Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 172031 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 331 PM EST Fri Feb 17 2017 .SYNOPSIS... High pressure situated over the Appalachians will gradually move offshore tonight, allowing a warm front to lift north across our region Saturday morning. A weak cold front will move through our area on Sunday, followed by high pressure, which will build southward out of Hudson`s Bay and into our region through Tuesday. This high will move offshore on Wednesday, with a cold frontal passage expected Thursday into Friday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... What can i say... not much going on and its been a beautiful day. Tonight...Fair with some cirrus at times and possibility of scattered clouds near 5000 ft toward morning. Wind becomes light south to southwest. Radiational cooling with best chill over the remaining snow pack north of I-78 as seen on the midday satellite imagery and NOHRSC (www.nohrsc.noaa.gov) interactive snow information with still an icy 4-8 inch snow depth northern Sussex County NJ and 4 to 10 inch northwest Monroe County PA. Guidance lowered slightly over nw NJ and ne PA due to radiational cooling over remaining snowcover. FCST basis: 12z/17 50 50 blended GFS/NAM MOS. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Sunny skies and milder...by around 15 degrees which would be also be about 16 degrees above normal. Southwest wind gusty around 20 mph during the afternoon. Increasing high clouds late. No record highs expected on Saturday. FCST basis: 12z/17 50 50 blended GFS/NAM MOS and then raised that by 3-4F per HIRES guidance which is only ~1 deg less than our 330 am fcst. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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An initially split flow pattern across North America will become more amplified late this weekend into early next week. A southern stream closed low lifting out of the Rio Grande Valley will traverse the mid-Atlantic states as an open wave on Sunday. As phasing of the northern and southern streams takes place across the inter-mountain west during this time frame, a high amplitude ridge will build across the eastern conus on Monday and Tuesday. By Wednesday, both streams decouple, with an active northern stream near the US/ Canadian border, and a southern stream closed low traversing the Gulf coast states. There is some uncertainty regarding the placement of these features through Friday. The main story during the Sunday thru Friday portion of the forecast will be continued above average temperatures. Across our region, daily means will generally range from 5 to 15+ degrees above average, and overall will favor 10 to 15 degrees across the entire period! In fact, some daily record high temperatures may be in jeopardy on Sunday at our long term climate sites. The primary chances for precipitation will be on Saturday night across the southern half of the area (Delmarva, S NJ, and SE PA), and again Tue night into Wed, albeit light in both cases. There is also the potential for a wintry mix Tuesday night and early Wednesday morning across N NJ and NE PA. Looking further ahead, low confidence on precip chances on Friday. Saturday night thru Tuesday...The main uncertainty during this time frame is the northward extent of light precipitation associated with an open southern stream shortwave moving just to our south Saturday night. In conjuction with this feature, a weak cold front also crosses the region, which aids in drawing low-level moisture northward. In addition, a vorticity streamer provides modest lift for the generation of precipitation. At this time, the highest PoPs (slight chance) are expected south of the PA Turnpike and I-195, with some sprinkles possible north. Rainfall amounts up to one-tenth of an inch are possible. Otherwise, a dry, and partly to mostly sunny Sunday thru Tuesday is expected. As for Sunday, some daily record highs may be in jeopardy, especially at PHL and ILG, given westerly surface flow and lack of snow cover. More on this in the climate section to follow. Tuesday night thru Wednesday...Low pressure moving well northwest of the area is expected to lead to a cold frontal passage on Wednesday. With high pressure receding offshore, an initially dry air mass will be in place on Tuesday night, which would favor a period of radiational cooling. Given the weak boundary layer winds in the warm sector, colder air, possibly near freezing, will be harder to overcome northwest of the fall line. If 2-meter temperatures maintain closer to freezing, and precipitation is able to overcome the drier low-level air mass in place, then there could be a short period of frozen precip across portions of northeast PA and northern NJ. With the uncertainty at this time range, confidence is very low in this outcome. Stay tuned. Wednesday night thru Friday...A couple shortwaves cross the region, but other than considerable cloudiness, a mainly dry period of weathe expected at this time.
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&& .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Remainder of this afternoon...VFR becoming sct clouds aoa 10000 ft toward sunset. West to northwest wind gusty 15 to 20 kt. Tonight...VFR cirrus. chance of sct clouds near 5000 ft 05z-10z moving ewd across the area. Light wind turning to the south and southwest. Saturday...VFR mainly clear. Cirrus mainly PHL southward late in the day. Southwest wind gusty around 20 kt during the afternoon. OUTLOOK... Saturday night and Sunday...Predominantly VFR. West-northwest flow with gusts 15 to 20 knots on Sunday. Sunday night and Monday...There is a low potential of MVFR ceilings developing below an inversion, mainly at ABE and RDG, otherwise VFR. North-northwest flow around 10 knots may become northeast at PHL by Monday afternoon, with gusts up to 20 knots. Monday night and Tuesday...Predominantly VFR. There is a signal that fog could develop Monday night, especially at the typically prone TAF sites, such as MIV, RDG, and ABE. This could lead to brief MVFR/IFR restrictions. With high pressure overhead, light and variable winds. Tuesday night into Wednesday...Clouds will lower in advance of a cold front, with MVFR ceilings likely. There could be a period of IFR late Tuesday night into early Wednesday morning. On Wednesday, expect MVFR ceilings, with some improvement to VFR at times. Winds will generally favor the southwest direction at 10 to 20 knots. .MARINE... No headlines at this time through Saturday. West to northwest winds gusty 15 to 20 kt this afternoon becoming southwest tonight with gusts under 15 kt and then southwest Saturday with gusts 15 to 20 kt. OUTLOOK... Saturday night and Sunday...Winds out of the southwest. Sub-SCA winds and seas expected. Sunday night and Monday...In the wake of a cold frontal passage, winds shift from southwest to west-northwest early Sunday night. With modest cold air advection and surface pressure rises, northwest winds will increase, possibly to SCA levels. The highest probability is generally across the northern NJ waters (ANZ-452 northward), with a low probability further south and across the Delaware Bay. Monday night and Tuesday...Winds gradually veer to the southwest. Sub-SCA winds and seas expected. Tuesday night and Wednesday...A cold front approaches the waters on Wednesday. Southwest flow will increase, but there is uncertainty w/ regard to reaching SCA criteria, given low-level inversion and the gradient contribution (low confidence). Given an anomalously warm and moist (high dew point) air mass traversing the water, areas of fog may develop by Wednesday. && .CLIMATE... Updated 1035 AM Fri Feb 17. Next update possibly not til Sunday or Monday when we recheck and adjust. We did spot check our past 24 hr max/mins, as well as the new max/min fcst fm our office issued at 330 AM and the FTPRHA guidance beyond. The fcst numbers as they are now posted herein would be too low... and so it could run warmer than our projections. However, there is day to day variability in the guidance so we are making no change in our data outlook for Feb and the winter (DJF) season. The GFS/EC ENSEMBLED expected transition to a cooler more wintry scenario at the end of the month or the first two weeks of March continues likely. Whether that means anything more than an inch or 3 of snow south of I-78 remains to be seen. We have now added ILG information, despite some of those questionably warm early years in the database back to 1893-94. Projecting widespread top 10 warmest February on record in our forecast area. Confidence: above average. Details below. Seasonal average (DJF) temperature projecting widespread top 14. PHL is projecting #9 warmest, ABE #6 and ACY #12. Confidence: above average. February: The month as a whole has so far averaged 3.4 to 5.5 degrees above normal through the 15th, except 1.4 above normal at KMPO. There still isn`t any sign of long duration substantially colder than normal air coming this month and in fact some of the guidance is suggesting near record warmth is possible either this weekend and maybe the middle of next week (date and climate location dependent). Just the 7 day period of tomorrow through the 23rd should average close to 10 degrees above normal. The following projection is for Philadelphia with remainder of the area relationship discussed. Using this mornings low of 33 and the NWS forecast through the 22nd (see SFTCTP), and then FTPRHA max/min for PHL D8-11, and the normal the last two days of February (max min of 47/30) we project a monthly average of 41.9 degrees at PHL (2 degrees higher than the current first 15 day average). Normal for February is 35.7 or a projection of 6.2 degrees above normal. This would make February the 2nd warmest in our period of record dating back to 1874. The warmest February on record was 42.2F in 1925. Ninth warmest is 40.1 degrees, so you see that we have 1.7 degrees to give = be wrong, and still enjoy a top 10 warmest February. Average temperatures at all our other climate sites should average at least a degree warmer than what has occurred through the first 15 days. Lack of snow cover is partly to blame and goes in tandem with the primary storm track northwest of our area across the Ohio Valley-Great Lakes this winter (DJF) as evidenced by above normal pcpn fm KY northward into the Great Lakes. Detailing ACY ABE and ILG for February as per PHL data process input. ACY projects #2 warmest at 41.1F with the record being 41.6F in 1890. The 30 normal is 35.3 or a positive departure of nearly 6 degrees. The projection has 1.2 degrees to give on the down side for a #9 rank with the POR back to 1874. ACY climate is subject to radiational cooling which at times may force a colder solution so confidence on ACY maintaining a #2 projection is less than PHL. Still, if the pattern doesn`t change significantly from the outlook of the past three days...it will be a noteworthy top 10 warmest February on record through most of our Mount Holly forecast area. ABE projects 7th warmest with a 36.1 average, or 5.4 degrees above the norm of 30.7. ABE has less room to give on the down side. ILG projects 41.4 or 2nd warmest on record...6.3 above the norm of 35.1. The record is 42.3 in 1903. This projection has 1.9 degrees to give on the low side to drop to about #10. Highly unlikely. Winter (DJF) Finally...PHL for the winter season (DJF) is projecting an average of 39.6 degrees...the 9th warmest DJF in the period of record dating back to 1873-1874. Room to give is 0.4 degrees on the down side to #10 warmest winter. Essentially its going to take all of at least a 1.2 degree warm side error to drop back to #10 warmest seasonal average. While this could happen, am thinking via ensemble guidance that this is unlikely. Projected seasonal rankings for ACY, ABE and ILG follow: ABE seasonal average temp projects 34.9 or #6 in the POR back to the winter 1922-23. 0.7 to give to drop out of top 10 so #6 looks pretty solid. ACY seasonal average temp projects to 39.2 or #12 in the POR back to the winter 1873-74. 0.6F to give to drop back to #14. ILG seasonal average temp projects to 38.9 or #9 in the POR back to the winter 1893-94. 0.4 to give to drop back to #10 warmest winter. Past two years: PHL through February 2017 will have recorded above average temperatures for 22 of the last 23 months. May 2016 was below normal. Then we have to go back to Jan Feb March 2015 for below normal monthly temps. For ABE: 23 consecutive months of above normal temps through February of this year with last below normal period, again JFM 2015! For ACY 19 of the past 23 months have been above normal. For ILG 17 of the past 23 months have been above normal. Split flow = no snow was something I heard in Boston and it seems to apply for the next 10 days as the pattern is devoid of much phasing of the northern and southern streams. Change is ensembled sometime between the 25th and the first week of March with a storm track nearby and a better chance for colder temps and some winter wx. Because of that, i hesitate to look at seasonal snowfall records. Allentown current #7 least snowy winter will most likely drop out of the top 10, needing only 1.5" the rest of the snow season. PHL ILG are already out of the top 10 least snowy. && .EQUIPMENT...
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Marine platforms: 44009 is not expected to be operational until sometime in May 2017. The pier for Brandywine Shoal is under reconstruction after being nearly destroyed by a storm last year. RTS unknown.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Franck Near Term...Drag Short Term...Drag Long Term...Franck Aviation...Drag/Franck Marine...Drag/Franck Climate... Equipment...

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