Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 130555 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1255 AM EST Fri Jan 13 2017 .SYNOPSIS... A cold frontal boundary will move into region tonight and settle south of the region for the weekend. High pressure will also build into the Great Lakes this weekend and move eastward through New England on Monday. Another low pressure system will track from the Southern Plains into the Great lakes for the early and middle part of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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The cold front is right on our western doorstep and will continue to push through our area, reaching the I-95 corridor overnight and coastal locations just before sunrise. The showers have started to fall apart as they push towards the coast but a few scattered showers will continue to over the next few hours.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... Minor adjustments were made to the temperatures for Friday based on the latest guidance. High temperatures for the calendar day are likely to occur prior to the fropa (around or just after midnight). For the daytime tomorrow, CAA will mostly offset daytime heating, so temperatures will generally remain steady during peak heating. Daytime highs range from the mid 30s in the southern Poconos to the mid 50s in southern Delaware. Previous Discussion... As the cold front progresses south of the area tomorrow, breezy northwest winds will develop across the area. Temperatures will struggle to climb from early morning readings, and daytime high temperatures will likely be well below readings seen at midnight. Skies will rapidly clear after cold frontal passage, but this will be short-lived as the next vort max in the Ohio Valley begins to approach the region, with associated upper-level lift increasing. High clouds are expected to move into the region by late in the day. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Friday night through Monday: High pressure will be located over he Great Lakes with waves of low pressure moving west to east along a frontal boundary in the Mid- South. Moisture will ride north of the boundary as well leading to the development of overruning light precipitation with each wave of low pressure. The first area of low pressure will track to our south in the Saturday timeframe. Right now it appears the best lift for light precipitation development will be across northern Maryland into the Delmarva. This light precipitation is likely to break out from southwest to northeast on Saturday. However, a fairly substantial dry layer around 3,500 feet up in atmosphere will likely mean virga will occur for a while across the region for a good portion of the day. A sharp gradient of where precipitation occurs over northern part of the forecast area will likely be present as well. High pressure will start to shunt the overruning moisture along the boundary further south allowing for clearing conditions over most of the region with continuing periods of light precipitation in Delmarva through Sunday night. The frontal boundary will then surge northward as a warm front Sunday night and Monday with a chance for some additional light mixed precipitation. Precipitation type as has been all winter gets a little more complicated. Typical model bias at this range is for the data to be cold in the mid-levels and to warm at the surface. Overall, these biases lead to higher prospects of ice as we get closer to an event. The NAM and GFS are more prominent with a warm layer surging toward Philly and ACY in the 850-925 mb range with the ECMWF only taking the warm layer into the Delmarva. This warm layer would allow for sleet and freezing rain to mix in with the light snow. Temperatures as well could rise a few degrees above freezing in Delmarva allowing for a change to rain. Right now total precipitation looks to be around a tenth of inch through Saturday night from a Reading to Toms River line and points south. A few hundredths of an inch of additional precipitation currently looks to fall for the remainder of the weekend into Monday. Around an inch of snow could fall on a Reading to Toms River with lower amounts further south due to mixing. Minor ice accumulations could occur throughout the weekend as well. Temperatures should be in the 20`s and low 30`s through Saturday, at or a little cooler than MET/MAV/ECMWF and then fairly close to the model data for the remainder of the weekend. Will have to watch to see how long it takes to scour out the low level cold in the Southern Poconos and Northwest New Jersey on Monday. Monday night through Thursday: A low pressure system will track into the Great Lakes with a surge of warm air advection. A CAD situation is showing up on the models on Tuesday which will likely delay the warm-up till Wednesday. A chance of rain showers is present as the warm front on tuesday, with additional chances of rain Wednesday and Thursday with a front nearby and warm moist air being advected northward. Temperatures have the potential to be 20 degrees above normal Wednesday and Thursday with a frontal boundary to our northwest. Long term ensemble guidance is likely underdoing the warm-up at this point given biases to stick closer to climatology that far out. Longer term: Temperatures should continue well above normal in the 8-14 day as a trough moves into the west coast and Alaska (+ EPO, - PNA) that will result in height rises along the east coast bringing warm air northward. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Gusty SW winds have started to diminish this evening as the cold front approached from the west. Fropa is expected to occur from NW to SE between 06Z- 09Z and is marked by a wind shift out of the NW. Some light showers continue to move through the area in advance of the fropa. The showers have been decreasing in coverage over the past couple of hours but a very brief shower remains possible through 08Z. Some MVFR ceilings may develop just in advance of and along the fropa but should quickly clear out of the terminals as the wind direction shifts to the northwest. Best chances for MVFR conditions are at KABE and KRDG where steadier rain was reported earlier this evening. Today should be VFR with breezy northwest winds 10-20 kts with gusts up to 25 kts. Winds will gradually diminish by late in the afternoon, then we should lose the gusts toward sunset. Ceilings are expected to lower towards the end of the TAF period as the next system arrives. OUTLOOK... Saturday through Saturday night: Visibilities and ceilings lowering to MVFR/IFR Saturday into Saturday night due to light snow developing. Possibly a wintry mix for KILG, KACY and KMIV. Winds 10 knots or less. Sunday and Sunday night: Lingering light mixed precipitation for KILG, KMIV and KACY with MVFR/IFR, improvement elsewhere. Winds under 10 knots. Monday through Tuesday night: MVFR/IFR throughout most of this period. A light wintry mix Monday morning changing to light rain. Winds under 10 knots.
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&& .MARINE... Will likely let SCA expire at 10 PM for the DE Bay. SW winds had increased this evening with the arrival of the SW low-level jet. Winds at SJSN4 were around 25 kt at 9 PM. The low-level jet will progress downstream of the area over the next hour or two and wind speeds should accordingly decrease to below SCA criteria. The SCA headline for the coastal waters was left as is but the wording was updated to reflect the higher wave heights that are have been observed early this evening (generally 5-7 ft; buoy 440025 reported 8.5 ft late this afternoon). Wind grids were also tweaked a bit to cap peak gusts in the 24-27 kt range (previously was 28-32 kt) this evening. As discussed previously, SW winds will weaken overnight and may drop below 25 kt for a period late tonight. A wind shift from the NW is expected behind a cold front early in the morning. NW winds will become gusty again during the day on Friday. The strongest wind gusts of 25-30 kt are most likely to occur mid to late morning. The SCA is in effect until 6 PM Friday for the coastal waters but it may be able to be cancelled earlier as the winds gradually weaken during the afternoon. Seas are forecast to drop below 5 ft by the afternoon as well. OUTLOOK... Sub-SCA conditions expected. Highest winds will be Saturday, around 15 knots on the ocean. Seas will fairly low of only a foot or two throughout the period. && .TIDES/COASTAL FLOODING... Model guidance continues to show low tides tonight approaching blow out tide thresholds. With the full moon today, astronomical low tides will be between -0.75 and -1.5 ft MLLW. Additionally, the southwest winds expected before low tide tonight are not optimal for blow out tides. Therefore, we still expect the total water level to stay above blow out tide thresholds. && .CLIMATE... Record high temperatures occurred today at Atlantic City, Wilmington and Reading (tied). Record Event Reports (RER) have been issued with some more details. Allentown and Georgetown missed their record highs by one degree. Another round of very warm temperatures is likely to occur next Wednesday and Thursday but potential cloud cover and CAD may limit the degree of the anomalous warmth. Will post records if the full potential of the warm up looks to transpire. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ450>455.
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&& $$ Synopsis...Gaines Near Term...Klein/Meola Short Term...CMS/Klein Long Term...Gaines Aviation...Gaines/Klein/Meola Marine...Gaines/Klein Tides/Coastal Flooding... Climate...

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