Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 240003 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 703 PM EST Thu Feb 23 2017 .SYNOPSIS... A cold front will move into the Northeast tonight before stalling, then moving northward as a warm front Friday night. A strong cold front will move through the Mid Atlantic on Saturday. High pressure will pass through the region Sunday and Monday. A front will set up near the area for much of next week, with several lows expected to move along it. A strong low will move through the Great Lakes and southeast Canada next Wednesday and Thursday, which will pull another strong cold front through the region by late in the week. && .NEAR TERM /THROUGH FRIDAY/...
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630 PM ESTF: updated temps warmer (because too much boundary layer wind), dewpoints lower (drier sfc air may be advecting northward from e VA) and confidence on shower occurrence is below avg. Just not much going on right now with the shower risk and we are well past sundown. From the 330 PM discussion: Showers may become increasingly organized along a pre- frontal trough in our far northwestern zones of the CWA (RDG- ABE-MPO- FWN north and west) during the mid to late evening hours. A slight chance for thunderstorms was also mentioned for these far northwestern zones given the potential for slightly elevated convection to tap into 400-700 J/kg of MUCAPE. This activity will weaken overnight. the clouds may dissipate by early morning, allowing for at least patchy dense fog to develop closer to sunrise, particularly where it rains. The S-SWly wind field at the top of the boundary layer looks slightly stronger tonight compared to last night, which favors more stratus vs. fog compared to last night. Nonetheless, there is a potential for dense fog again late tonight in parts of the region, but suspect not as widespread, at least not in the south and central portions of our area. Objective SREF NARRE guidance is significantly less robust than what we saw at this time last evening for this past Thursday morning. Otherwise...differences this evening from last evening. The main difference...it was much warmer this afternoon (record and near record) so temp-dewpoint spreads at 6 PM were generally larger south and less north which when combined with an increased boundary layer wind, and 40s dewpoints in e VA trying to advect north, favors delayed stratus and fog formation and probably reserved mostly north of I-78.
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&& .SHORT TERM / FRIDAY THROUGH 6 AM FRIDAY/... The cold front will dissipate inland by the morning. Similar to today, the day will start with low clouds and fog. The low-level flow is forecast to be ever-so-slightly backed tomorrow (Sly) compared to today (S-SWly), which may allow the stratus to hang on an hour or two later into the day than today. Regardless, there looks to be an opportunity for temperatures to spike to near record levels in the mid to late afternoon hours with clearing skies during peak heating. Trended warmer for tomorrow (closer to the RGEM), yielding highs in the low to mid 70s south of I-78 and mid to upper 60s farther north. && .LONG TERM /FRIDAY THROUGH THURSDAY/... The long term period looks active, as several systems are likely to affect the area through the middle part of next week. At 00Z Saturday, a strong vorticity maximum will approach the Great Lakes and Ohio Valley, with a 140-kt 250-mb jet streak positioned across much of the southern U.S. As the nose of this jet enters difluent flow near the Atlantic Coast, considerable upper-level divergence will collocate with differential cyclonic vorticity advection downstream of the aforementioned vort max. Strongly forced convection will develop along an associated cold front in the Midwest moving east into New York and Pennsylvania by late Saturday morning. A downstream jet streak will develop in the high-amplitude ridging nosing into eastern Canada, providing additional lift via jet coupling to produce widespread precipitation in Quebec, New York, and adjacent New England Saturday afternoon. As the vort max impinges upon the high- amplitude ridging, it will make a shift northward, leaving our region on the southern fringes of the stronger dynamics/lift and well within the warm sector of the system. Given sufficient diabatic heating, marginal boundary-layer based instability is expected by afternoon in our area, which may act to compensate for the somewhat weaker large-scale ascent. Vertical wind profiles will be quite strong, with deep-layer shear 40-60 knots. Unidirectional wind profile and orientation parallel to the initiating boundary will support a line of convection moving through the area during the afternoon. Strength of the wind profile and steep lapse rates near the surface suggest isolated damaging wind gusts are possible as the line moves through the region. The key to the extent of this threat will be the degree to which the boundary layer destabilizes during the day and the ability for updrafts to withstand the strong vertical wind profile -- the usual players in a high CAPE-low shear environment. Today`s simulations suggest there will be a window of at least partial surface heating just downstream of the cold front, with MUCAPE near 500 J/kg during peak heating. Maintained a threat of thunderstorms in the grids for Saturday afternoon. Models have sped up the timing of frontal passage a tad, and reflected this in the grids somewhat by increasing PoPs a bit earlier in the day and decreasing them a bit more Saturday evening/night. Temperature forecast on Saturday is a big challenge, as sky cover, precipitation, and timing of the frontal passage are all highly complicating issues. I went pretty close to statistical guidance, which was generally in good agreement despite the complex scenario. Nevertheless, there is large uncertainty and potential for error for highs Saturday, which currently are around five degrees lower than the values in place for Friday. A sprawling but progressive high will move in behind the front for Sunday and Monday, so a period of dry weather and much cooler (though still near to slightly above average) temperatures are forecast during this period. By Monday afternoon, model agreement becomes quite poor. These large discrepancies exist owing to an unusually high degree of spread associated with an upper-level low digging off the California coast this weekend and progressing eastward early next week. The GFS is very quick to move a perturbation from this upper low into the central plains by 00Z Monday and to the Mid-Atlantic States by 00Z Tuesday. Widespread precipitation breaks out on the East Coast Monday night in advance of this system. The ECMWF, meanwhile, is much weaker with this perturbation and basically shows no precipitation at all with its passage, but is more aggressive in breaking out scattered/light precipitation on Tuesday afternoon/evening as isentropic ascent increases downstream of a stronger system that develops in the central plains into the Great Lakes by midweek. As the low rapidly develops and lifts into southeast Canada by Thursday, a cold front sweeps through the East Coast Wednesday night and Thursday, bringing widespread precipitation through the area. Meanwhile, the GFS moves this low/associated precipitation mostly to the north of the area. Other guidance provides little insight, as the CMC becomes a strong outlier with the depth/orientation of the longwave trough beyond this weekend, and the ensemble guidance shows that the GFS/ECMWF solutions are nearly equally plausible. As a result, broadbrushed PoPs/sky cover/temps/winds Monday night through Thursday, with generally slight chance to chance PoPs during this period. There is at least some chance for a mix of rain and snow in the southern Poconos Monday night if the GFS solution pans out. Then again, if the ECMWF solution is closer to reality, there may be no precipitation at all... Temps during this period should be well above average. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR early may become IFR toward 10z... but confidence on IFR conditions is below average except vcnty KABE. Light south wind. Please see TAFS for timing details. Showers and perhaps an isolated thunderstorm may organize ahead of a cold front this evening, possibly reaching as far southeast as RDG-ABE during the late evening or overnight (02Z- 06Z). Another round of stratus and fog is likely late tonight (after 08Z), with the potential for LIFR conditions with 2-3 hours on either side of sunrise, mainly vcnty KABE. Confidence is low for the formation of stratus and fog. NARRE objective prediction is not very impressive as compared to ydy. Friday...IFR or MVFR conds in st/fog in the morning becoming VFR during the afternoon except possible MVFR CIGS contg vcnty KACY. South to southwest wind probably gusts 18 kt during the afternoon. OUTLOOK.. Friday night...Sub-VFR conditions possible with areas of low clouds and fog. Saturday and Saturday night...Line of showers/storms likely will move through the area during the day, with gusty/erratic winds and sub-VFR conditions likely during passage. South winds may gust at times above 20 kts before frontal passage. Winds will rapidly switch to west or northwest after the front passes, with gusts above 20 kts likely. Rapid improvement to VFR after frontal passage. Sunday...VFR with winds northwest 10-20 kts with gusts to 30 kts possible. Sunday night and Monday...VFR with winds near/below 10 kts becoming southerly by Monday. Conditions may become sub-VFR late in the day as another system approaches, but this is very low confidence. Monday night and Tuesday...Potential for sub-VFR conditions with precipitation, low ceilings, and reduced visibilities possible at times. Very low confidence.
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&& .MARINE...
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A S-SW wind around 10-15 kt this evening will weaken overnight and into the morning then strengthen out of the south or southeast Friday afternoon with a few gusts near 20 kt possible. Another round of dense fog may occur over the waters either late tonight or more likely Friday. No marine dense fog advisory yet due to uncertainty regarding when the dense fog forms and how widespread it will become. There is a potential for the dense fog to persist into the daytime a few miles off the Atlantic coast. OUTLOOK... Friday night through Saturday night...Fog may again develop on the coastal waters, with at least some potential for visibilities less than one mile, as very warm/moist air remains over the relatively cold waters. A line of storms will likely move through Saturday afternoon and evening, with any fog rapidly dissipating as this occurs. Seas are expected to build to small craft advisory (SCA) thresholds on Saturday, and winds will become westerly and become gusty after cold frontal passage. Gusts may approach gale levels late Saturday night. Sunday and Sunday night...SCA northwest winds continue but should decrease below advisory thresholds Sunday evening. Monday through Tuesday...Generally sub-SCA conditions expected, though winds may approach advisory levels for a brief period Monday afternoon.
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&& .CLIMATE... **Many records today contribute to a record warm Feb and a top 10 warmest winter in the period of record for Mount Holly FA** As of 5 PM...records were set at GED 75, MPO 63, RDG 73, ABE 72 As of 5 PM...records were tied ACY 72, ILG 73 For reference, here are/were the high temperature records for today, Friday and Saturday (not including the new records so far today). Location Thursday 2/23 Friday 2/24 Saturday 2/25 ACY 72-1985 75-1985 77-1930 PHL 75-1874 74-1985 79-1930 ILG 72-1985 78-1985 78-1930 ABE 71-1985 76-1985 74-1930 TTN 74-1874 74-1985 76-1930 GED 67-1985/1990 72-1961 76-1975 RDG 72/1932/1922 77-1985 77-1930 MPO 60-1977 60-1984 70-1930 Todays February rankings were updated at 515 PM. We`ll finish the seasonal AT 6 pm. The following are the monthly and seasonal expectations. It is virtually certain that these values will be at or below reality and that our forecast area is experiencing a record warm February and a top 10 warmest winter. Records date back to the late 19th century. Details below. February: PHL 43.9 #1 Normal 35.7 Record 42.2-1925 POR 1874 ABE 38.9 #1 Normal 30.7 Record 38.6-1998 POR 1922 ACY 42.9 #1 Normal 35.3 Record 41.6-1890 POR 1874 ILG 43.1 #1 Normal 35.1 Record 42.3-1903 POR 1895 Note for ABE: There is a pretty good chance ABE will end up warmer and possibly very close to their monthly temp record. Winter (DJF) PHL 40.3 #7 and solid. It wont slip. ABE 35.8 #5 and solid. It wont slip. ACY 39.8 #9 and may rise ILG 39.4 #5 tie Past two years of monthly average temperatures through February 2017, a summary of above normal months listed below: For ABE: 23 consecutive months of above normal temps! FOR PHL: 22 of the past 23 months have been above normal. For ACY: 19 of the past 23 months have been above normal. For ILG: 17 of the past 23 months have been above normal. (Jan Feb March 2015 was the last time we had significant and persistent below normal monthly temps.) Snow: Atlantic City should end up tied for 5th least snowiest February on record 0.3" && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...CMS Near Term...Drag/Klein 702 Short Term...Klein Long Term...CMS Aviation...CMS/Drag/Klein 702 Marine...CMS/Drag/Klein 702 Climate...

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