Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 280801 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 401 AM EDT Sun May 28 2017 .SYNOPSIS... A weak area of high pressure will shift east of the New England coast this morning, keeping a warm front to our south and west today into tonight. A stronger low pressure system will move into southeastern Canada Monday, bringing a cold front through our area. A couple of cold fronts will then move through our region through about midweek, before high pressure builds toward our area Thursday and Friday. A weak cold front however may settle across our area Friday night and Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure located off the New England coast early this morning will progress northeastward today. Meanwhile, a frontal boundary will extend from the Ohio River Valley and the Great Lakes southeastward to the waters off Virginia and North Carolina. The sky was mostly cloudy over the Poconos and far northern New Jersey, and over northeastern Maryland, Delaware and southern New Jersey around 3:30 AM. The sky was mainly clear over areas between the two. Where there is little cloud cover, we continue to anticipate the development of some stratus and fog early this morning. An onshore flow is expected to develop for today. Additional clouds will overspread our region from the west. It appears as though the daylight hours will be mainly rain-free with conditions remaining fairly stable. We may see some showers begin to spread into eastern Pennsylvania and the upper Delmarva from the west early this evening. High temperatures are expected to range from the upper 60s to the middle 70s. Readings should get no higher than the middle 60s right along the coast due to the onshore flow. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... A mid level trough over the central part of the country early this morning will work its way eastward. Showers and thunderstorms will develop ahead of the feature and they should move into our region from the west tonight. As a result, we will carry categorical or likely probabilities of precipitation for much of our forecast area. Generally, rainfall amounts should favor the quarter to half inch range. The continued onshore flow and the precipitation are anticipated to result in the development of low clouds over much of our region for tonight. Low temperatures should favor the upper 50s and lower 60s. && .LONG TERM /MONDAY THROUGH SATURDAY/... Summary...Remaining shower/thunder chances through the first half of this upcoming week. Temperatures overall on the mild/warm side. Synoptic Setup...A closed low initially centered near the upper Great Lakes will slowly shift eastward through much of this upcoming week. While the core of this feature is forecast to remain well to our northwest and north, spokes of energy will rotate around the parent closed low. A potentially stronger short wave is forecast to shift eastward Wednesday, which is tied to a cold front. This short wave may sharpen the southern extent of the long wave trough some, potentially enhancing a ribbon of lift. As we go toward the end of the week and to start next weekend, the closed low shifts closer to the Canadian Maritimes and perhaps weakens some. Additional short waves on the western and southern side may amplify the trough across the Northeast Friday into Saturday before the entire system shifts more eastward. This all results in a few episodes of possible showers/thunder, although exact timing and coverage is less certain. We used a model/continuity blend for Monday through Tuesday night, then blended in the 00z WPC Guidance thereafter. Some adjustments were then made following additional collaboration with our neighboring offices. For Monday and Tuesday...The center of a closed low is forecast to move to a position between the Great Lakes and James Bay Canada. A stronger short wave is forecast to be lifting across the Northeast Monday, with a narrow trough axis possibly taking on some negative tilt. This will produce a ribbon of enhanced forcing, resulting in a band of showers and perhaps thunder. This looks to quickly lift to our north and east during the morning. A weakening cold front then moves through during Monday, however there may not be much in the way of forcing once the earlier morning band of showers clears the area. The forecast soundings overall indicate the column dries out in the afternoon especially for the central and southern areas. As a result, PoPs were lowered faster but still kept in some low PoPs in through the day. Another cold front or surface trough arrives during Tuesday, and with short wave energy accompanying it a band or two of showers will be possible. There could be just enough instability to allow for some thunder Tuesday afternoon. Daytime temperatures are expected to be mild/warm, however the far north and northeast areas on Monday may be cooler depending on the amount of clearing. For Wednesday and Thursday...As the center of the closed low slowly shifts across southeastern Canada, a stronger embedded short wave allows for the southern part of the long wave trough to amplify across the Northeast Wednesday. This should be reflected by another cold front at the surface. While some instability is forecast to develop during Wednesday, soundings generally show it being meager with any convection being low-topped. If the boundary layer warms more, low-level lapse rates would steepen and result in a bit more instability. Therefore, a thunder mention was expanded south and eastward some in the afternoon. The challenge is how much coverage occurs with showers/thunder Wednesday. Some guidance suggest coverage could be fairly widespread in the afternoon. For now, kept mostly chance PoPs with the idea there will be at least scattered activity around. The flow aloft may start to turn more zonal Thursday allowing for a dry day, however more short wave energy diving into the base of the closed low looks to start another eastbound amplification. For Friday and Saturday...The details of the forecast during this time frame mostly depend on the speed of the closed low to our north. While it will gradually shift eastward and probably eventually weaken, some guidance shows more amplification as strong short wave energy slides across the southern portion of the trough. This sends another cold front our way, which may be mostly just to our north. The evolution of the energy and therefore chances for convection is less certain. The entire system eventually shifts closer to the Canadian Maritimes with less influence on our region. As of now, kept slight chance PoPs for Friday and dry on Saturday. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Variable conditions are expected through 1300Z. Ceiling and visibility values should favor VFR. However, areas of MVFR and possibly IFR conditions are possible, especially around KRDG, KABE and KTTN. VFR conditions are anticipated from about 1300Z until 0000Z although there should be a fair amount of cloud cover for much of the day. Ceilings are expected to lower into the IFR range for tonight with the arrival of showers and scattered thunderstorms from the west, along with an onshore wind flow. The timing and coverage of thunderstorms for tonight remains a bit uncertain so we have mentioned only showers in the TAF at this time. A light and variable wind early this morning should settle into the southeast today at 5 to 10 knots. The wind direction is forecast to back toward the east tonight. OUTLOOK... Monday...MVFR/IFR conditions with some showers and thunderstorms mainly in the morning, then improving in the afternoon and at night as a cold front moves through. Some fog or low clouds are possible late at night. Tuesday and Wednesday...Some possible fog or low clouds to start Tuesday, otherwise generally VFR through Wednesday. Some showers and thunderstorms possible mainly each afternoon and evening, however timing and coverage is less certain. Thursday...VFR is anticipated with dry conditions. && .MARINE... As high pressure moves away to our northeast today, a southeast to east wind is forecast to increase to 10 to 15 knots. Wind speeds may rise into the 15 to 20 knot range for tonight, especially on the waters off New Jersey. Wave heights of 2 to 3 feet on our ocean waters today should build to 3 to 4 feet tonight. It appears as though they may reach 5 feet on our coastal waters from north of Atlantic City to Sandy Hook. We have placed those areas under a Small Craft Advisory beginning at midnight. RIP CURRENTS... Waves off the coast are forecast to be in the 2 to 3 foot range for today. An southeast to east wind is expected around 10 knots or so. It appears as though the risk for the development of dangerous rip current will be low for much of the day. However, it may begin to approach moderate toward evening as wind speeds increase gradually. The outlook for Monday is a low risk for the development of dangerous rip currents, as winds should become about 10 knots or less mainly from the southeast and south and waves lower some. OUTLOOK... Monday through Thursday...East to southeast winds are forecast to be strongest (gusts near 25 knots) Monday morning across the northern ocean zones before diminishing. This should maintain seas to about 5 feet at least in the morning before subsiding. Therefore, a Small Craft Advisory has been issued for our three northern ocean zones through 16z Monday. Otherwise, generally sub-advisory conditions are expected through Thursday. Some showers and thunderstorms are expected, mainly Monday morning and again Tuesday and Wednesday afternoons. && .TIDES/COASTAL FLOODING... The development of an onshore flow for today into tonight and the continued high astronomical tides should result in another round of minor coastal flooding tonight. As a result, we will issue another Coastal Flood Advisory for tonight`s high tide. It will cover the coastal counties of New Jersey and Delaware, as well as the counties along Delaware Bay and the lower Delaware River up to the area just below the Commodore Barry Bridge. Based on the guidance and on the fact that the astronomical tides are decreasing as we move away from the new moon, tonight`s Coastal Flood Advisory should be the last one for a while. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Coastal Flood Advisory from 9 PM this evening to 3 AM EDT Monday for NJZ012>014-020>027. Coastal Flood Advisory from midnight tonight to 4 AM EDT Monday for NJZ016. DE...Coastal Flood Advisory from 9 PM this evening to 3 AM EDT Monday for DEZ002>004. Coastal Flood Advisory from midnight tonight to 4 AM EDT Monday for DEZ001. MD...None. MARINE...Small Craft Advisory from midnight tonight to noon EDT Monday for ANZ450>452. && $$ Synopsis...Gorse Near Term...Iovino Short Term...Iovino Long Term...Gorse Aviation...Gorse/Iovino Marine...Gorse/Iovino Tides/Coastal Flooding...Iovino

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