Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 211345 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 945 AM EDT MON JUL 21 2014 .SYNOPSIS... HIGH PRESSURE WILL ESTABLISH ITSELF OVER OUR REGION TODAY THROUGH TUESDAY NIGHT. A COLD FRONT IS ANTICIPATED TO ARRIVE WEDNESDAY NIGHT AND DRIFT JUST TO THE SOUTHEAST OF OUR FORECAST AREA THURSDAY NIGHT. WEAK HIGH PRESSURE FOLLOWS FRIDAY THEN MERGES WITH THE BERMUDA HIGH SATURDAY. A WARM FRONT IS THEN FORECAST TO APPROACH FROM THE SOUTH ON SUNDAY AS LOW PRESSURE DEVELOPS FROM THE GREAT LAKES TO THE MID ATLANTIC STATES. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... INCREASED CLOUD COVER ACROSS THE WESTERN ZONES THROUGH THE MORNING HOURS AS AN AREA OF STRATUS WITH THICKER STRATOCU ADVECTED IN FROM THE WEST. ACARS AND LAPS SOUNDINGS SHOW THE LOW-LEVEL INVERSION BREAKING BY NOON TODAY TO ALLOW A LIFTING OF THE STRATUS GIVING WAY TO A SCATTERED/BROKEN STRATOCU DECK. A FEW LIGHT SHOWERS ACROSS SOUTH CENTRAL PENNSYLVANIA COULD CLIP OUR WESTERN ZONES LATER THIS MORNING SO WE RETAIN THE SLIGHT CHANCE POPS. THE OVERALL SYNOPTIC SITUATION HAS NOT CHANGED MUCH...HIGH PRESSURE REMAINS OFFSHORE TO THE NORTHEAST AND EXPANDS BACK ACROSS OUR AREA TODAY. A WEAK UPPER TROUGH CROSSES THE AREA LATER TODAY AND TONIGHT IN RESPONSE TO BUILDING H5 HEIGHTS OUT WEST. A FAIR WEATHER DAY IS EXPECTED WITH PARTLY TO MOSTLY SUNNY SKIES. SOME CU/AC WILL CROSS THE ARE AT TIMES AND TEMPERATURES WILL BE A FEW DEGREES BELOW NORMAL FOR LATE JULY. HIGHS WILL MOSTLY BE IN THE LOW/MID 80S ACROSS THE AREA. DEW POINTS WILL BE A BIT HIGHER THAN OVER THE WEEKEND...BUT STILL NOT TOO UNCOMFORTABLE. WINDS WILL BE LIGHT FAVORING THE E OR SE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... LOW LEVEL MOISTURE WILL CONTINUE TO SLOWLY INCREASE TONIGHT WITH THE HIGH STILL OFF TO THE EAST. A PERIOD OF LOW CLOUDS AND MAYBE SOME FOG WILL DEVELOP ACROSS THE DELMARVA AND SRN NJ. NO PCPN IS EXPECTED TONIGHT. LOWS WILL BE A FEW DEGREES ABOVE NORMAL WITH UPPER 60S TO LOW 70S EXPECTED ACROSS THE REGION. && .LONG TERM /TUESDAY THROUGH SUNDAY/... 500MB: EXPANSIVE BROAD WARM RIDGE FROM THE ROCKIES TO THE WESTERN ATLANTIC WILL BE SPLIT BY EAST COAST TROUGHING LATE WEDNESDAY OR THURSDAY AND THEN POTENTIALLY MORE SUBSTANTIAL TROUGHING DEVELOPS LATE SUNDAY OVER THE UPPER MIDWEST. TEMPERATURES: THE MONTH SO FAR HAS AVERAGED ABOUT A DEGREE ABOVE NORMAL EXCEPT KACY AREA WHICH HAS AVERAGED A DEGREE BELOW NORMAL. TUESDAYS SLIGHTLY ABOVE NORMAL CALENDAR DAY AVG TEMPERATURES SHOULD BE ABOUT 6 DEGREES ABOVE NORMAL WEDNESDAY AND POSSIBLY STILL 5 DEGREES ABOVE NORMAL THURSDAY BEFORE COOLING TO NEAR OR SLIGHTLY BELOW NORMAL FRI-SUN. AS YOU MAY BE AWARE...THIS SUMMER IS NOT LIKE THE BOILERS OF 2010 (#2) AND 2013 (#3). STILL DESPITE THE RELATIVELY NUMBER OF NICE DAYS...THE AVG TEMP FROM JUNE 1-JUL 20 IS TIED FOR THE 14TH WARMEST ON RECORD HERE AT KPHL. FORECAST BASIS: UNLESS OTHERWISE NOTED THE LONG TERM PERIOD OF THIS FORECAST IS GENERALLY BASED ON A 50 50 BLEND OF THE 00Z/21 NAM/GFS MOS FOR THE PERIOD TUESDAY-WEDNESDAY... THE 00Z/21 GFS MOS WEDNESDAY NIGHT AND THURSDAY AND THEN THEREAFTER (THURSDAY NIGHT ONWARD) THE 0543Z/21 WPC GRIDDED GUIDANCE WHICH AT TIMES IS BLENDED 50 50 WITH THE 00Z/21 MEXMOS. ALL THIS IS EVENTUALLY CHECKED AGAINST THE 00Z/21 ECMWF TO SEE IF WE`RE IN THE BALLPARK WITH ECMWF CYCLICALLY PERSISTENT 18Z 2 METER TEMPERATURES. THE PRECIPITATION PROBABILITY GUIDANCE IS CHECKED AGAINST THE 21Z/20 SREF POPS FOR .01 IN 3 HRS THROUGH 12Z THURSDAY AND THEREAFTER THE 00Z/21 GEFS 6HR POPS FOR 0.05 . THE DAILIES... TUESDAY...CONSIDERABLE EARLY MORNING CLOUDINESS THEN HIGHS WARMING INTO THE UPPER 80S IN MUCH OF OUR REGION TUESDAY AFTERNOON. A FEW SPOTS MAY HIT 90 INCLUDING KPHL BUT AT THIS TIME SIDED WITH THE SLIGHTLY COOLER ECMWF. CONDITIONS ARE FORECAST TO REMAIN MARGINALLY STABLE ON THE COASTAL PLAIN. HOWEVER, THERE MAY BE ENOUGH INSTABILITY IN EASTERN PENNSYLVANIA AND NORTHERN NEW JERSEY TO RESULT IN ISOLATED SHOWERS OR A THUNDERSTORM TUESDAY AFTERNOON? TUESDAY NIGHT...PATCHY LOW CLOUDS AND THICK FOG MAY FORM LATE? MINIMUM TEMPERATURES ARE ANTICIPATED TO BE MOSTLY IN THE UPPER 60S AND LOWER 70S. WEDNESDAY...SHOULD BE THE HOTTEST DAY OF THIS LONG TERM FORECAST PERIOD. TEMPERATURES AT THE 850 HPA LEVEL ARE EXPECTED TO RISE TO AROUND 18C. WE WILL CONTINUE TO CARRY MAXIMUM TEMPERATURES MOSTLY IN THE LOWER 90S WITH PEAK HEAT INDEX VALUES MAINLY IN THE UPPER 90S WITH A 100F HEAT INDEX POSSIBLE IN CENTRAL NJ AND THE DELMARVA. IT WILL BE COOLER THAN THAT IN THE ELEVATED TERRAIN UP NORTH AND IN AREAS ALONG THE COAST. WE WILL CONTINUE TO MENTION A CHANCE OF THUNDERSTORMS MOVING INTO OUR REGION FROM THE NORTHWEST ON WEDNESDAY. MIXED LAYER CAPE VALUES ARE EXPECTED TO RISE AROUND 2000 J/KG ALONG THE INTERSTATE 95 CORRIDOR DURING THE AFTERNOON. HOWEVER, A BIT OF A CAP MAY INITIALLY PREVENT THE ACTIVITY FROM BECOMING WIDESPREAD. HOWEVER...AN APPROACHING COLD FRONT COULD SEND A BAND OF SCT STRONG TSTMS INTO E PA AND NJ. KI 34 TT 49 SWI -2. 0-6KM BULK SHEAR AND 500MB WINDS LOOK TOO WEAK TO SUPPORT MUCH SVR BUT IF THE TIMING IS CLOSE ENOUGH TO UTILIZE THE 2000J ML CAPE...THEN ISO SVR COULD BE POSSIBLE ALONG AND N OF I-78. WEDNESDAY NIGHT-THURSDAY...THE COLD FRONT WILL PROGRESS SLOWLY TO THE SOUTHEAST AND IT SHOULD CROSS OUR REGION LATER WEDNESDAY NIGHT OR THURSDAY. WE CONTINUE TO MENTION A CHANCE OF SHOWERS AND THUNDERSTORMS FOR WEDNESDAY NIGHT AND THURSDAY. SUSPECT THE STATISTICAL PROBABILITIES FOR CLUSTERS OF SHOWERS AND TSTMS WILL SHIFT TO THE PHL AREA SOUTHWARD THROUGH THE DELMARVA FOR THURSDAY AFTERNOON. HIGH TEMPERATURES ON THURSDAY SHOULD RANGE FROM THE UPPER 70S IN THE NORTH TO AROUND 90 IN THE SOUTH. IT MAY EVEN TOUCH 90 IN PHL ALTHOUGH THE ECMWF IS SIGNIFICANTLY COOLER. FRIDAY-WEEKEND...A MID LEVEL TROUGH OVER THE NORTHEASTERN STATES ON FRIDAY SHOULD LIFT TO THE NORTHEAST WITH ANOTHER TROUGH EXPECTED TO DROP OVER THE GREAT LAKES REGION ON SUNDAY. HIGH PRESSURE AT THE SURFACE IS ANTICIPATED TO BUILD ACROSS OUR REGION FOR FRIDAY AND SATURDAY WITH LOW PRESSURE AND A WARM FRONT APPROACHING FROM THE SOUTH ON SUNDAY. DAYTIME HIGHS ARE EXPECTED TO BE MAINLY IN THE 80S WITH OVERNIGHT LOWS GENERALLY IN THE 60S. SHOWERS AND ISOLATED TSTMS COULD DEVELOP WITH THE WARM FRONT SUNDAY....THE ECMWF HAS BEEN QUITE EMPHATIC ABOUT CONSIDERABLE SHOWER AND TSTM ACTIVITY FOR SUNDAY IN AT LEAST ITS PAST TWO CYCLES. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY WILL FEATURE MOSTLY SUNNY SKIES WITH SOME AFTERNOON CU AT TIMES. A ISOLATED SHOWER IS POSSIBLE FAR N/W...BUT NOT MENTIONED IN THE TAFS ATTM. WINDS MOSTLY 5 TO 10 KTS...AGAIN MOSTLY ERLY/SERLY EARLY THEN SRLY LATE. TONIGHT...MOSTLY VFR WITH LIGHT WINDS. MORE LOW CLOUDS/FOG POSSIBLE TOWARDS DAWN. OUTLOOK... TUESDAY...MAINLY VFR. A SLIGHT CHANCE OF AFTERNOON THUNDERSTORMS VICINITY KRDG AND KABE NORTHWESTWARD. TUESDAY NIGHT AND WEDNESDAY...MAINLY VFR. PATCHY LATE NIGHT AND EARLY MORNING MVFR OR IFR CONDITIONS IN LOW CLOUDS, FOG AND HAZE. A CHANCE OF AFTERNOON THUNDERSTORMS....ESPECIALLY THE I-78 CORRIDOR NORTHWARD INCLUSIVE OF KRDG AND KABE. WEDNESDAY NIGHT AND THURSDAY...MVFR AND IFR CONDITIONS AT TIMES IN SHOWERS AND THUNDERSTORMS...STRATUS AND FOG. THURSDAY NIGHT...IFR POSSIBLE IN PATCHY STRATUS AND FOG. FRIDAY...MAINLY VFR. && .MARINE... HIGH PRESSURE WILL STAY NORTH OF THE WATERS TODAY AND TONIGHT. WINDS WILL REMAIN MOSTLY ERLY OR SERLY...MOSTLY UNDER 10 KTS...THROUGH TONIGHT. SEAS 2-3 FT ON THE OCEAN AND 1-2 T ACROSS DEL BAY. FAIR WEATHER IS EXPECTED TODAY AND TONIGHT. OUTLOOK... TUESDAY THROUGH FRIDAY...NO MARINE HEADLINES ARE ANTICIPATED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG NEAR TERM...HEAVENER/O`HARA SHORT TERM...O`HARA LONG TERM...DRAG AVIATION...DRAG/O`HARA MARINE...DRAG/O`HARA

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