Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 270751 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 351 AM EDT Sat May 27 2017 .SYNOPSIS... As a front remains draped to our south today and tonight, weak low pressure will track along it and exit off the Mid Atlantic coast tonight into Sunday. Another low pressure system is forecast to consolidate just north of the Great Lakes Monday and then gradually shift eastward through Wednesday. An associated cold front moves through our area later Monday, then a secondary cold front arrives during Tuesday. High pressure builds from the Midwest to the Carolinas Wednesday and Thursday, then closer to our area Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A mid level short wave located over Lake Erie and vicinity early this morning will progress east southeastward and it is forecast to pass over our region during the late afternoon and early evening hours. We are anticipating an increase in cloud cover this morning in advance of the system. The short wave was producing a fair amount of shower activity in Ohio early this morning along with isolated thunder. The precipitation is expected to diminish a bit this morning as it moves to the east southeast. The showers may become reinvigorated this afternoon as they encounter marginal instability to the southwest of our forecast area. We are anticipating only isolated to scattered rain showers in eastern Pennsylvania and New Jersey for this afternoon. There appears to be a better chance for scattered showers and thunderstorms in northeastern Maryland and Delaware. A light west wind is expected for this morning. The direction should become variable in the afternoon. Highs should be within a couple degrees of normal for today, ranging from the upper 60s in the elevated terrain to the middle 70s on the coastal plain. Maximum temperatures are forecast to be in the middle and upper 60s right along the coast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... Lingering showers and thunderstorms are possible on the upper Delmarva this evening, then we are not expecting any additional precipitation overnight. Partial clearing is anticipated, mainly over eastern Pennsylvania, and northern and central New Jersey. Another mid level short wave trough is expected to move from the Ozarks vicinity this morning to North Carolina late tonight. A weak surface low associated with the mid level trough is forecast to pass off the coast between the Virginia Capes and Cape Hatteras late tonight. It is not anticipated to have much impact on our region. The wind should be light tonight, with its direction favoring southeast to northeast. Lows are expected to be mainly in the 50s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Summary...Unsettled at times through early next week. After a cooler Sunday especially closer to the coast, warmer temperatures (close to where they should be this time of year) are expected next week. Synoptic Setup...While a weak ridge slides across the Northeast Sunday, a closed low in south-central Canada is forecast to amplify south and eastward through the middle of next week before weakening some Thursday and Friday. It is forecast to remain centered well to our north, however cyclonic flow will be in place along with several short waves revolving around it. This will drive a couple of fronts eastward. The exact timing of the embedded features are less certain given an amplified pattern with a closed low involved, however a model consensus now indicates that Sunday is drier than Monday. We used a model/continuity blend for Sunday through Monday night, then blended in the 00z WPC Guidance thereafter. Some adjustments were then made following additional collaboration with our neighboring offices. For Sunday...A weak ridge is forecast to slide across the East, however it should quickly move off the coast in the afternoon. This will take weak surface high pressure to off the coast of New England through the afternoon, meanwhile a front remains draped to our south with weak low pressure slowly moving offshore of the Mid Atlantic coast. A closed low centered just north of the Great Lakes is forecast to expand south and east some through Sunday. This will drive weak surface low pressure up across the eastern Great Lakes, then it should consolidate eventually north of the Great Lakes at night. The frontal zone to our south should lift northward some, however weak surface high pressure wedged southwestward will keep an onshore flow in place and probably hold back the surface front. What appeared to be an unsettled day may end up being dry, at least for the daylight hours. A cold front or occluded front looks to arrive later at night, and enough lift and moisture should result in some showers and perhaps thunderstorms mainly at night as we wait for convection to our west to arrive. The onshore flow should result in a fair amount of clouds (perhaps low clouds/drizzle to start Sunday), and therefore temperatures are anticipated to be held down at least some especially closer to the coast. For Monday and Tuesday...The center of a closed low is forecast to slowly move across southeastern Canada, mostly near James Bay. A short wave trough with an embedded stronger short wave lifts up across the Northeast Monday. This will be accompanied by a weakening front, however enough lift and instability should be present to result in some showers and thunderstorms Monday. The greatest deep- layer shear is forecast to be to our south Monday, however if enough instability can develop then an isolated strong/severe thunderstorm is possible across our southern zones. The initial front may dissipate as it shifts east Monday night into Tuesday, however a secondary front is forecast to arrive during Tuesday. The forcing looks weaker for Tuesday with the incoming secondary front, however cyclonic flow combined with some height falls may allow for limited convective development in the afternoon especially near the higher terrain. We therefore have the highest PoPs on Monday, then lower on Tuesday when isolated to perhaps scattered convection is possible. We are anticipating warmer temperatures ahead of the weak fronts. For Wednesday and Thursday...As the center of the closed low gradually shifts east more across eastern Canada, it amplifies across the Northeast and northern Mid Atlantic for at least a time. At least some guidance shows a pronounced short wave rotating around the closed low late Wednesday into Thursday as it crosses the eastern Great Lakes then slides across interior New England. This may be accompanied by a surface trough especially during Wednesday with potentially some convection with it. There is still some resemblance of a surface trough on Thursday, however much of the forcing is forecast to shift into New England. Meanwhile, surface high pressure is forecast to build from the Midwest to the Carolinas during this time frame. Due to the cyclonic flow, daytime temperatures will be in the 70s to about 80 degrees each day. The Pops were kept at low chance or less. For Friday...As the closed low gradually weakens and heads toward the Canadian Maritimes, a lobe of vorticity may sharpen the western part of the upper-level trough as is swings across the Great Lakes and Northeast. Weak high pressure is forecast to be building much closer to our area from the west and south, however another weak front or surface trough slides across our area. Depending on the moisture available along with the sharpness of the trough, some convection cannot be ruled out especially in the afternoon and early evening. As of now, kept slight chance PoPs. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions are expected to prevail through the TAF period. We are anticipating an increase in cloud cover for today and partial clearing for tonight. There is a chance of showers from this afternoon into the early evening. The showers are expected to be isolated to scattered around KRDG, KABE, KTTN, KPHL, KPNE and KACY. There is a slightly better chance for showers around KILG and KMIV along with a small potential for thunder. The impact of the showers is anticipated to be limited. A light west wind this morning is forecast to become variable for this afternoon. The wind should favor the southeast to northeast tonight at 8 knots or less. OUTLOOK... Sunday...MVFR/IFR possible to start due to low clouds and/or some fog, otherwise mainly VFR during the remainder of the day. Lower confidence regarding low clouds/fog in the morning. Ceilings should then lower to MVFR or IFR at night as some showers and perhaps a thunderstorm moves through. Monday...MVFR/IFR conditions with some showers and thunderstorms. Some improvement may occur in the afternoon and at night as a cold front moves through. Some fog is possible later at night. Lower confidence regarding timing of improving conditions and timing/coverage of showers/thunder. Tuesday and Wednesday...Some fog possible to start Tuesday, otherwise generally VFR through Wednesday. Some showers and thunderstorms still possible mainly Tuesday afternoon and evening. && .MARINE... The wind is forecast to back from the northwest and west to the south and southeast today at speeds of 5 to 10 knots. The wind should become east to northeast tonight around 10 knots. Wave heights on our ocean waters will be mainly in the 2 to 3 foot range. Waves on Delaware Bay will be 2 feet or less. RIP CURRENTS... A light northwest to west wind this morning is expected to become south to southeast this afternoon. Wave heights off the coast should be 2 to 3 feet. As a result, we are anticipating a low risk for the development of dangerous rip currents for today. For Sunday, an onshore flow is forecast to strengthen some and this may result in the rip current risk approaching moderate especially for the coast of New Jersey. OUTLOOK... Sunday through Wednesday...The conditions are anticipated to be below Small Craft Advisory criteria. East to southeast winds however should increase Sunday with some gusts to around 20 knots at times. The seas are currently expected to be 4 feet or less. Some showers and thunderstorms are expected, especially later Sunday night and Monday. && .TIDES/COASTAL FLOODING... No coastal flooding is anticipated with this morning`s high tide. However, we will issue another Coastal Flood Advisory for tonight`s high tide. It will be in effect for the coastal counties of New Jersey and Delaware, and for the counties along Delaware Bay and the lower Delaware River up to near the Commodore Barry Bridge. The guidance is suggesting the tonight`s coastal flooding will be greater than that on Friday evening and a bit less than what occurred on Thursday evening. The loss of the offshore wind should allow some water to return back toward the coast, so the guidance seems reasonable. We will continue to keep an eye on Sunday evening`s high tide as well since the surface wind is expected to be onshore at that time and the astronomical tides will remain high. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Coastal Flood Advisory from 8 PM this evening to 2 AM EDT Sunday for NJZ012>014-020>027. Coastal Flood Advisory from 11 PM this evening to 3 AM EDT Sunday for NJZ016. DE...Coastal Flood Advisory from 8 PM this evening to 2 AM EDT Sunday for DEZ002>004. Coastal Flood Advisory from 11 PM this evening to 3 AM EDT Sunday for DEZ001. MD...None. MARINE...None. && $$ Synopsis...Gorse Near Term...Iovino Short Term...Iovino Long Term...Gorse Aviation...Gorse/Iovino Marine...Gorse/Iovino Tides/Coastal Flooding...Iovino is the U.S. government's official web portal to all federal, state and local government web resources and services.