Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 241407 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1007 AM EDT SUN JUL 24 2016 .SYNOPSIS...
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High pressure will remain in control over the area until a weak warm front returns back to the north and east by late tonight. This cold front is expected to approach from the northwest Monday before slowly moving into the area Monday night. The front may stall over the Delmarva or nearby to our south midweek as high pressure builds in from the north. Another front may affect the area late this week into next weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A weak cold front that moved through the area last night was located to our south across the southern half of VA. High pressure centered to our north was building into the forecast area in wake of this front. The term cold front may be somewhat misleading as the air is nominally cooler behind the front; certainly not enough to break the ongoing heatwave. High temperatures across most of the area will be in the mid 90s today (80s across the hilly terrain in northeast PA and northwest NJ as well as at the beaches). However, the post-frontal airmass will be drier with dewpoints dropping into the low 60s and even 50s. Therefore, humidity won`t be much of a factor today across most of the area with the heat index similar to the dry-bulb temperature. The one exception will be central/southern DE and adjacent eastern MD, where the surge of drier air will not make much advancement that far south with more of an onshore component to the flow today (either easterly or westerly winds will advect higher dewpoints inland this afternoon with bay breezes. Forecast heat indices in these southern most zones will range from 98-102F for this afternoon, just shy of heat advisory criteria. Although an offshore flow will develop later today in eastern PA and western NJ, the onset of it will be delayed late enough in the day and the winds will be light enough to allow the sea breeze to move inland this afternoon. Hi-res model guidance indicates the bay/sea breeze front reaching the I-95 corridor prior to sunset (6-8 PM). Winds will shift from W-SW to S-SE once the sea breeze passes through. 12Z RAOBs from IAD, OKX and PBZ captures a strong mid-level subsidence inversion overhead. Forecast soundings as well as modified RAOB soundings indicates this inversion should cap convection today, especially in the absence of deeper organized lift over the area.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... The evening will start off precipitation free, but as we go through the night, the frontal boundary to our south will begin lifting northward, while a short wave/vorticity impulse approaches from the west. This short wave is expected to interact with the lifting frontal boundary and create isolated/scattered showers or thunderstorms during the overnight hours. The best chance for any precipitation overnight looks to be the northern two-thirds of the area. There could also be some patchy fog north of the lifting warm frontal boundary overnight with a warm and moistening airmass moving northward. && .LONG TERM /MONDAY THROUGH SATURDAY/... The main impact will be the heat and humidity for the early part of the week. Expect high temperatures in the mid to upper 90s across the area Monday. This, combined with a very humid airmass will push heat index values above 100 degrees for most of the area. A weak cold front will push across the region late Monday and Monday night. This will spark off the next round of showers and thunderstorms with the potential for some to become severe. This cold front will slide to our south by Tuesday, bringing some slight moderation in temperatures and humidity levels. Still expect temperatures in the lower to mid 90s with heat indexes that approach 100. Much of the area should stay dry Tuesday and Wednesday, with just extreme southern New Jersey and the Delmarva with the threat of thunder due to the proximity to the stalled frontal boundary lingering across the mid-Atlantic. The slight downward trend of heat and humidity levels will continue on Wednesday with temperatures generally staying in the lower 90s. The front starts to approach back from the south as a warm front by Wednesday night into Thursday. A couple of weak waves of low pressure may develop and then ride up along this boundary giving us a couple of chances for shower and thunderstorm development for the latter part of the week. There does not look to be much in the way of a pattern chance into next weekend, so expect the warm, humid and unsettled weather to continue through the end of the week and next weekend. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. There is some patchy light fog this morning, mainly at MIV and other rural areas, but this will lift and burn off around/shortly after sunrise. The rest of the day will be VFR. It is possible that some patchy fog could develop again overnight tonight into Monday morning. Also, there is a chance for isolated/scattered showers or thunderstorms overnight tonight. Winds are light and variable at many locations this morning, but where they have a direction, they are more northwest and will likely become north to northeast later this morning. Winds are expected to become more south to southwest during by midday as high pressure weakens as it tries to move across the area. outlook... VFR much of the time. Scattered (mostly) late afternoon and evening showers and thunderstorms may limit cigs/vsbys at times through the period. The best chance for this will be Monday afternoon and evening and then again on Thursday. && .MARINE... Sub-small craft advisory conditions will continue today and tonight across the area. There is a chance of showers or thunderstorms late tonight into Monday morning. outlook... Mostly a period of sub-sca conditions expected. Scattered showers and thunderstorms will create locally higher winds and seas through the period. Best chance for this will be Monday afternoon and evening and Thursday. && .CLIMATE...
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Yesterday, July 23rd, was the hottest day in quite some time (3 to 4 years) at several of our climate sites: Philadelphia: The max temperature of 97F yesterday was the highest temperature observed at PHL airport in three years (since July 19, 2013 when it was also 97F). Reading: The max temperature of 98F yesterday at RDG airport was the highest reading in four years (since July 18, 2012 when it was 100F). Trenton: The max temperature of 96F yesterday at Trenton was the highest temperature recorded at the site in three years (since July 18, 2013 when it was also 96F). The forecast high temperature for Philadelphia tomorrow, Monday, 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 today through Thursday are below. Except maybe ABE, we`ll fall short of record highs today. We may tie or break daily record highs tomorrow at several of our climate sites. Site 24th 25th 26th 27th 28th ---- ---- ---- ---- ---- ---- PHL... 98-2011 96-1899 101-1892 101-1940 100-1941 ABE... 95-1999 95-1999 98-1940 98-1955 97-1949 ACY... 100-2011 99-2010 96-2011 99-2005 98-1999 ILG... 98-2011 96-1987 99-1894 100-1894 101-1894 TTN... 98-1910 97-1999 99-1892 100-1894 101-1894 GED... 99-2011 99-2010 97-2012 98-2005 99-1949 RDG... 96-2010 96-1999 99-1940 98-1955 99-1941 MPO... 91-1914 90-1999 89-1949 91-1955 93-1949
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...Heat Advisory from 11 AM to 6 PM EDT Monday for PAZ060>062-101- 103-105. Excessive Heat Warning until 6 PM EDT Monday for PAZ070-071- 102-104-106. NJ...Heat Advisory from 11 AM to 6 PM EDT Monday for NJZ001-007>010- 012>014-016-020>027. Excessive Heat Warning until 6 PM EDT Monday for NJZ015- 017>019. DE...Heat Advisory from 11 AM to 6 PM EDT Monday for DEZ002>004. Excessive Heat Warning until 6 PM EDT Monday for DEZ001. MD...Heat Advisory from 11 AM to 6 PM EDT Monday for MDZ008-012-015- 019-020. MARINE...None. && $$ Synopsis...Klein/JK Near Term...Klein Short Term...Robertson Long Term...JK Aviation...Robertson Marine...Robertson/JK Climate...Klein

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