Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 242344 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 744 PM EDT Sun May 24 2020 .SYNOPSIS... High pressure stretched across our region from the northeast this afternoon will gradually weaken some and shift eastward through early this week, then it remains anchored offshore through late this week. A cold front crosses our region later Friday into Saturday, then high pressure builds in for Sunday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... The onshore flow across the region continues this evening. Now that the daytime mixing has ended, an overall increase in cloud cover and perhaps some drizzle near the shore is expected overnight. Some breaks in the clouds could also lead to some fog formation, but it is not expected to be dense. These breaks will likely be more common across the far N or NW areas. Few changes were made to temps, dew point grids or winds. The lows tonight will be in the low to mid 50s for the most part. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... Monday is expected to begin under an overcast sky in northeastern Maryland and Delaware, and in much of New Jersey and eastern Pennsylvania. As the surface ridge retreats a bit, the flow should veer toward the southeast. The strong late May sunshine is forecast to produce enough mixing on Monday to cause the clouds to lift and break over much of our region for the afternoon hours. High temperatures are expected to be mostly in the 70s, with readings not getting above the 60s near the coast. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... Summary...A much warmer airmass (and more humid) surges into the region this week, followed by a little cooling over the weekend. Shower and thunderstorm chances increase mostly for Friday. Synoptic Overview...An upper-level ridge is forecast to build across the East through Tuesday before shifting more offshore. At the surface, high pressure initially centered just south of the Canadian Maritimes extends west and southwest into the Mid-Atlantic, then it becomes more centered into the western Atlantic as the aforementioned ridge shifts eastward. An upper-level trough sliding across southern Canada is forecast to amplify some into the Great Lakes and New England late in the week. An attendant surface low tracks well to our north, however its cold front moves through later Friday into Saturday. The trough should then amplify more into the East Sunday with surface high pressure building it. For Monday night and Tuesday...A ridge aloft builds across the region with surface high pressure becoming anchored more offshore and to our east. This will result in the low-level flow being southerly along with warm air advection occurring. Given the presence of the ridge, no precipitation is expected. However, the low-level moisture will continue to increase and with a subsidence inversion in place despite a more southerly flow, areas of low clouds should develop once again during the night and a portion of Tuesday morning. Some fog is anticipated as well. Once these dissipate during Tuesday morning, temperatures should be off to the races as ample boundary layer warming occurs with afternoon temperatures into the 80s for many places. The exception are the southeast or south facing beaches initially which will have a more onshore wind component and therefore cooler temperatures. The low- level flow is not forecast to be all that strong, therefore a sea/bay breeze is anticipated to develop during Tuesday as the land/water temperature differential increases quite a bit (increasing the onshore flow component all along the coast). For Wednesday and Thursday...While an upper-level ridge shifts more offshore it still remains over our region Wednesday before weakening a little Thursday. Surface high pressure will remain anchored well offshore, resulting in a continued southerly flow of warmer and more humid air. While much of this time frame may end up being dry, there looks to be some opportunity for some convection around the western flank of the ridge. This should be moreso during Thursday as an upper-level trough in eastern Canada starts to glance our region. There may be just enough cooling aloft along with perhaps a lee-side trough and terrain circulations to develop mostly some diurnally driven convection, especially in the western part of the area. A sea breeze each day (especially Wednesday) should result in cooling along the coast. For Friday and Saturday...The southern portion of the upper-level trough across eastern Canada will swing across the Northeast Friday with a more notable amplification during Saturday. At the surface, low pressure tracks well to our north pulling a cold front across our area later Friday into Saturday. While the timing of the frontal passage varies to a degree, some showers and thunderstorms are probable along and ahead of the front. The stronger flow may reside farther north and displaced from the greater instability Friday, therefore the intensity of any thunderstorms is less certain. The cold front should be clearing much of our area to start Saturday morning, therefore some drier air will be working in. Based on this and the arrival of the main trough aloft, instability should be on the way down however did hang onto some slight chance or low chance PoPs Saturday for a time. For Sunday...The upper-level trough is forecast to dominate the East with surface high pressure building in. This will result in dry conditions and also some cooler temperatures. The surface winds may once again turn onshore and therefore even cooler temperatures for the coastal communities. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR and MVFR ceilings this evening, with conditions lowering to IFR overnight. A little drizzle possible near KACY. Patchy fog possible. Northeast to east wind 4 to 8 knots. Medium to high confidence. Monday...IFR conditions improving to MVFR in the morning, then to VFR for the afternoon with a decrease in cloud cover at that time. East to southeast wind 5 to 10 knots. Medium to high confidence. Outlook... Monday night and Tuesday...MVFR to IFR ceilings develop then improve back to VFR during Tuesday. Some local fog possible Tuesday morning. East-southeast winds less than 10 knots. Low confidence with timing of flight category changes. Wednesday...Areas of MVFR ceilings possible to start, otherwise VFR. Southerly winds 5-10 knots, becoming light and variable at night. Moderate confidence. Thursday...Mainly VFR. Some showers and thunderstorms possible in the afternoon and evening especially west of PHL. South winds around 10 knots. Low confidence on timing of any thunderstorms. Friday...Times of sub-VFR conditions probable as showers and thunderstorms increase during the day. Southwest winds 10-15 knots, becoming west to northwest at night and diminishing. Low confidence. && .MARINE... A Small Craft Advisory is in effect for tonight and Monday morning on our ocean waters. A northeast wind 10 to 15 knots through Monday morning is expected to diminish to 5 to 10 knots on Monday afternoon as the direction begins to veer toward the east. Wave heights on our ocean waters should remain around 5 to 6 feet into Monday morning, before subsiding to around 4 feet in the afternoon. Outlook... Monday night through Wednesday...The conditions are anticipated to be below Small Craft Advisory criteria. Some fog possible later Monday night and Tuesday morning. Thursday and Friday...South to southwest winds increase with gusts approaching 25 knots. However, much warmer air will be moving over the cooler waters and therefore the amount of mixing is in question. The winds should shift to west and northwest Friday night. Shower and thunderstorm chances increase on Friday. Rip Currents... A prevailing medium period northeasterly swell will maintain a moderate risk for the development of dangerous rip currents into Monday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until noon EDT Monday for ANZ450>455. && $$ Synopsis...Gorse Near Term...O`Hara Short Term...Iovino Long Term...Gorse Aviation...Gorse/Iovino/PO Marine...Gorse/Iovino

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