650 FXUS61 KPHI 241615 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1215 PM EDT Sun Apr 24 2022 .SYNOPSIS... High pressure extends its way southward across New England and into the Mid-Atlantic, however it will then shift offshore on Monday as a warm front approaches from the southwest. A cold front will move across the area later Tuesday as an area of low pressure moves along the East Coast. Strong northwest flow will develop on Wednesday into Thursday as the low moves across the Canadian Maritimes. Winds will subside on Friday as high pressure moves overhead. && .NEAR TERM /THROUGH TONIGHT/... High will remain entrenched to our north and east this afternoon and if anything the surface ridging should actually strengthen a bit off the coast. This will result in a continuing easterly flow at the surface while warm air advection continues aloft in the 925 to 850 mb layer helping strengthen a developing inversion in this level. This set up should also keep the surface warm front at bay over PA extending into Delmarva so we are continuing to forecast a large variation in temperatures across the area. Expect highs only in the 50s over much of coastal NJ with upper 60s to low 70s not too far west of here over SE PA into adjacent southern NJ and 70s to near 80 over interior portions of southern DE into adjacent areas of our eastern MD counties. Expect an overall sunny day with just some high cloudiness around as well as some scattered low level strato cu. Overall, there won't be too much change in the large scale setup for tonight. Low pressure will advance northeast through northern Ontario while the ridge remains to our east keeping the easterly flow in place. This should eventually result in the lower levels becoming more saturated with the formation of a low stratus deck by the overnight period. It should remain dry through as upper level ridging crests along the east coast. Expect lows mostly in the 40s to low 50s. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Surface high pressure will remain stubbornly placed just east of MA Monday as the closed upper level low near Bermuda slowly moves further out to sea. Simultaneously, a seasonably strong mid-level ridge will center across the Mid-Atlantic. This will place the Delaware River Valley between the warm sector of the approaching wave from the west, and the cool moist air off of the Atlantic Ocean to the east. As of current, the most likely solution appears to be most of the day Monday being cloudy with high temperatures in the upper 60s towards the Lehigh Valley and mid 50s right along the Atlantic Coast. Precipitation is not expected Monday. The mid-level low over Ontario will finally eject northeast Monday night, with another closed low just to its west. As this occurs, a line of showers and embedded thunderstorms across eastern OH and western PA will likely begin to weaken as the primary forcing pulls northeast. This decaying precipitation will likely be in the form of showers or sprinkles as it moves across the region Tuesday morning. The secondary closed low will be crossing the Great Lakes Tuesday afternoon, but by this time low level flow has mostly turned from the west (or favoring more of a downslope component). Low level RH profiles on model guidance are in moderate agreement with rapid drying commencing. The NAM and latest ECMWF are the slower of the solutions here, and does show redevelopment of showers along the coast of NJ as a surface low forms. The GFS, CMC, and 12z ECMWF showed more sparse coverage. For now have only made a slight trend downward in PoPs for Tuesday afternoon, but confidence is low here. As of current, the best upper level lift, moisture, and instability appear to be just out of phase. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Extended probabilistic guidance continues to be very consistent in showing widespread below normal heights centered near the Gulf of Maine Wednesday into Thursday, with a slow progression towards above normal heights by the end of the long term. This consistency between the GEPS, GEFS, and EPS is fairly impressive this far out, and the latest runs of the NBM advertises a smaller IQR range in temperatures for the long term compared to the near and short term time ranges. The synoptic setup above favors slightly below normal temperatures initially translating to near normal temperatures by the end of the period. Little precipitation is expected through the period. This is all thanks to an upper level low that will be centered over western Quebec Wednesday morning. The trough axis will be centered over central PA at this time, with impressive DCVA finally crossing the region by Wednesday afternoon. At this point though, the mid-level dry slot has well pushed east over the region. Have kept some slight chance PoPs in for the higher terrain where some 850 MB moisture might be lingering, but most of the region will likely be dry Wednesday. Wednesday night into Thursday, the mid-level low that was over western Quebec will be located near the Canadian Maritimes and will be rapidly undergoing the occlusion process. As this occurs, surface high pressure will slowly translate east towards the OH/ PA border. Low temperatures Thursday morning will likely be mostly in the upper 30s to lower 40s as the PGF never weakens much. This continued tight gradient will likely keep winds elevated Wednesday night/ Thursday morning and therefore also keep temperatures a little bit higher than consensus is forecasting. The upper level low will become vertically stacked Friday morning with forward motion coming to a temporary halt. This will likely make Friday morning the coldest of the long term period, especially in rural areas where the PBL can fully decouple. Frost headlines might be required Friday morning. Dry weather will then persist into Saturday, with temperatures moderating back into the mid 60s. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This afternoon...VFR with some high thin cloudiness around as well as some scattered strato cu developing around 3000-3500 ft. Winds east around 10 knots. High confidence. Tonight...VFR through the evening with clouds thickening and cigs lowering overnight. MVFR cigs possible by late at night. Low confidence on how low cigs get overnight. Outlook... Monday...MVFR becoming VFR. E to SE winds 5 to 10 kts. Low confidence. Monday night...Mainly MVFR. Can't rule out IFR especially towards KACY and KMIV. E to SE winds 5 to 10 kts. Moderate confidence. Tuesday...MVFR becoming VFR. IFR again possible especially towards KACY and KMIV. Showers in the afternoon. E to SE winds around 5 kts, becoming W to NW 5 to 10 kts with gusts around 15 kts. Moderate confidence. Tuesday night through Wednesday...VFR with showers slowly coming to an end Wednesday morning. Northwesterly winds around 5-10 kts becoming 10-15 kts daytime Wednesday with up to 25 kt gusts. Winds decrease back to 5-10 kts Wednesday night. Moderate confidence. Thursday...VFR with few clouds. Northwesterly winds 10-15 kts with gusts up to 25 kts possible. Winds will diminish to 5-10 knots overnight. Moderate confidence. && .MARINE... High pressure will continue to dominate the waters through the near term. Winds will generally be east 10 to 15 knots with some gusts to 20 knots. Waves are expected to be 2 to 3 feet on our ocean waters, and 2 feet or less on Delaware Bay. Little change is expected through tonight. Outlook... Monday...Southeast winds 10 to 15 kts with gusts around 20 kts. Seas 3 to 4 ft. Sub-SCA conditions expected. Tuesday...Sub-SCA conditions expected with winds becoming more SW late in the day. Tuesday night through Wednesday...Winds turning from the northwest Tuesday night and slowly increasing in speed to 15 to 20 kts by Wednesday afternoon. Gusts around 25 kts are likely. Seas increasing 3 to 5 ft. An SCA may be required Wednesday. Thursday...Northwest winds 15 to 20 kts, with gusts up to 25 kts. Seas 4 to 6 ft. An SCA may again be required for Thursday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Haines/Kruzdlo Near Term...Fitzsimmons/Iovino Short Term...Haines Long Term...Haines Aviation...AKL/Fitzsimmons/Haines Marine...AKL/Fitzsimmons/Haines