Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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581 FXUS61 KPHI 301029 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 629 AM EDT TUE AUG 30 2016 .SYNOPSIS... High pressure across New York and New England will build across our region today and then move offshore tonight. Tropical Depression Eight is expected to pass well to our southeast on Wednesday as a strong cold front approaches from the northwest. The front is anticipated to pass through our region early on Thursday followed by high pressure for Friday into the upcoming holiday weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Today...Forecast 90F at PHL...since the 00z/30 GFS 2m temp has 88-89F from sw NJ through PHL and all of Montgomery County PA with cooler values to the northeast. Usually can add 2-3F to GFS 2m temps on p-msunny days. The 00z/30 NAM looks a little moist biased and a degree cooler than the GFS. 00z/30 NAM 28C BL temp can barely make 90 (and its 06z vsn is about 27c) so its support for 90F is less than the GFS. It hasn`t rained since the 21st so less energy is needed to evaporate, making it easier to rise a degree or 2 warmer than expected. 00z/30 ECMWF 2m temp is 85 at PHL which would favor 89f. So am fcstg PHL and ESN Day5 of heat wave but with a little less than average confidence. if it does make 90 today at PHL, then we`re on our way to a record equaling 17, 90 degree days that would occur with tomorrows 90. A sunny start but easterly boundary layer winds permit enough increase in moisture to probably develop a sct-bkn deck of clouds in much of NJ and coastal De this afternoon. The wind turns east but gusts remain under 15 mph. Of interest is multiple model guidance allowing for low top convection in the leftover boundary moisture anywhere from s DE to se NJ. I dont think it will occur but i do have low pop and called it sprinkles in the period of roughly 18z-21z. Presuming the generating mechanism is ocean/land ely flow sfc convergence in the convectively unstable boundary layer. Forecast elements were generally 50 50 blended 00z/30 gfs/nam mos except raised the temp guidance 1-3F to better equate to 2m temp relationship. Max temps about 7F above normal. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... The sct-bkn clouds in NJ may skirt PHL-TTN this evening as the guiding cloud layer wind turns south and advances what remains of the evening cu/sc cloudiness, into NNJ while elsewhere it turns clear. Surface winds should become nearly calm and the resultant cooling will probably allow patchy dense fog in the countryside toward dawn Wednesday. Forecast elements were a 50 50 blend of the 00z/30 gfs/nam mos with no modification of the temps. Min temps about 6F above normal. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... A mostly dry period with the best opportunity for showers and sct tstms will be Wed night thru Thu night as an upper trough and cold front move across the area. Pops for these periods mostly in the chc range attm. Depending on the track of tropical systems, there could be some showers near the coastal areas Mon, so we have slgt chcs then, low confid. Temperatures well above normal Wed before cold front swings thru Thu and brings readings back to normal or a little below normal for Thu-Sun. There are signals that temps may trend back above normal next week, and we have above normal temps in there for Mon attm. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR with sct clouds aoa 4500 ft developing late morning/early afternoon, particularly KACY/KMIV where an afternoon sprinkle may occur in a broken deck near 5000 ft. a light north wind this morning turns easterly midday. Tonight...VFR with sct-bkn clouds near 5000 ft grazing kPHL-KTTN this evening as they edge north. patchy shallow IFR stratus fog possible KACY/KMIV/KTTN after 06z/31. wind becoming nearly calm. OUTLOOK... Wednesday morning...Mainly VFR. Late night and early morning visibility restrictions are possible. Wednesday afternoon into Wednesday night...Mainly VFR. However, there is a chance of showers and thunderstorm. Thursday...Mainly VFR with a chance of showers. Thursday night through Saturday...Mainly VFR. && .MARINE...
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No marine headlines through tonight. Wave heights 3 to 4 ft as an ese swell of 3 ft continues to our shores from the slowly departing central Atlantic Hurricane Gaston. There is a chance that wave will rise to near 5 feet today and if they get to 5.2 or higher and are expected to last for several hours we would then issuance an SCA, the long period swell making wave steepness less than for a shorter period equivalent wave height. Winds northeast gusting 15-20 kt early today turn east by afternoon and continue tonight as light easterly. Water temps are generally in the 70s..above normal. OUTLOOK... Wednesday through Saturday...No marine headlines are anticipated for Wed - Fri night. Then SCA flag possible Sat. for seas with 4-6 ft expected on the ocean. Through the period, long period swells may create rough conditions in and around the inlets along the coasts of New Jersey and Delaware. RIP CURRENTS... With the 3-4 foot long period swells across the ocean and a northeast to east flow, the rip current risk for today is moderate. If the onshore easterly winds increase a bit more than forecast or the waveheights are slightly higher than the 3-4 ft forecast, then we would upgrade to a high risk but for now we think a moderate risk for the formation of dangerous rip currents is reasonably accurate. Wednesday: GFS and tropical modeled swell/period wave groups strongly suggest another day of moderate risk for the formation of dangerous rip currents. The beach hazards statement (thank you for disseminating) was reissued at 431 am for not only the Gaston swells but then a probable renewal of moderate to high risk rip current formation conditions between Friday and Labor day. This in part based on NHCs outlook compared with the cyclic continuity of GFS/EC operational model cycles. Thursday: RC risk probably eases back to low enhanced, but it may rain. Friday-Sunday: RC risk increases with cool boundary layer wind transfer as high pressure develops to our north, with an ensembled fairly extensive broad easterly fetch developing south of New England. In terms of safety, follow the advice of local lifeguards who will be observing the waves and swimmers. There may be some beach closures, all dependent on the reality that develops. This is not a time to swim on your own without lifeguard presence. Additionally, waders are cautioned not to turn their backs to the waves when coming out of the water. Wave knock down can result in upper torso injury (dislocations/spinal cord injuries).
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&& .CLIMATE...
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This section is up to date through 3 AM Today-Tuesday August 30. A top 4 warmest August appears assured most of our forecast area with record monthly warmth likely at PHL. A top 3 warmest June-July-August for Philadelphia, Allentown and possibly Atlantic City. Philadelphia will establish its warmest August on record (dating back to 1874). More than 4 degrees above normal. This Philadelphia August ranking includes our forecast temps (SFT specific values) through the 31st. The 30 year normal is 76.6 Records date back to 1874. 1. ~81.0 2016 2. 79.9 1980 3. 79.8 2001 and 1995 Regarding whether August can tie its record of 17 90F days. Its possible. Today is the critical day for extending the heat wave. The record of 17 was set in 1995. The mean for the month is only 5. Tomorrow reaching 90 at PHl looks to be relatively easy. Allentown will rank #2 warmest August. Records date back to 1922. Normal is 71.7 and we are projecting a positive departure of around 5 degrees. 1. 78.2 1980 2. ~76.6 2016 3. 76.0 1937 Atlantic City records date back to 1874. The August monthly normal is 74.4 and we`re projecting a positive departure of nearly 4 degrees. As it stands, Atlantic City will rank #1 warmest August with very little chance of slipping to #2. The forecast and climate for Atlantic City has greater variability than Allentown and Philadelphia due to proximity to water on sea breeze days and notable radiational cooling on some nights. 1. 78.2 2016 2. 77.9 2005 3. 77.1 2009 Seasonal: This summer 2016 for Philadelphia will probably be the 2nd warmest June-July-August (JJA) in the period of record dating back to 1874. 1. 79.6 2010 2. 78.8 2016 3. 78.6 1995 4. 78.3 1994 Allentown seasonal avg is projecting 75.0 or a ranking of around #2 in the por. 1 75.3 1949 2 75.0 2016 3 74.6 2005 and 1980 Atlantic City seasonal average is projecting 75.8...4th warmest in the por. 1. 77.5 2010 2. 77.0 2011 3. 75.9 2005 4. 75.8 2016 5. 75.5 2008 90 degree days through the 29th. season mean Aug Aug Aug Season mean rer rer abe 33 17 12 4 16-1980 41-1966 acy 28 10 11 3 11-2010 46-2010 phl 39 21 15 5 17-1995 55-2010 ilg 33 20 14 5 23-1895 59-1895 Rainfall: Some uncertainty exists regarding additional rainfall in August, so this part of the climate is stated with caution. Presuming no further measurable rain this month of August...the current ACY value of 1.10 would rank the 6th driest August on record, after a 6th wettest July. For Philadelphia, the June-August seasonal total of 7.45 inches is so far, the 12th driest summer...again this presumes no further measurable rain in August.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Beach Hazards Statement through Wednesday evening for NJZ014- 024>026. DE...Beach Hazards Statement through Wednesday evening for DEZ004. MD...None. MARINE...None. && $$ Synopsis...O`Hara Near Term...Drag Short Term...Drag Long Term...O`Hara Aviation...Drag/O`Hara Marine...Drag/O`Hara 628A Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.