Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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043 FXUS61 KPHI 140136 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 936 PM EDT Sun Oct 13 2019 .SYNOPSIS... A weak area of low pressure will track along a stalled front, which is south and east of our area, then it exits off the Delaware and New Jersey coasts late tonight. High pressure then builds into the area Monday and Tuesday. Low pressure and its associated fronts will approach the area on Wednesday, while a secondary area of low pressure develops offshore. Once this system moves away from our area, high pressure will build in for Friday and Saturday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 930 PM update: Ongoing warm air advection around 925 mb across Delmarva and across southern New Jersey is assisting in lift and a continuation of showers. These showers are being enhanced this evening by a 250 mb jet streak which is resulting in weak surface low pressure developing along a stalled front. In addition, jet streaks at 500 mb and 850 mb are forecast and this is expected to focus much of the showers across southern New Jersey southward. Some earlier light showers or sprinkles along the I-95 corridor have mostly exited, and guidance overall does not show much more getting this far west for the remainder of the night. Given the main forcing farther south and east, tightened up the PoP gradient in that direction. A mesoscale analysis this evening shows a lack of instability, although some weak MUCAPE is overspreading the southern areas. Held off on a thunder mention given how weak the instability is. Showers are expected to shift east and then offshore overnight. Tweaked the hourly temperature, dew point and wind grids to match the current observations and also trends. Also adjusted the cloud cover upward and farther westward given the expansion of lower clouds so far this evening. As the low lifts to our northeast overnight, the showers will come to an end between midnight and daybreak. As the low lifts to the northeast and showers ends, patchy fog should develop overnight. Widespread dense fog is not expected at this time, but visibilities could drop down to about a mile in several locations. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... Any low clouds and fog from the overnight and early morning will lift and burn off through the morning hours. Then the remainder of the day will end up pretty nice as skies begin to clear out and temperatures warm up several degrees above normal. A reinforcing cold front will swing across the area late in the day, so drier and cooler air will begin to move in late in the afternoon. Winds will also increase through the day, and may begin to gust 15-20 mph by the afternoon our of the west to northwest. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... Summary... The long term period will be characterized by quiet weather Tuesday, a period of widespread moderate-heavy rainfall Wednesday, a wind day on Thursday, followed by quiet weather Friday-Sunday. Tuesday...The extended period will begin tranquil as surface high pressure crests the area on Tuesday. Highs should be seasonable with abundant sunshine. Wednesday... The most active period of the long-term will be on Wednesday as low pressure progress eastward across the Great Lakes. At this point a secondary low looks to form over the SE US on Wednesday, with most guidance depicting this low rapidly deepening as it moves northeastward. This seems reasonable given that upper support will be quite favorable in its vicinity with the left exit region of a near 150kt upper lvl jet approaching. In terms of sensible weather expect widespread moderate rain during the day on Wednesday, initially in the prefrontal warm advection regime, and then just ahead of the cold front Wednesday afternoon. Given the deepening low and associated h850 FGEN more or less overhead Wednesday afternoon, went fairly bullish with QPF. Although there is still some uncertainty (as is common in these coastal low setups) would not be surprised to see amounts over an inch in spots (particularly over northern and eastern portions of the forecast area). Some isolated thunder can`t be ruled out but didn`t have enough confidence to include any mention at this time. Wednesday night/Thursday... Rainfall will taper off fairly rapidly off from SW to NE Wednesday night as the low speeds off to the northeast (deepening further as it does so), and drier westerly flow filters in behind it. On Thursday the main story will be the gusty westerly winds as a tight gradient will develop between the departing low and high pressure over the Mississippi valley. Right now assuming efficient mixing overland peak gusts look in the 30-35 kt range, but can`t rule out some locally higher gusts, particularly near the coast. Additionally some fairly dense stratocu will be possible in the cool post-frontal northwesterly flow over the northwestern half of the area, and can`t even rule out a few light showers over the Poconos as a backside shortwave slides down. Highs will generally generally run in the mid 50s to low 60s. Friday-Sunday... Quiet/dry weather resumes as mid-lvl ridging moves in, and surface high pressure progresses eastward. Highs Friday should be similar to Thursday, before a warming trend commences Saturday as the high slides to our east and southerly flow develops. High temperatures could reach the lower 70s by Sunday. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR ceilings lowering to MVFR this evening then to areas of IFR overnight. Showers mainly at MIV and ACY will result in MVFR visibilities at times into the overnight before ending. Some fog overnight will result in MVFR to even IFR visibilities. Southeasterly winds 4-8 knots, becoming light and variable to calm. High confidence in the winds; moderate confidence in the ceilings; low confidence in the visibilities. Monday...MVFR/IFR conditions start the day, then improving to VFR during the morning. Light and variable winds, becoming west to northwest 5-10 knots. Some gusts to around 15 knots are possible during the afternoon. Moderate confidence in the morning; high confidence during the afternoon. Outlook... Monday night thru Tuesday night...VFR with increasing clouds Tue night. Variable winds generally 5 kts or less. High confidence. Wed/Wed night...Sub-VFR conditions in steady rain expected, conditions may improve Wednesday night as rain tapers off. Winds initially from the south-southeast around 10 kts (possibly higher and gusty towards ACY) Winds then veering sharply to the west-northwest around 15 kts, behind a cold front Wednesday night. Medium confidence Thu...VFR conditions prevailing. West-northwest winds sustained 15-20 kts, gusting over 30 kts at times during the day. Medium confidence. Fri... VFR with northwest winds around 10-15kts. && .MARINE... Tonight...An area of low pressure will move across southern Delaware and Maryland, then across southeastern New Jersey this evening and overnight, before lifting to our northeast through daybreak. Winds will become variable during this time period, before shifting to the west to northwest behind the system. Winds are expected to increase and gust around 20 knots, but likely remain below advisory levels. Monday...Conditions expected to remain below advisory levels through the day, although winds could gust around 20 knots at times. Outlook... Monday night thru Tuesday night...Sub SCA expected. Mostly fair with light winds. Wednesday...SCA conditions likely as seas build to 5-7 ft by the late afternoon and SE winds gust over 25kts. Rain expected. Wednesday night/Thursday...Gale conditions possible as westerly gusts increase to near 35 kts. Seas decreasing below 5 ft by Thursday evening. Rain diminishing by Wednesday night. Friday...Winds diminishing below SCA criteria on Friday although northwest wind gusts 20-25kts will be possible, with seas around 2-3 ft. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Carr/Gorse Near Term...Gorse/Robertson Short Term...Robertson Long Term...Carr Aviation...Carr/Gorse/Robertson Marine...Carr/Robertson

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