Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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848 FXUS61 KPHI 010242 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 942 PM EST Wed Nov 30 2016 .SYNOPSIS... Low pressure moving eastward across the Great Lakes into New England will drag a cold front through our region overnight. This low pressure will elongate and move slowly north through New England and Atlantic Canada through Friday night. High pressure over the Ohio Valley on Saturday will move into the mid-Atlantic on Sunday. Meanwhile, a complex low pressure system stretching from the midwest to the Gulf of Mexico will impact our weather during the early into perhaps the middle of next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... It appears that we will have at least two more rounds of showers and thunderstorms. One ill-defined line moving into western portions of our region now. A second area over western and central PA is just ahead of the cold front. As for the thunderstorm potential, we did have one cell that produced occasional lightning earlier (has since weakened), but it appears that the warm front has stalled, so do not expect any increase in the instability. Therefore, kept mention of isolated thunderstorms, but it will remain the exception, most of the precip should just be showers. Showers will clear out behind the cold front, mainly after midnight and from west to east. Dense fog will be possible again tonight, especially in advance of the cold front and possibly just behind the front before the winds start to pick up. Westerly winds will become breezy overnight and persist through early morning. A mild night temperature-wise as lows will range from the 40s to lower 50s across the region. Adjusted the temps slightly with this update now that it looks like the warm front will likely not make much more progress north. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... The front exits offshore and conditions should clear out fairly rapidly. Relatively clear skies with breezy conditions are expected through the day Thursday. Clouds will push into our northwestern zones by the afternoon and there will be partly to mostly cloudy conditions expected in those areas. Cooler air will start to make its way to the region but overall near normal temperatures are expected with highs in the 50s across the area. The strong northwest flow will allow for lake effect precipitation to develop but the flow across our area will become more westerly (as opposed to northwesterly) which should prevent any precipitation from making its way into our forecast area. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... Overview... A cyclonic flow aloft will be maintained over the region through at least Friday, w/Friday night being the inflection point/transition to an anticyclonic flow. Mid-level ridging will be prominent across the area through Saturday night, with the eventual breakdown of the ridge and subsequent unsettled weather being the primary source of uncertainty for the remainder of the long term. This uncertainty derives from the models` handling of multiple shortwave impulses over the midwest, and the resultant degree of phasing between the northern and southern streams. There are two camps of model solutions for Sunday and beyond: GFS /UKMET/Canadian, and the Euro. The GFS/UKMET/Canadian show minimal stream phasing, which leads to a flatter eastern conus ridge, and allows a quick moving clipper-like system to move through the mid Atlantic Sunday into Monday. The Euro/Canadian indicate a more robust phasing between the streams, leading to a higher amplitude eastern conus ridge, and a primary storm system moving from the lower Mississippi Valley on Sunday to the mid Atlantic in the Mon- Tue time frame. A look at both the ECENS and GEFS ensemble means tell a similar story to the operational runs, with no additional clarification as to which of the two solutions may be favored. Given the degree of model disparity, it`s also unrealistic to compromise between the extremes. Per WPC, the operational ECMWF appears to be the outlier, so this forecast will lean more toward the GFS/UKMET/Canadian camp. The end result is the best chance of precip focused in the late Sunday into Monday period. Temperature-wise, dailies will not stray too far from their climatological means, ending up near normal. Daily details... Thursday night through Saturday night... The cyclonic flow aloft will eventually transition to shortwave ridging over the region by Saturday. Friday is shaping up to be a nice day with dry weather. Cannot rule out patchy fog Thursday night in the normally prone locations where the boundary layer decouples more, especially given the recent rainfall. With the cyclonic flow aloft and westerly downsloping flow off the Great Lakes, expect extensive stratocumulus across the far northwest, otherwise mostly sunny. By Friday night, a shortwave swings by just northeast of the area, with little in the way of moisture and lift. Just an increase in cloudiness expected, in addition to the upper jet cirrus over the area. On Saturday, similar to Friday in terms of sky conditions. Cannot rule out a flurry in northwest NJ and the Poconos, given greater low-level moisture and instability across this area. Sunday... Clipper-type system approaches the region, but enough short- wave ridging should be maintained aloft to stave off precip during the day. At this point, an increase in cloudiness is expected thru the day. Sunday night thru Monday... A weak shortwave moving quickly thru the northwest flow aloft will traverse the region. There is inherent uncertainty in the timing of this feature, given it`s over four days out, but the primary period of impact is expected to be Sunday night. Given the origins of the system and the absence of Atlantic inflow (northwest flow), feel the precipitation will be light, focused northwest of the area closer to the Great Lakes. The thermal profile is supportive of snow, but with limited moisture, amounts will be light. The primary concern is the timing, as a minor shift forward could lead to impacts for the Monday morning rush hour. Otherwise, a clearing trend will take hold from southwest to northeast during the day. Monday night thru Wednesday... At this time, fair weather is expected the first half of this period, Monday night thru Tuesday. As the mid-level ridge crests over the region late Tuesday, precipitation could make it into the region as early as Tuesday night. Model profiles indicate a warming trend, but cannot rule out some wintry precip, especially at the onset given a cold air damming signature. Given the time frame, above average model uncertainty, and borderline thermal profile, it`s too early to speculate any further on the sensible weather details. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Widespread IFR conditions should continue through at least 06Z. There have been temporary breaks in the low clouds from KPHL to the south, but do not expect this improvements to be long lived especially with another round of showers moving in from the west. Visibilities will be variable and will lower at times in heavier rain showers and fog. There may be isolated thunderstorms, but confidence is too low to include in the TAFs at this time. The cold front is expected to arrive between 06 and 09Z. Behind the cold front, expect conditions to quickly return to VFR as low clouds break up and rain moves off shore. VFR conditions are expected during the day tomorrow, but gusty northwesterly winds are expected (gusts near or above 20 kt possible between 15 and 00Z. OUTLOOK... Thursday night thru Sunday...Predominantly VFR conditions expected. Winds out of the west-northwest may gust up to around 20 to 25 knots at all TAF sites both Friday and Saturday afternoons. Sunday night and Monday...Predominantly VFR conditions. A brief period of light snow is possible Sunday night into Monday morning, especially to the northwest of I-95. Monday night and Tuesday...Predominantly VFR. && .MARINE... The marine dense fog advisory has been extended through 3 AM EST. There may be areas where fog has dissipated south of the warm front, but it looks like fog is persisting along the shore for many locations and now that we are past sunset, do not expect much additional improvement. Otherwise...the Small Craft Advisory remains in effect through Thursday. Seas have risen above 5 feet and are expected to remain elevated through Thursday afternoon. In addition, winds will increase later this evening and gusts around 25 to 30 knots overnight, mainly in the vicinity of and just behind a cold front. The gusts should subside once the cold front has moved further to the east of our region on Thursday. There is a chance for some brief gale gusts overnight but there is also a slight chance of some convection occurring with the frontal passage and this may be short lived enough to be handled with an SMW as opposed to a longer fused gale warning. The gradient will start to weaken on Thursday and winds and seas should both start to subside as we head into Thursday evening. OUTLOOK... Thursday night...The current SCA expires at 23Z Thu, and this may need to be extended further into Friday night. At this time, we opted to leave the expiration time as is, given model soundings disagree on whether west-northwest winds will be at or just below SCA criteria. Friday...West-northwest winds expected to be predominantly below SCA criteria, but cannot rule out a couple of gusts to 25 knots, especially in the afternoon. This will need to be monitored, and upgrade to SCA will be needed if more frequent 25 knot gusts are apparent. Friday night and Saturday...Return of SCA conditions in a north- westerly more likely during this period. A shortwave disturbance will traverse the waters, leading to cold air advection/steeper lapse rates, and more efficient momentum transfer. Thus, expect frequent northwest wind gusts around 25 knots during this time- frame over the ocean waters, with highest confidence northern NJ waters (ANZ450-451). Saturday night thru Monday...some residual SCA wind gusts over the northern NJ waters possible early Saturday night. Otherwise, sub-SCA conditions expected. && .CLIMATE... November based on the following calendar day max min temp. PHL 64 55. Nov avg 50.0 or 2.4F above normal. Ranked 14th warmest Nov in the PHL period of record (tied 14). ABE 57 50. NOV avg 45.9 or 3.2F above normal. Ranked #16 warmest in the ABE period of record. ACY 66 54. NOV avg 48.3 or 1.5F above normal. Not ranked top 16. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Dense Fog Advisory until 3 AM EST Thursday for ANZ431-450>455. Small Craft Advisory until 6 PM EST Thursday for ANZ450>455. Small Craft Advisory until 3 AM EST Thursday for ANZ430-431. && $$ Synopsis...Franck Near Term...Johnson/Meola Short Term...Meola Long Term...Franck Aviation...Franck/Johnson Marine...Franck/Johnson/Meola Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.