Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 240939 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 539 AM EDT FRI JUN 24 2016 .SYNOPSIS... A cold front will over the northern Delmarva and southern New Jersey early this morning will gradually push south of the area today. High pressure will build into the region for this weekend. As the high moves offshore Monday, a slow moving cold front will approach from the northwest Tuesday, and move through the region Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 530 AM update...Made some slight changes to the hourly PoPs and weather grids based on the latest mesoanalysis and radar trends. The focus of scattered showers and isolated thunderstorms early this morning will be along the frontal boundary in northeast MD, DE and southern NJ. Previous discussion... A cold front was located over the area (somewhere near the I-95 corridor) early this morning. The front was marked by surface winds from the north or northeast and temps/dewpoints in the upper 50s to lower 60s north of the boundary while southerly winds and temps/dewpoints in the upper 60s to lower 70s resided to the south. There were isolated showers present for much of the night near the frontal boundary in southern NJ and the northern Delmarva. These showers have been very light thus far. Interestingly, the HRRR has been remarkably persistent/consistent over the past five or so runs (ending with the 05Z run) that showers and thunderstorms form over the Delmarva early this morning, resulting in a localized area of heavy rainfall of 2+ inches (the 03Z HRRR showed a band of 5-8 of rainfall in 4 hours but successive runs have since backed off from these extreme amounts). Though it`s an extremely unlikely scenario that is not supported by other model guidance, LAPS/SPC mesoanalysis shows about 500-750 J/kg of MUCAPE and a local PWAT maximum near 1.7 inches over the northern Delmarva, which would be enough to support low-topped heavy rain producers in this environment. PoPs early this morning were raised to about 40 percent across these southern zones. The front will eventually push south of the area later this morning and afternoon as high pressure build in from the Great Lakes. With breaks in the clouds today, temperatures could peak in the mid 80s along and west of I-95. An easterly wind off the ocean will keep temperatures cooler (70s) in the coastal plain today. We could see a fair amount of stratocu develop in this maritime airmass during the afternoon. While most of the CWA should remain dry today, there are two areas for potential shower development this afternoon. First, the juxtaposition of lower-tropospheric convergence at the nose of weak easterly jet to the north of a H9-H8 trough and upper-tropospheric divergence in the right entrance region of a jet streak implies forcing for ascent that is needed to maintain any convection across the Delmarva today. Model forecast soundings support adding in a slight chance for thunderstorms during peak heating. There is lesser confidence for the development of upslope showers in our far western zones in eastern PA but a mid-level shortwave trough could potentially provide a brief period of deeper lift as it approaches from the west this afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... The center of the surface high retreats off the New England coast tonight. However, the high will still control our weather pattern with the ridge axis expected to extend southwestward from the high in to the northern mid-Atlantic region. Surface winds will back from easterly at the start of the period to northeasterly by early morning as low pressure moves offshore. There is a potential for marine stratus to advect inland tonight owing to the onshore flow. These low clouds in addition to higher convective debris clouds are anticipated to curb radiational cooling, especially the closer you are to the coast. Forecast lows are in the mid to upper 50s in northeast PA/ northwest NJ and low to mid 60s elsewhere. && .LONG TERM /SATURDAY THROUGH THURSDAY/... The weekend will be dry with high pres over the region. The high will slowly move ewd and offshore by Mon. As the high departs, low pres in Ontario will move ewd. Its attendant cdfnt will approach from the w, and cross the area on Tue. The GFS then keeps things dry Wed into Thu. However, the ECMWF (with some support from the CMC) wants to bring a second front through on WEd and another shot of precip, before drying things out later Wed into Thu. For right now, will carry low pops Tue wino erly Wed and no pops after that. Temps look to be nr nrml with comfortable humidity values thru the pd. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Brief/local MVFR restrictions is possible early this morning at ILG, MIV or ACY if a shower moves over the terminal. Coverage of showers are too low to include in 06Z TAFs but will issue amendments if necessary. Additionally, brief visibility restrictions are possible farther north if patchy fog develops toward sunrise. Otherwise, expect mainly VFR today. Winds are currently light and variable, but will become northeasterly around 5-10 kt after sunrise. Winds veer to easterly this afternoon with speeds of 10-15 kt. There is a potential for low clouds to develop offshore and move inland late this evening and overnight. This may yield MVFR or IFR restrictions. Forecast confidence decreases farther away from the coast. Therefore, limited IFR restrictions in the forecast to MIV and ACY. Outlook... Sat and Sun...Predominantly VFR. Patchy ground fog may lead to sub-VFR conditions late Saturday night and early Sunday morning, mainly at ABE, MIV, and RDG. Moderate Confidence. Mon and Mon night...VFR. High Confidence. Tue...A cdfnt will move slowly acrs the region and be accompanied by shra/tsra. VFR will prevail, then MVFR/IFR psbl with fropa. Still some timing diffs with cfp. Moderate confidence. && .MARINE... Light onshore flow will develop this morning and increase to 10-15 kt with gusts to 20 kt this afternoon and tonight. Seas will accordingly build to around 4 ft in our coastal Atlantic waters by tonight. There is a potential for wave heights to approach 5 ft by late tonight but confidence in this happening was too low to issue a SCA at this time. Outlook... Sat...Latest guid indicates that we cud have sca conds with a e to ne flow which cud linger into Sat night. Sun thru Tue...No marine headlines anticipated. RIP CURRENTS...Seas off the coast will build to 3-4 ft in response to an onshore flow that develops this morning and strengthens this afternoon. Medium-period southerly swells will be around 2 or 3 ft. In this setup, the risk for the formation of dangerous rip currents will approach moderate this afternoon. Based on the expected wind, wave and swell conditions a moderate risk for the development of dangerous rip currents may persist into Saturday along the New Jersey shore and at the Delaware Beaches. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Klein/Nierenberg Near Term...Klein Short Term...Klein Long Term...Nierenberg Aviation...Klein/Nierenberg Marine...Klein/Nierenberg is the U.S. government's official web portal to all federal, state and local government web resources and services.