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Area Forecast Discussion
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000
FXUS61 KPHI 021031
AFDPHI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
631 AM EDT TUE SEP 2 2014

.SYNOPSIS...
A FRONTAL BOUNDARY WILL MOVE THROUGH THE REGION TONIGHT, THEN
THIS FRONT WILL BE LOCATED SOUTH OF OUR REGION WEDNESDAY AS HIGH
PRESSURE BUILDS OVERHEAD. HIGH PRESSURE WILL GRADUALLY MOVE FROM
WEST TO EAST ACROSS THE EASTERN UNITED STATES THROUGH THE SECOND
HALF OF THE WEEK. ON SATURDAY, A COLD FRONT WILL MOVE THROUGH THE
REGION. THIS FRONT WILL STALL TO OUR SOUTHEAST FOR THE EARLY PART
OF NEXT WEEK WITH HIGH PRESSURE OVER THE GREAT LAKES.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WHILE THE CALENDAR SAYS SEPTEMBER, IT WILL CONTINUE TO FEEL LIKE 
THE HEART OF SUMMER AS THE HEAT AND HUMIDITY REMAINS ACROSS THE 
AREA. THERE COULD BE SOME SLIGHT RELIEF THROUGH THE DAY AS THE 
SURFACE DEW POINTS ARE FORECAST TO LOWER SOME. SYNOPTICALLY, HIGH 
PRESSURE CONTINUES TO BE CENTERED IN THE WESTERN ATLANTIC HELPING TO 
PUMP UP THE HEAT AND HUMIDITY WITHIN A SOUTHWESTERLY FLOW. THERE IS 
HOWEVER A NOTABLE UPPER-LEVEL TROUGH THAT WILL BE SWINGING ACROSS 
THE GREAT LAKES REGION AND THE UPPER OHIO VALLEY THROUGH THE DAY. 
THERE IS A SURFACE FRONT WITH THIS FEATURE, HOWEVER IT WILL REMAIN 
WELL TO OUR WEST DURING THE DAY. THERE SHOULD BE A PRE-FRONTAL 
TROUGH DEVELOPING GIVEN THE WARM TO HOT AIRMASS. THE EVENTUAL 
SURFACE FRONT MAY JUMP INTO THIS TROUGH AS WE WORK OUR WAY INTO THE 
SHORT TERM /TONIGHT/. THE FORECAST CHALLENGES FOR TODAY REVOLVES
AROUND THE CONVECTIVE CHCS AND ALSO THE HEAT INDICES.

AS THE UPPER-LEVEL TROUGH PROGRESSES EASTWARD, THE MAIN SHORT
WAVE IS FORECAST TO LIFT TO OUR NORTH LATE THIS AFTERNOON. THIS
LEAVES BEHIND THE TAIL END OF IT SLIDING INTO OUR AREA. AS A
RESULT, THE LARGE SCALE FORCING SHOULD SLIDE TO OUR NORTHWEST
LATER THIS AFTERNOON. THERE WILL HOWEVER BE INSTABILITY IN PLACE
ALTHOUGH THIS CAN BE AFFECTED BY THE LOWERING DEW POINTS /AT LEAST
SBCAPE/. THERE IS SOME INCREASE IN THE MID LEVEL FLOW, HOWEVER THE
CORE /50-60 KNOTS/ OF IT IS FORECAST TO REMAIN WELL TO OUR WEST
WHICH IS WHERE THE SLIGHT RISK FOR SEVERE THUNDERSTORMS IS
INDICATED. THAT STRONGER FLOW IS EXPECTED TO ALLOW FOR CONVECTIVE
DEVELOPMENT WELL TO OUR WEST AND THIS IS WHAT WE WILL PROBABLY
HAVE TO WAIT AND SEE WHAT SURVIVES AS IT TRACKS EASTWARD. IN
ADDITION, SOME ISOLATED ACTIVITY COULD FIRE ALONG THE PRE-FRONTAL
TROUGH. AS A RESULT, WE SLOWED DOWN THE POP INCREASE FROM WEST TO
EAST. WHILE AN ISOLATED CELL COULD FORM THIS AFTERNOON FARTHER
EAST FROM LOCAL CONVERGENCE, MUCH OF THE TIME WILL PROBABLY BE
RAIN-FREE.

REGARDING THE HEAT, THE 850 MB TEMPERATURES ARE FORECAST TO BE A FEW 
DEGREES WARMER THAN YESTERDAY. THE FORECAST SOUNDINGS INDICATE THE 
POTENTIAL FOR BETTER MIXING BEING PRESENT AS THE PRESSURE GRADIENT 
TIGHTENS SOME AND THE LOW-LEVEL LAPSE RATES STEEPEN. THEREFORE THIS 
SHOULD RESULT IN HIGH TEMPERATURES INTO THE LOWER TO EVEN MID 90S 
FOR MANY INLAND AREAS. THE MIXING HOWEVER SHOULD LOWER THE SURFACE 
DEW POINTS SOME IN THE AFTERNOON, KEEPING THE HEAT INDICES A BIT 
LOWER. AS A RESULT, WE ARE EXPECTING THE HEAT INDICES TO REMAIN 
UNDER ADVISORY CRITERIA INCLUDING THE PHILADELPHIA METRO AREA.

HIGH TEMPERATURES WERE A BLEND OF THE NAM/GFS MOS, ALTHOUGH THE 
WARMER NAM MOS WAS FAVORED FOR SOME AREAS WHICH ALSO GOT US CLOSE TO 
CONTINUITY. THE HOURLY GRIDS WERE TWEAKED USING THE LAMP/LAV 
GUIDANCE, ESPECIALLY THIS MORNING TO HELP ASSIST WITH 
TEMPERATURE/DEW POINT TRENDS THUS FAR.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
THE AFOREMENTIONED UPPER-LEVEL TROUGH WILL GENERALLY GLANCE OUR 
AREA, WITH A FRONTAL BOUNDARY SWEEPING THROUGH. THE MAIN FORCING AND 
ASSOCIATED MID LEVEL JET MAX IS FORECAST TO BYPASS OUR AREA TO THE 
NORTHWEST. THERE STILL IS SOME INCREASE IN THE FLOW WITH THIS SYSTEM 
AS THE TAIL END OF THE SHORT WAVE MOVES THROUGH. THIS IN CONJUNCTION 
WITH ENOUGH INSTABILITY SHOULD SUPPORT SOME CONVECTION THIS EVENING 
BEFORE WEAKENING TAKES PLACE. THE AMOUNT OF SHEAR LOOKS LOW AND 
THEREFORE STORM ORGANIZATION SHOULD BE WEAK AND POTENTIALLY EVEN 
DISAPPEAR AS THE EVENING WEARS ON.

THE FORECAST SOUNDINGS INDICATE SOME OPPORTUNITY FOR SOME STRONGER 
CORES ACROSS OUR WESTERN ZONES AND TOWARDS THE DELMARVA, HOWEVER 
GIVEN THE BEST FORCING AND SHEAR MISSING OUR AREA THE SEVERE WEATHER 
THREAT LOOKS RATHER LOW AS OF NOW. THEREFORE, NO ENHANCED WORDING 
WAS CARRIED ATTM. WE USED CHC POPS THIS EVENING THEN THESE LOWER 
FROM WEST TO EAST. ANY LINGERING CONVECTION SHOULD BE DONE AFTER 
MIDNIGHT AS THE FRONTAL BOUNDARY SHIFTS EASTWARD. THE MODEL GUIDANCE 
SHOWS A PLUME OF PW AROUND 2 INCHES SURGING AHEAD OF THE SURFACE 
FRONT, THEREFORE ANY CONVECTION WILL HAVE THE POTENTIAL TO PRODUCE 
BRIEF TORRENTIAL DOWNPOURS. ANY FLOOD THREAT SHOULD BE LIMITED 
HOWEVER. 

THERE IS NO SIGNIFICANT AIRMASS CHANGE BEHIND THE SURFACE FRONT 
DESPITE A WIND SHIFT TO THE NORTHWEST. AS THE CLOUDS THIN OUT SOME 
SURFACE COOLING WILL TAKE PLACE, HOWEVER THE DEW POINTS LOOK TO 
REMAIN ON THE MUGGY SIDE FOR MUCH OF THE NIGHT. SOME LOWERING SHOULD 
START TO TAKE PLACE THOUGH LATE MAINLY OVER OUR WESTERN ZONES. THE 
COMBINATION OF LIGHT WINDS AND LINGERING LOW-LEVEL MOISTURE, MAY 
ALLOW FOR SOME FOG TO DEVELOP PARTICULARLY WHERE DRY AIR ADVECTION 
IS DELAYED. WE ARE NOT EXPECTING A LOT OF FOG, AND GIVEN LOWER 
CONFIDENCE WE HELD OFF INCLUDING A MENTION ATTM.

AS FOR LOW TEMPERATURES, AN EVEN BLEND OF THE GFS/NAM WAS MAINLY 
USED.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
WEDNESDAY THROUGH FRIDAY: DRY WITH FEW CLOUDS, FLOW TURNING 
GRADUALLY TO THE SOUTHWEST BY FRIDAY. THINK THE 00Z GFS IS TO QUICK 
SHOWING SOME RETURN FLOW POPS. MUGGY AND HOT AS WELL BUT TEMPS WILL 
BE UNDER HEAT ADVISORY CRITERIA. FAIR SHOT AT 90 THU/FRI FOR PHL. 
WENT AT OR A TOUCH ABOVE MET/MAV GUIDANCE ON TEMPERATURES BASED ON 
THE 925/850 MB TEMPERATURE PROFILES. 

FRIDAY NIGHT THROUGH SATURDAY NIGHT: A FRONTAL BOUNDARY MOVING SOUTH 
FROM THE GREAT LAKES WILL BE A TRIGGER FOR SOME SCATTERED SHOWERS 
AND THUNDERSTORMS. CLOUDS SHOULD INCREASE FROM NORTHWEST TO 
SOUTHEAST FRIDAY NIGHT AND SATURDAY. CONTINUED SOUTHWEST FLOW WILL 
BE IN PLACE AS WELL AHEAD OF THE FRONT. 925 MB TEMPS ARE LIKELY TO 
BE A TOUCH HIGHER THAN THU/FRI INDICATING SLIGHTLY WARMER SURFACE
TEMPERATURES. TEMPERATURES COULD POSSIBLY MAKING A RUN AT THE LOW
PERHAPS MID 90'S BASED ON HOW QUICKLY THE CLOUDS INCREASE. WENT
WARMER THAN WPC/MEX GUIDANCE IN THESE PERIODS TO ACCOUNT FOR THE
WAA AHEAD OF THE FRONT. IN TERMS OF ANY STRONG TO SEVERE STORMS. A
MODEST AMOUNT OF INSTABILITY (CAPE AROUND 1500 J/KG) WILL BE
PRESENT WITH MODERATELY STEEP LAPSE RATES. HOWEVER THE LACK OF
SHEAR IN PLACE WILL LIKELY PREVENT ANY WIDESPREAD COVERAGE OF
STRONG TO SEVERE STORMS. CONTINUED THUNDER IN GRIDS FOR SAT-SAT
NIGHT WITH CHANCE POPS.

SUNDAY THROUGH TUESDAY: NORTHEAST FLOW WILL DEVELOP EARLY NEXT WEEK 
WITH THE FRONT TO OUR SOUTH AND HIGH PRESSURE OVER THE GREAT LAKES. 
THE 00Z GFS IS THE MOST AGGRESSIVE CLEARING THE FRONT DURING THE DAY 
SUNDAY WITH ONLY LINGERING SHOWERS ACROSS THE SOUTH. THE 00Z ECMWF 
AND CMC SLOW THE FRONT ALLOWING FOR ADDITIONAL SHOWER CHANCES FOCUSED 
ACROSS THE SOUTH, PARTICULARLY ON SUNDAY BUT LINGER ISOLATED SHOWERS 
INTO MONDAY AND TUESDAY. THE ECMWF APPEARS TO BE FASTER THAN IT'S 
PREVIOUS RUN AND SOME MEMBERS WITHIN THE 18Z GFS ENSEMBLE SUITE 
ARGUE FOR A SLOWER FRONTAL PASSAGE. A MIDDLE GROUND WILL BE USED 
WITH CHANCE POPS DECREASING FROM NORTH TO SOUTH SUNDAY WITH SLIGHT 
CHANCE POPS ACROSS THE SOUTH MONDAY. CLOUDS AND SHOWERS MAY KEEP 
HIGHS DOWN ON SUNDAY AND LOWS HIGHER AT NIGHT. ON MONDAY AND TUESDAY 
AMPLE SUNSHINE MAY ALLOW MOST AREAS TO GET A TOUCH WARMER THAN WHAT 
MODELED TWO METER TEMPERATURES OR WPC GUIDANCE SUGGEST. RADIATIONAL 
COOLING MONDAY NIGHT IS LIKELY AS WELL ACROSS MOST OF THE REGION 
WITH THE FAVORED REGION JUST INLAND OFF THE NJ COAST AND NW PHL 
COULD HAVE A RELATIVITY CHILLY NIGHT.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY AND SURROUNDING AREAS.

TODAY...SOME MVFR/IFR VISIBILITIES DUE TO FOG EARLY MAINLY AT
KABE AND KTTN, OTHERWISE VFR. A FEW SHOWERS AND THUNDERSTORMS
SHOULD DEVELOP LATER THIS AFTERNOON MAINLY WEST OF KPHL AND
THEREFORE A TEMPO GROUP WILL BE ADDED TO KRDG AND KABE. A VCSH WAS
CARRIED ELSEWHERE LATE. LIGHT TO EVEN CALM WINDS, BECOMING
SOUTHWEST AND INCREASING TO 10-15 KNOTS TOWARD MIDDAY. SOME LOCAL
GUSTS UP TO 20 KNOTS SHOULD OCCUR THIS AFTERNOON AS ENOUGH MIXING
DEVELOPS.

TONIGHT...A FRONTAL BOUNDARY WILL MOVE THROUGH WITH SOME SHOWERS AND 
THUNDERSTORMS ARRIVING FROM THE WEST, WHICH MAY TEND TO DIMINISH 
WITH AN EASTWARD EXTENT. A WIND SHIFT TO THE NORTHWEST IS ANTICIPATED
WITH ANY CONVECTION AND ALSO AS THE FRONT MOVES THROUGH. MVFR 
CEILINGS WITH VISIBILITIES AS LOW AS IFR WILL BE POSSIBLE WITH ANY 
SHOWER OR THUNDERSTORM, OTHERWISE VFR. THERE IS A CHANCE SOME LOCAL 
FOG DEVELOPS LATE AS CLOUDS THIN AND THE WINDS DROP OFF WITH THE 
LOW-LEVEL MOISTURE REMAINING.

OUTLOOK...
WEDNESDAY THROUGH FRIDAY NIGHT: VFR. 

SATURDAY: MVFR TO IFR RESTRICTIONS POSSIBLE IN ANY AFTERNOON OR 
EVENING THUNDERSTORMS.

&&

.MARINE...
A SOUTHERLY FLOW WILL BE MAINTAINED TODAY WELL AHEAD OF A SURFACE 
FRONT. THERE WILL BE SOME INCREASE LATER THIS AFTERNOON AND EVENING 
AS THE PRESSURE GRADIENT TIGHTENS SOME, HOWEVER THESE ARE EXPECTED 
TO REMAIN BELOW ADVISORY CRITERIA. THE WINDS WILL SHIFT TO THE WEST 
AND NORTHWEST LATER TONIGHT BEHIND THE FRONTAL PASSAGE. SOME 
THUNDERSTORMS ARE POSSIBLE WITH THE FRONT MAINLY THIS EVENING, 
HOWEVER THESE COULD WEAKEN BEFORE REACHING OUR MARINE AREA. SEAS 
WILL BE IN THE 2 TO 4 FEET RANGE OVER THE COASTAL WATERS, AND 2 FEET 
OR LESS ON DELAWARE BAY.

OUTLOOK...
WEDNESDAY THROUGH FRIDAY NIGHT: SUB SCA SEAS AND WINDS EXPECTED 
ATTM. 

SATURDAY: SOME STRONG WIND GUSTS POSSIBLE FROM THUNDERSTORMS, 
OTHERWISE SUB SCA SEAS AND WINDS.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...GAINES/GORSE
NEAR TERM...GORSE
SHORT TERM...GORSE
LONG TERM...GAINES
AVIATION...GAINES/GORSE
MARINE...GAINES/GORSE




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