Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 190828 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 328 AM EST Thu Jan 19 2017 .SYNOPSIS... High pressure will build into the region today and move offshore early Friday. Meanwhile, weak low pressure will impact the region Friday afternoon into Friday evening. High pressure will return for Saturday. Then a stronger and more complex area of low pressure will impact the Mid-Atlantic beginning Sunday and continuing through Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Broad surface high pressure was centered over the Ohio Valley and Mid-Atlantic region overnight. The high will remain over the area today. A weakness in the NW flow was noted over the area as H9-H8 the axis of a shortwave ridge is overhead. Extensive low clouds are noted over the forecast area overnight as a lull in the NW winds and dry air advection has allowed moisture to remain trapped beneath the mid- level subsidence inversion. These low clouds are expected to erode from west to east during the early to mid morning as the primary ridge centered over the Gulf Coast states builds downstream toward our area. Expect additional stratocu development during peak heating this afternoon but overall, the majority of the locations should turn out mostly sunny from the late morning onward. Forecast temperatures today weighted more toward the warmer MAV stat guidance in anticipation of the sunshine returning. Adiabatic compression from building large-scale subsidence and even light downsloping W-NW winds will provide a secondary contribution to the warming. The end result is highs in the low to mid 50s this afternoon across most of the area (except 40s across the higher terrain in NE PA/NW NJ). && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... High pressure at the surface and shortwave ridging aloft will result in a quiet weather pattern for tonight. Expect temperatures to drop rather quickly after sunset this evening under mainly clear skies and light winds. Forecast low temperatures range from the mid to upper 20s in the rural areas N of I-78 and the NJ Pine Barrens to the mid 30s in the cities, at the coast and in the Delmarva region. The arrival of mid to high clouds from our SW overnight is the primary motive for keep low temps slightly higher in E MD and DE. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Fri mrng starts off dry, but a wk low will bring rain to the area by aftn and continue into the eve. Overall, this shud be a quick hitter and most areas will see light qpf. This precip moves out durg Fri night and high pres builds in, bringing a dry day Sat into erly Sun. Then, an area of low pres over the srn plains will move newd and begin to impact the region durg the day Sun. Mdls differ on the timing of onset with the ECMWF being faster than the GFS. The NAM/WRF and CMC are supportive of the slower timing so have trended the fcst in that direction. Nevertheless, rain will develop durg the day from s to n and continue into Sun night. As the low approaches, ely flow will increase and wind will pick up and precip will get steadier and heavier Sun night into Mon. The guid is still differing on where the axis of heaviest precip will be as well as the timing, but it appears that there will be one wave of precip Sun night into early Mon, then potentially a break and another shot later Mon into Mon eve. Precip will then end from s to n Monday night into Tue. Certainly by the time this is over we could be looking at 1 to 2 inches of rain, and possibly more depending on the track and strength of the low. Additionally, due to the persistent ely flow there could be several tidal cycles of coastal flooding, but this will also be dependent on the track of the low and will become more evident as we approach Sun night and Mon. Once the low passes by, wk high pres will build back in making for an improving Tue and dry Wed. ATTM, temps genly look to bee way too warm for any precip type other than rain. However, there is at least a small potential for some freezing rain Fri night before the precip ends in the Poconos. If temps end up being colder than currently fcst than that potential cud increase. With that said, temps are expected to be aoa nrml thru the pd, in some cases by 10 to 15 degrees. Monday will likely be the coolest day, with an abundance of clouds and rain. Many areas will be aoa 50 degrees thru the pd. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. MVFR CIGs between 2-3 kft AGL have expanded eastward over the I-95 terminals overnight. Expect these MVFR CIGs to move downstream to ACY shortly. However, improvement was already noted back to the west with RDG, ABE and ILG CIGs rising to just above 3 kft AGL. CIGs are expected to increase just enough for Phila and S NJ terminals to become VFR between 09-12Z. Skies will clear later in the morning with mainly VFR conditions expected today. However, with stratocu developing this afternoon , there is a possibility that we see localized MVFR CIGs develop sometime between about 18-22Z. Forecast soundings hint at this happening at ABE-RDG but overall confidence in MVFR CIGs this afternoon is low. Under mainly clear skies and light winds tonight, there is a potential for radiational fog overnight at the typical fog-prone rural TAF sites. IFR conditions would be a possibility where fog forms. OUTLOOK... Fri through Fri night...Sub-VFR conditions possible in -RA. Moderate confidence. Fog possible Fri night. Sat/Sat night...Improving conditions Saturday morning, otherwise VFR. High confidence Sun...E winds 10-15 KT. Conds deteriorating from s to n durg the day. Moderate confidence. Sun night thru Monday...IFR and lower conds possible in RA. E winds 15-20 KT with 20-30 KT gusts. LLWS possible with 60-65 KT LLJ Mon aftn. Moderate confidence. && .MARINE... A Small Craft Advisory for Hazardous Seas is in effect for the coastal waters of central NJ (ANZ450/451). Observed wave heights overnight continue to be in the 5-6 ft range at buoys 44091, 44065 and 44025. Seas are modeled to slowly diminish today before dropping below 5 ft sometime during the mid to late afternoon. Elsewhere, winds and seas will be below SCA criteria. No marine headlines expected tonight. W winds 5-10 kt early this eve will veer out of the N late this eve and overnight, then NE before daybreak Friday OUTLOOK... Fri through Sun morning...No marine headlines anticipated durg this time. Seas will genly be around 2 ft with wind 10 kts or less. Sun aftn thru Mon...Ely flow increases to 15-20 KT with 25-30 KT gusts starting Sun aftn, and then gale force gusts of 35-40 KT likely Monday and Monday night. Moderate to heavy rain with low VSBY expected. Storm conds can not be ruled out for a time, especially n on Mon. Conditions improve late Monday night, and winds decrease to sub-SCA levels. However, seas on the ocean should remain above SCA criteria. Mon night thru Wed...wind decreases below headline criteria, but ocean seas will remain above SCA criteria. It is psbl that some areas, especially s may drop below SCA seas on Wed. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 PM EST this evening for ANZ450-451. && $$ Synopsis...Nierenberg Near Term...Klein Short Term...Klein Long Term...Nierenberg Aviation...Klein/Nierenberg Marine...Klein/Nierenberg

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