Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 250815 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 415 AM EDT MON JUL 25 2016 .SYNOPSIS...
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A warm front will slowly push northward across the region today. meanwhile, a cold front will approach from the west, moving into the region tonight and Tuesday, before stalling near or just to the south of the area through the midweek period. A couple of areas of low pressure may develop and move along this boundary as it remains over the area for the end of the week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A warm frontal boundary will lift northeastward this morning into New England. After the warm frontal passage, relative humidity will climb across the region. Temperatures will also quickly rise throughout the day as an even warmer airmass moves northward. A look at boundary layer temperatures and modeled two meter temperatures show the potential for many locations to see highs in the mid and upper 90`s, which match that of the ECMWF and the MET guidance sets. Coupled with the increased relative humidity, heat index values will likely push 105 in many locations near and south of the Philadelphia region with values near 100 degrees north and west. Carbon and Monroe counties were added to the advisory given the potential for values near 100 degrees across portions of the counties. Stay indoors if possibile, drink plenty of water and keep an eye on the elderly, children and pets through this prolonged heat wave. A potential uncertainty with the exact magnitude of the heat today will be the development of showers and thunderstorms to our northwest focused near a cold front. Agree with the thinking of the HRRR, NAM and GFS which show thunderstorms moving southeast into the region by late afternoon that then move toward Philadelphia by early evening. This timing allows for peak heating to occur before the arrival of any storms for most of the area. These storms then would decrease in intensity tonight over Delmarva. An ample amount of instability is modeled around 1,500 J/KG of CAPE with steep low level lapse rates. The steep low level lapse rates would suggest some gusty winds could occur with a few storms today. The lack of mid-level dry air may be a limiting factor for downburst potential today from storms. The current expectation is a few storms could have gusty winds. For now, thinking most places that see storms will see around 1/4-1/2 inch of rainfall with lower amounts in the Delmarva further away from the frontal boundary. Raised pops to likely for a few hours from north to south across the region north of Delmarva. Outside of storms, enough mixing looks present in the soundings across the region to suggest some wind gusts near 20 mph could occur from the southwest.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
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The cold frontal boundary will push through tonight with thunderstorms clearing the coast early in the evening. However, another muggy night is expected with lows still in the mid and upper 70`s for most of the region.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
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The cold front will be through much of the area before it stalls in the vicinity of Delmarva Tuesday and Tuesday night. It will then remain nearly over the Delmarva through the middle of the week. Drier and less hot air will try to filter into the region from the north. Areas north of Philadelphia will see some relief from the heat and humidity with high temperatures trending down to the lower 90s by Wednesday with dew point temperatures dropping into the lower to mid 60s. Philadelphia metro and southern New Jersey will also see high temperatures drop into the low 90s, but will likely see dew point temperatures remain in the middle to upper 60s. Finally, further south across the Delmarva, the only relief will be the lower temperatures as dew point temperatures will remain in the 70s. This area will also likely continue to have a chance of a few showers and thunderstorms due to the more humid airmass and the proximity to the frontal boundary. Areas further north should stay dry for the middle of the week. As the week progresses, the frontal boundary will shift slightly northward resulting in a return to more humid conditions and a threat of showers and thunderstorms across the entire region. The models are starting to hint that a couple of areas of low pressure will develop and move along the boundary. This will increase the amount of clouds, humidity levels and the chance of showers and thunderstorms for the end of the week and the weekend.
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&& .AVIATION /08Z MONDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions this morning and into the afternoon. Showers and thunderstorms will likely begin to develop to our northwest by mid afternoon and move southeast through the early evening. Tempo groups have been added to the TAF`s to account for this potential of lower ceilings and VSBYS. Storms should only last for an hour or two at any given location. However, the exact timing is still uncertain. Some southwesterly wind gusts up to 20 knots could occur in the afternoon as well. VFR tonight after thunderstorms end with winds shifting to westerly late under 10 knots. Outlook... Tuesday through Friday...Mainly VFR conditions expected. Scattered showers and thunderstorms Thursday and Friday, with MVFR/IFR conditions possible at times.
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&& .MARINE...
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Seas will start the day near two feet likely rising in the southern waters during the afternoon and evening hours getting close to four feet. Some southwest wind gusts around 20 knots could occur in the afternoon hours today. Outlook... Tuesday through Friday...Sub-advisory conditions are expected to continue on the area waters through much of the week. Expect higher winds and waves in and near scattered showers and thunderstorms that become more likely at the end of the week. Rip Currents...Today`s risk for formation of dangerous rip currents is low. However if the wind were to turn south 15 kt and a 4 ft 5 second southerly swell were to develop late in the day, we`d probably experience a low enhanced risk along the NJ coasts. A south to north longshore current will prevail. Beyond Monday: with the Atlantic Basin continuing quiet tropically, unless we get a strong onshore flow...RC risk this coming week should be generally low. Tstms and pockets of chilly upwelling water may the greater concerns. There is some sign of colder upwelling along the coasts this evening.
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&& .CLIMATE...
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The forecast high temperature for Philadelphia today, July 25th, is currently 98F. The last time the temperature reached or exceeded 98F at PHL was three years ago on July 18, 2013. The last 100-degree day at PHL occurred four years ago on July 18, 2012. Record high temperatures for Monday through Thursday are below. We may tie or break daily record highs tomorrow at several of our climate sites. KABE and KRDG had record equaling highs on Sunday the 24th. Site 25th 26th 27th 28th ---- ---- ---- ---- ---- PHL... 96-1899 101-1892 101-1940 100-1941 ABE... 95-1999 98-1940 98-1955 97-1949 ACY... 99-2010 96-2011 99-2005 98-1999 ILG... 96-1987 99-1894 100-1894 101-1894 TTN... 97-1999 99-1892 100-1894 101-1894 GED... 99-2010 97-2012 98-2005 99-1949 RDG... 96-1999 99-1940 98-1955 99-1941 MPO... 90-1999 89-1949 91-1955 93-1949
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Heat Advisory from 11 AM this morning to 6 PM EDT this evening for PAZ060>062-101-103-105. Excessive Heat Warning until 6 PM EDT this evening for PAZ070- 071-102-104-106. Heat Advisory from noon today to 6 PM EDT this evening for PAZ054-055. NJ...Heat Advisory from 11 AM this morning to 6 PM EDT this evening for NJZ001-007>010-012>014-016-020>027. Excessive Heat Warning until 6 PM EDT this evening for NJZ015- 017>019. DE...Heat Advisory from 11 AM this morning to 6 PM EDT this evening for DEZ002>004. Excessive Heat Warning until 6 PM EDT this evening for DEZ001. MD...Heat Advisory from 11 AM this morning to 6 PM EDT this evening for MDZ008-012-015-019-020. MARINE...None.
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&& $$ Synopsis...JK Near Term...Gaines Short Term...Gaines Long Term...JK Aviation...Gaines/JK Marine...Gaines/JK Climate...Staff

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