645 FXUS61 KPHI 210551 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 151 AM EDT Sat Mar 21 2020 .SYNOPSIS... A cold front will move across the area overnight. High pressure will build out of the Great Lakes region and across the New England states over the weekend. A coastal storm will affect the Mid Atlantic region around Monday, followed briefly by high pressure Tuesday, before another storm affects the area around midweek. A cold front is forecast to move across the east coast late next week. && .NEAR TERM /THROUGH TODAY/... The cold front is expected to progress through the region and shift off shore by mid day today. Lingering rain showers are possible through late this morning, but should mainly be confined to Delmarva and southeast NJ. Expect considerable dry and cold air advection in the wake of the cold front. One caveat to this is that an inverted trough may result in a weak on shore flow this afternoon along the coastal plains, but it should have a very limited impact to the temperature and dew point trends. Highs are expected to be slightly below normal, in the 40s and 50s, or 20 to 30 degrees below highs on Friday. && .SHORT TERM /TONIGHT THROUGH 6 PM SUNDAY/... Continued clearing tonight into Sunday as the surface high will be the dominant feature (however, the center of the high will remain to our north with our region on the southern periphery). Low level flow will shift more easterly, especially during the day Sunday as the high shifts further east. What this means is that we will see modest dew point recovery during the day on Sunday ahead of the next system. However, cold air advection will continue, so highs on Sunday will likely be at or a few degrees lower than Saturday's highs, with most areas topping out in the 40s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... By Sunday night, an area of low pressure will be strengthening offshore of the Carolina coasts while high pressure shifts into the Canadian Maritimes. This low will lift northward along the east coast and approach the Mid Atlantic region through the day Monday, before quickly exiting to the northeast Monday night. The 12z models have come into better agreement with the placement of the low, although there are still some slight differences. Another thing they are all agreeing on is cold air being in place when the precipitation moves into the area. This cold air should be enough for snow to develop across much of northeastern Pennsylvania and northern New Jersey. Accumulating snowfall is expected along and north of I-78 corridor, with the highest amounts along and north of the I-80 corridor. Generally an inch or less is expected along the I- 78 corridor, with as much as 2-5 inches across the I-80 corridor. Warm air will move northward through the day, and many areas should change over to all rain, which is why snowfall amounts will be less for the southern tier of the snowfall areas. However, the cold air will likely last longer across far northeast Pennsylvania and northwest New Jersey which is why their snow amounts are higher. Another concern will be total QPF amounts which will likely total at least 0.75-1.00 inches, with some locally heavier amounts. Currently no river points are expected to reach flood stage, but some locally poor drainage flooding could be possible. The low will quickly move northeastward and away from the area Monday night. Precipitation may linger for a few hours into Monday evening, before ending through the night. High pressure briefly builds in early Tuesday, which will bring dry weather briefly to the area, before shifting offshore later in the day. As we move into Tuesday night into Wednesday, a low pressure system is forecast to move across the Midwest states and into the eastern Great Lakes, while a second low develops along an occluding frontal boundary as it moves across our area. This will bring a period of rainfall beginning late overnight Tuesday/early Wednesday morning, and continuing through the day Wednesday, before ending Wednesday evening. All precipitation is expected to be rain. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Overnight...VFR conditions are expected. Isolated showers are possible at KMIV and KACY through 12Z, but should not affect the flight category. Northwest wind 10 to 20 knots. High confidence. Today...VFR conditions with decreasing clouds. North wind 10 to 15 knots with gusts up to 20 knots in the morning, diminishing to 5 to 10 knots in the afternoon. Wind direction will shift to northeasterly during the afternoon, especially at KACY and KMIV. High confidence. Tonight...VFR conditions expected. Winds generally out of the north northeast at 10 kt or less (though the direction may start variable at KACY and KMIV). High confidence. Outlook... Sunday...VFR conditions expected. Northeasterly winds shifting to easterly in the afternoon with wind speeds of 10 to 15 kt. Moderate confidence. Sunday night through Monday...Sub-VFR conditions developing as mainly rain showers move through the terminals with a chance for mixed precipitation at KRDG/KABE, becoming all rain on Monday. Rain will taper off through the afternoon. Easterly winds around 10 to 15 knots. Moderate confidence. Monday night through Tuesday...Sub VFR conditions in rain/snow showers expected to end Monday night with a return to VFR expected by late morning/early afternoon on Tuesday. North to northwest winds around 5 to 15 knots. Moderate confidence. Tuesday night through Wednesday...A return to sub-VFR conditions as rain starts to overspread the terminals Tuesday night and continues through Wednesday. Light southeast winds Tuesday night will become more easterly around 10 to 15 knots on Wednesday. Moderate confidence. && .MARINE... Elevated seas are expected to linger on the Atlantic coastal waters through at least sunrise before gradually decreasing. Wind gusts near 20 kt are possible through sunrise, but at this point, expect gusts to stay below 25 kt. Winds and seas should stay below SCA criteria overnight Saturday night. Outlook... Sunday...Conditions expected to remain below advisory levels, although winds could gust around 20 knots at times. Seas may build above 5 feet late in the day. Sunday night-Monday...Small Craft Advisory Conditions likely as winds likely increase to advisory levels late Sunday into Monday, and seas likely also build above 5 feet or higher. Monday night-Tuesday...Winds likely lower below advisory levels, but may gust around 20 knots at times. However, seas may remain above 5 feet into early Tuesday, before lowering below 5 feet later in the day. Tuesday night-Wednesday...Winds may approach Small Craft Advisory levels late Tuesday night into Wednesday morning. Seas may also build back to 5 feet or higher late Tuesday into Wednesday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for ANZ450>453. Small Craft Advisory until 1 PM EDT this afternoon for ANZ454- 455. && $$ Synopsis...Robertson Near Term...Johnson Short Term...Johnson Long Term...Robertson Aviation...Johnson/Meola Marine...Johnson/Robertson