Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 140340 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1140 PM EDT SUN APR 13 2014 .SYNOPSIS... HIGH PRESSURE CONTINUES TO MOVE OUT TO SEA TONIGHT. A COLD FRONT WILL APPROACH FROM THE WEST TOMORROW NIGHT AND PUSH THROUGH THE REGION TUESDAY AFTERNOON. IN THE WAKE OF THE COLD FRONT, HIGH PRESSURE WILL SETTLE IN OVER THE REGION THROUGH THE REMAINDER OF THE WORK WEEK. AN UPPER LEVEL TROUGH COULD SLIDE OVER OUR REGION EARLY NEXT WEEKEND. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... WIND GUSTS HAVE DIMINISHED FOR MOST SITES NOW THAT DAYTIME MIXING HAS SUBSIDED AFTER THE SUN HAS SET. ANY PLACES THAT REMAIN GUSTY THIS EVENING, EVEN CLOSER TO THE COAST WHERE WINDS ARE THE STRONGEST, SHOULD LOSE THEIR GUSTINESS. SOME ADJUSTMENTS HAVE BEEN MADE TO THE HOURLY GRIDS, BUT OVERNIGHT LOW TEMPERATURE FORECAST WAS NOT CHANGED. AN INCREASE IN CLOUD COVER OVERNIGHT, THE EXPECTATION THAT SOME WINDS WILL REMAIN OVERNIGHT, AND THE FACT THAT DEWPOINTS REMAIN RELATIVELY HIGH SHOULD KEEP TEMPERATURES FROM DROPPING SIGNIFICANTLY OVERNIGHT. IF MORE SIGNIFICANT BREAKS IN THE MID-HIGH LEVEL CLOUD COVER OCCUR, AND WINDS BECOME LIGHTER THAN EXPECTED, TEMPERATURES COULD DROP MORE THAN CURRENTLY FORECAST. STILL UNSURE HOW MUCH STRATUS AND/OR FOG FORMS LATE TONIGHT ACROSS THE REGION. DEWPOINTS ARE MUCH HIGHER THAN THEY WERE LAST BUT THE BOUNDARY LAYER WINDS WERE ALSO MUCH WEAKER LAST NIGHT ALLOWING BETTER MOISTURE POOLING TO OCCUR. STILL, GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR MOSTLY STRATUS TO FORM OVERNIGHT TOWARD DAYBREAK MONDAY NEAR THE TOP OF THE INVERSION, SO WE WILL INCREASE CLOUD COVER OVERNIGHT. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... ANY LOWER CLOUDS AND FOG SHOULD BURN OFF LATE MORNING GIVING WAY TO THE MID AND HIGHER LEVEL CLOUDS. THE RIDGING OFFSHORE SHOULD CONTINUE TO PUSH EASTWARD AND SOME LOWER HEIGHTS AND THICKNESSES ADVECT INTO THE REGION FROM THE WEST. THE GRADIENT FLOW WILL STILL BE FROM THE SOUTH-SOUTHWEST WHERE THE GUIDANCE IS SHOWING SLIGHTLY COOLER LOW-LEVEL TEMPERATURES. ALL INDICATIONS SHOW MONDAY BEING A COUPLE DEGREES COOLER THAN SUNDAY WITH THE NEUTRAL/COOLER AIR ADVECTION OCCURRING AND MORE CLOUD COVER IN PLACE. THAT BEING SAID STILL WENT ABOVE GUIDANCE FOR TOMORROW AS THE AIRMASS ON A WHOLE REMAINS UNCHANGED. NUMERICAL GUIDANCE AND PROBABILISTIC QPF GUIDANCE SHOW THE MAIN SHOWERY ACTIVITY WITH THE COLD FRONT, AGAIN WELL TO OUR WEST TOMORROW, HOLDING OFF THROUGH THE DAYTIME. THEREFORE WE KEEP TOMORROW DRY. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... THE BIG WEATHER STORY OF THE WEEK IS GOING TO BE THE STRONG COLD FRONT AND ASSOCIATED PRECIPITATION TO BEGIN THE LONG TERM PERIOD. OVERVIEW...THERE IS MUCH BETTER MODEL AGREEMENT TODAY WITH THE TIMING AND TRACK OF THIS COLD FRONT, WITH THE TREND GENERALLY TOWARDS A MORE PROGRESSIVE SOLUTION. STILL EXPECTING STRONG SOUTHERLY/SOUTHWESTERLY FLOW TO DEVELOP IN THE WARM SECTOR, AND WITH THAT WIDESPREAD PRECIPITATION AHEAD OF THE FRONT. THE FRONT IS NOW EXPECTED TO COMPLETELY PUSH THROUGH THE REGION BETWEEN 18Z TUESDAY AND 00Z WEDNESDAY. THERE MAY BE A BRIEF PERIOD (LESS THAN 6 HR) OF PRECIPITATION BEHIND THE FRONT, BUT CONSIDERING THE SOURCE REGION OF THE POLAR AIR MASS, EXPECT CONSIDERABLE DRY AIR ADVECTION BEHIND THE FRONT. HEAVY RAIN...MODELS CONTINUE TO SHOW MAXIMUM PRECIPITABLE WATER VALUES AROUND 1.5 INCHES...OR ABOUT 2 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF THE YEAR. IN ADDITION, THE 0-6KM MEAN FLOW TUESDAY NIGHT CONTINUING INTO TUESDAY MORNING IS NEARLY PARALLEL TO THE APPROACHING FRONT, INCREASING THE RISK FOR TRAINING STORMS. HOWEVER, WARM CLOUD LAYER IS MARGINAL FOR AN ENHANCED HEAVY RAIN THREAT, PWAT VALUES ACTUALLY DECREASE BEFORE THE MAXIMUM LIFT ARRIVES OVER THE REGION, AND WITH THE TREND TOWARDS A FASTER COLD FRONT THE PERIOD FOR HEAVY RAIN POTENTIAL IS SHORTER THAN PREVIOUSLY EXPECTED. WILL CONTINUE WITH SIMILAR WORDING IN THE HWO HIGHLIGHTING THE POTENTIAL FOR HEAVY RAIN AND POSSIBLE BRIEF POOR STREET DRAINAGE FLOODING. THUNDERSTORMS...MODELS DEPICT MARGINAL ML CAPE VALUES (<100 J/KG) IN THE WARM SECTOR. HOWEVER, THERE IS POTENTIAL FOR ELEVATED INSTABILITY AS WELL THROUGH THE ENTIRE PERIOD THAT THE REGION IS IN THE WARM SECTION. WINTRY MIX OF PRECIPITATION BEHIND THE FRONT...AS MENTIONED PREVIOUSLY, EXPECT THE PERIOD OF PRECIPITATION BEHIND THE FRONT TO BE RATHER BRIEF. THE HIGHER TERRAIN OF THE POCONOS COULD SEE SOME WINTRY MIX THROUGH THIS PERIOD, BUT GIVEN WARM GROUND TEMPERATURES, DO NOT EXPECT MUCH IN THE WAY OF ACCUMULATION. AT THIS TIME OUR GRIDS HAVE LESS THAN 1 INCH. WPC PROBABILISTIC GUIDANCE HAS A SMALL CHC OF 1 INCH OF SNOW OCCURRING VCNTY THE POCONOS. THE 15Z/31 SREF PROB FOR 1 INCH OF SNOW VCNTY KMPO IS ABOUT 60 PCT. WIND TUESDAY AFTERNOON...CONFLICTING INFORMATION. THE 12Z AND 18Z GFS IS MORE SUBDUED THAN THE 12Z AND 18Z NAM REGARDING SOUTHERLY FLOW WIND GUSTS. THE GUIDANCE WILL NEED TO BE MONITORED AND HOPEFULLY THE THE SUBDUED GFS VERSION WILL BE MORE ACCURATE AND GUSTS WONT EXCEED 30 KT. THE NAM IS MUCH MORE ROBUST...OFFERING OPPORTUNITY FOR SOUTHERLY FLOW WIND GUSTS OF 40-45 KT FROM WESTERN MONMOUTH COUNTY NJ SOUTHWEST THROUGH BURLINGTON COUNTY INTO DELAWARE. WIND TUESDAY NIGHT...COMBINATION OF STRONG CAA AND ASSTD STRONG 3 HRLY PRES RISES OF POSSIBLY 6 MB IN 3 HRS OFFERS OPPORTUNITY FOR WIDESPREAD 30-35 KT WIND GUSTS WITH ISOLATED 40 KT GUSTS POSSIBLE THE ENTIRE CWA. WEDNESDAY AND THURSDAY...EXPECT THE SURFACE RIDGE TO BE THE DOMINANT FEATURE FOR THE REGION. EXPECT ONLY A MODEST WARMING TREND THROUGH THIS PERIOD MAINLY DUE TO AIR MASS MODIFICATION. BEGINNING THURSDAY, WE`RE WATCHING AN UPPER LEVEL THROUGH DIGGING SOUTHEAST OVER THE GREAT BASIN REGION. THAT MUCH THE MODELS AGREE ON. BY FRIDAY MODEL DIFFERENCES AND ENSEMBLE SPREAD INCREASE CONSIDERABLY. THE GFS SHOWS THE TROUGH CUTTING OFF, DEEPENING AND INTENSIFYING IN THE THE NORTHERN STREAM, EVENTUALLY PROPAGATING TO THE GREAT LAKES REGION. WITH THIS SOLUTION, OUR REGION COULD BE IN THE WARM SECTOR, WITH STEADY RAIN THROUGH THE WEEKEND. THE ECMWF ON THE OTHER HAND, CUTS OFF THE LOW IN THE SOUTHERN STREAM, AS IT PROPAGATES OFF THE COAST OF THE CAROLINAS BY SUNDAY. THIS WOULD RESULT IN COOLER CONDITIONS, AND ONLY A BRIEF PERIOD OF PRECIPITATION FOR MOST OF OUR REGION. CONSIDERING THE LOW CONFIDENCE, HAVE STAYED CLOSE TO THE PREVIOUS FORECAST AND WPC GUIDANCE THROUGH THIS PERIOD. && .AVIATION /04Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. OVERNIGHT...MOSTLY VFR. WIND GUSTS HAVE DIMINISHED FOR MOST SITES NOW THAT DAYTIME MIXING HAS SUBSIDED. ANY PLACES THAT REMAIN GUSTY, EVEN CLOSER TO THE COAST WHERE WINDS ARE THE STRONGEST, SHOULD LOSE THEIR GUSTINESS. THERE IS STILL A QUESTION ABOUT HOW MUCH STRATUS FORMS LATE TONIGHT. GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR MOSTLY STRATUS TO FORM TOWARD DAYBREAK MONDAY NEAR THE TOP OF THE INVERSION, SO WE NOW HAVE MVFR CIGS AND VSBYS FOR ALL SITES TOWARD THE PRE-DAWN HOURS AND AROUND DAYBREAK MONDAY. MONDAY...ANY STRATUS/FOG THAT DOES FORM SHOULD LIFT/BURN OFF BY MID-MORNING. SOUTHERLY WINDS WILL PICK UP AGAIN AND BEGIN TO GUST, SLIGHTLY STRONGER, IN THE AFTERNOON. OUTLOOK... MONDAY NIGHT AND TUESDAY...DETERIORATING CONDITIONS TO WIDESPREAD MVFR AND POSSIBLY WIDESPREAD IFR. RAIN COULD BE HEAVY AT TIMES, AND ISOLATED THUNDERSTORMS ARE POSSIBLE DURING THE DAY TUESDAY. LLWS IS FLAGGED IN THE WIND SHEAR GUI WITH SUSTAINED SOUTH WIND 15-20 KT AND 2000 FT WIND 200 DEGREES AT 55-60 KT FOR A FEW HRS TUE AFTN. TUESDAY NIGHT...ALL TAF SITES SHOULD SEE NW WIND GUST 30-35 KT WITH ISOLATED 40 KT GUST POSSIBLE. WEDNESDAY THROUGH THURSDAY NIGHT...GENERALLY VFR CONDITIONS EXPECTED. && .MARINE... SOME GUSTS TO NEAR 25 KNOTS CONTINUES MAINLY NEARSHORE WHERE THE BETTER MIXING IS BEING MAINTAINED LONGER. WHILE THE GUSTS OVERALL HAVE SUBSIDED FOR DELAWARE BAY, ANOTHER ROUND OF DEEPER MIXING MONDAY SHOULD RESULT IN GUSTS TO ABOUT 25 KNOTS FROM ABOUT MIDDAY AND THE EVENING /ESPECIALLY NEARSHORE/. THEREFORE, WE OPTED TO KEEP IT SIMPLE AND JUST EXTENDED THE SMALL CRAFT ADVISORY THROUGH MONDAY NIGHT TO MATCH UP WITH THE OCEAN ZONES. SEAS ARE SLOWLY RESPONDING TO THE PERSIST SOUTHERLY FLOW ESPECIALLY ON THE ATLANTIC COASTAL WATERS, AND THIS SHOULD BE MORE NOTED ON MONDAY AHEAD OF AN APPROACHING COLD FRONT. OUTLOOK... TUESDAY...SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY. A COLD FRONT WILL MOVE THROUGH LATE TUESDAY AFTERNOON BRINGING AN ABRUPT SHIFT FROM SOUTHERLY TO NORTHWESTERLY WINDS. ISOLATED SOUTHERLY FLOW GALE FORCE GUSTS POSSIBLE. THERE IS A BETTER CHC OF NW FLOW GALE FORCE GUSTS OF 35 TO 40 KT AT TIMES TUESDAY NIGHT IN STRONG COLD AIR ADVECTION WITH STRONG PRESSURE RISES. A GALE WATCH MAY BE NEEDED...ESPECIALLY FOR TUESDAY NIGHT/EARLY WEDNESDAY. WEDNESDAY...SMALL CRAFT ADVISORY CONDITIONS LIKELY...ESPECIALLY EARLY IN THE DAY, BUT EXPECT WINDS TO DECREASE WEDNESDAY AFTERNOON. WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...WINDS NEAR OR JUST BELOW 25KT. HOWEVER, WAVE HEIGHTS COULD BE ABOVE 5 FT THROUGH THE ENTIRE PERIOD. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ430-431- 450>455. && $$ SYNOPSIS...JOHNSON NEAR TERM...HEAVENER/ROBERTSON SHORT TERM...HEAVENER LONG TERM...DRAG/JOHNSON AVIATION...DRAG/HEAVENER/JOHNSON MARINE...DRAG/GORSE/HEAVENER/JOHNSON

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