Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 202102 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 402 PM EST Mon Nov 20 2017 .SYNOPSIS...
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High pressure over the Tennessee Valley will track east and move off the Mid-Atlantic coast tonight, and then will slowly drift out to sea on Tuesday. A cold front approaches from the west Tuesday night as low pressure moves along the Southeast U.S. coast. The low passes south and east of the area Wednesday morning, and then the cold front passes through the region late Wednesday. High pressure builds through the region Thursday and Friday. A cold front passes through the region on Saturday, and then high pressure builds in from the west for the start of the new week.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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As high pressure moves offshore tonight, the wind will gradually back from the west to southwest, and diminish this evening with the loss of the diurnal boundary layer. A few high clouds associated with a mid- level shortwave overnight, otherwise mostly clear skies. We have lowered temperatures a couple degrees, mainly over the favored radiators, as winds become light. Overall, still near seasonal averages.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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The area will be under the influence of weak shortwave ridging aloft, with a cold front over the central Great Lakes and high pressure well offshore, proving a southwest flow at the surface. Expect some increase in mid and high level cloudiness during the afternoon, mainly across Delmava and south Jersey, as a southern stream jet advects moisture northward. Otherwise, mostly sunny. It will be brisk, with model soundings supporting wind gusts up to around 30 mph across the coastal plain, and 20 to 25 mph elsewhere. Temperature-wise, highs will be a couple degrees above average.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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The extended period starts out Tuesday night a bit rainy and above average in temperature, but the remainder of the period tends toward seasonably cooler and mostly dry weather. The larger scale pattern over the CONUS shows ridging aloft in the Eest and more troughing in the East, with a couple of shortwave trofs and associated frontal systems moving through the mid- Atlantic region mid-week and again next weekend. A cold front is forecast to approach from the west Tuesday evening and cross the forecast area overnight. The fropa will trigger a few showers N/W of PHL. A sfc low pressure is also forecast to develop off the NC/SC coasts with moisture spreading north ahead of it along the DE/NJ coastal areas. The highest PoPs are thus over south NJ and Delmarva, counter to climo. Overnight temps should remain warm enought so that all precip will be in liquid form. However a few showers may linger past sunrise, and with cold advection behing the front a few snow showers or flurries are possible in the Poconos Wednesday morning. The weather for Wed afternoon through Friday night should be dominated by hight pressure moving across the mid-Atlantic region and a fairly dry airmass associated with it. Temperatures will be a few degrees below normal on Thursday but should return to near normal by Friday as the high shifts offshore and a more swly flow develops. A cold front may push south in to NY state and New England on Friday but probably will not affect our area to the south, Another fast-moving frontal system is forecast to push through our area on Saturday. In part becouse of its fast movement it will not be able to pick up much moisture. The current forecast has chance PoPs, higher N/W of PHL, but even this may be overdone. Again, temps on Saturday appear to be warm enough to avoid any frozen precip. However, the airmass behind this front seems to be colder than the one mid-week, with strong low level cold advection beginning Saturday night and continuing through the rest of the weekend. This pattern of NW flow will favor lake effect snow with some streamers possibly reaching the Poconos and vicinity.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR conditions. West-southwest winds gusting up to 20 knots early this evening, diminishing to around 10 knots by 00Z. Winds will also gradually from the west-southwest to southwest through around 00Z. Confidence: above average. Tuesday...VFR conditions. Southwest winds increasing with gusts up to around 20-25 knots from late morning into the afternoon. Confidence: above average. There is also some potential for Low- Level Wind Shear (LLWS) to develop in the I-95 corridor terminals, e.g., PHL, Tuesday evening. However, latest guidance is just at the cusp of LLWS criteria, so no mention in the TAF at this time, with low confidence with regard to LLWS. Outlook... Tuesday night and Wednesday...Mainly VFR. Rain possible south and east of I-95 Tuesday night through Wednesday morning with MVFR or lower conditions. SW winds 5-10 KT become NW Wednesday afternoon and increase to 10-20 KT. Wednesday night and Thursday...VFR. NW winds gradually diminishing. A storm system is currently expected to remain offshore. Forecast confidence: Medium to High. Friday...VFR. NW winds 5-10 KT. Saturday...VFR early...then MVFR or lower conditions possible in rain showers later in the day. SW winds 10-15 KT.
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&& .MARINE...
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SCA conditions prevailing across the NJ coastal waters through Tuesday, with the combination of southwest winds and seas meeting criteria. Further south across the DE coastal waters, SCA conditions are expected to return just before daybreak Tuesday morning and persist through the day, with the combination of southwest winds and seas meeting criteria. The Delaware Bay waters are expected to remain below SCA criteria, although the southern Bay will have to be watched for a possible upgrade if winds strengthen a few more knots. Outlook... Tuesday night...SCA conditions should persist through Tuesday evening but diminish overnight. Wednesday...Lull in SCA conditions possible Wednesday morning. Otherwise, winds shift to the NW and increase to 15-20 KT with 25-30 KT gusts. Thursday through Friday...Sub-SCA conditions expected. Saturday...SCA conditions are possible with a strong cold front passage.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 1 AM EST Wednesday for ANZ450>453. Small Craft Advisory from 5 AM to 7 PM EST Tuesday for ANZ454- 455.
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&& $$ Synopsis...AMC Near Term...Franck Short Term...Franck Long Term...AMC Aviation...AMC/Franck Marine...AMC/Franck

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