Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 172239 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 639 PM EDT SUN AUG 17 2014 .SYNOPSIS... A COLD FRONT CLEARING THE AREA TO THE SOUTH TONIGHT WILL STALL OVER THE LOWER DELMARVA ON MONDAY. A WAVE OF LOW PRESSURE WILL TRACK EASTWARD ALONG THE STALLED BOUNDARY MONDAY NIGHT AND MOVE OFFSHORE TUESDAY. THE FRONTAL BOUNDARY SHOULD REMAIN NEARLY STATIONARY FROM THE GREAT LAKES TO THE SOUTHERN MIDDLE ATLANTIC STATES INTO FRIDAY AS WEAK WAVES OF LOW PRESSURE RIDE ALONG IT. HIGH PRESSURE IS EXPECTED TO SETUP ANCHOR ACROSS THE REGION ON SATURDAY AND SUNDAY. THIS AREA OF HIGH PRESSURE WILL BE SANDWICHED BETWEEN AN AREA OF LOW PRESSURE MOVING OFFSHORE OF THE MID- ATLANTIC ON SATURDAY AND ANOTHER AREA OF LOW PRESSURE APPROACHING LAKE SUPERIOR ON SUNDAY. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... A FEW ISOLATED SHOWERS WILL CONTINUE TO POP UP ACROSS DELAWARE AND THE EASTERN SHORE OF MARYLAND THIS EVENING BUT AS THE COLD FRONT CONTINUES TO PUSH TOT HE SOUTHEAST, ANY LINGERING ACTIVITY WILL DIMINISH. THE COLD FRONT WILL CONTINUE TO MOVE SOUTHEAST THROUGH THE REGION TONIGHT WITH MID-LEVEL CLOUDS GRADUALLY CLEARING OUT. IT WILL BE A CLEAR CRISP NIGHT WITH FAVORABLE CONDITIONS FOR RADIATIONAL COOLING. WENT A TOUCH COOLER THAN THE MAV/MET ON LOWS TONIGHT DUE TO THE RADIATIONAL COOLING AS NORTHWEST WINDS BECOME LIGHT TONIGHT. THE NEXT SIX TO TWELVE HOURS ALSO INCORPORATE ELEMENTS OF THE LAV WHICH APPEARS TO HAVE A GOOD HANDLE ON THE CURRENT SETUP. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... HIGH PRESSURE WILL MOVE THROUGH THE REGION ON MONDAY. CLOUDS WILL INCREASE SOME INT HE AFTERNOON FROM SOUTH TO NORTH. MODEL CONSENSUS SUGGESTS A LOW CHANCE FOR RAIN SHOWERS LATE IN THE DAY ACROSS THE SOUTHERN DELMARVA AND USED THE 09Z SREF FOR SOME VERY LIGHT QPF. GIVEN THE LAST FEW DAYS HAVE ENDED UP COOLER THAN THE MAV AND PARTICULARLY THE MET THE LAST FEW DAYS, FORECASTED HIGH TEMPERATURES ARE AT OR JUST BELOW THE MET. LIGHT AND VARIABLE WINDS SHOULD COME AROUND TO THE SOUTHWEST IN THE AFTERNOON UNDER 10 MPH. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... THE NEW WRF-NMMB INITIALIZATION WAS SLIGHTLY BETTER THAN THE GFS. OVERALL THERE IS SOMEWHAT BETTER MODEL CONSENSUS OVER EASTERN NOAM TODAY THAN THERE WAS YESTERDAY, ESPECIALLY WITH THE FIRST SYSTEM PASSING TO OUR SOUTH. A BLOCKY WEATHER PATTERN IS EXPECTED TO PERSIST. THIS WILL PREVENT THE HEAT RIDGE FROM MAKING IT THIS FAR NORTH. REGARDLESS, FOR MOST OF THE LONG TERM THERE IS A RETURN OF MORE TYPICAL WARMER AND MORE HUMID (SOUTH ESPECIALLY) AUGUST WEATHER IN OUR CWA WITH THE LIKELIEST DAY FOR SHOWERS AND THUNDERSTORMS ON THURSDAY. AT THE END OF THE LONG TERM MODELS CONTINUE TO STRUGGLE WITH THE EVOLUTION OF THE MID-LEVEL FLOW OVER THE NORTHEAST CONUS AND ATLANTIC CANADA DURING THE D+6 AND D+7 TIMEFRAME. THIS IS LARGELY ATTRIBUTED TO MODEL DIFFERENCES IN THE HANDLING OF SHORTWAVE ENERGY CURRENTLY OVER THE ALEUTIAN ISLANDS. THE MID-LEVEL HEIGHT FIELD WILL EVOLVE INTO A TROUGH IN THE WEST AND SUBSEQUENT RIDGING IN THE EAST...BUT THIS WILL BE COMPLICATED BY PERSISTENT BLOCKING /POSITIVE HEIGHT ANOMALIES/ INVOF THE DAVIS STRAIGHT...LEADING TO A REX-BLOCK OVER THE NORTHEAST CONUS AND ATLANTIC CANADA. THE 12Z/17 EURO/GFS ARE IN BETTER AGREEMENT TODAY WITH THE POSITION OF THE REX BLOCK AT 00Z SUNDAY...INDICATING A CLOSED HIGH OVER QUEBEC AND A CLOSED LOW SOUTH OF NOVA SCOTIA AT 500 HPA. ALTHOUGH BOTH THE EURO AND GFS OPERATIONAL RUNS ARE IN GENERAL AGREEMENT WITH THEIR RESPECTIVE ENSEMBLE MEANS...THERE IS CONSIDERABLE SPREAD AMONGST THE INDIVIDUAL MEMBERS WITH REGARD TO THE MID-LEVEL HEIGHT FIELDS...WHICH TRANSLATES INTO UNCERTAINTY WITH RESPECT TO THE POSITION OF SURFACE FEATURES. MORE IMPORTANTLY... THE MODELS HAVE SHOWN LITTLE RUN-TO-RUN CONSISTENCY AT THIS POINT... ESPECIALLY GIVEN THE TIME RANGE AND THE PLACEMENT OF THE MAIN SHORT-WAVE ENERGY WHICH IS STILL OVER THE DATA-SPARSE PACIFIC OCEAN. THE GFS. WRF AND CAN GGEM ALL TRENDED TOWARD THE ECMWF AND UKMET FOR MONDAY NIGHT. THE DP/DT ON THE TRIGGERING CLOSED LOW CONTINUES TO BE SLIGHTLY FASTER AND SLIGHTLY MORE SOUTHEAST WHICH CORROBORATE THE EUROPEAN MODEL EVOLUTION. THUS THE TREND STARTED BY THE MID SHIFT WAS CONTINUED AS WE SHAVED POPS DOWNWARD EXCEPT FOR DELMARVA. WE ALSO EDGED SOUTHWARD THE MENTION OF HEAVY RAIN AND THUNDER. OUR THINKING IS CLOSEST TO THE HI RES ARW SOLUTION. IT NOW APPEARS MORE LIKELY TO BE SOUTH OF WHERE THE HEAVIEST RAIN FELL LAST WEEK. MIN TEMPERATURES WERE CLOSE TO STAT GUIDANCE NORTH WHERE CLOUD COVERAGE IS NOT AS CONFIDENT AND HIGHER THAN STAT GUIDANCE SOUTH BECAUSE OF CLOUDS. A FASTER EXIT TO PCPN CHANCES IS FORECAST FOR TUESDAY MORNING. IN THE WAKE OF THE DEPARTING LOW PRESSURE SYSTEM, THE GENERAL SYNOPTIC SCALE FLOW REMAINS ONSHORE. NORTH OF ABOUT 40NISH THE ONSHORE FLOW IS PREDICTED TO BE RELATIVELY DRY. SOUTH OF THERE THE ONSHORE FLOW SHOULD BE MORE PROBLEMATICAL AND WE ARE CLOUDIER. GFS MLCAPE FORECAST WAS CONTAMINATED BY MDL SFC DEW POINTS 5 TO 8F HIGHER THAN ITS STATISTICAL MOS. WITH NO OTHER MODEL CORROBORATION WE ARE EXPECTING ANY UPSLOPE OR DAYTIME HEATING CONVECTION TO REMAIN WEST OF OUR CWA THE REST OF TUESDAY. WE WENT ABOVE STAT GUIDANCE NORTHWEST BECAUSE OF MORE SUNSHINE, NEAR CENTRAL AND BELOW SOUTHEAST BECAUSE OF ONSHORE FLOW. ON TUESDAY NIGHT SOME RESIDUAL SHOWERS MIGHT MAKE IT INTO OUR CWA AND WE KEPT LOW POPS WEST. GIVEN THE TREND TOWARD A FASTER RESOLUTION AND THAT THE KICKER CLOSED LOW INITIALIZED OVER SASKATCHEWAN IS ALSO TRENDING FASTER, WE HAVE UPPED POPS FOR WEDNESDAY AND EXTENDED THEM FARTHER TO THE EAST. THERE IS STILL A NOSE OF STABILITY OVER OUR CWA FROM A WAKE HIGH IN NEW ENGLAND. SO, IT LOOKS AS THOUGH CONVECTION IS NOT HOME GROWN, BUT MOVES EASTWARD. EITHER WAY, THERE ARE ENOUGH SHORT WAVES UPWIND TO BELIEVE SOME ARE FOR REAL. THE AIR MASS ITSELF IS PREDICTED TO BE SLIGHTLY WARMER AND WE UPPED MAX TEMPS EVER SO SLIGHTLY. THURSDAY RIGHT NOW LOOKS TO BE THE DAY WITH THE MOST WIDESPREAD CONVECTIVE ACTIVITY WITH HEAVY RAIN MORE OF A CONCERN THAN SEVERE AT THIS POINT. PREDICTED PWATS SHOULD GET ABOVE 1.50 INCHES AND RIGHT NOW THE MID LEVEL LAPSE RATES AND 0-6KM BULK SHEAR VALUES NOT THAT FOREBODING. OF COURSE, IF SOLUTIONS KEEP ON ADVANCING IN TIME, THE GO TO PERIOD MIGHT BE WEDNESDAY NIGHT. WITH TROFINESS LINGERING, WE KEPT IN A CHANCE FOR INSTABILITY SHOWERS AND THUNDERSTORMS FOR FRIDAY. ON THE WEEKEND...A GENERAL AREA OF LOW PRESSURE IS EXPECTED TO BE INVOF THE MID-ATLANTIC COAST ON SATURDAY...GRADUALLY MOVING OFFSHORE...AS A RIDGE OF HIGH PRESSURE NOSES IN FROM THE NORTHEAST. ALTHOUGH THIS WOULD IMPLY A DRYING TREND ON SATURDAY...THE REGION WILL STILL BE UNDER THE INFLUENCE OF A CYCLONIC FLOW ALOFT AS WELL AS AN ONSHORE FLOW...SO KEPT A CHANCE OF SHOWERS IN THE FORECAST. THE MODELS MAY BE TO PROGRESSIVE BUILDING A MID-LEVEL RIDGE INTO THE REGION ON SUNDAY GIVEN THEIR TYPICAL BIAS OF BREAKING DOWN /REX/ BLOCKS TOO QUICKLY. THEREFORE...KEPT A SLIGHT CHANCE OF SHOWERS IN THE FORECAST. OVERALL...EXPECT TEMPERATURES SLIGHTLY BELOW NORMAL. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. A COLD FRONT WITH SOME ASSOCIATED MID-LEVEL VFR CEILINGS IS MOVING SOUTHEAST ACROSS THE REGION. WINDS HAVE INCREASED SLIGHTLY THIS AFTERNOON WITH A FAVORABLE SET-UP FOR SOME WIND GUSTS CLOSE TO 20 KT FOR THE MID AND PERHAPS LATE AFTERNOON HOURS FROM THE NORTHWEST. WINDS WILL RELAX LATER THIS EVENING AND CLOUDS WILL CONTINUE TO CLEAR OUT. NO FOG OR LOW VISIBILITIES ARE EXPECTED TONIGHT. VFR TONIGHT. SOME MID-LEVEL CLOUDS MAY ENTER THE PICTURE MONDAY AFTERNOON, BUT STILL VFR WITH WEST-SOUTHWEST WINDS UNDER 10 KTS AFTER STARTING THE DAY LIGHT AND VARIABLE. OUTLOOK... MONDAY NIGHT AND TUESDAY...LOPRES TRACKS SOUTH OF THE AREA. BEST CHANCE FOR SHRA AND POSSIBLY TSRA SHOULD BE FOR AIRPORTS SOUTH OF THE TERMINALS. A PERIOD OF MVFR OR IFR CONDITIONS POSSIBLE AT TIMES OF HEAVIER SHRA AND ALSO AT AIRPORTS/TERMINALS NEAR THE COAST WITH ONSHORE FLOW. VFR (OR REMAINING VFR) MOST AREAS BY TUESDAY AFTN. TUESDAY NIGHT AND WEDNESDAY MORNING...PREDOMINATELY VFR. WEDNESDAY AFTERNOON THROUGH FRIDAY...SCT SHRA/TSRA AS MULTIPLE DISTURBANCES TRACK THRU THE REGION. SOME FLIGHT RESTRICTIONS LIKELY, ESPECIALLY CENTERED AROUND THURSDAY. && .MARINE... SEAS WILL BE 2 TO 3 FEET IN THIS PERIOD. NORTHWEST WINDS WILL DIMINISH OVERNIGHT BECOMING VARIABLE. A SOUTHERLY WIND UNDER 10 KNOTS WILL DEVELOP IN THE AFTERNOON ON MONDAY. OUTLOOK... MONDAY NIGHT THROUGH TUESDAY...SMALL CRAFT ADVISORY CONDITIONS CHANCES ARE LOOKING SLIGHTLY LESS AS THE LOW PRESSURE SYSTEM AND ONSHORE FLOW HAVE TRENDED WEAKER. STILL LOWEST CONFIDENCE ON SOUTHERN OCEANIC WATERS. TUESDAY NIGHT THROUGH FRIDAY...ONSHORE FLOW CONTINUES BUT WILL WEAKEN AND GENERALLY REMAIN WEAK OVER TIME. GREATEST MARINE CONCERN LOCALIZED STRONGER WINDS AND SEAS IN THUNDERSTORMS, CENTERED ON THURSDAY. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...GIGI/KLEIN NEAR TERM...GAINES/MEOLA SHORT TERM...GAINES LONG TERM...FRANCK/GIGI AVIATION...GAINES/GIGI/KLEIN/O`HARA MARINE...GAINES/GIGI/KLEIN/O`HARA

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