Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 210936 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 536 AM EDT SUN AUG 21 2016 .SYNOPSIS... A cold front extended from eastern Ontario across Ohio to the lower Mississippi River Valley early this morning. The front will progress eastward and it is forecast to pass through our region this evening. High pressure is expected to follow for much of the new week. A cold front is anticipated to approach from the northwest on Friday and it should arrive on Friday night. Another area of high pressure is expected for next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Any fog early this morning should burn off around sunrise. A cold frontal boundary located from the eastern Great Lakes into the southeast states will continue moving eastward and into our region today. Also, a warm front across Virgina will lift northward through the region this afternoon. The winds and flow ahead of this front will continue to be from the southeast allowing even more moisture to advect in. Both fronts will likely serve as lifting mechanisms for the development of showers and thunderstorms to our west that then move through our region in the afternoon hours. The abundance of moisture is shown in the modeled PW values of over 2 inches along with a deep moist layer in modeled soundings. Both of the aspects support the likelihood for heavy rainfall with thunderstorms that move through, maintaining hvy rain wording in the products. In terms of any thunderstorms becoming severe, both the instability and shear reflect a more marginal possibility. Modeled CAPE values are around 1,000 J/KG in the afternoon with modestly steep low level lapse rates. However, a lack of dry air in the sounding is present as well. While a few thunderstorms with strong or damaging wind gusts can not be ruled out it is a more limited threat than that of heavy rainfall at this time. Northern parts of our region will be near the triple point (intersection of fronts), modeled helicity values particularly on the NAM 00z run increase in the lowest 1KM of the sounding (over 100 m2/s2). Some turning of winds near the surface and looping in the hodographs are present as well. These aspects of the sounding data suggest a tornado can not be ruled out from the Lehigh Valley into northern NJ. This possibility wains quickly further south away from the expected position of the triple point. Showers and thunderstorms will start to end from west to east as the cold front enters the picture. Many spots could pick up a quick inch or even more of rainfall leading to ponding of water on roads and other localized flooding issues. Outdoor plans have the highest chance of being rain free in the morning with chances going downhill by early afternoon west of Philly and mid afternoon east. Temperatures yesterday ended up a few degrees warmer than MAV/MET, so we have gone in this direction again for areas that will see some sunshine throughout most of the day. These spots are from Philadelphia and points to the southeast where highs will be near 90 with 80`s further NW. Momentum transfer in the sounding also shows the potential for some wind gusts near 20 mph in the afternoon hours. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... The cold front will quickly plow eastward through the region during the evening. A gradual clearing trend from west to east will come in behind the front. Lows should drop into the 60`s for most locations. Any lingering showers/storms near the shore will end in the early evening. && .LONG TERM /MONDAY THROUGH SATURDAY/... High pressure is forecast to be located over the Ohio River Valley on Monday. The air mass will build eastward with its center expected to settle over or near our region for Tuesday and Tuesday night. As a result, we are anticipating a mostly clear sky and low humidity for the period from Monday through Tuesday night. Maximum temperatures should favor the 70s up north and the lower and middle 80s elsewhere. Overnight low are expected to be mainly in the 50s except in urban areas and along the coast where minimum readings will likely be in the 60s. A clear sky and light wind may allow for the development of late night river valley fog across parts of eastern Pennsylvania and northern New Jersey, an early sign of the coming autumn. The center of the high is forecast to pass off the coast on Wednesday before moving out to sea. Our region should be in the southerly return flow on the back side of the high late in the week with a gradual increase in both heat and humidity anticipated. Maximum temperatures may again approach 90 in our central on southern counties on Friday. No precipitation is expected for Wednesday and Thursday. However, the model guidance continues to bring a cold front from the northwest toward our region on Friday with the boundary arriving on Friday night. We will continue to mention a chance of showers and thunderstorms with the front. && .AVIATION /10Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. An occasional scattered to broken deck around 2,500 feet has been present over the last several hours. This will likely persist for a few more hours before lifting around sunrise. With light winds, some patchy fog has formed impacting KMIV now. This may spread to a few other terminals toward sunrise but would burn off fairly quick. VFR conditions are expected throughout the morning after any fog burns off. However, Showers and thunderstorms in the afternoon will lead to ceiling and visibility restrictions moving in from to west across the region. Start times at KRDG and KABE will be closer to 18z, while at PHL 20z looks to be a more reasonable start time and a couple of hours later at KACY. Showers and thunderstorms should last a few hours at any given location with clearing starting to take place by evening. Some wind gusts of 15-20 knots from the southeast are possibile in the afternoon hours as well. VFR conditions tonight with winds shifting to the west and northwest around or just under 10 knots. OUTLOOK... Monday through Thursday...Mainly VFR. && .MARINE... Wave heights are expected to increase gradually throughout the day reaching three feet in the afternoon and evening hours. Southeast wind gusts from 15-20 knots are likely in the afternoon ahead of a cold front. Both the seas and winds are expected to continue a slight ramp up toward sunrise Monday with the passage of a cold frontal boundary. An SCA starts at 5am Monday for the increased seas and winds. OUTLOOK... Monday...Northwest wind gusts around 25 knots are expected. A Small Craft Advisory is in effect until 11:00 AM Monday for our coastal waters from around Atlantic City southward and for Delaware Bay. The Small Craft Advisory is in effect until 5:00 PM Monday for our coastal waters north of Atlantic City. Monday night through Thursday...No marine headlines are anticipated. RIP CURRENTS... Wind gusts from the southeast in the afternoon coupled with wave heights around three feet will allow conditions to be more representative of a moderate risk day across the New Jersey beaches. These conditions yield a lower risk for the Delaware beaches. The probable risk for the development of dangerous rip currents on Monday is low. A northwest wind is expected. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 5 AM to 11 AM EDT Monday for ANZ430- 431-452>455. Small Craft Advisory from 5 AM to 6 PM EDT Monday for ANZ450- 451. && $$ Synopsis...Iovino Near Term...Gaines Short Term...Gaines Long Term...Iovino Aviation...Gaines/Iovino Marine...Gaines/Iovino is the U.S. government's official web portal to all federal, state and local government web resources and services.