Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 242008 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 408 PM EDT SUN JUL 24 2016 .SYNOPSIS... A warm front will slowly push northward through the area through Monday morning. A cold front will approach from the west, moving into the region late Monday night and Tuesday, then stalls near or just to the south of the area through the midweek period. Another system may impact the area over the weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... A frontal boundary was located to south and west over VA and western PA. This front will return back northeastward as a warm front tonight. A shortwave trough associated with an MCS over the Ohio Valley this afternoon is expected to track eastward through the forecast area tonight. This complex should start to weaken by the time it reaches our area as the atmosphere stabilizes with the loss of heating. Still expect at least scattered showers and a few embedded thunderstorms to move into our western zones of eastern PA around midnight, the I-95 corridor between 2-4 AM, and then our coastal communities between 4-6 AM. The clouds associated with the MCS will limit our fog potential. However, if clouds clear across our far western zones during the pre dawn, then fog could become more widespread and/or dense toward sunrise. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... Monday is expected to be on par with this past yesterday (Saturday, June 23) in terms of the heat and humidity. Both this past Saturday and upcoming Monday represent the peak of excessive heat during this extended heatwave that started Friday and continues through late in the week. No changes were made to the heat headlines; Excessive Heat Warning in effect for the heat-sensitive population in the urban I- 95 corridor from Wilmington to Philadelphia to Trenton with maximum heat indices forecast to be around 105F. To the southeast of the warned area, including the rest of our Delmarva zones and southern NJ, a Heat Advisory is in effect tomorrow with the heat index peaking somewhere between 105 and 110F. Advisories are also in effect to the north of the I-95 corridor that includes northwestern NJ and eastern PA, where heat indices are expected to fall between 98-103F. The shortwave trough associated with whats left with the overnight MCS is forecast to move off the coast during the early to mid morning. Model RH fields indicates the potential for mid- and high- level clouds to hang around during the day. The clouds will play an important role in how the forecast unfolds for Monday afternoon. Exactly how early in the day and how persistent these breaks occur with these leftover debris clouds will determine how hot and unstable we get during the afternoon. Based on the latest guidance. we think subsidence in wake of this early morning shortwave will provide an opportunity for most of the area to at least partially clear out by late Monday morning. Strong heating will allow for temperatures to rise quickly into the 90s during peak heating hours and for the atmosphere to rebound/destabilize. A pre-frontal surface trough is forecast to sharpen on the lee side of the Appalachians during the day. Convection will likely initiate during the first half of the afternoon to our west near the lee trough and also to our north with deeper lift arriving in advance of an upper shortwave disturbance moving over the Great Lakes. This activity is then expected to progress eastward late in the day. The greatest confidence in showers and storms (and thus highest PoPs) arriving before the short term period ends is north and west of the fall line. A slight chance of showers and storms are forecast for Philadelphia between 4 and 6 PM. The latest D2 outlook from SPC includes northeast PA and northwest NJ in a slight risk for severe storms. The marginal risk for severe storms farther southeast into the I-95 corridor though the bulk of thunderstorm activity may still be upstream of Philadelphia through 6 PM. The main threats with these storms will be locally damaging winds. Storms that form in such a hot and very humid airmass (e.g., yesterday) tend to produce severe thunderstorm episodes. Although the amount of instability Saturday should be similar to yesterday (MLCAPE 1500- 2500 J/kg), DCAPE values may be slightly less tomorrow with not as pronounced mid level drying. The other concern will be locally heavy rainfall that could result in flash flooding as storms develop in a moisture-rich environment (PWATS exceed 2) and a slow-moving boundary approaching to our west. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... Showers and thunderstorms are expected Monday night into Tuesday as the cold front makes its way into the area. The cold front stalls as it moves south and looks to remain in the vicinity of Delmarva through the midweek period. Areas that manage to stay behind the stalling boundary will have some cooler and drier air moving in, which will allow for the hot and stickiness of the past several days to finally decrease. While it will still be fairly hot outside, those lower dewpoints will help us to remain at a more comfortable level and we do not anticipate any headlines will be needed at this time. Areas closer to the stalled boundary will remain a bit more humid and will continue to have a chance for showers and thunderstorms. The front will waver and start to push northward as a warm front late Wednesday or Thursday. Showers and thunderstorms will remain possible in areas closer to the boundary. The front will also serve as transport for a few waves of low pressure, which will move fairly quickly through the area. Overall, showers and thunderstorms will be a threat from midweek through the weekend. && .AVIATION /20Z SUNDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR through midnight. Scattered showers and isolated thunderstorms are expected to move in from the west overnight into the early morning. A 3-4 hour tempo group for shra and MVFR restrictions were included at each TAF site. Confidence in thunder and potential for lower restrictions was too low to include with the 18Z TAFs. Expect winds to shift from SW to S or S-SE before sunset across the I-95 terminals, including PHL as a sea breeze front moves inland. Winds will generally be in the 8-12 kt range when this happens. Light and variable winds tonight. SW winds 5-10 kt Monday morning become more westerly toward midday and the afternoon. Showers and thunderstorms may reach ABE-RDG during the mid to late afternoon Monday. This activity will likely remain upstream of the I-95 TAF sites through 23Z. Outlook... Monday night through Friday...Mainly VFR conditions expected. Scattered showers and thunderstorms on Monday and Wednesday through Friday, with MVFR/IFR conditions possible at times. && .MARINE... Sub-small craft advisory conditions will continue tonight and Monday. There is a chance of showers and a slight chance of thunderstorms late tonight into the first half of Monday morning. Additional showers and storms will likely remain inland through the afternoon on Monday. Outlook... Monday night 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, mainly Monday night into Tuesday and again on Wednesday through Friday. Rip Currents....The risk for formation of dangerous rip currents is low today. The setup for rip currents is better on Monday with a strengthening SW flow during the day but it will likely still be in low risk category. && .CLIMATE... 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 for Monday through Thursday are below. We may tie or break daily record highs tomorrow at several of our climate sites. 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 && .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...Meola Near Term...Klein Short Term...Klein Long Term...Meola Aviation...Klein/Meola Marine...Klein/Meola Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.