Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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634 FXUS61 KPHI 171745 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1245 PM EST Wed Jan 17 2018 .SYNOPSIS... Low pressure will move into the Canadian Maritimes today. High pressure will build across the Gulf coast through the end of the week, then offshore over the weekend. An area of low pressure will move across eastern Canada over the weekend as a back door cold front approaches from the north. Another area of low pressure will move through the Great Lakes Monday night into Tuesday, pulling a cold front across the area. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Snow has mostly ended across the area, with the exception of the NJ shore and southern Delaware. We may continue to see very light snow move into these areas until the mid and upper level low, moves further east into the Carolinas this evening. With the cold front earlier this morning, temperatures will continue to slowly fall through the afternoon. Northwesterly winds of 10 to 15 mph are expected to continue through the afternoon && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... The low is forecast to move across Canada`s Maritime Provinces tonight as high pressure begins to nose into our region from the west and southwest. We are anticipating a mostly clear sky along with a northwest to west wind around 5 to 10 MPH. Cold temperatures will return for tonight with lows mostly in the teens. Single digit readings are possible in the Poconos and in far northern New Jersey. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Main focus of the long term is the warmup late this week through this weekend and a storm system moving through the region early next week. Most of the focus today was on the first 36 hours of the forecast, so overall made few changes from the previous shift. Trough axis swings through the Eastern Seaboard Wednesday night, with a broad surface high building into the Mid-Atlantic and Southeast for the rest of the week into the weekend. After a small- scale perturbation moves through the Northeast Thursday night (which should be dry), midlevel zonal flow will be present Friday through the weekend, allowing the surface high to slide eastward and promoting southwesterly surface flow to develop east of the Appalachians this weekend. This pattern will result in a lengthy dry period and a distinct warming trend after a chilly Thursday (when heights/thicknesses will be lowest, owing to the proximity of the trough). Forecast highs are in the 50s for Philly this weekend, based on a consensus blend of statistical guidance...though I leaned a little on the higher side of consensus given the tendency for MOS to be on the low side in warming patterns. Operational models develop a strong surface cyclone in the central plains this weekend (with downstream ridging further contributing to warmth Sunday and Monday in our area) before lifting it rapidly northeastward into the Great Lakes and adjacent southeast Canada early next week. A strong cold front will progress through the East Monday and Tuesday, with showery precipitation developing near the front. Temperatures will likely be warm enough for liquid in most locations for the event, with the exception being the far northwest CWA during the precip`s waning stages. Regarding timing, models generally agree on Monday afternoon through Monday night. Given such good agreement this far out, boosted PoPs to high chance or likely during this time frame. The greater uncertainty lies with the intensity of the precipitation (given the southern origins of the system and the warmth it advects downstream, there is some potential for decent precipitation totals, especially if embedded convection can develop), extent of cold air on the upstream side of the system (i.e., precipitation type issues as the system departs), and the speed with which the precipitation moves out before the colder air moves in. As previously mentioned, did not change the details during this time frame too much, but my initial thoughts were to go on the warm side and on the quick side given typical model biases with northeast- progressing inland surface lows originating from the southern/southwestern U.S. By midweek, temperatures will be slightly cooler, and conditions should dry out. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...With the exception of localized low clouds and visibility restrictions at KTTN, KACY, and KMIV, the rest of the TAF sites have returned to VFR conditions and should remain there for the rest of the TAF period. Northwesterly wind of 10 to 15 knots is expected through the afternoon. High confidence. Tonight...VFR with a mostly clear sky and a northwest to west wind at 5 to 10 knots. High confidence. OUTLOOK... Thursday through Sunday...VFR. West to southwest winds; winds may gust 15-20 knots at time. High confidence. && .MARINE... A northwest wind is expected to increase to 15 to 20 knots today with gusts of 25 to 30 knots. As a result, a Small Craft Advisory is in effect for today and tonight. OUTLOOK... Thursday...Small Craft Advisory extended through the day Thursday as winds expected to gust to 25 knots. Thursday night...Conditions expected to drop below advisory levels. Friday-Sunday...Conditions expected to remain below advisory levels, but winds may periodically gust around 20 knots. && .EQUIPMENT... The NOAA All-hazards weather radio transmitter in Sudlersville remains off the air as technicians continue to work on phone line issues. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ450>455. Small Craft Advisory until 10 AM EST Thursday for ANZ430-431. && $$ Synopsis...AMC Near Term...Iovino/Johnson Short Term...Iovino Long Term...CMS/Robertson Aviation...Iovino/Johnson/Robertson Marine...Iovino/Robertson Equipment...

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