Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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044 FXUS61 KPHI 210152 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 952 PM EDT Tue Jun 20 2017 .SYNOPSIS... High pressure will gradually build east towards the region through Thursday. That high will shift off shore by the end of the week. A pair of cold fronts are expected this weekend or early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Water vapor satellite loop depicts an upper trough over the Great Lakes/Midwest region. The northern Mid-Atlantic region was situated in southwesterly flow downstream of the trough. At the surface, a trough/dewpoint gradient was analyzed near the I-95 corridor with dewpoints in the 60s southeast of the boundary and 50s to the northwest. As mentioned earlier, scattered showers were added to the forecast database for this evening for northeastern Maryland and northern Delaware with sustained convection that developed in central Maryland earlier this evening was moving into Cecil County as of 930 PM. It appears the convection initiated in the right-entrance region of a mid-level jet streak and along the aforementioned surface boundary. Expect this activity to dissipate by midnight as instability wanes with the loss of heating. A mention of showers was added back into the forecast for early Wednesday morning in southern Delaware where hi-res models indicates precip shield currently over far southeastern VA expanding back northward in the far southern zones of our CWA. This would be favored with mid-level steering flow backing slightly ahead of an approaching shortwave trough.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... A weak boundary settling across the CWA during the late morning and early afternoon hours will bring some additional cloudiness and isolated showers and storms mainly during the afternoon. Southwesterly winds are expected to pick up from late morning through the afternoon hours with gusts around or over 20 mph possible at times, especially across inland areas. High temps in the mid 70s are expected in the far north, and in the mid 80s in the south. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Wednesday night and Thursday...Surface high slowly builds east towards our region before shifting off shore. As a result, expect mostly dry conditions unless the high weakens or moves off shore faster than currently anticipated. Friday...southwesterly flow over our region, thanks in large part to the Bermuda high once again develops. The biggest impact will be increasing dew point temperatures. Though temperatures won`t be appreciably higher than what we will see through mid week, expect heat index values to be increasing. Saturday through Monday...A pair of cold fronts are expected through this period. There is considerable model disagreement as to both the timing of the fronts and if the first or second cold front will be the stronger front. Looking at the larger picture, it looks like the pattern will tend to be less progressive through this period (3 or 4 Rossby waves depending on the model and time period you look at). Therefore, the forecast favors a solution closer to the ECMWF with the initial front arriving Saturday, but likely only resulting in a modest temperature gradient. The second, and likely stronger, cold front should arrive Monday night. Have kept precip chances through much of this period, given the uncertainty of the timing of the fronts. However, I do not expect the weekend to be a complete washout as the highest chances for showers and thunderstorms will likely be with and just ahead of the first cold front. Tuesday...Assuming the cold front arrives Monday night, temperatures by Tuesday should be 5 to 10 degrees below normal, with highs ranging from the upper 60s to mid 70s. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Scattered showers moving into NE MD may reach ILG by 0230Z. With the anticipation that these showers weaken before then, kept a VFR TEMPO group for SHRA through 03Z though there is certainly a possibility of a brief MVFR visibility restriction. Otherwise, VFR conditions with SW winds below 10 kt. Note, the winds were still gusting to 22 kt at PHL at 01Z, but this is the only observation site reporting gusts still. Generally VFR conditions are expected again on Wednesday, but an isolated shower or even a thunderstorm is possible, particularly during the afternoon. SW wind gusts around 20 kt are anticipated during the afternoon. Outlook... Thursday...mostly VFR conditions are expected. Friday through Sunday...Increasing chances for showers and thunderstorms through this period. MVFR or lower conditions are possible with any showers or thunderstorms. Otherwise, expect mostly VFR conditions.
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&& .MARINE... The SCA for for the northern coastal waters of NJ was cancelled as seas have dropped below 5 ft. Winds and seas will remain below SCA criteria tonight and Wednesday. Outlook... Thursday...winds and seas are expected to remain below SCA criteria. Friday...winds and seas will begin to build and may be at or just below SCA criteria by late in the day. Saturday and Sunday...SCA conditions are possible, especially for seas on the ocean waters. RIP CURRENTS... A moderate risk for the development of dangerous rip currents is expected Wednesday and possibly continue into Thursday along the coast of Delaware and New Jersey. Although the surf will continue to gradually weaken over the next couple of days, a long-period southeasterly swell and the approach of a new moon will contribute to this moderate risk. && .TIDES/COASTAL FLOODING... Very high astronomical tides are expected in association with the new moon on Friday. That, combined with a brief period of on shore flow on Thursday could result in minor coastal flooding with the Thursday afternoon and evening high tide primarily for the Atlantic coastal areas and the shores of the Delaware Bay. Minor coastal flooding may continue with the Friday afternoon and evening high tide. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Johnson Near Term...Klein Short Term...Klein/Miketta Long Term...Johnson Aviation...Johnson/Klein/Miketta Marine...Johnson/Klein/Miketta Tides/Coastal Flooding...

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