Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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754 FXUS61 KPHI 200542 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 142 AM EDT Thu Jul 20 2017 .SYNOPSIS... High pressure will remain offshore through early next week and it will keep hot and humid conditions across the Mid-Atlantic. A weak front will approach the area Thursday and cross the area Thursday night and Friday. The front will remain nearby this weekend and keep conditions unsettled through the period. Cooler temperatures will arrive over the area Monday and Tuesday of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... High pressure located over the Atlantic will continue to influence our weather tonight. It will maintain a light south to southwest flow of warm humid air into our region. The isolated/scattered showers and thunderstorms from this afternoon and earlier this evening continue to dissipate as daytime heating wanes. However, there will continue to be a couple of showers for another hour or two before all precip ends by midnight. The rest of the night is expected to be precipitation free, with clearing skies except possibly some high level clouds overnight. There may be a come patchy light fog overnight, but it is not expected to be widespread. Minimum temperatures should be mainly in the 70s with some readings in the upper 60s in the elevated terrain. The wind is anticipated to be light and variable. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
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We have issued an Excessive Heat Warning for the urban corridor from Wilmington to Philadelphia/Camden to Trenton beginning at noon on Thursday. Maximum temperatures in our region should be mainly in the middle 90s. Readings will be a little lower in the elevated terrain and at the shore. The high humidity will likely result in heat index values around 100 in southeastern Pennsylvania and in much of New Jersey. Maximum heat index values of 101 to 104 are expected in much of northeastern Maryland and Delaware. Based on the highly urbanized area`s sensitivity to the heat and humidity, we have confined the Excessive Heat Warning to those locations. Areas to the northwest and to the southeast of the urban corridor should fall short of their Heat Advisory criteria. Isolated showers and thunderstorms are anticipated again for Thursday afternoon. The most likely areas to receive the isolated precipitation will be the Poconos, the Lehigh Valley and northwestern New Jersey as another mid level short wave trough approaches from the northwest late in the day. There may be a bit of a cap over our southern and central counties limiting any convective development there. The wind should favor the west and southwest around 5 to 10 MPH.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Hot and humid conditions will continue through the weekend with some relief expect beginning Monday. An excessive heat warning for the Philadelphia metro areas will extend on into Friday with temps and dew points about what they will be on Thursday. Heat index values of Friday may be a degree or two lower than Thursday, but still in the upper 90s to low 100s across most areas. Clouds will be more frequent Saturday and Sunday, so while it will still be hot, a bit less so than Thu and Fri. By next week, cooler air from N/W will arrive over the area behind a cold front. Showers will be frequent during the long term and it`s tricky to find a period when then chances are too low to put in the grids. Operational models are not great at predicting convection in general, so a broad brush with help from the ensembles usually works well in these kind of patterns. Thursday night will have a good chance for tstms especially across the northern part of the area as a front and accompanying tstms will be affecting the area. The storms will be stronger across NW PA and NY with severe weather possible Thu. The activity will begin to diminish as it arrives over our area. This bears watching however with the hot/humid air masses often not caring whether the sun goes down or not to remain intense. (July!) I have left pops out of Friday for now, with the front settling south of the area. The front returns northward for the weekend and chc or low likely pops for tstms are in for these periods and also Monday. It will not rain all of the time, but you should plan on showers when making weekend plans. Another cold (or cool) front passes the area Monday. It appears for now, that this will finally bring drier and cooler air to the region. We could have a few rain-free days early next week, if the present predictions hold. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. For the 06Z TAFs...Generally VFR through the period. However, there is some chance of locally lower visibilities this morning at favored locations (specifically, KRDG and KMIV) before any fog dissipates rapidly after sunrise. A cumulus deck around 5000 feet is anticipated through much of the day. Storms may reach areas north/west of KPHL near/after sunset tonight, with restrictions possible, especially at KABE. Winds generally light west or southwest through the period. OUTLOOK... Thu night...Sct showers and tstms, especially N/W with restrictions possible. Fri...VFR expected. Fri night thru Monday...Mostly VFR. Patchy haze and Sct tstms. Areas of fog possible in the pre-dawn hours.
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&& .MARINE... High pressure over the Atlantic will continue to influence the coastal waters of Delaware and New Jersey for tonight and Thursday. The wind should favor the south and southwest at less than 15 knots. Wave heights on our ocean waters will remain around 2 to 3 feet and waves on Delaware Bay should be 2 feet or less. OUTLOOK... Thu night thru Monday...Sub-SCA conditions overall. The main hazard will be sct tstms Thu night and also Fri night thru Monday. Locally higher winds and seas with tstms. Bring your NOAA weather radio along to get alerts. RIP CURRENTS... The underlying 12 to 16 second southeasterly swell is forecast to persist into Thursday. As a result, we will continue the moderate risk for the development of dangerous rip currents through that time. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Excessive Heat Warning from noon today to 8 PM EDT Friday for PAZ070-071-102-104-106. NJ...Excessive Heat Warning from noon today to 8 PM EDT Friday for NJZ015-017>019. DE...Excessive Heat Warning from noon today to 8 PM EDT Friday for DEZ001. MD...None. MARINE...None.
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&& $$ Synopsis...O`Hara Near Term...Iovino/Robertson Short Term...Iovino Long Term...O`Hara Aviation...CMS/O`Hara Marine...Iovino/O`Hara

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