Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 261709 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 109 PM EDT Tue Mar 26 2024 .SYNOPSIS... Strong high pressure centered across the Canadian Maritimes extends southwestward across our area. This will remain in place through tonight. Meanwhile, low pressure continues to meander around well offshore. A cold front is forecast to cross our region tonight, then it becomes nearly stationary along the coast. Low pressure tracks northward along this front Thursday and Thursday night before moving out to sea on Friday. A weak clipper system may move through on Saturday. && .NEAR TERM /THROUGH TONIGHT/...
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High pressure centered over the Canadian Maritimes, with a ridge extending southward along the East Coast to the Carolinas will remain in control of our weather today. This will join forces with an upper-level ridge also amplifying along the East Coast, to result in continued dry and stable conditions through sunset. A layer of lower clouds across NJ/ern PA earlier thinned out and moved to the NW earlier. Breaks across NJ lately are beginning to decrease in size as another batch of low clouds over the ocean are starting to track/form back into our area. Adjustments to temps/dewpoints and winds were made for the latest update. As we head into tonight, low pressure lifting across Lake Superior will send a cold front toward the Appalachians by Wednesday morning, while the trailing end of a weak warm front will near northwestern portions of our region. CAMs and the NAM are more bullish with at least some light showers pushing in during the predawn hours Wednesday, perhaps amounting to a few hundredths of an inch of rain by sunrise from northwest of Reading to Allentown. As ceilings lower and boundary layer moisture increases with continued light onshore flow, some patchy mist or light fog may develop in spots toward morning, but visibility should stay at or above 1 to 3 miles. It will be a mild night, with lows staying in the 40s.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... Troughing across the Southwest will amplify and shift eastward this week toward the East Coast by late Thursday. Some subtle jet dynamics will be at play with a developing low pressure system, which will have implications on direct impacts we receive from the system Wednesday through Thursday night. Surface low pressure should develop across the Southeast Wednesday and then lift northeastward and eventually offshore on Thursday along a baroclinic zone in place due to a stalled frontal boundary. The latest trend in some of the deterministic and ensemble guidance was for a farther eastward and thus drier solution. However, the synoptic forcing modeled does not exactly support this trend. There was no significant changes to the forecast with this update aside from some adjustments to the PoPs. Some areas of light rain should develop on Wednesday, primarily inland where PoPs are higher during the daytime. This will be in response to the initial height falls and diffluence aloft. Stronger forcing will arrive late in the night and especially by early Thursday as the surface low begins making its closest pass to our area. This is when more widespread, steadier/heavier rain is currently anticipated. The system and rain will depart late Thursday and Thursday night. Currently, QPF ranges from 0.5-1" in the far interior areas of eastern PA and northwest NJ, to 1-1.5" along I-95, to near 2" along the coast. This forecast is subject to change though, given the aforementioned subtle synoptic features at play. This will have implications on an impacts due to flooding as soils remain very saturated from the weekend rain. This rain may lead to additional rises on creeks, streams, and river across the area. Winds will be light on Wednesday favoring an easterly direction. As the departing system strengthens and high pressure pushes into the area, winds will then settle out of the north to northwest on Thursday and increase into Thursday night to near 15-20 mph with gusts up to 35 mph possible. Temperatures will remain mild in the 40s and 50s for much of this period, although the cold advection beginning Thursday night will drop us back into the mid to upper 30s. && .LONG TERM /FRIDAY THROUGH MONDAY/... Long wave ridging building across the central CONUS should result in seasonable temperatures and relatively benign weather conditions this weekend into Monday of next week. A quick moving shortwave trough may impact the area Saturday with a 20-30% chance of rain and increasing clouds, however it will not be the washout last Saturday was. The next system looks to impact the area late Monday into Tuesday with more widespread rain possible. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas... Tonight... Lower CIGS expected to increase over the area this evening and continue overnight. MVFR then IFR expected most sites after midnight. While no VSBY issues are expected for most sites, some fog may develop closer to the coast, so we`ve included some KACY/KMIV with low/medium confid. Light East to Southeast winds overnight. Wednesday... Low confid with a decent possibility of CIGS becoming VFR again (like today). We`ll probably offer some improvement to MVFR after 14Z/15Z again with limited confid. Lower conditions likely during the afternoon with rains arriving SW to NE. Light NE/E winds expected. Outlook... Wednesday through Saturday...Overall, periods of sub-VFR conditions, mostly Wednesday through Thursday evening in periods of moderate to heavy rain late Wednesday through Thursday. VFR returns on Friday. Scattered SHRA may result in brief sub- VFR conditions Saturday. Light east winds on Wednesday becoming 10-20 kts and gusty from the north to northwest Thursday through Saturday.
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&& .MARINE... Some gusts to around 20 kt or so may continue early this morning around the mouth of Delaware Bay, but conditions will remain below Small Craft Advisory criteria today. Meanwhile, winds will continue to gust to 25 kt or so through early this morning across the open ocean, but gradually ease through this evening. However, a large storm well offshore will meander today. Along with the elevated, albeit lessening northeasterly winds, a substantial easterly swell will persist today, with seas of 8-12 ft much the day, only gradually lowering into the 5-8 ft range later tonight. Small Craft Advisories will remain up as a result. Outlook... Wednesday through Saturday...SCA conditions continue into at least Wednesday due to elevated seas, then seas diminish Wednesday night. A storm will develop and lift along the coast Wednesday night through Thursday night, departing on Friday. Strong NW winds develop Thursday night and continue into Saturday. SCA conditions expected with marginal gales possible on Friday. && .TIDES/COASTAL FLOODING... A low pressure system lingering well off the coast will result in an extended duration of long period swells and rough surf impacting the Atlantic coast through early this week. Widespread minor flooding has occurred with the nighttime high tide, including the tidal Delaware River. This may be due to increasing fresh water inflow from the recent heavy rains. Elsewhere, tidal surges remain around 2-3 feet above normal, though many stations are closer to 2 feet rather than 3 feet. This resulted in a lack of moderate flooding that was forecast with the previous high tide, likely owing to underwhelming northeast winds across much of the coastal waters earlier Monday. Widespread MINOR flooding is forecast to occur with at least the next two high tides through tonight and early Wednesday morning. For the eastern shore of the Chesapeake Bay, tidal surge anomalies will continue to rise to near 2-3 feet above normal by Wednesday morning, which is also forecast to result in widespread MINOR tidal flooding with the Wednesday morning high tide. Coastal Flood Advisories were expanded to include the tidal Delaware River and eastern shore of the Chesapeake Bay, and are now in effect for all tidal areas in the forecast area to cover the impacted high tides. Tidal surge anomalies are forecast to begin receding by late Wednesday. This combined with a lessening influence of the offshore storm and moving further away from the full moon are forecast to result in a cessation of coastal flood impacts. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Coastal Flood Advisory until 7 AM EDT Wednesday for PAZ070-071- 106. NJ...Coastal Flood Advisory until 4 AM EDT Wednesday for NJZ016. Coastal Flood Advisory until 2 AM EDT Wednesday for NJZ012>014- 020>027. Coastal Flood Advisory until 7 AM EDT Wednesday for NJZ017>019. DE...Coastal Flood Advisory until 4 AM EDT Wednesday for DEZ001. Coastal Flood Advisory until 2 AM EDT Wednesday for DEZ002>004. MD...Coastal Flood Advisory from 8 AM to noon EDT Wednesday for MDZ012. Coastal Flood Advisory from 5 AM to 10 AM EDT Wednesday for MDZ015-019-020. MARINE...Small Craft Advisory until 6 PM EDT Wednesday for ANZ450>455. && $$ SYNOPSIS...Gorse/MPS NEAR TERM...Dodd/OHara SHORT TERM...Staarmann LONG TERM...Staarmann AVIATION...Dodd/MPS/OHara MARINE...Dodd/MPS/OHara TIDES/COASTAL FLOODING...

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