Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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032 FXUS61 KPHI 010625 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 125 AM EST Thu Dec 1 2016 .SYNOPSIS... Low pressure over southeast Canada will redevelop eastward to the Canadian maritimes by Friday. Its cold front will be crossing the mid Atlantic states early this morning. High pressure over the Ohio Valley on Saturday will move into the mid-Atlantic states on Sunday. Meanwhile, a complex low pressure system stretching from the midwest to the Gulf of Mexico will impact our weather early or the middle of next week. && .NEAR TERM /THROUGH TODAY/...
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Boundary between modified warm air to the north (Wednesdays max temps 10F warmer than normal) and the 15-20F warmer than normal air to the south, never made it past ILG/PHL. it was an overestimation on the northward push on my part. In this case, the combined GFS/EC was a little better on handling the area temps on Wednesday. One more band of showers will race newd through the area between now and 5 am, then it clears with the variable turning southerly flow(except gusty southwest flow 30-35 mph along the coastal plain) shifts to west. After sunrise...a sunny or mostly sunny starts gives way to diurnal caa cloudiness with a bkn deck for a time during midday- afternoon. Gusty west winds of 25-030 mph are expected midday and afternoon. Temps during the day still warmer than normal. The forecast - already posted at 1230 AM - was based on a 50 50 blend of the 00z/01 GFS/NAM MOS, favoring the slightly warmer NAM/ECMWF temps.
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&& .SHORT TERM /TONIGHT/... Clear or mostly clear skies with diminished wind and some radiational cooling. Lows maybe a couple of degrees warmer than normal. Forecast basis: a 50 50 blend of the 00z/01 GFS/NAM MOS. && .LONG TERM /FRIDAY 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 /07Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 12z...mixed variable conditions in showers, patches of stratus/fog, becoming vfr CIGS everywhere by 09z. gusty southwest winds 25-30 kt VCNTY KACy through 08z. otherwise light winds tending to briefly become south or southwest before shifting to west and gusty to 20 kt everywhere between 07z-10z subsequent to an eastward moving cold front. After 12z today...VFR sct-bkn aoa 4000 ft. Westerly winds will gust 25-30 kt by 17z. Tonight...VFR clear with sct cirrus possible late. West winds, generally under 10 kt. OUTLOOK... Friday 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...
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Marine dense fog advisory was just cancelled at 120am. Considering a GLW for ANZ450-451 but no decision on that til 3am. Otherwise the SCA continues posted as previously. More at 300 am. OUTLOOK... 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.
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&& .CLIMATE... November based on the following calendar day max min temp for November 30. Will recheck averages and rankings by 230 am and repost. PHL 61 55. Nov avg 50.0 or 2.4F above normal. Ranked 14th warmest Nov in the PHL period of record (tied 14). ABE 56 48. NOV avg 45.9 or 3.2F above normal. Ranked #16 warmest in the ABE period of record. ACY 63 57. NOV avg 48.3 or 1.5F above normal. Not ranked top 16. Allentown and Trenton will post RER rainfalls for ydy at 135 am. && .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. Small Craft Advisory until 3 AM EST early this morning for ANZ430-431.
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&& $$ Synopsis...Drag/Franck Near Term...Drag Short Term...Drag Long Term...Franck Aviation...Drag/Franck Marine...Drag/Franck 125A Climate...

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