Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 051505 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 1105 AM EDT TUE MAY 5 2015 .SYNOPSIS... A COLD FRONT WILL SLOWLY PROPAGATE SOUTH OVER THE REGION TODAY THROUGH WEDNESDAY. IN THE WAKE OF THE FRONT, HIGH PRESSURE WILL BUILD OVER THE MID ATLANTIC REGION BY THURSDAY AND THEN SLIDES OFF SHORE BY THE WEEKEND. ANOTHER SLOW MOVING COLD FRONT IS POSSIBLE EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... NO MAJOR CHANGES TO THE OVERALL FORECAST SO FAR. THE COLD FRONT HAS MADE ITS WAY HALFWAY THROUGH THE AREA THIS MORNING, AND WILL CONTINUE TO SLOWLY SAG SOUTHWARD. OVERALL DRY CONDITIONS WILL CONTINUE INTO THE EARLY AFTERNOON, BUT AN AREA OF SHOWERS ASSOCIATED WITH THE FIRST OF SEVERAL SHORT WAVE/VORTICITY IMPULSES IS PROGRESSING EASTWARD THROUGH CENTRAL PENNSYLVANIA. THESE SHOWERS MAY WEAKEN SOME AS THEY CONTINUE EASTWARD, BUT AS A SECOND VORTICITY IMPULSE APPROACHES LATER THIS AFTERNOON, SHOWERS AND A FEW THUNDERSTORMS MAY REDEVELOP AND INCREASE IN COVERAGE THROUGH THE AFTERNOON, ESPECIALLY AS THEY INTERACT WITH DAYTIME INSTABILITY. THE STEERING FLOW ALOFT IS RATHER WEAK AND THERE IS STILL SOME DRY AIR TO OVERCOME IN THE SUB-CLOUD LAYER...PSEUDO-INVERTED V FEATURE. THIS WOULD GENERATE SOME ENHANCED WIND GUSTS AND A SLOW MOVING HEAVY RAIN PRODUCER. TEMPERATURES THIS AFTERNOON WILL BE A TAD COOLER THAN THEY WERE ON MONDAY GIVEN THE INCREASE IN CLOUD COVER AND LESS THERMAL ADVECTION AND SHALLOWER VERTICAL MIXING EXPECTED...STILL WELL ABOVE NORMAL FOR EARLY MAY. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... ON GOING SHOWER/CONVECTIVE ACTIVITY WILL CONTINUE THROUGH THE OVERNIGHT HOURS, THOUGH MOST OF THE LIFT SHOULD BE OCCURRING TO OUR NORTH-NORTHWEST WHERE A PASSING MCV/MCS FEATURE MOVES INTO LOWER NEW YORK STATE...THE COMPLEX CURRENTLY OVER THE UPPER MID-WEST STATES. A BETTER SHOT OF RAIN MAY OCCUR ACROSS OUR NORTHERN ZONES DEPENDING ON THE AFOREMENTIONED FEATURE BUT WE CAP POPS AT HIGH END CHANCE FOR THE TIME BEING GIVEN THE UNCERTAINTY OF ITS SOUTHWARD PROGRESSION. SKIES WILL REMAIN MOSTLY CLOUDY/OVERCAST TONIGHT WITH THE STALLING COLD FRONT ACROSS OUR SOUTHERN ZONES. WINDS WILL BECOME LIGHT AND VARIABLE ON EITHER SIDE OF THE FRONT. TEMPERATURES WILL DROP INTO THE MID-50S IN A LOT OF PLACES, STILL WELL ABOVE AVERAGE. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... WEDNESDAY...COLD FRONT SHOULD STILL BE SLOWLY MOVING THROUGH THE REGION TOMORROW. ALTHOUGH BY TOMORROW MORNING, FRONTOLYSIS SHOULD BEGIN. EVEN SO, SHOULD REMAIN ENOUGH ISENTROPIC LIFT AND INSTABILITY FOR LINGERING SHOWERS, AND OVER DELMARVA (WHERE CAPE VALUES ARE ABOVE 500 J/KG), THUNDERSTORMS. BY WEDNESDAY NIGHT HOWEVER, SHOULD SEE LARGE SCALE SUBSIDENCE AS BOTH A SURFACE HIGH BUILDS IN AND AN UPPER LEVEL RIDGE APPROACHES FROM THE WEST. THEREFORE, EXPECT WEDNESDAY NIGHT TO BE DRY. THURSDAY THROUGH FRIDAY...SURFACE HIGH AND UPPER LEVEL RIDGE SHOULD REMAIN THE MAIN INFLUENCING FEATURES FOR OUR REGION THROUGH THIS TIME...LEADING TO DRY CONDITIONS AND A WARMING TREND. STILL KEEPING AN EYE ON THE LOW OFF THE COAST OF THE SOUTHEASTERN U.S. THROUGH THIS TIME, BUT THERE IS GOOD MODEL AGREEMENT THAT IT WILL REMAIN NEARLY STATIONARY THROUGH THIS TIME, WHICH WOULD BE REASONABLE GIVEN THE OVERALL PATTERN. THUS, THIS STILL SEEMS TO HAVE LITTLE IMPACT FOR OUR REGION. SATURDAY THROUGH TUESDAY...SOME QUESTION AS TO HOW QUICKLY THE UPPER LEVEL TROUGH WILL SLIDE EAST. GFS SHOWS A FAR MORE PROGRESSIVE SOLUTION AS COMPARED TO THE ECMWF AND CMC. GIVEN A LOW ROSSBY WAVE NUMBER, AND THE RELATIVELY SLOW MOVING LOWS (BOTH OFF THE SE COAST AND IN THE DESERT SW), SUSPECT THE SLOWER SOLUTION IS THE WAY TO GO. IN THE WAKE OF THE HIGH, ANOTHER VERY SLOW COLD FRONT SHOULD MOVE IN. IT IS UNLIKELY THE FRONT WILL MAKE SIGNIFICANT PROGRESS SOUTH SO LONG AS THE RIDGE REMAINS OVER THE REGION. THUS KEPT MOST OF THE REGION DRY SATURDAY, ASIDE FROM A SMALL CHANCE OF STORMS ACROSS THE HIGHER TERRAIN DURING THE DAY. THEN, BEGIN INCREASING POPS SUNDAY INTO MONDAY. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...MOSTLY VFR. SOME SHOWER ACTIVITY WITH ISOLATED THUNDER IS POSSIBLE THIS AFTERNOON AT MOST OF THE TERMINALS. ACY/MIV MAY HAVE A BETTER CHANCE OF THUNDER WITH SEABREEZE ADVANCEMENT. WINDS WILL BE OUT OF THE SOUTH-SOUTHWEST BEFORE VEERING TOWARDS THE WEST LATER TODAY. TONIGHT...MOSTLY VFR. CONTINUED SHOWER THREAT TONIGHT WITH LIGHT AND VARIABLE WINDS. BETTER CHANCE FOR MVFR OR LOWER SHOWERS EXISTS NORTH OF ABE. OUTLOOK... WEDNESDAY...LINGERING SHOWERS AND THUNDERSTORMS POSSIBLE. MVFR EXPECTED WITH ANY PRECIPITATION...OTHERWISE VFR CONDITIONS EXPECTED. WEDNESDAY NIGHT THROUGH FRIDAY NIGHT...VFR CONDITIONS EXPECTED. SATURDAY...MOSTLY VFR CONDITIONS EXPECTED. THERE IS A SMALL CHANCE OF THUNDERSTORMS FOR KRDG AND KABE. && .MARINE... TODAY - TONIGHT...SUB-SCA CONDITIONS EXPECTED. SEAS WILL REMAIN AROUND 4 FEET TODAY AND TONIGHT AS A SLOW SAGGING COLD FRONT STALLS ACROSS THE WATERS TONIGHT. WINDS WILL VEER FROM THE SOUTH-SOUTHWEST TODAY TOWARDS THE WEST TONIGHT BUT REMAIN LIGHT. OUTLOOK... WEDNESDAY THROUGH SATURDAY...WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...JOHNSON NEAR TERM...HEAVENER/ROBERTSON SHORT TERM...HEAVENER LONG TERM...JOHNSON AVIATION...HEAVENER/JOHNSON MARINE...HEAVENER/JOHNSON

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