Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 261401 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1001 AM EDT Wed Oct 26 2016 .SYNOPSIS... High pressure centered in eastern Canada today will shift eastward tonight and Thursday. Low pressure is then forecast to track from the upper Ohio Valley tonight eastward to southeastern New England Thursday night. This will pull a warm front across our area Thursday morning, following by a cold front Thursday night. High pressure briefly builds in during Friday before shifting to our south over the weekend. Low pressure and an associated cold front should then move through later Sunday with high pressure returning Monday into Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure centered over southern has been building slowly southeast across the mid-Atlantic region overnight and into this morning. The air mass aloft is rather dry with generally downward VV resulting in mostly clear skies for today. Some high level clouds to the west may begin spreading into east PA and vicinity this afternoon. With limited heating from the late October sun, current temps seem on track to reach forecast highs in the lower to mid 50s this afternoon, except for 40s in far northwest NJ and the Poconos. With overnight temperatures below freezing in many locations, the growing season is judged to be over for the following counties. In Pennsylvania: Berks, Lehigh, Northampton, Chester, Montgomery and Bucks. In New Jersey: Morris, Hunterdon, Somerset, Ocean, Burlington, Camden, Gloucester, Salem, Cumberland and Atlantic. Growing season ended earlier this month for Carbon and Monroe counties in PA, and for Sussex and Warren counties in NJ. No additional Frost Advisories or Freezing Warnings will be issued for these areas.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... The low will continue to track further east overnight, reaching north central or northeastern Ohio by morning. Still quite a bit of uncertainty as to how far east the precip shield will move overnight. At this point, think it will mostly be confined to the Poconos in our region. Mid level clouds should move over the region by late this evening, which should help to limit radiational cooling. In addition, surface winds will be northeasterly by this time which could further limit radiational cooling. NAM MOS and GFS MOS seem to be downplaying these factors with lows much lower than the deterministic models. I went a bit above the MOS guidance as I do think these factors should lead to temps being a bit higher than what we are seeing this morning. Still, locations in the Poconos and NW NJ could drop below freezing. Based on the latest model soundings, it looks to be more of a rain or freezing rain event (depending on the surface temperature at the time that precipitation begins), though can`t rule out some snow mixing in. For more details on precipitation type, see the long term discussion. && .LONG TERM /THURSDAY THROUGH TUESDAY/... The synoptic setup is comprised of a trough that amplifies across the Northeast during Thursday before exiting on Friday. An active but progressive pattern looks to be in place, therefore a ridge quickly moves across the area to start the weekend before the next trough arrives. This trough should also amplify as it arrives in the Northeast Sunday but then exits Monday. Some ridging is then forecast to return Monday into Tuesday. The forecast challenge is mostly centered on Thursday as strong warm air advection with a warm front will be clashing with lingering cold surface high pressure to the north and northeast. This should keep in colder air for a time in the lowest levels across the north, opening the door for a period of mixed precipitation. For Thursday and Friday...A potent short wave will amplify an upper- level trough from the Great Lakes to the Northeast during Thursday before shifting east Friday. This will drive surface low pressure from the upper Ohio Valley to start Thursday then to the southeastern New England coast Thursday night and Friday morning. The associated wind fields will respond and enhance the downstream warm air advection. It still looks like a decent shot of overrunning precipitation overspreads at least the northern half of the area during the morning hours, on the nose of a 40-50-knot 850 MB jet. As this occurs, strong high pressure at the surface to the north will gradually give way however it will keep some cold air trapped for a time in the lower levels. This should allow for a wintry mix to occur mainly across the Poconos to far northwestern New Jersey, although if the precipitation arrives fast enough then some brief mixing may occur into the Lehigh Valley. The forecast soundings indicate mostly a sleet/freezing rain to rain scenario, however there is a decent amount of dry air in the lowest levels to start. This may allow for enough cooling of the column initially for snow to occur at the onset. The warming does look quick though therefore we continued with the idea of any snow to quickly change to sleet or freezing rain then to rain. Any accumulations of snow/sleet and freezing rain look to be light. The extent of the cooling into early Thursday morning will depend on how fast the clouds increase and thicken. Given the idea of some icing, a winter weather or freezing rain advisory may be needed for the far northwestern zones. However given some uncertainty with the timing we held off for now. Farther to the south, there may not be much rain for awhile Thursday until a cold front arrives late in the day. Overall though the precipitation may become more showery through the day. Some instability looks to develop during the course of the day especially for the southern areas, however the prospects of deeper convection looks low given marginal instability and weak mid level lapse rates. Therefore no thunder was included at this time. The cold front crosses the area Thursday night with some cooling taking place and some increase in the winds. For Friday, surface low pressure is forecast to strengthen as it tracks to the northeast from coastal New England. This will allow for a tightened pressure gradient and as mixing improves, Friday should feature a gusty northwesterly wind (which then diminishes early in the evening). For Saturday and Sunday...Some upper-level ridging migrates across the area with surface high pressure centered to our south. A trough in the Midwest will slide eastward with downstream warm air advection occurring. This will send a warm front north of our area later Saturday, then a surface low generally tracks just to our north later Sunday pulled a cold front across our region. We should be within the warm sector as a result, with a surge of much warmer air Sunday ahead of the cold front. If thicker clouds and any showers can hold off then Sunday could feature temperatures well into the 70s for a good part of the area especially from the I-95 corridor on south and east. This could be held back some though given the potential for the cold front to arrive during the afternoon and cap the overall warming. Much of the forcing looks to be tied along and north of the surface low track, with perhaps a broken band of showers with the cold front. At this point, instability looks to be low enough and therefore thunder was not added to the forecast. Cooler and breezy conditions arrive behind the cold front. For Monday and Tuesday...As a trough shifts east to start Monday some ridging arrives. This allows surface high pressure from the north to build across our area Monday before shifting offshore Tuesday. A similar setup looks to be taking shape for Tuesday as low pressure tracks up across the Great Lakes sending a warm front to our north later Monday, then a cold front arrives Monday night into Tuesday. Given the general quick progression of the systems, moisture return may tend to be limited and therefore any POPs were kept on the low side. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions should continue through at least 09Z. Increasing clouds, and ceilings lowering to 10K ft AGL are possible after 00Z. After 09Z, lower clouds and precip will start to move in from the southwest. Through 12Z, only KRDG and KABE have a risk of seeing precip, and with it possibly MVFR ceilings and visibilities. Winds will be light...less than 10kt, but wind direction will shift from northwesterly through much of the day today to northeasterly this evening. Outlook... Thursday...Conditions lower to MVFR or IFR with a period of rain moving across the area. The greater chance of a steady rain is near and north of KPHL. A wintry mix should occur in the morning north of KABE. The rain tapers off in the evening with conditions improving to VFR. Southeast winds near 10 knots Thursday shifting to west- southwest early in the evening, then becoming northwest 10-15 knots and potentially gusty during the night. Friday...VFR overall. Northwest winds 10-15 knots with gusts to about 25 knots, diminishing early in the evening. Saturday and Sunday...Generally VFR. A cold front moves through later Sunday with a wind shift to the northwest. && .MARINE... Along the coastal waters, gusts above 20 kt will be possible through the morning, but should remain below SCA criteria and continue to decrease through the day. On the Delaware Bay, winds should generally stay less than 20 kt. Seas should be below SCA criteria today and tonight. Outlook... Thursday and Friday...Southerly flow increases Thursday with a warm front with advisory conditions looking to be reached later in the day. There is a window of opportunity Thursday evening where gusts could reach gale force as a low-level jet moves through, however this is during a warmer airmass which may limit the mixing. Small Craft advisory conditions should continue at night and Friday behind a cold front as cooler air moves in. The winds and seas should then settle Friday night. Saturday and Sunday...The conditions are anticipated to be mostly below Small Craft Advisory criteria. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...None.
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&& $$ Synopsis...Gorse Near Term...AMC Short Term...Johnson Long Term...Gorse Aviation...Gorse/Johnson Marine...Gorse/Johnson is the U.S. government's official web portal to all federal, state and local government web resources and services.