Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 280503 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 103 AM EDT Tue Mar 28 2017 .SYNOPSIS...
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A warm front from central New Jersey through the Delmarva will drift south today as low pressure in the Ohio Valley heads east, exiting seaward from the mid Atlantic coast this evening. High pressure will build down from Canada for Wednesday and Thursday. Low pressure in the lower Mississippi Valley Thursday night will move through our area on Friday and Saturday. Weak high pressure returns for late Sunday and Monday.
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&& .NEAR TERM /THROUGH TODAY/...
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1230 AM ESTF: Has new 5050 blended 00z/28 GFS/NAM MOS guidance for temps/dews/winds through 12z Wednesday. This blend is cooler than prior guidance, in part due to ne flow, showery rains, and cloudy skies. The fog and shower fcst was not changed for the 1230 am update as it seems to be working quite well, showers sprouting up and moving ne from ne PA and NJ...some are briefly moderate to heavy. Isolated thunder is possible early this morning. It is possible that the Dense Fog Advisory may need to be expanded westward in the 330 am fcst, but confidence on how widespread it will be, is low, at this time. Today...in addition to the info in the 1230AM ESTF...yesterdays fcst discussion for today still works. am not as confident in thunder this afternoon as i was ydy, in part due to cooler new flow with MLC suppressed swd a bit. Here is that discussion: Surface low in the Ohio Valley at 12Z moves east along or just south of the Mason-Dixon Line into Maryland/Virginia by 00Z Wednesday as the shortwave trough begins a curve toward the southeast on the outer fringe of a subtropical ridge in the Gulf of Mexico. Degree of cooling in the midlevels combined with strong ascent downstream of the vort max will promote the development of storms in much of the Mid- Atlantic on Tuesday. Most model guidance suggests two rounds may occur. The first would occur early in the day as elevated convection along the nose of enhanced low-level isentropic ascent. After a brief lull in the late morning and early afternoon, more convection is expected to develop along/east of the low and southward- extending cold front, aided by substantial cooling in the midlevels and large-scale ascent via differential cyclonic vorticity advection. Vertical shear looks relatively weak, and MUCAPE values will generally remain at or below 1000 J/kg (MLC aob 600J and mostly Delmarva), especially if early- day convection eradicates preexisting instability. Prospects for severe convection look limited at best, but scattered storms are still a good bet as the rounds of precipitation move through the region, particularly in the afternoon. Best chances appear to be along and south of the Mason-Dixon Line given the track of the low and the associated lifting mechanisms. However, overall uncertainty remains given the multiple rounds of precipitation that may occur. Therefore, a general broadbrush of chance to likely PoPs was placed in the grids for now. There is better potential for locally heavy rainfall given the decent PWATs of ~1.25", multiple rounds of precipitation expected, and potential for localized training storms, especially if storms can align along the baroclinic zone. Though widespread flooding is unlikely, think isolated instances of nuisance short-term flooding is a possibility. This will continue to be monitored in later forecasts. Temperature forecast remains a concern with the placement of the eastward-extending warm front again a complicating factor. Errors in these values are likely given timing of the rain cooling factor and where skies may thin to allow a little sun.
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&& .SHORT TERM /TONIGHT/...
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Any remaining showers end from west to east with a slightly faster modeled end to the rain than 24 hours ago. There could be some patchy fog, especially early at night in the still moist boundary layer with a light north wind increasing a bit late at night and trending northwest. FCST Basis was a 50 50 blend of the 00z/28 GFS/NAM MOS.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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Canadian high pressure will start to push southward into our area on Wednesday and persist across the region through Thursday. While the system itself isn`t particularly strong, it should allow for us to dry out as a decent northwest flow is across the area on Wednesday. Winds will lighten up for Thursday with cooler air settling over the Mid-Atlantic. Highs will be slightly above normal on Wednesday and much closer to normal on Thursday. The next system starts to advance towards our area on Thursday. Low pressure will develop to our west and then move into the Tennessee Valley by late Thursday. AS the low continues to move towards our area, we will start to see cloud cover increase and showers will once again start to move into the area. Expect some light rain to develop in the vicinity of the approaching warm front The center of the low will cross just to the south of the region on Saturday, by around mid morning. The rain will end from west to east and we should see a little bit of clearing occur. However, there is not much of a flow behind this system and it may end up remaining pretty cloudy, especially for areas inland. Weak high pressure will again be around the region for Sunday and Monday. Models indicate that a shortwave may move through later on Sunday, which may trigger a few light showers. Confidence is low at this time.
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 12z...vfr or MVFR vsby gradually deteriorating to IFR conds in st/fog by 12z with scattered showers. light wind, mostly east or northeast at the TAF locations. After 12z Tue...IFR variable MVFR conds in st/fog scattered showers and a generally light east to northeast wind. Tonight...MVFR/IFR conditions possible in showers and fog... becoming VFR late. Light north winds will become north to northwest overnight around 10 knots. OUTLOOK... Wednesday...VFR conditions expected. Winds will be north around 10 to 15 knots, some gusts up to 25 knots possible. Thursday...VFR conditions expected. Light north winds... becoming east late afternoon. Friday...IFR or MVFR conds in periods of rain. East to southeast winds around 10 to 15 knots. Saturday...MVFR/IFR conditions early in rain... becoming VFR late. North to northeast winds around 10 knots or less.
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&& .MARINE...
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Dense Fog Advisory has been issued for the New Jersey coastal waters north of Little Egg. Areas south may also develop fog overnight, but it is less certain at this time. This will be monitored closely this evening. Winds/seas will be under advisory criteria through Tuesday night. Scattered showers/isolated thunderstorms through today, with showers ending this evening. OUTLOOK... Tuesday night...Southerly winds will become west then northwest overnight. Speeds around 10 to 15 knots. Seas 2 to 4 feet. Wednesday...Northerly winds around 10 to 20 knots with gusts around 25 knots late. Seas increasing to around 5 feet . A SCA will likely be needed as conditions near criteria by Wednesday evening. Thursday...Decreasing seas through the day. North winds becoming easterly late in the day, mainly around 10 to 15 knots. Friday...East to southeast winds around 10 to 20 knots with gusts up to 30 knots possible. Seas will build through the afternoon, exceeding 5 feet by Friday evening. A SCA looks likely. Saturday...SCA conditions continue. Northerly winds around 10 to 15 knots. Seas will remain above 5 feet through Saturday, starting to subside a bit late.
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&& .EQUIPMENT...
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KNEL appears to be reading 10F too warm the past several days.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...Dense Fog Advisory until 10 AM EDT this morning for NJZ013-014- 020-026. DE...None. MD...None. MARINE...Dense Fog Advisory until 10 AM EDT this morning for ANZ450-451.
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&& $$ Synopsis...Meola/Drag 103 Near Term...Drag/Robertson 103 Short Term...Drag 103 Long Term...Meola Aviation...Drag/Robertson/Meola 103 Marine...Drag/Meola 103 Equipment...103

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