Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 200119 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 919 PM EDT Wed Oct 19 2016 .SYNOPSIS... A weak cold front will move southward through the region today and tonight, before returning to the north as a warm front on Thursday. Low pressure developing over the Ohio Valley will pass to the north on Friday, dragging a strong cold front through the region. At the same time, another area of low pressure will move northward in the Atlantic and merge with the front in New England. High pressure then builds in from the south as low pressure deepens to our north over the weekend. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... 9:30 pm update: Cloudcover will be slow to increase overnight ahead of a low pressure moving northeast along a frontal boundary from the Ohio Valley eastward across our region. This frontal boundary has led to a sharp divide between seasonable and a very humid airmass. This will make a challenging forecast for dewpoints in the overnight, dewpoints were raised quite a bit along the Jersey coast based on the latest position of the front. The HRRR and RAP are both showing enough moisture overruning the boundary to develop some scattered showers toward daybreak along the Eastern Shore that move northward during the morning hours on Thursday. QPF continues to look very light overall. Temperatures also started off the evening warmer than modeled but the slow increase of cloudcover may compensate for the warmer start this evening. Previous still applies: Cold front through much of PA and into central NJ. With ridging along the Mid-Atlantic coast, and high pressure anchored over the Southeast U.S., it will be hard for that front to make much southward progression tonight, but it should get through much of NJ before stalling out across the Delmarva, most likely just north of MD/DE and extreme S NJ. Tonight, H5 trough with several strong shortwaves will dig into the central U.S., and this combination will allow weak surface low pressure currently over the Midwest to intensify as it lifts into the OH Valley. As that low lifts to the north and east, the stationary front over the Delmarva will begin to lift back to the north as a warm front late tonight. Latest model QPF fields keep much of the CWA dry, with only some light precip encroaching into western zones late in the period. Since there is not much support for precip across the region, will go ahead and forecast dry conditions, with slight chance PoPs moving into the Lehigh Valley and Pocono Mountains towards daybreak. Clouds ahead of the low will spread into the region tonight, and this should inhibit the development of fog. Lows tonight will range from the low to mid 50s across far northern zones to the low 60s across southern zones. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... Deepening H5 trough will continue to dig into the Midwest and then into the Great Lakes region throughout the day Thursday. Low pressure continues to intensify over the OH Valley, and will lift to the north and east throughout the day, mainly lifting into western NY/PA. This will also continue to lift that warm front north through the region. In terms of precip, the heaviest of the rain will remain well to the west, around the center of the low. But ahead of that low, and along the warm front, rain will develop over eastern PA and into northern NJ. Most precip will be light, and there is the possibility that DE/MD, and most of NJ will be caught in the dry slot and not see much, if any, precip. The bulk of the rain across the CWA will be over the Lehigh Valley, Pocono Mountains, and into northern NJ, where up to 1/4 inch QPF is possible. With that warm front lifting to the north, southerly winds will usher a warm airmass into the region. Northern areas will not be quite as warm as southern areas, mainly due to rainfall, and highs will top off in the low to mid 60s there. Temps will generally warm through the 70s through SE PA and most of NJ, and will be around 80 across DE/MD. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... At the start of the extendd pd, a complex wx scenario will be setting up. A strong cdfnt will be approaching from the w Thu night and low pres will be movg nwd in the Atlc. Attm, it appears that the bulk of the precip with the cdfnt will stay to our w, but the fropa will occur Fri or Fri eve. At the same time, the low over the Atlc will merge with the front and move nwd and rapidly intensify over New Eng. So, it looks like there will be some rain chcs beginning Thu night, with the best chcs on Fri and then tapering off Fri night, though its psbl there could be some lingering pops into Sat AM, especially n. Then, the next story will be the gusty nw wind Sat into Sat night before subsiding on Sun. The pgrad between the aforementioned low and high pres overt the sern states will make for a stiff nw wind that make it feel even colder than it is and with temps that will struggle out of the 50s both Sat and Sun it will be a sharp change, especially with the unseasonably warm wx we have had. The high pres will then build in for the start of next week and bring dry wx with temps at or slightly below seasonal values. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Cold front continues to slowly work its way south through the region, and then will return north as a warm front on Thursday as low pressure passes to the north and west. VFR forecast for the rest of the afternoon and through tonight. Not expecting much, if any, rain until after 12Z Thursday. CIGs gradually lower to MVFR over KABE/KRDG by 12Z, and then MVFR CIGs will continue to spread east through 18Z Thursday. Rain will develop first over western terminals, and will spread east Thursday morning. Possible that KMIV/KACY/KILG will remain dry through the TAF period, and conditions at those terminals my remain VFR through 18Z. NW winds less than 10 KT, veering to the NE 5 KT or less through this evening. Winds become E-SE 5-10 KT Thursday morning. OUTLOOK... Thu night through Fri night...SHRA developing Thu night, becoming more widespread into Friday, especially n, then tapering off Friday night. MVFR conditions likely, with the chance for IFR and lower. Moderate confidence. Sat through Sun...Some MVFR psbl erly Sat, especially n, then mainly VFR. NW winds with 25-35 KT gusts psbl. Moderate to high confidence. Mon...VFR. High Confidence. && .MARINE... Sub-SCA conditions on tap through tonight. A warm front lifts north across the waters on Thursday. Gusts to 20 KT possible on northern ocean waters in the afternoon, but conditions should remain below Small Craft Advisory levels. OUTLOOK... Thu night through Fri afternoon...Forecast winds and seas below SCA criteria. Scattered showers Thu thru Fri. Fri night through Sun...A strong cdfnt passes across the waters Friday night and strengthening low pressure moves into ern Canada with high pres building to the sw. Tight pressure gradient develops over the weekend with winds gusting to at least 30 KT with the potential for gale force wind gusts, especially Fri night thru erly Sat night, then wind subsiding to SCA on Sun. Sun night and Mon...Winds and seas will drop back below SCA criteria. && .CLIMATE... he following sites tied or set daily record high temperatures today (Wednesday, 10/19) New RecordOld Record Allentown, PA 84 82 (1963) Trenton, NJ 86 83 (1963) Philadelphia, PA 86 80 (1947) Atlantic City, NJ 86 80 (1991) Wilmington, DE 87 81 (1963)* record tied Georgetown, DE8681 (1953) Warmth of this magnitude seen yesterday (and potentially again today) was/is a rare occurrence for this late in the year: For Allentown, the only other year that recorded a high temperature of at least 85 degrees this late in the calendar year was 1947. In 1947, the high was 85 degrees on the 21st and 23rd of October. Climate records at Allentown go back to 1922. Here are the record high temperatures for Thursday (10/20). THU OCT 20 Mount Pocono, PA 75 in 1963 Reading, PA 80 in 1947/1953/1969 Allentown, PA 78 in 1936 Trenton, NJ 80 in 1969 Philadelphia, PA 80 in 1916/1938 Atlantic City, NJ 85 in 1987 Wilmington, DE 82 in 1969 Georgetown, DE 83 in 1953 Monthly average temperatures are projecting 3 degrees or so above normal, which would rank in the top 15 warmest Octobers at Philadelphia and Allentown. This is stated with the usual mid month uncertainty. What we do know is that the warmth of this week will virtually lock in an above normal month, especially since the pattern for the last week of October does not indicate any lengthy period of below normal temperatures. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Nierenberg Near Term...Gaines/MPS Short Term...MPS Long Term...Nierenberg Aviation...Nierenberg/MPS Marine...Nierenberg/MPS Tides/Coastal Flooding... 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