Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 141436 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 936 AM EST Tue Nov 14 2017 .SYNOPSIS... High pressure from Quebec to Ohio will slide across our area tonight and tomorrow. A cold front approaching from the northwest crosses the mid Atlantic coast Thursday morning, followed by high pressure for Friday. A stronger cold front is expected to pass through our region on Saturday afternoon or night. A blustery west to northwest flow follows Sunday and next Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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930 am update: Adjusted sky cover a little bit based on latest satellite trends, and tweaked temperatures/dew points based on latest short-term guidance. However, forecast is in good shape overall. Previous discussion below... A quick update has been sent to increase the cloud cover faster into the I-95 corridor this morning, as a stratocumulus deck is gradually expanding eastward. Also made some adjustments to the temperature and dew point grids early this morning, and removed fog since visibilities have improved. A surface analysis early this morning placed high pressure centered in the upper Ohio Valley. Meanwhile, low pressure was well southeast of Cape Cod. An upper air analysis indicated a short wave trough from near the central Great Lakes northward toward Hudson Bay. There is a 250 mb jet from the northern Plains eastward into New England. The fog has improved due to some drier air making southward progress and also clouds on the increase. Leftover surface moisture from yesterday`s rain may result in a few icy spots especially on vehicles early this morning. As the flow aloft is more zonal, a short wave trough quickly moves into New England during the course of the day. As this occurs, surface high pressure centered to our west gradually builds eastward. This will result in a northerly wind, which will increase a little this afternoon as the aforementioned short wave trough moves into New England. The lift over our region is negligible and moisture is limited, therefore no precipitation is expected with the passage of the short wave trough. The forecast soundings overall suggest that an area of stratocumulus develops farther southeastward this morning. This already exists from parts of the I-95 corridor on westward, via satellite imagery and surface observations. This should be more prevalent from about the I-95 corridor on westward for awhile. The northerly flow combined with a surface trough offshore which is forecast to shift southwestward may result in some lower clouds making an approach to the coast later this afternoon. Despite the northerly flow, the airmass should be a bit milder and with at least some sunshine afternoon temperatures will be higher than yesterday. We used a blend of MOS and continuity for the high temperatures.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... As surface high pressure becomes elongated from New England to the central Appalachians tonight, a north to northeast surface flow is expected. There should be enough subsidence to keep much of the area clear to perhaps partly cloudy, however the guidance shows a surface trough sliding southwestward toward our coast during the course of the night. While some showers cannot be ruled out close to the coast, some increase in clouds is indicated into the coastal locations and a little farther inland. This cloudiness may get farther inland however especially from near Atlantic City on southward given the low-level trajectory. Pending that clouds remain less farther inland, it will be a cold night. A north to northeast wind and the idea of more clouds will keep temperatures up some closer to the coast. We opted to carry no fog tonight as the low-level airmass looks a little drier. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... 500 MB: A short wave in the upper Midwest Wednesday morning strengthens as it heads across the northeast USA on Thursday. Short wave ridging follows Friday ahead of what will probably be a large cold trough developing from the Great Lakes into the northeast states this weekend. That trough only slowly weakens early next week. Temperatures: It appears we on our way to be a below normal month for average temperatures. Calendar day averages near normal Wednesday, about 3 above normal Thursday, then near normal Friday and Saturday. and probably wind driven below normal chill Sunday and Monday averaging close to 5 degrees below normal. Forecast basis: A 50 50 blend of the 00z/14 GFS/NAM MOS for Wednesday-Thursday, the 00z/14 GFS MEX MOS for Thursday night and thereafter the D4-8 (Friday-Monday) elements begin with the 05z/14 WPC 12 hr max/min/pop and the 6 hourly td/wind/sky. Note: the 00z /14 Operational ECMWF is not digging a big trough into the ne USA this weekend and so while we`ve yet to see its ensembles... the GEFS looks very strong and this forecast favors the rather cold trough aloft with colder than normal temperatures. The 00z/14 UK and GGEM tend to side with the 00z/14 GEFS. The dailies... Wednesday...A sunny start, maybe after some early morning patchy fog? then considerable cloudiness during the afternoon. This cloud cover will probably be developing inland from the coast during the morning over S NJ and DE and turning-developing nwwd in the afternoon. There appears to be an inversion around 800 mb which will trap moisture as well. Confidence: Average. Wednesday night...Mostly cloudy. The NAM and EC are both spewing 0.10 along coastal NJ-DE late at night and have favored this option with POPS raised considerably along the coast due to convergence associated in part with approaching cold front but also a little assist in moisture advection into the mid Atlantic states from a weak low off the Delmarva. Confidence: Average. Thursday...Still a small chance of showers lingering during the early morning, then breezy-windy during the afternoon with partly sunny skies or considerable cloudiness. Scattered gusts 30-35 mph. Confidence: Well Above Average. Thursday night...Mostly clear. Northwest wind with diminishing gustiness. Confidence: Above Average. Friday...Sunny. Confidence: Above Average. Friday night...Increasing cloudiness during the beginnings of waa ahead of what should be a strengthening cold front. A small chance of showers toward dawn Saturday west of I-95, which if arrive soon enough, could be mixed pcpn in ne PA and far nw NJ. Below average confidence on any pcpn occurring Friday night. Saturday...Showers likely, especially afternoon. Confidence: Average. Saturday night...EC much slower, weaker and warmer than the GFS and GEFS and so the EC was not used. Confidence on how long rain might last past 7 PM Saturday is below average. Sunday and Monday...Blustery with variable cloudiness... snow flurries or even snow showers possible, mostly high terrain far nw NJ and ne PA. Confidence: Above Average. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Localized marginal MVFR visibility early this morning due to fog, otherwise a ceiling in the 3500-5000 foot range expands southeastward some more this morning. Northerly winds mainly 10 knots or less. Tonight...VFR overall as clouds thin out for most, however a VFR to perhaps MVFR ceiling could move onshore into ACY to perhaps MIV. Northerly winds 5 knots or less. OUTLOOK... Wednesday...Chance patchy IFR to start the day, otherwise mainly VFR sct clouds in the morning then broken cigs near 4000 ft developing during the afternoon. Confidence: Average. Wednesday night...Mainly VFR cigs with showers late at night... especially NJ. Confidence: Average. Thursday...VFR with a west northwest wind gusty to around 30 kt during the afternoon and 20-25 kt early evening. Confidence: Well above Average. Friday...VFR clear or sct cirrus. Confidence: Above Average. Friday night...VFR CIGS lowering to MVFR in spots? A slight chance of showers late. Confidence: Below average on any showers arriving late at night. Saturday...A period of MVFR conditions in showers with the cold front during the afternoon or at night. Gusty southwest wind shift northwest at night. Confidence: A bit above average. && .MARINE...
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Contemplated adding Lower Delaware Bay to the small craft advisory today for wind gusts, but I think the strongest gusts are occurring now with a gradual downward trend this afternoon. May see an occasional gust around 25 kts at the mouth of the bay this morning, but I do not think this is sufficient for an advisory. Meanwhile, monitoring seas closely today to determine if an expansion of the advisory is required. At this point, the latest guidance is awfully marginal, so will hold off for now. OUTLOOK... Wednesday..May need an SCA for hazardous seas portions of the s NJ and DE Atlantic waters, but elsewhere including DE bay-none. Confidence: Average. Thursday afternoon and Thursday night...A Gale watch is anticipated to be needed for the period roughly 22z/15 through 06z/16. Mixing to about 900 mb. Confidence: Above Average for a marginal gale event. Friday and Friday night...No marine headlines are anticipated. Confidence: Average. Saturday...A Small Craft Advisory may be needed for southwest wind gusts of 25 to 30 knots. Gale force gusts are possible on Saturday afternoon. Confidence: Above Average.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EST Wednesday for ANZ454-455. && $$ Synopsis...Drag Near Term...CMS/Gorse Short Term...Gorse Long Term...Drag Aviation...Drag/Gorse Marine...CMS/Drag

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