABLE LOCATION OF THE FRONT AND ASSOCIATED CLOUDINESS. DALIES... SUNDAY...S/WV RIDGING ALOFT W/ HIGH PRES MOVING IN BEHIND THE DEPARTING COLD FRONT. THIS WILL PROMOTE A MOSTLY SUNNY AND DRY DAY. THE GRADIENT MAY RELAX ENOUGH FOR A SEA-BREEZE TO DEVELOP ALONG PORTIONS OF THE COAST. MONDAY...SHRA/TSRA ARE POSSIBLE MON AFTN AS S/WV IMPULSE SKIRTS TO THE NORTH AND A STRONGER COLD FRONT APPROACHES FROM THE WEST. THE APPROACH OF THE S/WV WILL LEAD TO STEEPER LAPSE RATES...BUT MOISTURE IS LIMITED...SO POPS WERE FOCUSED TO THE WEST OF I-95 WHERE BETTER FORCING SHOULD RESIDE. THE CONVECTIVE POTENTIAL IS STILL IN QUESTION AT THIS POINT...AND MAY BE MORE FOCUSED JUST TO OUR WEST. THE MODELS APPEAR TO BE OVERDOING VERTICAL MIXING AHEAD OF THE FRONT...BUT THERE IS THE POTENTIAL FOR 20-25 KNOT WIND GUSTS. MONDAY NIGHT AND TUESDAY...THE AFOREMENTIONED COLD FRONT WILL MOVE JUST OFFSHORE MON NIGHT WHERE IT IS EXPECTED TO BECOME STATIONARY. THERE IS STILL UNCERTAINTY AS TO THE EXTENT OF SHRA/TSRA CROSSING THE CWA MON NIGHT...SO LOW POPS CONFINED N/W OF I-95 FOR NOW. ON TUESDAY...THE CWA IS SITUATED BETWEEN THE STALLED FRONT OFFSHORE AND ANOTHER S/WV DISTURBANCE JUST TO OUR NORTH. W/ SUCH A SETUP...COULD EASILY SEE SOME PRECIP IN DELMARVA AND ESPECIALLY OVER THE POCONOS AND LEHIGH VALLEY. HAVE LOW POPS CONFINED N/W OF I-95 FOR NOW. WED THRU FRI...THERE REMAINS ABOVE AVERAGE UNCERTAINTY DURING THIS TIME FRAME. THE SYNOPTIC SETUP FAVORS A STATIONARY FRONT IN THE VICINITY AND THE MODELS ALSO ADVERTISE A WAVE OF LOW- PRESSURE TRAVERSING THIS BOUNDARY ON THURSDAY. THE MODELS ARE ALSO SUFFERING CONVECTIVE FEEDBACK ISSUES DURING THIS PERIOD WHICH FURTHER ADDS TO THE UNCERTAINTY. THE MAIN CONCERN IS THE POTENTIAL FOR SOME HEAVY RAINFALL DURING THIS TIME FRAME...AS WPC HAS THEIR MAX QPF AXIS ACROSS THE SRN HALF OF OUR CWA. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. OVERNIGHT, WESTERLY OR SOUTHWESTERLY WINDS SHOULD BE LIGHT (GENERALLY NEAR OR BELOW 5 KT). BY LATE TOMORROW MORNING, WINDS (STILL OUT OF THE WEST OR SOUTHWEST) MAY GUST TO 20 KT AT TIMES AS THE PRESSURE GRADIENT INCREASES. MAY SEE MID LEVEL (AROUND 5000 FT AGL) CUMULUS BETWEEN 15 AND 00Z. THERE IS A SLIGHT CHANCE, 20 PERCENT, OF LATE AFTERNOON THUNDERSTORMS AT KABE, BUT CHANCE IS TOO LOW TO MENTION IN THE TAFS AT THIS TIME. OUTLOOK... SAT NIGHT AND SUNDAY...VFR. MONDAY THRU WEDNESDAY...SHRA/TSRA ARE POSSIBLE...ESPECIALLY EACH AFTERNOON. OTHERWISE VFR. && .MARINE... WINDS AND SEAS WILL CONT RATHER LIGHT OVER THE FORECAST WATERS TONIGHT AND TOMORROW MORNING. TODAYS NW FLOW WILL TURN TO THE S AND THEN SW TONIGHT AND SATURDAY AS A SFC TROF BECOMES MORE PRONOUNCED ALONG THE MID-ATLANTIC SEABOARD. SEAS OF 2 TO 3 FT TONIGHT WILL BUILD SLIGHTLY ON SATURDAY AS SWLY WINDS INCREASE...GUSTING TO 15 OR 20KT SAT AFTN. OUTLOOK... SUNDAY THROUGH WEDNESDAY... WEAK HIGH PRESSURE OVER THE CENTRAL APPALACHIANS WILL EXTEND OVER THE WATERS ON SUNDAY INTO MONDAY. A STRONGER COLD FRONT WILL MOVE OVR THE WATERS MON NIGHT AND STALL IN THE VICINITY THRU WEDNESDAY. THERE MAY BE A PERIOD OF WIND GUSTS TO ABOUT 20 KNOTS ASSOCIATED WITH THE PASSAGE OF A COLD FRONT LATE MONDAY INTO EARLY TUESDAY. THIS WILL RESULT IN SEAS INCREASING...BUT THEY ARE EXPECTED TO REMAIN BELOW 5 FEET ATTM. OTHERWISE SUB-SCA CONDITIONS ARE ANTICIPATED THRU THE PERIOD. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...FRANCK NEAR TERM...AMC/JOHNSON SHORT TERM...AMC LONG TERM...FRANCK AVIATION...AMC/FRANCK/JOHNSON/MEOLA MARINE...AMC/FRANCK/MEOLA

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