Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 242124 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 424 PM EST Sat Feb 24 2018 .SYNOPSIS...
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An east west warm front extending from just south of Delaware into central Virginia will edge up into southern New Jersey Sunday morning where low pressure will develop on this front and move to eastern Long Island by evening. The trailing cold front may stall in the Carolinas on Monday awaiting the passage of another wave of low pressure to our southeast. Strengthening high pressure builds into the mid Atlantic states Tuesday. A cold front will drop down through the region on Wednesday night while low pressure develops over Illinois. That low slides to the mid Atlantic coast by Friday morning, then intensifies into a strong storm over the western Atlantic Friday night before heading only slowly out sea over the weekend.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... The entire area remains north of a warm front through the overnight hours as low pressure moves well to our northwest. Several short wave disturbances will lead to areas of showers, which will be most pronounced along a line roughly from Cecil County MD to Northern Ocean County NJ and points north, where isentropic ascent along the 290K surface is most prevalent. We are expecting one half to three-quarters of an inch of rainfall across this area through daybreak. Fog and low clouds will redevelop again overnight, with the potential for dense fog, especially over portions of Delmarva. Temperatures will be steady or rising through the night. Northeast winds 10 to 20 mph. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... The warm front will make progress north late in the morning and into the afternoon hours, roughly from Chester County PA to Ocean County NJ. Fog will likely linger into the morning hours, and may be dense, especially over portions of Delmarva.Precipitation will gradually taper off during the afternoon, especially to the south of the front, where the sun may make an appearance from time to time. There is some weak instability in the warm sector, but not enough to include thunder in the forecast, which is in agreement with SPC. Temperatures south of the front into the 60s, with some lower 70s possible across southern Delmarva. Further north, mid-50s to mid-60s are expected. Southwest winds could gust up to around 20 mph in the warm sector. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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Hazards: None explicitly attm and maybe there wont be as many as currently possible in the Thursday-Saturday time frame but potential exists for a powerful storm. A small stream hydro hazard may develop somewhere in the CWA Friday, and possible winter wx hazard for elevations of ne PA and nw NJ, a coastal flood hazard appears likely but we just dont have any confidence on severity. For now minor tidal inundation flooding expected for at Thursday and Friday morning high tide cycles, with at this time the higher departures (flooding potential) expected in NJ, but always depending on the position of the western Atlantic cyclone as well as its intensity. A Gale event, the first 2 hour or longer gale since Feb 5, is expected but we just dont know when. It will again be dependent on the latitude of the cyclone. Its even possible storm force gusts could occur. 500 mb: a short wave in the central plains Sunday night will cross the Mid Atlantic coast Monday evening with east coast ridging to follow during mid week. Then a weakening closed low in the desert southwest Tuesday night starts reenergizing in the Ohio Valley Thursday, becoming a large cyclonic circulation system along the mid Atlantic coast Friday, and slowly weakening seaward next weekend. Temperatures: Please see the climate section for updated February climate stats. Calendar day averages should be nearly 10 degrees above normal Monday, Tuesday and Wednesday, 10 to 15 degrees above normal Thursday, before cooling to between 5 and 10 above normal Friday and 5 degrees or less above normal next Saturday. Forecast basis: Unless otherwise noted, a 50 50 blend of the 12z/24 GFS/NAM MOS will be used Sunday night - Monday night, the 12z/24 GFS MEX MOS for Tuesday, and the 15z/24 WPC 12 hr elements of max/min temp and pop, as well as 6 hourly dewpoint/wind/sky for Wednesday- Saturday. I did modify WPC using 1/3 WPC, 1/3 EC and 1/3 GGEM max temps Thursday and Saturday. The dailies... Sunday night...Variable cloudiness. There may be some leftover evening stratus near and N of I78 during the evening, then that should clear to reveal cirrus but there could be some patchy fog later at night due to an expected decoupled northwest wind. Confidence: Average. Monday...Northwest wind gusts 15 mph during the day and possibly 15 to 20 MPH at night as instability transfer deepens with cold air advection aloft. Expecting considerable mid and high cloudiness into early afternoon Monday then clearing late in the day and at night. The short wave may spread a little rain northward into far southern DE for a time during the day. Confidence: Average. Tuesday...Sunny and beautiful! Light wind. Confidence: Well above average. Wednesday...Partly sunny (lots of cirrus) and a few degrees warmer. Southwest wind may gust 20 mph in the afternoon. Confidence: Above Average. Wednesday night-Thursday...In association with either a cold frontal passage or a warm front extension east-southeastward from the developing Midwest low pressure system, rain will be developing either late Wednesday night or Thursday. It may become heavy in the afternoon. Winds becoming east. Confidence: Below average on any details. Friday into Saturday...Probably gusty northerly winds and periods of precipitation. As of now, rain most of Friday and thereafter unknown, but potential exists for some elevation snow. Confidence: below average Please see the WPC Day 7 winter wx outlook graphic and their day 4-7 qpf graphics issued this Sunday afternoon to gain further appreciation for the upcoming modeled-outlooked potential.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This evening...Ceilings: VFR conditions initially, except at ACY and MIV, with occasional MVFR elsewhere in rain showers. Winds either light and variable or out of a north-northeast direction around 5 knots. Confidence: High. Tonight...Ceilings will lower to IFR at all TAF sites, with LIFR possible later tonight, especially in rain showers. There will also be visibility restrictions as fog redevelops. Winds becoming East-Northeast and increasing to 10-15 knots. Confidence: Moderate. Sunday...Ceilings in the IFR to LIFR range during the morning will slowly improve, with MVFR possible during the afternoon. There will also be visibility restrictions with lingering fog in the morning. Some improvement, especially at ACY and MIV, which have the greatest potential for MVFR in the afternoon. Confidence: Moderate. Outlook... Sunday night...There may be some leftover IFR conds in stratus during the early evening, but probably improving to VFR cirrus by midnight. Any rain showers will quickly end by 9 PM. Patchy IFR fog is possible late at night vicinity KRDG, KABE, KTTN, KMIV. Northwest wind. Confidence: average. Monday...Probably VFR bkn clouds aoa 8000 ft, clearing late. Northwest wind gusting 15-20 kt, especially late day. Confidence: above average. A little concerned about low pressure forming vcnty N Carolina and spreading rain into southern DE for a time during the morning. Tuesday...VFR virtually clear. Light wind. Confidence: well above average. Wednesday...VFR cirrus. Southwest winds may gust 20 kt during the afternoon. Confidence: Above average. Thursday...Conditions should deteriorate to MVFR or IFR in rain. east to southeast wind. Confidence: Average.
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&& .MARINE...
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SCA for winds and seas remains up on the Atlantic Waters for Sunday. There is a low potential of a SCA for Delaware Bay as southwest winds increase during the late morning into the afternoon hours. A Dense Fog Advisory is in effect until 7 PM tonight for the Atlantic Waters off southern NJ and Delaware. This may need to be extended into the overnight hours. Dense fog is possible across all of the Atlantic Waters on Sunday. Outlook... Sunday night...Lingering SCA seas possible, mainly the NJ Atlantic coast. Have reduced the duration of the SCa. Confidence: Average. Monday through Wednesday...Sub-advisory conditions are expected on the area waters with northwest winds gusting 15-20 kt Monday becoming light Tuesday and southwest on Wednesday. Confidence: Average. Thursday...an easterly SCA likely with a possible Gale for the NNJ waters. Confidence: Average.
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&& .HYDROLOGY...
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Periods of rain through the weekend could result in minor and poor drainage flooding. The heaviest rain is expected Saturday night and Sunday, when up to additional inch of rain will fall. By the time the rain ends Monday morning, the region will have received between 1 and 2 inches of rain since Thursday, with the highest amounts falling over the northern third of the forecast area. By Sunday night and Monday, there will be rises on areas rivers and streams, with some possibly approaching bankful. Of note will be how much rain falls over the Susquehanna, as there is the potential for inconvenience flooding below the Conowingo Dam on Monday. We may need to think about a new hydrology section for late this coming week to cover NJ/PA but just too far in advance with plenty of uncertainty to add any confidently stated information, except that a fairly potent weather pattern appears to evolving for a portion of our forecast area.
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&& .CLIMATE...
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**Top 3 warmest February on record and top 10 wettest February on record.** February projected climate ranking as of Noon today-Saturday Feb 24, based on our mid shift fcst through the 28th and mins this Saturday morning; and for rainfall, amounts 1201 AM today. RDG and TTN not included due to too much missing data. ABE #3 warmest 38.0 or 7.3F warmer than the 30.7 norm. 39.2-2017 38.6-1998 38.0-2018 36.8-1954 ACY #1 warmest 42.7 or 7.4F warmer than the 35.3 norm. 43.0 -2017 42.7 -2018 40.6 -1954 ILG #3 warmest 41.3 or 6.3F warmer than the 35.0 norm. 43.1-2017 42.3-1903 41.3-2018 41.2-1976 PHL #3 warmest 42.5 or 6.8F warmer than the 35.7 norm. 44.2-2017 42.5-2018 42.2-1925 41.8-1998 41.4-1890 Water equivalent February pcpn as of 1201 AM today. PHL ranked #10 with 5.30". An additional .50 would raise to #5. All time 6.87-1896 ILG ranked #8 with 5.48". An additional .50 would raise to #5 All time 7.02-1979 ABE ranked #13 with 4.47". An additional .50 would raise to #5. All time 7.62-2008 ACY ranked #2 with 6.12". Wettest is 6.50-2010. Our expectation still is that ACY will exceed the previous all time record rainfall for February, by the end of the weekend. It could be a close though.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 7 AM Sunday to 2 AM EST Monday for ANZ452-453. Dense Fog Advisory until 7 PM EST this evening for ANZ430-431- 453>455. Small Craft Advisory from 4 AM Sunday to 7 AM EST Monday for ANZ450-451. Small Craft Advisory from 7 AM to 6 PM EST Sunday for ANZ454- 455. && $$ Synopsis...Drag 423 Near Term...CMS/Franck Short Term...CMS/Franck Long Term...Drag 423 Aviation...CMS/Franck 423 Marine...CMS/Franck 423 Hydrology...423 Climate...423

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