Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 260730 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 330 AM EDT Mon Jun 26 2017 .SYNOPSIS... A large area of surface high pressure builds into the eastern United States early in the new week before moving offshore on Wednesday. A series of upper troughs will swing through the East Coast during this time as well. A series of low pressure systems will pass north of the region late this week and into the new weekend, and each low will drag a weak boundary through the region during this time. A more developed area of low pressure is possible Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A strong short wave dropping southeastward from the Midwest and upper Great Lakes early this morning will amplify an upper- level trough eastward through the day. This will result in gradual height falls across our area by late in the day. At the surface, a weak cold front across the area early should tend to dissipate through the day or become a surface trough. The model guidance shows several short waves within the flow out ahead of the aforementioned amplifying trough. This along with cooling aloft should generate enough lift and instability to develop showers and thunder (probably low-topped) to our northwest and west. Much of the guidance keeps this activity just to our west/northwest by late in the day, however terrain influence may help pop a few isolated showers in the northwestern zones after 18z/2 PM. The forecast soundings overall show a fair amount of dry air, however there is some instability that develops this afternoon. The forecast amount of instability within these soundings looks to be minimal and given that convection will probably be low-topped, we only carried a shower mention and kept PoPs across the northwest zones no higher than slight chance. We also slowed down the arrival of the mentionable PoPs. The forecast soundings show the convective temperatures being reached more likely across the interior, therefore placed the higher sky cover mainly near and west of I-95. Based on the incoming height falls through the day, the thickness values will also lower some and therefore high temperatures are expected to be a bit cooler than yesterday. The flow should be light enough to allow the surface winds to turn more southerly along the coast. The high temperatures are mostly a blend of MOS and continuity. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... An upper-level trough will continue to sharpen across the eastern Great Lakes and Ohio Valley through the night. This will drive weak low pressure just north of the Great Lakes, with either a weak cold front or surface trough extending southward from it. There is plenty of short wave energy within this trough, however much of this looks to hang back over the Great Lakes and Ohio Valley. The main short wave is forecast to move across the eastern Great Lakes late tonight, and this is where much of the shower activity should be focused. For our area, some guidance is a bit more robust with a lead short wave and want to produce a few showers/thunder overnight near the Delaware Valley. This cannot be ruled out as there may still be a surface trough in place or weak incoming cold front, however confidence is not all that high and therefore kept it dry for now. Otherwise, there should be more cloudiness around for awhile tonight especially the mid level variety as some instability may linger with cooling aloft. The lowering of the dew points during the day today should recover some tonight as winds go light, however despite more cloud cover for a time the temperatures are expected to be cooler given the overall air mass will be cooling with the incoming upper-level trough. Low temperatures were mainly a blend of continuity and MOS. && .LONG TERM /TUESDAY THROUGH SUNDAY/... The long term period will start off relatively cool and dry, as high pressure and an upper trough build in from the west. When both the high and the trough move offshore during the mid-week period, return flow will usher a hot and humid airmass back into the region for the end of the week and into next weekend. By Tuesday, the center of the surface high positions itself over the Southeast U.S. and the base of the upper trough digs into the Ohio Valley and Appalachians. A few strong shortwaves will dive into the base of the trough, and this trough will traverse the East Coast in the afternoon and evening. There is not much moisture associated with this systems, as a drying west winds result in surface dewpoints in the upper 40s to around 50.Although isolated to scattered showers and thunderstorms are possible, do not think they will be long lived or widespread. Highest PoPs will be to the north and south, where the strongest shortwaves will be. Highs remain several degrees below normal, generally in the mid to upper 70s, though the Poconos will be about 10 degrees cooler. Any lingering showers will taper off in the evening as the trough moves offshore. By Wednesday morning, the center of the high establishes itself over the Mid-Atlantic. Dry and pleasant conditions on tap with low humidity values as highs will approach 80 for most of the region, and dewpoints will be in the low 50s. Surface high pressure begins to move offshore Wednesday night. This results in a pattern shift for the end of the week and weekend, as heat and humidity gradually build. With surface high pressure entrenched off the Southeast U.S. coast, and an upper ridge gradually builds east through the end of the week, return flow sets up and pushes temps through the 80s on Thursday, and gradually into the lower 90s Friday and Saturday. In addition, surface dewpoints rise back up, first into the low 60s Thursday, and then approaching 70 and low 70s over the weekend. Meanwhile, several strong shortwaves will dive into the northern states, and several areas of low pressure will develop to the west and will pass north of the region. As they track north of the region, they will drag a weak frontal boundary through the Northeast and Mid-Atlantic. Will carry slight chance-chance PoPs from Thursday through Saturday. Upper ridge moves offshore late Saturday, and then an upper trough begins to dig towards the East Coast. Sunday could feature a bit more precip across the region as low pressure develops south of the region and lifts to the north. Will carry high chance PoPs for Sunday. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR. An isolated shower is possible after 18Z north and west of KRDG and KABE. Light and variable winds becoming northwest to west 5-10 knots, however turning from the south at KACY in the afternoon with some sea breeze influence. Tonight...VFR ceilings at times, mainly at or above 7000 feet. While a shower around is possible, coverage and occurrence is rather low. Southwest winds (locally south) less than 10 knots, becoming light and variable at most terminals. OUTLOOK... Tuesday: Mainly VFR. Isolated to scattered SHRA/TSRA possible with brief MVFR or lower conditions. W-SW winds 10-15 KT with gusts to 20 KT in the afternoon. Tuesday night...VFR. Any lingering SHRA/TSRA taper off in the evening. Light W-NW winds. Wednesday...VFR. W winds 5-10 KT. Gusts 15-18 KT possible in the afternoon. Wednesday night...VFR. S winds 5-10 KT. Thursday...VFR. Isolated SHRA/TSRA possible at KABE/KRDG. S winds 5- 10 KT north and west of I-95, and 10-15 KT with 20-25 KT gusts at terminals south and east of I-95. Thursday night and Friday...Mainly VFR, but scattered SHRA/TSRA possible, mainly north and west of I-95. SW winds 10-15 KT with gusts up to 20 KT. && .MARINE... The conditions are expected to remain below Small Craft Advisory criteria through tonight. A northwesterly wind will turn southwest to south this afternoon and tonight (possibly south-southeast in Delaware Bay for a time as a sea/bay breeze occurs). While some gustiness will occur at times, gusts are expected to be less than 25 knots. OUTLOOK... Tuesday...Sub-SCA conditions. Scattered showers and thunderstorms. possible. Tuesday night...Any showers and thunderstorms taper off in the evening. Sub-SCA conditions. Wednesday...Sub-SCA conditions. Thursday through Friday: SCA winds/seas possible as stronger southwesterly winds become established. A slight chance of storms on Friday. .RIP CURRENTS... The forecast conditions through this evening should result in a low risk for the development of dangerous rip currents. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...MPS Near Term...Gorse Short Term...Gorse Long Term...MPS Aviation...Gorse/MPS Marine...Gorse/MPS

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