Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 290057 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 857 PM EDT THU JUL 28 2016 .SYNOPSIS...
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Low pressure in the Virginias will organize and move along a warm front through the Delmarva early Friday then off the New Jersey coast by midday Friday. Weak high pressure follows across New York and New England Saturday. Low pressure develops near the Delmarva Sunday and moves out to sea Monday. Drier and less humid weather is expected for much of next week as high pressure builds over the region.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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830 PM: Watch continues. Temporarily quiet. We expect svr potential to increase in waa toward 11 PM on the Delmarva. Please do not think watch cancellation means its all clear all night. Its only all clear through about midnight in the cancelled area. FF potential continues fairly high and the watch continues. Greatest concern is se PA, S NJ, ne MD, central and northern DE, where it rained hard this afternoon, and/or where 3 hrly ffg is under 3". Svr wx threat is mainly delmarva and s tip of NJ through midnight and then it may expand northward after midnight to near ILG-ACY axis as low pres in northern VA cuts enewd through s NJ. Tor parameter remarkably large toward 09z on the sref in snj. LSR`s and PNS will be updated during the night. We can benefit from all damage reports, as well as unusual flooding reports and any rainfall over 2 inches. PWAT increase to 2.3" by 09z philly area. If it thunders at that time, short term rainfall could easily be excessive for urban areas. Normally heaviest rainfall occurs near the path of the sfc low, near the most unstable air which tends to pool near the wind shift between south-northeast sfc wind convergence zone. Am expecting modeled qpf to be too far north. So, another round of heavy rain looks to move in late tonight as a wave of low pressure tracks northeastward along the stalled front. Heavy rainfall with this second round may be more widespread. Also, backed flow in the low levels ahead of the low may provide a source of low- level helicity. Given very low LCL heights, a weak tornado or two may occur toward early morning near the front as long as instability remains near surface based. ZFP wording in parts of the area has repetitive phrasing due to nearly identical grids (except gusty wind replacing damaging wind after 04z)
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Precipitable water values of 2.2 to 2.4 inches will overspread our forecast area from the south for tonight. Conditions are expected to remain unstable, especially across our southern counties. Also, surface low pressure approaching from the west will result in the development of a favorable low level wind profile for organized convection tonight. The surface wind should begin to favor the east to south quadrant late tonight, especially on the coastal plain, while winds around 800 HPa will be from the southwest. The very high precipitable water values should result in heavy rainfall in any organized convection. As a result, the Flash Flood Watch remains in effect for southeastern Pennsylvania, central and southern New Jersey, Delaware and northeastern Maryland. The cloud cover and high humidity will keep temperatures from falling below the 70s for tonight except in the Poconos and far northern New Jersey. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Highlights... * Scattered showers/t-storms w/locally heavy rainfall this weekend * Drier/less humid weather for much of the next work week Details... Friday night... Dry weather expected Friday night with subsidence behind departing shortwave. May see some patchy fog develop overnight with wet ground and lingering low level moisture. Saturday and Sunday... A couple of additional shortwaves will move across our region this weekend along with a frontal boundary in the vicinity. Timing is uncertain this far out, but more scattered showers and thunderstorms are expected at times this weekend. Pwats will still be between 1.5 and 2 inches, so the threat will exist for locally heavy rainfall. Clouds and the threat of precipitation should hold high temps mainly in the 80s both days. Monday through Thursday... High pressure will build over the region, bringing us drier and less humid weather. There still will at least be a low risk for a few showers early in the work week, but either way dry weather should dominate through Thursday. High temps will mainly be in the 80s. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...vfr showers with probably periods of ifr conds and gusty winds to 25 kt in sct tstms, especially after 04z/29. otherwise sustained winds under 10 kt will tend to become northeast toward morning. Confidence is low for the timing of heaviest oncoming convection at any particular TAF site, but high that storms will be in the region through early Friday morning. Friday...showers and thunderstorms end from west southwest to east northeast. mvfr or ifr conds 12z-15z in showers/sct tstms then improving to vfr cigs in the afternoon with a northeast backing to north wind gust 20 kt. Outlook... Sat through Sun...Shra/tsra will lower cigs/vsbys at times Otherwise VFR expected. Moderate Confidence. Mon...Mainly VFR. Moderate Confidence.
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&& .MARINE...
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A severe thunderstorm watch is in effect for the southern waters. There is a potential for storms through this evening to produce locally strong winds. An isolated waterspout is also possible through early Friday morning. The svr risk will probably increase early friday morning along the De and S NJ coasts as low pressure crosses the area. Winds turn northeast to north behind the low Friday morning then more north to northwest late Friday afternoon. Expect seas to respond by building to 2 ft in the morning and possibly 3 to 4 ft during the afternoon in our coastal waters. Outlook...Friday night through Tuesday... There is a low risk for marginal small craft seas Friday night but for now kept them just below 5 feet. Otherwise, winds/seas should generally remain below small craft advisory thresholds through the period. Biggest concern for mariners will be the risk for thunderstorms this weekend. Drier weather should arrive early next week. RIP CURRENTS...We have forecast low risk Friday but if the wind turns onshore with gusts 15-20 kt, we may need to increase the risk to mdt for a portion of the NJ coast. Outlooking: Still generally low risk for awhile, possibly low enhanced. we do note some longer period swells anticipated by the GFS around the 3rd/4th which may increase the rc risk. Also the tropics have been quiet this July, but there are a couple of disturbances in the eastern Atlantic that are being monitored.
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&& .CLIMATE...
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PHL heading for top 10 warmest July on record. July avg temp for PHL will be about 80.9F, 8th warmest July in the period of record since 1874. ACY... already as of 850 pm this evening...is 7th wettest on record with its monthly record of 13.09 set in 1959, the por back to 1874. total for the month as of 850 PM: 8.34" with 1.17 today, so far. daily record rainfall today friday the 29th acy 2.05 2012 2.21 - 1884 phl 8.02 2013 3.53 - 1980 ilg 2.34 1914 1.85 - 1913 abe 3.00 1916 1.64 - 1979 ttn 2.35 2012 2.84 - 1961 ged 1.98 1994 1.07 - 1969 rdg 3.57 1969 2.51 - 1961 mpo 2.15 1969 4.59 - 1969
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flash Flood Watch through Friday morning for PAZ054-055- 060>062-070-071-101>106. NJ...Flash Flood Watch through Friday morning for NJZ001-007>010- 012>027. DE...Flash Flood Watch through Friday morning for DEZ001>004. MD...Flash Flood Watch through Friday morning for MDZ008-012-015- 019-020. MARINE...None. && $$ Synopsis...99 Near Term...Klein/drag 856P Short Term...Klein/drag 856p Long Term...99 Aviation...Klein/99/drag 856P Marine...Klein/99/drag 856p Climate...drag 856P

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