Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 221458 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1058 AM EDT FRI JUL 22 2016 .SYNOPSIS... A frontal boundary is expected to move into the area late tonight into Saturday, and thereafter slowly sag south of the area Sunday. High pressure will briefly follow Sunday. Another frontal boundary is expected late Monday into Tuesday and stall nearby or to our south Wednesday and Thursday. && .NEAR TERM /THROUGH TONIGHT/... 1040 AM: upgraded Cape May county to mdt risk for dangerous rip current formation. 935 AM ESTF: adjusted for more morning skycover, and increased temp and dewpoints through midday but nothing else. Ultimately: No major changes to mid afternoon temps/dews-peak heating. Still monitoring and may need to make last minute upward shift and add an associated advisory for the TTN-PHL-ILG-New Brunswick corridor. Also, we may need to issue SPS/SVR this afternoon e Pa and N 2/3rds NJ. From the mid shift: 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. Tonight...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). && .SHORT TERM /SATURDAY/... Will update from below by 330 pm. && .LONG TERM /SATURDAY NIGHT 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 /15Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR sct-bkn aoa 5000 ft with a sw wind gusting 15-20 kt this afternoon. Considerable cirrus this morning-midday from blowoff of sewd moving-initially decaying convection in nw pa, then sct- bkn clouds develop near 5000 ft this afternoon. Anticipating redevelopment of convection 17z-20z near and N of KRDG-KABE-KTTN. North-northwest wind gusts to 40 kt possible in tstms. Tonight...VFR with possible MVFR haze/fog late at night, especially wherever it rain after 21z/22 (today). There may still be some leftover decaying evening convection vcnty PHL-ACY as it runs into the capped mid lvl thermal profile. Southwest wind with gusts to 15 kt early shifting to light northwest late at night. Saturday...VFR sct-bkn aoa 5000 ft. Potential for convection may still exist vcnty KPHL/KILG/KACY/KRDG. Light northwest wind in the morning turning westerly in the afternoon with gusts 15 to 20 kt. OUTLOOK... Saturday night-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... Today...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. Tonight...Winds and seas should subside before daybreak Saturday. Saturday...Sub small craft advisory conditions anticipated. OUTLOOK... Saturday night-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...Added Cape May county to the moderate risk for the formation of dangerous rip currents this afternoon so that all of the NJ coast is now Moderate, while we`ve maintained low risk for the Delaware Beaches. Confidence on how much southerly component is a little below average so the moderate risk may end up low enhanced. Essentially... a 3-4 ft chop driven by gusty southwest wind of 15-20 mph is near parallel to shore. This will create a decent south to north long shore current and could result in some surprisingly strong rip currents by mid afternoon along the NJ shore, when also low tide occurs. Looking further ahead, with the Atlantic Basin still devoid of tropical storms, the probable risk for the formation of dangerous rip currents should be low this weekend, especially with lighter winds and tendency more of an offshore component. Next Monday the 25th, we might have enough wave height to around 4 feet late in the day 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 fallen about 4 degrees since our initial 6am forecast, implying upwelling. Values were variably down into the mid 60s to lower 70s....colder along the NJ coast. Even colder upwelling may develop Saturday when the wind turns more westerly. && .CLIMATE... Barring afternoon convective cloud debris, record breaking heat is likely in our forecast area Monday. These records Monday are vulnerably low. Our 330 am grids fcst record warm values of 97 at Philadelphia and Wilmington Monday, 96 Allentown and a record equaling 96 at Reading. Other near record (within 2F) or record warmth can occur on other days, especially the 24th and 26th. Based on 12z guidance we may extend the records to the 28th... if we still are showing rather high modeled 2m temps. There may be a slight warm bias on these modeled 2m temps at extended ranges...so we are cautious about adding any additional days. 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 && .EQUIPMENT... Lewes weather radio is off the air with an ac replacement needed. We hope to have it going late today. 44009 data has stopped. It may not be replaced til August 1. && .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...Drag/Robertson Near Term...Drag Short Term...Drag Long Term...Robertson Aviation...Drag/Robertson Marine...Drag/Robertson 1058a Climate... Equipment...

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