Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 280903 AFDPHI AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 503 AM EDT TUE JUL 28 2015 .SYNOPSIS... WEAK HIGH PRESSURE COVERS THE NORTHEAST UNITED STATES THROUGH WEDNESDAY. A VERY WEAK COOL FRONT PASSES THROUGH THE MID ATLANTIC STATES THURSDAY NIGHT. ANOTHER COOL FRONT MAY APPROACH FROM THE NORTHWEST NEXT MONDAY. MEANWHILE LOW PRESSURE CENTERS ALONG THE SOUTHEAST COAST OF THE UNITED STATES THIS WEEK WILL BE MONITORED FOR POSSIBLE NORTHWARD DEVELOPMENT NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... THE SYNOPTIC SETUP IS COMPRISED OF AN UPPER-LEVEL TROUGH AXIS NOW TO OUR EAST WITH A RIDGE BUILDING TO OUR WEST. THIS ALLOWS A NORTHWESTERLY FLOW ALOFT REGIME TO BE MAINTAINED ACROSS THE NORTHEAST AND MID ATLANTIC. AT THE SURFACE, WEAK HIGH PRESSURE IS FORECAST TO SETTLE INTO OUR AREA TODAY. AS THE RIDGE TO OUR WEST GRADUALLY BUILDS NORTH AND EASTWARD SOME THROUGH TODAY, THERE DOES NOT APPEAR TO BE MUCH IN THE WAY OF SHORT WAVE ENERGY /AT LEAST ORGANIZED/ SLIDING SOUTHEASTWARD. AS A RESULT, NO ORGANIZED AREAS OF LIFT IS FORECAST TO OCCUR TODAY WITHIN A VERY WARM TO HOT AND HUMID AIR MASS. THE FORECAST SOUNDINGS DO SHOW DECENT INSTABILITY DEVELOPING THROUGH THE AFTERNOON, HOWEVER ABOVE ABOUT THE 850 MB LEVEL IT IS DRY. THE WATER VAPOR IMAGERY EARLY THIS MORNING SHOWS A LOT OF MID LEVEL DRY AIR FROM AROUND THE EASTERN GREAT LAKES TO THE MID ATLANTIC. AS A RESULT, ANY CONVECTION THAT CAN DEVELOP SHOULD BE ISOLATED AND ALSO PULSE DRIVEN GIVEN LITTLE FLOW IN THE LOWER TO MID LEVELS. IT APPEARS THAT SEA AND BAY BREEZE BOUNDARIES ESPECIALLY THIS AFTERNOON COULD FOCUS SOME CONVECTIVE DEVELOPMENT AND WE CONTINUED WITH SLIGHT CHC POPS FOR THE EASTERN ZONES AND PORTIONS OF THE DELMARVA. ELSEWHERE, WE OPTED TO CARRY A DRY FORECAST ATTM AS THERE IS NOT MUCH TO LATCH ONTO FOR CONVECTIVE INITIATION OTHER THAN TERRAIN. SOME WARMING AROUND THE 925 MB LEVEL MAY ALSO TEMPER CONVECTIVE DEVELOPMENT. A POCKET OF NEAR +25C AIR AT 925 MB IS FORECAST TO ADVECT INTO OUR AREA THROUGH THE AFTERNOON. DESPITE SOME CUMULUS DEVELOPMENT, PLENTY OF HEATING IS EXPECTED /ALTHOUGH A LACK OF MIXING DUE TO THE WEAK FLOW/ AND THEREFORE SOME AREAS ARE ANTICIPATED TO REACH 90 DEGREES THIS AFTERNOON. THE STRONG WARMING OF THE BOUNDARY LAYER MAY ALLOW THE SURFACE DEW POINTS TO DECREASE AT LEAST SOME ESPECIALLY FARTHER NORTH ACROSS THE CWA, AND WITH WEAK FLOW SEA AND BAY BREEZES ARE EXPECTED. THIS WILL PROVIDE SOME COOLING ALONG THE COAST. AS FOR THE HIGH TEMPERATURES, WE USED AN EVEN BLEND OF THE NAM/GFS MOS THEN MADE SOME LOCAL TWEAKS. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... A WEAK SURFACE HIGH IS FORECAST TO BE OVER OUR AREA TONIGHT AS AN UPPER-LEVEL RIDGE AXIS SLIDES ACROSS THE EASTERN GREAT LAKES AND OHIO VALLEY. THIS STILL MAINTAINS NORTHWESTERLY FLOW ALOFT, BUT LIGHT AND VARIABLE FLOW AT THE SURFACE. DUE TO A LACK OF ORGANIZED SHORT WAVES TO PROVIDE ENOUGH LIFT, AN ISOLATED SHOWER OR THUNDERSTORM INITIATED PROBABLY BY ANY LOW-LEVEL CONVERGENCE /I.E. SEA AND BAY BREEZES/ ARE EXPECTED TO DISSIPATE EARLY IN THE EVENING. IN ADDITION, ANY CUMULUS FIELD IS EXPECTED TO FLATTEN AND DISSIPATE WITH PERHAPS SOME HIGH CLOUDINESS OCCURRING AT TIMES. IT WILL BE A WARM AND MUGGY NIGHT FOR MUCH OF THE CWA AS THE SURFACE DEW POINTS SHOULD RECOVER FROM ANY DAYTIME HEATING INFLUENCE. THE COMBINATION OF LIGHT TO CALM WINDS, A MOIST BOUNDARY LAYER AND NOT A LOT OF CLOUDINESS COULD RESULT IN PATCHY LOW CLOUDS/FOG DEVELOPMENT LATE. AS FOR THE LOW TEMPERATURES, A MOS BLEND WAS GENERALLY USED. && .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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**POTENTIAL SEVEN DAY OR LONGER HEAT WAVE FOR PHL BEGINNING TODAY AND PROBABLY CONTINUING THROUGH NEXT MONDAY OR TUESDAY** 500 MB: HIGH PRESSURE IN THE SOUTHERN PLAINS WILL BE THE DOMINANT INFLUENCE HERE THROUGH THURSDAY. OTHERWISE A TROUGH TRIES TO EVOLVE OVER THE EASTERN STATES NEXT WEEKEND. TEMPERATURES: THE MONTH OF JULY SO FAR HAS BEEN NEAR NORMAL (TEMPS). THIS EXTENDED PERIOD WILL SEE CALENDAR DAY AVERAGES ABOVE NORMAL EVERY DAY. TEMPS SHOULD AVERAGE 5 TO 7 DEGREES ABOVE NORMAL WEDNESDAY AND THURSDAY AND 3 TO 5 DEGREES ABOVE NORMAL FRIDAY THROUGH SUNDAY AND THEN MORE THAN 5 DEGREES ABOVE NEXT MONDAY AUGUST 3. FORECAST BASIS: UNLESS OTHERWISE NOTED, A 50 50 BLEND 00Z/28 GFS/NAM MOS GUIDANCE WEDNESDAY-THURSDAY, 00Z/28 MEX MOS THURSDAY NIGHT AND FRIDAY, THEN THE 0521Z/28 WPC GRIDDED ELEMENTS OF MAX/MIN TEMP, 12 HOUR POP, 6 HOUR DEWPOINT-SKY-WIND FROM FRIDAY NIGHT THROUGH NEXT MONDAY. THE DAILIES... WHILE NOT IN THE SYNOPSIS DUE TO ITS POTENTIAL TO CAUSE CONFUSION... AND ITS LACK OF SIGNIFICANT WEATHER IMPACT, IT LOOKS LIKE THERE WILL BE A LEFTOVER WIND SHIFT BOUNDARY SOMEWHERE NEAR I-95 THROUGH THURSDAY BEFORE A MORE STRUCTURED WEAK COOL FRONTAL PASSAGE OCCURS THURSDAY NIGHT. WEDNESDAY...RELATIVELY DRY HEAT. PWAT ~1.35 INCHES. HEAT INDEX BELOW 100F. SOUTHWEST WIND GUST 15 MPH DURING THE AFTERNOON EXCEPT WEAK SEA BREEZES COASTAL LOCATIONS BEGINNING AROUND NOON. USED THE WARMER MAV TEMPS FOR THE DAYTIME FCST. FCST MAX TEMPS MAY BE A DEGREE TOO LOW. OVERALL CONFIDENCE: ABOVE AVERAGE. THURSDAY...APPROACHING WET BULB FRONT WITH THE 850 MB HOT PROD OF 18-20C AHEAD OF THE CF AND A QUICK START TO 90F THURSDAY MORNING. AFTERNOON DEWPOINTS ARE EXPECTED TO BE MUCH HIGHER THAN WEDNESDAY (BY ALMOST 10F). RAISED THE 00Z/28 NCEP GUIDANCE USING THE 00Z/28 ECMWF BUT DID SO WITH LESS THAN IDEAL CONFIDENCE. MLCAPE BUILDS IN CENTRAL PA TO 1400J BY 18Z THU AND 600J NJ. APPEARS UNLIKELY TO HAVE ANY SHOWERS OR TSTMS GOING IN OUR AREA BEFORE 16Z AND PROBABLY NOT TO THE I-95 CORRIDOR TIL NEAR 22Z. THAT SHOULD ALLOW MORE WARMING THAN MODELED AND HI NEARING 100F BY 18Z. MAX TEMPS SHOULD REMAIN BELOW RECORDS WHICH ARE 97-99F EXCEPT KMPO 90. SSW WIND GUST 15-20 MPH DURING THE AFTN. WHAT WOULD PREVENT THE HEAT INDEX REACHING 100F? THURSDAY MORNING SHOWERS AND TSTMS VCNTY KPHL SOUTH AND EAST WOULD LESSEN SUNSHINE AND MAKE IT MUCH MORE DIFFICULT FOR THE AIR TEMPERATURE TO EXCEED 90F. THERE ARE 00Z/28 EC/GFS MODEL HINTS OF A WEAK INSTABILITY BURST TRYING TO SHOVE NEWD INTO THE DELMARVA AND SNJ THURSDAY MORNING AND PRODUCE MORNING SHOWERS. A SCT-BKN BAND OF SHOWERS AND TSTMS SHOULD DEVELOP AND PASS ACROSS THE AREA THU AFTN/NIGHT. PWAT INCREASES TO 1.9 INCHES ALONG THE I- 95 CORRIDOR DURING THURSDAY EVENING SO HEAVY RAINERS AND LOCAL POOR DRAINAGE FLOODING ANTICIPATED AND CANT RULE OUT ISOLATED FF. WHILE TIMING IS EXCELLENT FOR STRONG TSTM DEVELOPMENT, SVR UNLIKELY SINCE 0-6KM BULK SHEAR IS PRETTY WEAK AND LAPSE RATES VIA TT INDEX LOOK PRETTY POOR. SREF MODELED PWAT BACK EDGE OF 1.5 INCHES DOWN TO A KDOV- KBLM LINE BY 12Z FRIDAY. FRIDAY...DEWPOINTS LOWER BY 10 TO 12F ON LIGHT NLY FLOW AND AIR TEMPS DOWN 2-3F. BLUE MOON AND POTENTIALLY NICE HOT SUMMER DAY FOR THE END OF JULY. ABOVE AVERAGE CONFIDENCE. SATURDAY AND SUNDAY...HEATS UP MAYBE A BIT MORE EACH DAY ON WSW AFTERNOON WIND GUSTS 10-15 MPH. A NICE WEEKEND SINCE AFTERNOON DEWPOINTS STILL REMAIN PRETTY MODEST...LOW TO MID 60S. SMALL CHC OF A TSTM NE PA SAT EVE IN WAA - THIS PER 1400J NEAR KHZL MIDDAY REACHING KBLM BY 00Z/SUNDAY. AVERAGE CONFIDENCE. NEXT MONDAY...MORE HUMID AND CONTD HOT. 2000J MLCAPE I95 SEWD. AVERAGE CONFIDENCE ON THE FCST DETAILS.
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&& .AVIATION /09Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. TODAY...LOCAL LOW CLOUDS/FOG DISSIPATE BY MID MORNING, OTHERWISE VFR WITH A CLOUD BASE MOSTLY BETWEEN 3500-5000 FEET. AN ISOLATED SHOWER OR THUNDERSTORM MAY DEVELOP THROUGH THE DAY ESPECIALLY SOUTH AND EAST OF KPHL. SEA/BAY BREEZES ARE EXPECTED TO DEVELOP BY MID AFTERNOON AND AFFECT KACY, KMIV AND KILG WITH WINDS TURNING MORE FROM THE SOUTHEAST. TONIGHT...MAINLY VFR. HOWEVER DUE TO THE MOIST AIR MASS IN PLACE, SOME LATE NIGHT LOW CLOUDS/FOG MAY DEVELOP, AND OUR CONFIDENCE IS ON THE LOWER SIDE AT THIS TIME. LIGHT SOUTHERLY TO CALM WINDS. OUTLOOK... WEDNESDAY THROUGH THURSDAY MORNING...MAINLY VFR. HOWEVER, THE HIGH HUMIDITY LEVELS MAY RESULT IN SOME LATE NIGHT AND EARLY THURSDAY MORNING MVFR OR IFR LOW CLOUDS, HAZE AND FOG. LIGHT SW WIND. THURSDAY AFTERNOON AND THURSDAY NIGHT...A CHANCE OF SHOWERS AND THUNDERSTORMS THAT MAY RESULT IN MVFR OR IFR CONDITIONS AT TIMES. GRADIENT SW WIND GUSTS 15-20 KT THU AFTN. FRIDAY THROUGH SATURDAY...MAINLY VFR. LIGHT WIND, MAINLY NORTH FRIDAY MORNING WITH SEABREEZES BOTH FRIDAY AND SATURDAY. && .MARINE... THE CONDITIONS ARE EXPECTED TO REMAIN BELOW SMALL CRAFT ADVISORY CRITERIA THROUGH TONIGHT. A SOUTHERLY FLOW WILL CONTINUE WITH SOME ENHANCEMENT OCCURRING THIS AFTERNOON AND EARLY EVENING AS A SEA AND BAY BREEZE DEVELOPS. THE SEAS SHOULD RUN IN THE 1-3 FEET RANGE THROUGH TONIGHT. OUTLOOK... WEDNESDAY THROUGH SATURDAY...NO MARINE HEADLINES ARE ANTICIPATED. && .RIP CURRENTS... A LONG PERIOD /AROUND 10 SECONDS/ SWELL FROM THE EAST-SOUTHEAST WILL CONTINUE TODAY. A SOUTHERLY WIND AT 10-15 MPH WITH SOME AFTERNOON SEA BREEZE ENHANCEMENT ALONG WITH WAVES OF AROUND 2 FEET IN THE SURF ZONE ARE FORECAST TODAY. THE SETUP IS SIMILAR TO YESTERDAY AND THEREFORE WE WILL MAINTAIN A MODERATE RISK OF DANGEROUS RIP CURRENTS FOR BOTH THE NEW JERSEY AND DELAWARE COASTS. SST`S CONTINUE ABOVE NORMAL! && .CLIMATE... KACY RAINFALL 6.33 RANKED 15TH WETTEST WITH THE POR DATING BACK THROUGH 1874. WETTEST 13.09 IN 1959. KABE MAY EXPERIENCE NEAR RECORD WARMTH ON WEDNESDAY JULY 29. THE RECORD THERE IS IS 96 SET IN 1954. RIGHT NOW WE`RE FCSTG 94. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...NONE. NJ...NONE. DE...NONE. MD...NONE. MARINE...NONE. && $$ SYNOPSIS...DRAG NEAR TERM...GORSE SHORT TERM...GORSE LONG TERM...DRAG 503 AVIATION...DRAG/GORSE MARINE...DRAG/GORSE RIP CURRENTS... CLIMATE...

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