Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 221756 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 156 PM 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/...
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145 PM update: Just a heads up. We will probably issue an excessive heat warning for the period Saturday through Monday, with the specific caveat that it will be more comfortable sunday (lower dewpoints). We still have other model data to review Noon:12z/22 GFS 1400J MLC at 21z vcnty TEB-ABE-RDG axis with KI 35+, TT49, SWI -3. 0-6KM bulk shear poor-20-25kt. But the heat, waa and 30kt at 500mb should allow 40-45 kt gusts, IF storms can get going. That is an uncertainty. Also appears to me to be weak mid lvl cap of around 10C trying to develop late in the day that could impact the life of any strong thunderstorm cells. pwat 1.75" would also mean poor drainage flooding in a few locations. No advy for today but a close call...many 99`s and 1 hr of 100 anticipated. 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 wind shift should slide at least partially through the region, possibly getting hung up along the MD border to KACY which would impact tomorrow afternoons weather. Fcst elements were produced using a 50 50 blend of 12z/22 GFS/NAM MOS guidance. Unlikely for much if any fog/haze late at night.
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&& .SHORT TERM /SATURDAY/...
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Sunny, hot and humid Saturday with HI 100 or greater most areas, and Day1 of an excessive heat warning. While Saturdays values are less than warning criteria, it is probably D2 of mid 90s actual max temps that will likely last into the middle of next week. Prolonged literal mid 90s heat will take a toll. Additionally our extended forecaster will probably be indicating HI 105+ for Monday. If the boundary hangs up near the Mason Dixon line to ACY, then the potential would exist for late afternoon svr Delmarva. Still plenty of instability there with better 0-6km bulk shear. Fcst elements were produced using a 50 50 blend of 12z/22 GFS/NAM MOS guidance.
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&& .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 /18Z FRIDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Remainder of this afternoon...VFR sct-bkn aoa 5000 ft with a sw wind gusting 15-20 kt. Anticipating redevelopment of convectionnear and N of KRDG-KABE-KTTN later today. North-northwest wind gusts to 40-45 kt possible in any tstms ne and e central PA and n 1/2 NJ...mainly near and n of KABE and KTTN. Tonight...VFR with small chance MVFR haze/fog late at night, especially wherever it rained after 21z/22 (today). There may still be some leftover decaying sewd moving 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 KILG/KACY/KMIV. Light west 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.
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&& .MARINE...
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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. Max gusts around 20 kt. 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 fell about 4 degrees between 6 am and 10 am, 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.
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&& .CLIMATE...
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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 27th 28th PHL 101-2011 98-2011 96-1899 101-1892 101-1940 100-1941 ABE 99-1955 95-1999 95-1999 98-1940 98-1955 97-1949 ACY 105-2011 100-2011 99-2010 96-2011&1963 99-2005 98-1999 ILG 100-2011 98-2011 96-1987 99-1894 100-1894 101-1894 TTN 104-2011 98-1910 97-1999 99-1892 100-1894 101-1894 GED 104-2011 99-2011 99-2010 97-2012 98-2005 99-1949 RDG 100-2011 96-2010 96-1999 99-1940 98-1955 99-1941 MPO 91-1955 91-1914 90-1999 89-1949 91-1955 93-1949
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&& .EQUIPMENT...
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Lewes weather radio is intermittently off the air with an ac replacement needed. We hope to have it going late today. 44009 data has stopped transmitting (batteries failed). It may not be replaced til November.
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&& .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 until 5 AM EDT Saturday for ANZ450>453. && $$ Synopsis...Drag/Robertson Near Term...Drag 156P Short Term...Drag 156p Long Term...Robertson Aviation...Drag/Robertson 156P Marine...Drag/Robertson 156P Climate... Equipment...156P

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