Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 112351 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 751 PM EDT Wed Oct 11 2017 .SYNOPSIS... An area of high pressure will build across northern New England through the end of the week. An area of low pressure will pass to our south tonight as it moves along a frontal boundary located to our south. The high to our north will build down into our area late Thursday, then offshore Friday. A weak surface trough may lift toward the area, just offshore of the coast, Friday into Saturday. A cold front is expected to affect the area around Sunday night. High pressure is then expected to build into the area Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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Weak low pressure lies near the OH/PA border. A warm front extends out ahead of that low, through the Appalachians, and into southern VA, while a cold front extends behind the low. Meanwhile, high pressure centered over western Quebec will nose down into the Northeast U.S. The low to the west will weaken, but precip still expected out ahead of that low associated with the approaching warm front. The first wave of showers lifted through northern NJ and the Lehigh valley earlier, and there are some lingering showers passing through northern NJ at this time. Additional precip lies over SE PA, and is tracking east. Another swath of rain is likely to impact the region after midnight tonight and through Thursday morning. Possible for some heavier precip across the Delmarva associated with a weak low over the Delmarva Peninsula on that warm front. Lows temperatures range from the upper 40s across the S Poconos to mid 60s across far S NJ and mid Delmarva.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... High pressure centered over SE Canada will continue to build southward down the eastern side of the Appalachians and into our area on Thursday. Persistent onshore flow on the southern periphery of the high will inhibit drying of the low levels and keep the area socked in low clouds for most of the day. Ongoing rain at the start of the day should gradually shift southward across the southern half of the CWA during the morning. Expect limited coverage/intensity of rain (probably drizzle at times) owing to a lack of deep, organized lift on the synoptic lift. Breezy onshore winds and cloudy skies will keep temperatures nearly steady in the 60s for much of the day. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... As we move into the overnight Thursday, the high pressure that builds across northern New England will begin to build down the east coast and into the Mid Atlantic region. There will be a slight chance of showers Thursday night across the southern half of the area as there will be plenty of moisture associated with the easterly flow with the high to our north. Even without rain, it is expected to remain fairly cloudy with the easterly flow remaining in place. On Friday the high builds offshore, and there is an indication that a weak surface trough may try to lift northward just offshore of the Mid Atlantic coast later Friday through Saturday. This could bring an enhanced chance showers to the area. Again, even without rainfall, it should remain fairly cloudy Friday through the early part of Saturday. Saturday night into the first half of Sunday should be a dry period as high pressure at the surface builds farther offshore, setting up a southwest flow at the surface, and southwest flow aloft develops as well. With this return flow, Sunday will be the warmest day in the extended period. A cold front begins to approach late in the day Sunday, but probably will not move into the area until Sunday night. It would not be surprising for a few showers to develop doing the day if enough instability develops. The cold front is forecast to move across the area overnight Sunday night, which will lead to an increase in shower chances. Depending on how fast the front moves, showers could linger into early Monday. Once the front moves through, dry weather returns through Wednesday as high pressure builds across the region Tuesday into Wednesday. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Widespread MVFR CIGs will overspread the terminals tonight as rain develops out ahead of low pressure over the Ohio Valley and spreads east. There is the potential for localized/temporary IFR CIGs at a few terminals between 06-12Z where rain/drizzle is more persistent but confidence was too low to include as a prevailing group in the 00Z TAFs. MVFR CIGs should persist through much of the day on Thursday with gradual improvement from N to S late in the day. E-NE winds 5-10 kt thru this evening will increase to 11-17 kt with gusts 20-25 kt late tonight into Thursday morning. We may lose the stronger gusts during the afternoon. OUTLOOK... Thursday night...Possibly VFR early, but a return to MVFR CIGS overnight. East winds may gust 15-20 knots at times. Friday-Friday night...MVFR CIGS, possibly lowering to IFR overnight. Slight chance of showers. Saturday...MVFR or IFR CIGS early, possibly improving to VFR during the day. Saturday night...Fog and low clouds may develop overnight leading to MVFR or IFR conditions. Sunday...Improving conditions through the day. Gusty southwest winds 15-20 knots. Sunday night...Rain showers possible with lowering conditions to MVFR. Monday...Improving to VFR. Northwest wind gusts 15-20 knots.
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&& .MARINE...
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Gale Warning remains in effect for the Atlantic coastal waters of NJ and DE for late tonight into Thursday. E-NE winds will increase quickly from N to S as high pressure builds in. Expect gusts 30-35 kt to occur mainly late tonight thru mid morning Thursday for our far northern waters and early morning thru early evening farther south. A SCA was issued for the DE Bay waters for late tonight and Thursday with winds 15-20 kt gusting 25-30 kt. OUTLOOK... Thursday night-Friday...Small Craft Advisory conditions expected to continue Thursday night through into Friday. Near gale force gusts may continue into the evening Thursday. Friday night-Saturday night...Wind gusts likely to lower below advisory levels, but seas expected to remain elevated through the night Friday into Saturday night. Sunday-Monday...Winds and seas could both be near Small Craft Advisory levels.
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&& .TIDES/COASTAL FLOODING...
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Minor coastal flooding is possible during the Thursday afternoon high tide cycle, especially from Atlantic City southward and up Delaware Bay. A gusty onshore flow will strengthen tonight through Thursday, then will ease some Thursday night Guidance continues to indicate most locations increasing to a 1.0-1.5 foot surge which gets to minor coastal flood levels. If these values continue to look attainable, a Coastal Flood Advisory will be needed for the Thursday afternoon high tide.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Warning from 4 AM to 8 PM EDT Thursday for ANZ452>455. Gale Warning from 1 AM to 10 AM EDT Thursday for ANZ450-451. Small Craft Advisory from 1 AM Thursday to 6 AM EDT Friday for ANZ430-431. && $$ Synopsis...Robertson Near Term...Klein/MPS Short Term...Klein Long Term...Robertson Aviation...Klein/Robertson/MPS Marine...Klein/Robertson/MPS Tides/Coastal Flooding...

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