Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 220738 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 338 AM EDT FRI JUL 22 2016 .SYNOPSIS... A frontal boundary is expected to move into the area overnight tonight into Saturday, and slowly sag south of the area through Sunday. High pressure will briefly affect the area Sunday. Another frontal boundary is expected late Monday into Tuesday and stall to our south through Wednesday and Thursday. High pressure should briefly affect the area Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Southwesterly flow ahead of the weak cold front tonight will lead to the continuation of the warming trend. Expect highs to be around 5 degrees higher than Thursday, but we should still fall short of heat advisory criteria, with maximum heat index values generally in the mid to upper 90s. A pre frontal trough is expected to slide over our region by this afternoon. Along this trough, expect surface and low level convergence. With the heating, expect mixed layer CAPE values to be above 1000 J/kg across the northern half of our region. Bulk shear values are modest, and there is limited mid and upper level support which should limit the coverage of storms. However, with a dry mid level layer (around or just above 700 mb), any storms that are able to sustain an updraft to that level will have potential for downbursts. Thus, will mention the threat for strong winds (especially across the north) in the HWO. Hail threat looks to be limited thanks to a very high melting layer (between 14 and 15k ft AGL). Also not that concerned about heavy rain as storm motions should be near 20 kt and precipitable water values are just slightly above normal. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... The pre frontal trough should still be over the region at least through the evening hours continuing the risk for thunderstorms with strong winds. Very late in the night though, the cold front should slide into the Poconos and NW NJ. Given the timing of the front, and continued mid level drying, do not expect any storms with the front (expect nearly all the convection to develop near the trough). && .LONG TERM /SATURDAY THROUGH THURSDAY/... Hot and humid conditions are continued to be forecast for much of the extended period, with Saturday, Monday and possibly Tuesday expected to be the warmest days. It is possible that Sunday may be slightly "cooler" and have lower dewpoints, leading to lower heat index values, but it will still be quite hot. With 925 mb temperatures forecast to be around 25/26 degrees, this would yield highs into the mid/upper 90s Saturday, Monday and Tuesday. The combination of the heat and humidity will lead to dangerously high heat index values over the weekend into Monday, and possibly into Tuesday. With several days of dangerously high heat index values expected, we continue with the Excessive Heat Watch for all of our forecast area except Carbon and Monroe counties in Pennsylvania and Sussex county in New Jersey and have extended it into Monday. There could be some isolated showers/thunderstorms late Sunday into Sunday night across the far southern areas as a couple of short wave/vorticity impulses move across the area. However, most areas will remain dry. On Monday, a pre-frontal trough will be in place across the east coast, with a frontal boundary approaching the area late in the day and overnight. As these features move eastward, along with the associated short wave aloft, scattered showers/thunderstorms could begin moving into the area late in the day Monday into Monday night. There is a fair amount of instability forecast with the heat and humidity, and there will be some weak shear present as well. If any thunderstorms do develop, the could produce a brief period of heavy rainfall and gusty winds. There will be a chance of showers/thunderstorms each day from Tuesday, Wednesday, and Thursday as several short wave/vorticity impulses move across the area. The strongest of these short waves may move across the area later on Thursday, leading to a greater chance of showers/thunderstorms. && .AVIATION /07Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Scattered thunderstorms are possible this afternoon and evening. Coverage will be quite limited, so have only mentioned a PROB30 at KABE and KTTN for now. However, if any storms do move over TAF sites, downbursts leading to variable and gusty winds will be possible, along with brief IFR visibilities. Aside from the storms, VFR conditions are expected today and tonight. Winds will be southwesterly and will be around 10g18kt between 15 and 00Z (excluding in the vicinity of storms, where winds could be stronger). OUTLOOK... Saturday-Sunday. VFR. Monday-Monday night...Generally VFR. A chance of showers and thunderstorms which may briefly lead to lower conditions. Gusty southwest winds 15-20 knots. Tuesday-Tuesday night...VFR. && .MARINE... Southwesterly winds will continue through the day today, increasing this afternoon. For the New Jersey coastal waters, expect gusts above 25 kt to develop by mid afternoon, with seas expected to subsequently increase to 5 feet by this evening. For the Delaware coastal waters and the Delaware Bay, wind gusts above 20 kts are possible, but should stay below SCA criteria. Winds and seas should subside before daybreak Saturday. OUTLOOK... Saturday-Sunday...Sub-Small Craft Advisory conditions expected. Monday-Monday night...Near Small Craft Advisory conditions possible with increasing winds ahead of an approaching cold front. Tuesday-Tuesday night...Sub-Small Craft Advisory conditions expected. RIP CURRENTS...The risk for the formation of dangerous rip currents today is moderate along the NJ shore from Atlantic County northward and low for the Delaware Beaches and Cape May county. Confidence on how much southerly component is a little below average so the moderate risk may end up low enhanced. Looking further ahead, with the Atlantic Basin still devoid of tropical storms, the risk for the formation of dangerous rip currents should be Low. Next Monday the 25th, we might have enough wave height to around 4 feet and water buildup due to southerly winds, to have a more widespread low enhanced or even moderate risk but confidence on seas building that high is below average. Water temperatures have rebounded after the massive upwelling event associated with the squall line passage late Monday. Water temps today were in the low to mid 70s, above normal for this time of year and quite a rebound from the lower 60s of Tuesday. Colder upwelling might develop again late Friday or Saturday. && .CLIMATE... Near record (within 2f) or record warmth is anticipated for many sites on 1 or 2 days of the following listed. 23rd 24th 25th 26th PHL 101-2011 98-2011 96-1899 101-1892 ABE 99-1955 95-1999 95-1999 98-1940 ACY 105-2011 100-2011 99-2010 96-2011, 1963 ILG 100-2011 98-2011 96-1987 99-1894 TTN 104-2011 98-1910 97-1999 99-1892 GED 104-2011 99-2011 99-2010 97-2012 RDG 100-2011 96-2010 96-1999 99-1940 MPO 91-1955 91-1914 90-1999 89-1949 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Excessive Heat Watch from Saturday morning through Monday afternoon for PAZ060>062-070-071-101>106. NJ...Excessive Heat Watch from Saturday morning through Monday afternoon for NJZ007>010-012>027. DE...Excessive Heat Watch from Saturday morning through Monday afternoon for DEZ001>004. MD...Excessive Heat Watch from Saturday morning through Monday afternoon for MDZ008-012-015-019-020. MARINE...Small Craft Advisory from 2 PM this afternoon to 5 AM EDT Saturday for ANZ450>453. && $$ Synopsis...Robertson Near Term...Johnson Short Term...Johnson Long Term...Robertson Aviation...Johnson/Robertson Marine...Johnson/Robertson Climate...Staff

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