Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 240721 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 321 AM EDT TUE MAY 24 2016 .SYNOPSIS...
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Low pressure offshore of Long Island this morning will track northeastward during today. High pressure will then build to our south tonight through Wednesday before shifting offshore. A frontal boundary is forecast to be draped mainly from the Great Lakes to New England Thursday through Monday as some weak low pressure systems track along it. This front may settle southward into at least northern Pennsylvania and northern New Jersey at times late this week and during the holiday weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The upper low will continue to spin across the offshore waters this morning before weakening and moving further out to sea. Scattered showers and perhaps an isolated tstm will occur today mostly across ern PA and NJ. More isolated activity for the Delmarva and western parts of the forecast areas. Temperatures today will be near normal across the wrn/srn areas where more sunshine is expected. The abundant cloud cover n/e may hold temps just below normal today. Overall highs low 70s north/east and upper 70s south/west. Winds will be mostly n or nw this morning and then w or sw this afternoon. Winds speeds mostly 5 to 10 mph.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
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High pressure will begin to build across the area tonight. Except for a few sct showers n/e during the early evening...it should be a dry fcst. Clouds will thin out across the area as drier air moves in. Low temperatures tonight will drop into the low 50s across the north and bottom out in the mid/upper 50s over the Delmarva and Sn NJ. A little patchy fog is possible away from the urban areas.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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Summary...A pattern change leads to a stretch of very warm to hot conditions through much of the holiday weekend, with some increase in the humidity especially starting on Friday. A frontal boundary nearby Thursday through Monday though may help trigger some showers and thunderstorms mainly each afternoon and evening. The synoptic setup is comprised of the pesky closed low that will weaken as it shifts farther away from our area Wednesday. This allows ridging to arrive in the east for the second half of the week, and this ridge which becomes centered offshore looks to remain over or near our area right through Monday. There will be several pieces of energy deflected around this ridge with a sharp trough possibly occurring in the vicinity of the Canadian Maritimes. This setup should result in a frontal zone becoming draped from about the Great Lakes to New England. This front looks to meander north and south from Thursday through Monday, with it potentially getting into at least our northern areas at times. Some energy along this front combined with plenty of heating to the south of it may result in mainly some diurnally driven convection Thursday through the holiday weekend. Overall though, a washout is not anticipated. We used a model blend approach for Wednesday through Thursday night, then blended in the 00z WPC Guidance with continuity thereafter. Some adjustments were then made based on additional collaboration with our neighboring offices. For Wednesday and Thursday...The pattern finally makes a transition to much warmer air as the slow moving closed low weakens as it shifts into the Canadian Maritimes Wednesday. This allows a ridge to the west to slide eastward, with surface high pressure sliding to our south Wednesday and then anchored just off the southern Mid Atlantic coast Thursday. This results in considerable height rises through this time frame along with a more southerly flow regime. This will boost the warm advection and the model guidance increases the 925 mb temperatures to +20C Wednesday and between +20C and +25C Thursday. This combined with west to southwest flow will drive the temperatures well into the 80s for much of the area both days. The exceptions will be the higher terrain and especially the coastal areas where the surface flow may back more southerly and allow some cooler ocean influence. We bumped up the temperatures some especially away from the coast. As the ridge axis is still to our west Wednesday, energy sliding across northern New England will drag a cool front southeastward. Given the presence of the incoming ridge, this front should stay to our north although it may get rather close to our northern areas late Wednesday and Thursday. There may be some convection with it Wednesday which may brush our very far northern zones in the afternoon. For now though we left the forecast dry. Low pressure tracking into the Great Lakes Thursday should provide enough of a downstream push to move the front back north. A few showers and thunderstorms may develop Thursday afternoon across our western zones due to terrain circulations and the presence of a lee-side trough, however much of the convection should reside well to our west. For Friday through Monday...The ridge axis may build right across our area through much of this time frame. This will result in very warm to hot conditions along with a more noticeable increase in the surface dew points. Some mainly diurnally driven convection cannot be ruled out each afternoon and early evening Friday and Saturday. At least some guidance brings low pressure off the Atlantic into the Carolinas Sunday as the ridge aloft remains. Depending on the organization of this feature and if it exits may push some additional moisture our way into Monday. In addition, the ridge may amplify enough as a deep trough passes near the Canadian Maritimes Sunday and Monday to push a frontal boundary down through our area. If this were to occur, then Monday would be much cooler and potentially be prone to more showers/thunder. There is much less certainty with the details regarding this, therefore we followed close to the WPC Guidance which brings the front into our northeastern areas Monday.
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&& .AVIATION /07Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. The weather disturbance offshore early today will continue to weaken and pull away from the region. occasional showers and vfr cloudiness will continue through the morning in most areas...before some improvement from s/w to n/e thru the day. The forecast at the taf sites will basically be VFR today and tonight with only one exception. There may be some MVFR fog around this morning. Winds will be light and variable early today and then become w pt nw at 5 to 10 knots for the late morning and into the afternoon. Tonight...vfr is expected with mostly clr skies. We may put some patchy fog in a few of the taf sites with the 12z taf issuance. Outlook... Wednesday...VFR. West to southwest winds up to 10 knots. Thursday through Saturday...VFR overall, however brief times of MVFR/IFR conditions are possible each afternoon and evening due to a few showers and thunderstorms.
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&& .MARINE...
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A few seas near 5 ft early this morning...but a trend towards lessening winds and seas today. No SCA flag will be needed for today or tonight. Winds will be mostly n or nw today and then w or sw tonight. Scattered showers and perhaps a tstm is expected for the waters. Winds and seas will be locally higher in any tstm. Outlook... Wednesday through Saturday...A ridge aloft over the area combined with high pressure at the surface to our south and east will allow for mainly a southerly flow regime across our area. The flow looks like enough and therefore the conditions are expected to be below Small Craft Advisory criteria.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse Near Term...O`Hara Short Term...O`Hara Long Term...Gorse Aviation...Gorse/O`Hara Marine...Gorse/O`Hara

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