Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 311959 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 359 PM EDT Tue Mar 31 2020 .SYNOPSIS... A low pressure system crossing off the Carolina coast tonight is expected to meander off the eastern seaboard through the rest of the week. However, high pressure from the west is anticipated to build slowly across our region through Saturday, keeping our region mostly dry through this period. A weak cold front is expected to cross the region Sunday into Monday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... A potent and progressive mid-level wave is making its way across the southeastern US. The main vorticity lobe associated with this wave will pass just to the south of the forecast area overnight. At the surface, a strengthening area of low pressure will move up the Carolina coast this evening and rapidly intensify (perhaps as low as 980 mb) as it continues offshore overnight. As the low draws a bit farther north and east, the pressure gradient will increase particularly across southern Delmarva and southern New Jersey. Winds will shift from easterly to northeasterly and increase along the coast to 15-25 mph with gusts of 35-40 mph. The main axis of precipitation associated with this system is forecast to remain mostly to our south, however the shield of stratiform precip (in the form of rain) may nudge just across our southern-most areas of Delmarva, mainly across Talbot, Caroline, and Sussex Counties, where I`ve introduced some low end likely PoPs overnight. Otherwise, the area will remain mostly dry and overcast overnight. Expect low temperatures in the upper 30s to around 40 degrees. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... An upper trough axis will pivot across the area on Wednesday as a strong surface low continues pushing offshore from the North Carolina coast. Weak high pressure will begin to build toward the end of the day. As heights begin to increase toward the latter half of the day with the system departing, clouds should begin to break up throughout the day. The HRRR indicates some showers across the area during the afternoon, but this seems to be an outlier even among other CAMs, so I`ve left the forecast dry. It`ll be a breezy start to the day along and south of the I-95 corridor with higher winds and gusts along coastal areas (see Near Term discussion). Winds will subside later in the day as the surface low moves farther away from the East Coast. Expect high temperatures mainly in the lower 50s. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Overview: No significant concerns in the long term until we get to early next week, when another cold front approaches our region. Details: Thursday through Saturday...A mid level ridge is expected to build from the southern Mississippi Valley to the Great Lakes region starting mid week. The air mass should build slowly eastward with the axis of the ridge passing off the coast on Saturday. The surface low that will be crossing off the Carolina coast tonight is expected to lift north and meander just off the eastern seaboard through the week, even retrograding Thursday into Friday. The proximity of this low will keep a relatively tight pressure gradient over our region Thursday and Friday, and consequently breezy conditions are expected to continue. Sunday and Monday...The weak cold front is still expected to approach and cross our region late this weekend. In the mid and upper levels, there is a weak short wave trough which will be crossing at the same time. With relatively weak support, it doesn`t look like a significant precipitation event. The only change from yesterday is it looks like the guidance is trending later with the arrival of the front, now expected to cross our region Sunday night, which seems like a reasonable trend given how stagnant the overall pattern will be through the week. Tuesday...A mid level ridge may try to build in behind the cold front, but there is a lot of uncertainty given the lack of any well defined features early next week. Thus, have stayed close to the previous forecast. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Initially MVFR ceilings will lift to around 3kft after 00Z. Expecting mainly lower end VFR ceilings after this time, but some patch MVFR may linger for a few hours. Initially easterly winds will increase from 5-10 kts and shift northeasterly to around 10-15 kts after 06Z. Gusts of 20-25 kts possible mainly PHL and south toward the coast. Moderate confidence. Wednesday... VFR. Winds initially northeasterly will gradually shift northerly then northwesterly between 18-21Z. High confidence. Outlook... Wednesday night through Thursday night...Mostly VFR conditions expected. Northwest wind 10 to 20 kt with gusts near 25 kt during the day Thursday. Moderate confidence. Friday...Mostly VFR conditions expected, although there is a chance for MVFR ceilings to develop. Northwest wind 5 to 15 knots, becoming northeast. Moderate confidence. Saturday...Mostly VFR conditions expected with light and variable winds. Moderate confidence. Sunday...Starting with VFR conditions, though ceilings could lower to MVFR through the day. Southerly and southwesterly winds of 5 to 10 kt. Moderate confidence. && .MARINE... Conditions will quickly deteriorate later this evening into the overnight with Small Craft Advisory criteria expected area wide overnight along with winds increasing with gusts of 35-40 kts for the southern-most ocean zones. Expect seas of 6-9 feet or higher across the southern ocean zones as well. Have upgraded the SCA to a Gale Warning for the impacted areas. Winds and seas are forecast to peak around daybreak Wednesday then slowly diminish throughout the day. Outlook... Wednesday night through Thursday night...SCA conditions are expected. On Thursday, there may be a brief period of gale force gusts on the Delaware and southern New Jersey coastal waters, but confidence in this is low at this time. Friday through Sunday...SCA conditions are expected, primarily on the coastal waters due to elevated seas. && .TIDES/COASTAL FLOODING... The strengthening East to Northeast flow across the waters this evening and overnight will create favorable conditions for the enhancement of the tides the next few cycles. We have updated the TWL forecasts early this afternoon to catch the latest guidance and show these updated trends. It appears the the present tide cycle up Delaware Bay may affect Reedy Point with that site reaching the `low- end` range minor flooding. The overnight cycle (after midnight) could affect more (DE and srn NJ) coastal and Delaware Bay sites with action stage to possibly low end minor flooding. At this point, an advisory doesn`t appear warranted, but we will continue to monitor overnight in case anything changes. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ450>452. Gale Warning until 6 PM EDT Wednesday for ANZ453>455. Small Craft Advisory until noon EDT Wednesday for ANZ430-431. && $$ Synopsis...Johnson Near Term...Staarmann Short Term...Staarmann Long Term...Johnson Aviation...Johnson/Staarmann Marine...Johnson/Staarmann Tides/Coastal Flooding...O`Hara is the U.S. government's official web portal to all federal, state and local government web resources and services.