Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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451 FXUS61 KPHI 192041 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 341 PM EST Mon Feb 19 2018 .SYNOPSIS...
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A warm front approaches tonight and lifts through the region Tuesday morning. Bermuda high pressure is then in control through Wednesday. Low pressure develops ahead of a cold front and moves through the region Wednesday night. A series of low pressure systems will then impact the Northeast and Mid-Atlantic through the upcoming weekend and into the start of the new week.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Low clouds, showers and eventually fog will fill in across the area tonight as a warm front develops and pushes across the region. A decent SW flow just off the surface is bringing in warmer and more humid air with the front. Pops will be highest across the northern areas with showers already heading for these areas attm. The models are showing that these showers will lift northward, but if the front slows, it could end up lasting longer than earlier expected. The warmer air moving in will also result in fog developing, especially closer to the marine areas. Once the showers diminish, some drizzle is possible. Somewhat low confid, with regards to when the periods of drizzle and rain will develop / end, so a rather broad brush was used with the fcst attm. Temperatures will probably not change much, a slow rise overnight if anything.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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The warm front should be north of the area Tuesday as low pressure across the Great Lakes starts to move into Canada. The steady rains will mostly by done by dawn, but still plenty of low clouds, fog and some drizzle too. We will keep a chc for showers near the shore areas during the morning however. Conditions will improve from SW to NE thru the day as drier air arrives on a SW flow. Temperatures will climb thru the day, and readings will reach the upper 60s to low 70s in many areas. These readings will be reached once the sun return, so any delay in that, may cause readings to be lower than fcst. Winds will be mostly SW at around 10 mph.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
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Bermuda high pressure is in control for much of Wednesday. SW flow behind the high continues to advect an anomalously warm airmass into the region as 1000-500 MB thicknesses climb to around 565 dam and 850 MB temps climb to around 13C. What is fairly interesting is that the 12Z/19 NAM is similar to the 12Z/19 ECMWF and the 12Z/19 GFS in terms of 1000-500 MB thicknesses and 850 MB temps, yet the NAM MOS guidance is almost 10 degrees colder than the MAV MOS guidance. Unless there is widespread fog and stratus across the region, and with SW flow, that is unlikely, so NAM MOS temps were discounted. Mixed down from 925 MB, and blended with the MAV MOS. As a result, still have highs in the upper 60s to low 70s generally north and west of the Fall Line, and in the mid to upper 70s across southeast PA, southern NJ, and the Delmarva. Several high temperature records are likely to be broken. Meanwhile, a strong cold front will be digging through the central U.S. Low pressure develops out ahead of that front, and will nose its way into the region by Wednesday evening, and then the cold front swings through Wednesday night and becomes nearly stationary over the Mid-Atlantic. There is not much in the way of mid-level shortwave energy with the passage of the front, and strong upper jet will stay well north and west of the region. Will expect some showers with it, but despite going from a warm and relatively humid airmass to a closer to seasonal airmass, not seeing the dynamics to support thunder Wednesday evening. With the front nearly stationary to our south and several mid- level shortwaves approaching from the west, can expect unsettled weather through the end of the week and even into the weekend. Although the record level warmth will be gone, temperatures will generally be above the seasonal norm. The pattern seems to alternate between the warmer air to the south and the colder air to the north. If the colder air settles in, especially north of I-80, that may result in some ice issues as the warmer air returns Thursday night and Friday morning. For now, looks like snow, but bears watching.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...CIGs will diminish thru the rest of the afternoon then remain low (IFR/LIFR) at the terminals overnight. Much of the guidance is in agreement with this scenario. Lesser confid in VSBYS with fog expected and also some -ra and dz too. Winds mostly S or SW 5 to 10 knots. Low-end LLWS with 40-45 knots at 020-025. Tuesday...Slow improvement probable. Drying from SW to NE thru the day with winds increasing behind the warm front. Timing of the improvement is highly uncertain with conditions improving last close to the shore. Winds becoming SW around 10 knots by afternoon. OUTLOOK... Tuesday night...Fog and stratus with MVFR/IFR conditions possible. Light south winds. Confidence: Average. Wednesday...Fog and stratus dissipate in the morning, giving way to VFR conditions. SW winds 10-15 kt with gusts to 20 kt. Confidence: Above average. Wednesday night...Scattered showers and patchy fog possible with sub-VFR conditions. Winds shift from SW to N around midnight. Confidence: Average. Thursday...Sub-VFR conditions possible in scattered showers. NE winds 10-15 kt. Confidence: Average. Thursday night...Sub-VFR conditions possible in scattered showers. Some rain/snow showers possible at KRDG/KABE. Confidence: Below average. Friday through Saturday...Sub-VFR conditions in showers. Confidence: Below average.
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&& .MARINE...
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Conditions will remain below SCA criteria tonight an Tuesday. Winds will be mostly south to southwest through the period with speeds 5 to 10 knots tonight and 10 to 15 knots Tuesday. Fog will become an issue as the more humid air arrives across the cold waters. We`ll mention areas of fog in the fcst for now. There is possibility for MWW and dense fog developing. We`ll hold on that for now. OUTLOOK... Tuesday night through Wednesday morning...Sub-SCA conditions. VSBY restrictions in fog likely. Wednesday...SW winds 15-20 kt, seas around 4 feet. Morning fog dissipates. Wednesday night...Seas around 5 feet early, then subsiding to 3-4 feet. SW winds turning NW late. Thursday...SCA conditions possible, at least on the ocean waters. Friday through Saturday...Sub-SCA conditions anticipated.
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&& .CLIMATE...
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Record high temperatures are possible on Tuesday and Wednesday. Tuesday, February 20: Atlantic City...70 in 1930 Philadelphia....70 in 1939 Wilmington......71 in 1930 Allentown.......68 in 1930 Trenton.........70 in 1930 Georgetown......68 in 2002 Mount Pocono....59 in 1930 Reading.........72 in 1930 Wednesday, February 21: Atlantic City...74 in 1930 Philadelphia....72 in 1930 Wilmington......70 in 1953 Allentown.......67 in 1953 Trenton.........70 in 1930 Georgetown......71 in 2014 Mount Pocono....60 in 1930 Reading.........71 in 1930 A record warm minimum temperature may be set for Atlantic City on Tuesday. The current record is 44 in 1949. The following are the record warm minimum temperatures for Wednesday, all which should be exceeded. ABE 46-1981 ACY 49-1954 PHL 49-2002 ILG 47-2002 RDG 48-1930 TTN 48-2002 The all time February max temps may be approached on Wednesday at ILG, TTN, GED RDG MPO. All the all time monthly max`s are listed below: ACY 77 2/25/30 PHL 79 2/25/30 ILG 78 2/24/85 ABE 77 2/24/17 TTN 76 2/25/30 GED 77 2/25/17 RDG 77 2/24/17 MPO 70 2/25/30 Our expectation is that ACY will exceed the previous all time record rainfall for February, by the end of the weekend. The record is 6.50 inches in 2010. #2 is 1958 with 5.98 inches. And...adding only half an inch to PHL and ILG will put both locations in the top 9 ranking for Feb rainfall. Have rechecked the monthly projection at PHL and the avg temp continues at 41.0 or 5.3F above avg which is 8th warmest on record, if it holds. Add or subtract a degree to the average/departure and the ranking changes from 3rd to 11th. The forecast 5.3F departure is ~2f warmer than the current departure. I`d expect similar for the rest of our area...a bit less in the north which will have better chances for colder air, and a bit more warming in the south where the positive departure as of yesterday was already 5F above normal, heading for 7+. So all in all it appears we`re heading for a top 10 warmest February. Last year was the warmest on record, a whopping 3+F degrees warmer than our current projection.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...MPS Near Term...O`Hara Short Term...O`Hara Long Term...MPS Aviation...MPS/O`Hara Marine...MPS/O`Hara Climate...

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