123 FXUS61 KPHI 021704 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 104 PM EDT Thu Apr 2 2020 .SYNOPSIS... An ocean storm will continue to churn offshore of the mid-Atlantic through Friday. That storm will finally move out to sea by Saturday as high pressure builds in for the weekend. A weak cold front will move through Sunday night or early Monday, with weak high pressure then building in for Monday. One or two frontal systems then may affect the region heading into the midweek period. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 12:30 pm update... Few changes to the forecast as breezy northwest winds continue and the coastal low continues to churn to our north and east. A few mid-level cumulus clouds will develop into the afternoon and fill in as the we move into the evening from northeast to southwest as the aforementioned low retrogrades westward. 9:30 am update... Adjusted temperatures and dew points to account for morning trends. Winds are beginning to gust currently and thus, adjusted timing in minor detail to account for this. Otherwise, no significant changes to note. This is the most sunshine we have seen in what feels like ages, so enjoy before clouds retreat back into the region late this afternoon and evening from the northeast. The Northeast and Mid-Atlantic will be caught in between two systems today: surface high pressure building over the Great Lakes and surface low pressure approximately 400 miles southeast of Nantucket Island. Meanwhile, a deep upper trough lies over much of the Northeast and western Atlantic Ocean, with a weak H5 low over eastern Lake Ontario. Several strong shortwaves will rotate around this low and through the local forecast area today. Surface high pressure builds east today. Meanwhile, the oceanic low will lift to the north, then retrograde back a bit towards the mainland, and should be approximately 325 miles due east of nantucket Island. A tight northwest pressure gradient develops over the area, and with a 30-40 kt LLJ passing through the region, will have gusty winds developing throughout the day, generally starting out at 15-20 mph with gusts to 30 mph, increasing as high as 20-30 mph with gusts to 40 mph in the afternoon. Winds will remain below Wind Advisory criteria. Skies start off sunny, but clouds will develop as shortwaves pass through the region, and then clouds associated with the offshore low will rotate back towards northern New Jersey and the southern Poconos. Highs today will be right around normal, generally in the 40s in the southern Poconos, and otherwise in the low to mid 50s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... The coastal low continues to retrograde back towards the mainland tonight, and should be about 180 miles east of Nantucket Island late in the overnight period. Winds diminish after sunset, but remain elevated through the overnight at around 15 mph with 20-25 mph gusts. Waves of light rain will rotate back towards northeast New Jersey and the southern Poconos starting this evening and continuing through the overnight. Not much QPF expected, generally a few hundredths of an inch or so. Lows tonight generally in the mid 30s in the southern Poconos, otherwise in the upper 30s to low 40s north of the Fall Line and in the lower 40s across southeast Pennsylvania, southern New Jersey, and Delmarva. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Overview... Some gradual changes for the end of this week and the beginning of next as the blocking pattern that has been in place slowly breaks down. A West Coast trough (-PNA in place) will be a prominent feature in the days ahead, and consequently can expect a rebuild/reload of ridging over the Southeast, similar to what we have dealt with much of the past few months. We will finally rid ourselves of the large and powerful offshore storm system which has been lurking nearby, though it will take until Saturday for it to pull away in earnest. In terms of the sensible weather, the result of all this will be a gradual warming trend heading into the weekend and the start of next week, though no particularly anomalous warmth is expected. Some light rain associated with the ocean storm is possible on Friday before we dry out for the weekend. As the blocking pattern eases up and the atmospheric wheels begin to turn a little quicker, our precipitation chances should start to increase, but it looks like it won't be until early to mid next week that we see better chances of more widespread rain. Dailies... Friday-Friday night... The offshore ocean storm will retrograde southwestward beneath the influence of strong higher latitude blocking. As it does so, its long moisture fetch will try to throw some rain back into the region. Overall, Friday does not look like a great day especially in the eastern half of the area. Lots of clouds and probably some spotty light showers especially towards the coast. Much of the guidance looks suspiciously warm for a mostly overcast day. Went a little on the cooler side especially towards the coast, with highs mostly in the mid 50s. We should dry out overnight with winds also decreasing overnight after a breezy daytime period as the storm gradually shifts back off further to the east. Saturday-Saturday night... The weakening ocean storm finally pulls away out to sea on Saturday. So it should be a dry day, though there are questions as to cloud cover extent. Likely to still be some leftover moisture in the lower levels especially with winds turning more easterly, albeit light. So may still be mostly cloudy especially through the morning, but better chances of more sunshine developing later in the day. Highs in the mid to upper 50s. Sunday-Sunday night... A very weak cold front starts to approach during this time, associated with weak low pressure over Ontario. Ahead of it, should be a nice day Sunday with some WAA in developing light southwesterly flow. Most areas will return to the 60s for highs. Clouds will increase as the front slowly approaches, with a frontal passage likely overnight. With such weak forcing and unfavorable diurnal timing, expect very little fanfare with this front. Maybe just a few light showers overnight. Monday-Wednesday... As mentioned above, the pattern starts to turn more progressive here. Southeast ridging becomes more prominent during this time, with the ridge axis centered several hundred miles to our west. Temperatures should run a few degrees above average, mainly in the mid to upper 60s with maybe some 70 degree readings towards Delmarva. Precipitation chances are a bit unclear. Behind the weak frontal passage Sunday night, Monday has a good chance to stay dry with weak high pressure building in out of the Great Lakes. Beyond then, rain chances may increase as a couple pieces of shortwave energy get entrained into the ridge, but low confidence as to the timing and evolution. Went with a very generic and non- committal forecast of chc and slgt chc PoPs for now which will be narrowed down as this comes into clearer view. && .AVIATION /17Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR with clear skies early on with SCT-BKN CIGs around 15000 ft developing in the afternoon. NW winds around 10 kt, increasing to 15-20 kt with 25-30 kt gusts late this morning and through the afternoon. A few gusts to 35 kt possible at KPNE- KPHL-KILG. High confidence. Tonight...VFR. CIGs lowering to 5000-7000 ft through the overnight. NW winds lowering to 10-15 kt with 20-25 kt gusts. High confidence. Outlook... Friday-Friday night... Mainly MVFR conditions expected, especially near and east of PHL. Rain showers possible. Slow improvement to VFR possible overnight especially near and west of PHL. North-northwest winds of 10 to 15 kt with gusts up to 25 kt during the day. Overnight, winds becoming northerly or north-northeasterly at 5 to 10 kt. Moderate confidence. Saturday-Saturday night... Mainly VFR, though lingering MVFR is possible early. Northeast winds of 5 to 10 kt becoming light and variable for the evening and overnight. High confidence. Sunday-Sunday night... Mainly VFR. Localized MVFR ceilings possible overnight along with a slight chance of showers. Southwest wind 5 to 10 kt, becoming more westerly late Sunday night. Moderate confidence. Monday-Monday night... Mainly VFR. Light westerly or southwesterly winds becoming light and variable overnight. Moderate confidence. && .MARINE... A tight NW pressure gradient will develop on the waters today, and SCA conditions will be in place through tonight. NW winds will range from 15-20 kt with 25-30 kt gusts on the Atlantic Coastal waters and Delaware Bay. A few gusts to 35 kt are possible at the mouth of Delaware Bay and the Delaware and southern New Jersey Atlantic coastal waters late this afternoon, but do not think gusts will be frequent enough nor widespread enough to warrant a Gale Warning. Strong winds and rough seas continue through tonight. Outlook... Friday-Sunday night... A prolonged period of continued SCA conditions is expected on the Atlantic coastal waters. North- northwesterly winds could gust 25 to 30 kt on Friday, especially early. Beyond then, winds will decrease with gusts no greater than 20 kt through the remainder of this period, so SCA flags will be able to come down for Delaware Bay. However, seas on the ocean will be very slow to subside thanks to a large offshore storm slowly departing the area. Seas will run 5 to 9 ft through the period, slowly diminishing towards Sunday and Sunday night. Monday... Conditions look to finally return to sub-SCA levels with seas 3 to 4 ft and light winds. && .FIRE WEATHER... A tight pressure gradient will develop over the area today between high pressure building in from the west and low pressure over the western Atlantic Ocean. Northwest winds will range from 15-25 mph with 25-35 mph gusts across the region. However, min RH values will range from 35-40 percent across the region, and there has been rain across the region over the last week or so. && .TIDES/COASTAL FLOODING... A large and powerful ocean storm will continue to churn offshore of the region through Friday before it finally starts to move away on Saturday. As it sits offshore it will gradually pile water up along the coast. We will also begin to draw closer to the April 7 full moon. This combination is likely to lead to coastal flooding for the end of the week, especiallly with the Saturday morning high tide cycle. Widespread, advisory level minor flooding appears likely on the oceanfront with that cycle. There is potential for a few areas to reach moderate flood stage especially in coastal southern New Jersey and coastal Delaware, though currently that looks like it would be more the exception than the rule. Coastal interests are encouraged to continue monitoring the tidal forecast over the next few days. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 7 PM EDT Friday for ANZ450>455. Small Craft Advisory until 4 PM EDT Friday for ANZ430-431. && $$ Synopsis...Davis/O'Brien Near Term...MPS Short Term...MPS Long Term...O'Brien Aviation...Davis/MPS/O'Brien Marine...Davis/MPS/O'Brien Fire Weather... Tides/Coastal Flooding...