Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 021129 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 729 AM EDT WED SEP 2 2015 .SYNOPSIS... HIGH PRESSURE REMAINS NEAR THE AREA TODAY AND TONIGHT, THEN A BACKDOOR COLD FRONT SLIDES ACROSS OUR REGION THURSDAY NIGHT INTO FRIDAY. HIGH PRESSURE WILL BUILD ACROSS THE NORTHEAST AND INTO THE MID ATLANTIC LATER FRIDAY AND SATURDAY, BEFORE WEAKENING SOME SUNDAY AND MONDAY. A COLD FRONT MAY THEN ARRIVE LATE TUESDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A DENSE FOG ADVISORY WAS ISSED FOR CENTRAL AND SOUTHERN NJ, NORTHERN AND CENTRAL DE, AND SOUTHEAST PA THRU 9 AM. THE DENSE FOG HAS BECOME MORE WIDESPREAD SINCE THE SUN CAME UP AND PRETTY MUCH ALL ASOS/AWOS OBS IN THIS AREA ARE REPORTING VISIBILITY OF 1/4 MILE OR LESS. THIS WILL ADVERSELY IMPACT THE REST OF THE MORNING RUSH BUT THE SHALLOW FOG LAYER SHOULD BE LIFTING DURING THE MID MORNING AS MIXING STRENGTHENS. PREVIOUS DISCUSSION... UPDATE TO EXTEND FOG THROUGH 15Z. STILL SEVERAL SITES THAT ARE NEAR OR BELOW ONE HALF MILE. THUS, IT MAY TAKE A FEW MORE HOURS FOR THE FOG TO DISSIPATE THAN PREVIOUSLY EXPECTED. PREVIOUS NEAR TERM DISCUSSION...A SHORT WAVE TROUGH, WHICH WAS OVER OHIO AS OF 3 AM EDT, SHOULD DIG SOUTHEAST OVER THE MID ATLANTIC REGION TODAY. MODELS ARE IN RELATIVELY GOOD AGREEMENT THAT THE TRACK WILL BE TOO FAR SOUTH FOR MOST OF THE REGION, SAVE FOR DELMARVA, TO SEE ANY ASSOCIATED RAIN CHANCES. THERE IS ONE CAVEAT THOUGH, WITH DECREASING THICKNESSES, MID AND UPPER LEVELS SHOULD COOL THROUGH THE DAY, IF THEY COOL ENOUGH, AND IF THE SEA BREEZE DEVELOPS EARLY ENOUGH IN THE DAY, THEN ISOLATED CONVECTION IS POSSIBLE ALONG THE SEA BREEZE. AT THIS POINT, THOUGH IT APPEARS LIKELY THAT THE SEA BREEZE WILL DEVELOP, MUCH LIKE YESTERDAY, NO MODEL SHOWS THE MID LEVEL CAP ERODING COMPLETELY BY SUNSET, SO HAVE KEPT NJ AND PA DRY THROUGH THE NEAR TERM FOR NOW. TEMPERATURE WISE, WE SHOULD BE NEAR OR SLIGHTLY BELOW YESTERDAY, SO ONCE AGAIN EXPECT THAT HEAT INDEX VALUES WILL NOT REACH CRITICAL LEVELS FOR AN ADVISORY. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... WITH THE SAME AIR MASS STILL IN PLACE TONIGHT, IT LOOKS LIKE ANOTHER ROUND OF PATCHY FOG IS LIKELY OVERNIGHT AS ONCE AGAIN RADIATIONAL COOLING WILL LEAD TO LOWS NEAR THE DEW POINT TEMPERATURES. && .LONG TERM /THURSDAY THROUGH TUESDAY/... THE SYNOPTIC SETUP IS COMPRISED OF A WEAKENING TROUGH ACROSS THE EAST THURSDAY WHICH LIFTS OUT DURING FRIDAY AS A RIDGE TO THE WEST SLIDES EASTWARD. THIS RIDGE IS FORECAST TO REMAIN IN PLACE OVER THE WEEKEND, THEN IT SHOULD FLATTEN OUT EARLY NEXT WEEK AS A SHORT WAVE TROUGH SLIDES ACROSS THE NORTHERN TIER OF STATES. OVERALL, THIS PATTERN SHOULD TEND TO FAVOR WARMTH AND DRYNESS ALTHOUGH A BRIEF BREAK OCCURS DUE TO A BACKDOOR COLD FRONT. THE REGION NEEDS RAIN, HOWEVER IT LOOKS LIKE THE CHCS ARE RATHER LOW GIVEN NO ORGANIZED SYSTEM MOVING THROUGH. WE USED A MODEL/CONTINUITY BLEND FOR THURSDAY INTO SATURDAY, WITH A 00Z WPC GUIDANCE/CONTINUITY BLEND THEREAFTER. SOME ADJUSTMENTS WERE THEN MADE AFTER ADDITIONAL COLLABORATION WITH OUR NEIGHBORING OFFICES. FOR THURSDAY AND FRIDAY...AS AN UPPER-LEVEL TROUGH GRADUALLY LIFTS OUT OF THE EAST AND RIDGING MOVES EASTWARD FROM THE GREAT LAKES AND PLAINS, SURFACE HIGH PRESSURE WILL BUILD INTO NEW ENGLAND. THIS SHOULD SEND A BACKDOOR COLD FRONT THROUGH OUR AREA LATE THURSDAY INTO FRIDAY. SOME SHORT WAVE ENERGY EMBEDDED WITHIN THE LINGERING TROUGH COMBINED WITH SOME CONVERGENCE MAY RESULT IN SOME CONVECTION THURSDAY FROM SOUTH TO NORTH. THIS IS NOT ANTICIPATED TO BE ALL THAT WIDESPREAD AS THE LIFT GENERALLY LOOKS WEAK. ANY CONVECTION ON FRIDAY SHOULD BE SHIFTING SOUTHWESTWARD AS SURFACE HIGH PRESSURE BUILDS DOWN FROM NEW ENGLAND. THIS WILL RESULT IN THE LOW-LEVEL FLOW TURNING FROM THE EAST OR NORTHEAST, AND WITH MORE OF AN OCEAN INFLUENCE A COOLER AIRMASS IS ANTICIPATED. AS OF NOW, IT APPEARS THAT THE DRY AIR MAY WIN OUT AND THEREFORE DESPITE THE ONSHORE FLOW WE SHOULD CLEAR THE CLOUDS OUT FROM NORTH TO SOUTH DURING THE COURSE OF FRIDAY. IF THE TRANSITION IS DELAYED OR IS NOT CLEAN, THEN A PERIOD OF LOW CLOUDS AND FOG MAY BE POSSIBLE WITH THE ONSET OF THE ONSHORE FLOW. SINCE THE PROSPECTS OF SHOWERS AND THUNDERSTORMS IS ON THE LOW SIDE DURING THIS TIME FRAME, WE KEPT THE POPS AT OR BELOW LOW CHC. THERE DOES APPEAR TO BE A WINDOW WHERE BREEZY CONDITIONS DEVELOP ESPECIALLY CLOSER TO THE COAST FRIDAY. FOR SATURDAY AND SUNDAY...AS THE UPPER-LEVEL RIDGE BUILDS ACROSS THE AREA, SURFACE HIGH PRESSURE OVER THE REGION SHOULD EASE EASTWARD. THIS WILL ALLOW THE ONSHORE FLOW TO WEAKEN AND EVENTUALLY TURN SOUTHERLY. THERE COULD BE SOME RESIDUAL CLOUDINESS ACROSS THE FAR SOUTHERN ZONES TO START SATURDAY DEPENDING ON THE DRY AIR PUSH, OTHERWISE A FAIRLY QUIET WEEKEND IN THE WEATHER DEPARTMENT. AS WE LOSE THE ONSHORE INFLUENCE, DAYTIME TEMPERATURES ARE ANTICIPATED TO REBOUND FAIRLY QUICKLY WITH SOME INLAND AREAS NEARING 90 DEGREES SUNDAY. FOR MONDAY AND TUESDAY...A SHORT WAVE TROUGH SLIDING ACROSS THE NORTHERN TIER OF STATES SHOULD FLATTEN THE RIDGE. THIS WILL ALSO FORCE HIGH PRESSURE MORE OFFSHORE, AND A WEAK COLD FRONT MAY MOVE THROUGH LATE TUESDAY. THE BULK OF THE ENERGY LOOKS TO TRACK WELL TO OUR NORTH TUESDAY, THEREFORE THE CHCS FOR CONVECTION AS THE FRONT ARRIVES IS LESS CERTAIN. WE THEREFORE HAVE A DRY MONDAY FORECAST AND THEN BRING IN SOME SLIGHT CHC POPS DURING TUESDAY. ONCE AGAIN AHEAD OF THIS FRONT, VERY WARM TO HOT CONDITIONS LOOK TO OCCUR. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. FOG AFFECTING MANY OF THE TAF SITES NOW COULD PERSIST AS LATE AS 15Z. AFTER THAT, VFR CONDITIONS ARE EXPECTED THROUGH THE DAY. FOG COULD REDEVELOP AGAIN TONIGHT AFTER 03Z, ESPECIALLY FOR THE COASTAL TAF SITES. LIGHT AND VARIABLE WINDS SHOULD CONTINUE THROUGH 12Z, BEFORE WINDS PICK UP OUT OF THE WEST AFTER 12Z (BUT SHOULD REMAIN BELOW 10KT. ONCE AGAIN, IT LOOKS LIKELY THAT A WELL DEFINED SEA BREEZE COULD DEVELOP BY MID DAY. THUS HAVE INCLUDED A SHIFT TO SOUTHEASTERLY NOT ONLY AT THE COASTAL (KACY AND KMIV) BUT ALSO KPHL, KPNE, AND KTTN, WHICH SAW THE SEA BREEZE YESTERDAY. THE SEA BREEZE SHOULD DISSIPATE NEAR OR SHORTLY AFTER SUNSET, LEADING TO MOSTLY LIGHT AND VARIABLE WINDS OVERNIGHT. OUTLOOK... THURSDAY AND FRIDAY...VFR OVERALL, ALTHOUGH LOCAL FOG/STRATUS IS POSSIBLE TO START EACH MORNING. A FEW SHOWERS OR THUNDERSTORMS ARE POSSIBLE ESPECIALLY LATER THURSDAY AND INTO FRIDAY. THE WINDS SHIFT TO NORTHEASTERLY BEHIND A FRONT AND MAY TURN A BIT GUSTY FRIDAY ESPECIALLY CLOSER TO THE COAST. SATURDAY AND SUNDAY...MOSTLY VFR AS HIGH PRESSURE BUILDS IN FROM NEW ENGLAND. EAST TO NORTHEAST WINDS MAY GUST TO 20 KNOTS SATURDAY, THEN DIMINISH AT NIGHT AND TURN SOUTHEASTERLY DURING SUNDAY. && .MARINE... WINDS AND SEAS SHOULD REMAIN WELL BELOW SMALL CRAFT ADVISORY CRITERIA, WITH PEAK WIND GUSTS ONLY EXPECTED TO BE NEAR 15KT, AND SEAS SHOULD STAY AROUND OR BELOW 2 FT. OUTLOOK... THURSDAY...THE CONDITIONS ARE ANTICIPATED TO BE BELOW SMALL CRAFT ADVISORY CRITERIA AS A BACKDOOR COLD FRONT STARTS TO ARRIVE LATE. A WIND SHIFT TO THE EAST AND NORTHEAST AT NIGHT FROM NORTH TO SOUTH IS ANTICIPATED. FRIDAY AND SATURDAY...SEAS BUILD TO SMALL CRAFT ADVISORY CRITERIA ON THE OCEAN WITH AN EASTERLY FLOW BEHIND A BACKDOOR COLD FRONT DURING THE DAY FRIDAY AND CONTINUE INTO SATURDAY. THE WIND GUSTS LOOK TO REACH SMALL CRAFT ADVISORY CRITERIA ACROSS MUCH OF THE AREA DURING THE COURSE OF FRIDAY, THEN DIMINISH DURING SATURDAY. SUNDAY...SEAS ARE ANTICIPATED TO HAVE SUBSIDED BELOW SMALL CRAFT ADVISORY CRITERIA AS HIGH PRESSURE BUILDS IN. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...DENSE FOG ADVISORY UNTIL 9 AM EDT THIS MORNING FOR PAZ070-071- 104-106. NJ...DENSE FOG ADVISORY UNTIL 9 AM EDT THIS MORNING FOR NJZ012>027. DE...DENSE FOG ADVISORY UNTIL 9 AM EDT THIS MORNING FOR DEZ001-002. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GORSE NEAR TERM...JOHNSON/KLEIN SHORT TERM...JOHNSON LONG TERM...GORSE AVIATION...GORSE/JOHNSON MARINE...GORSE/JOHNSON

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