Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 251319 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 919 AM EDT SAT JUN 25 2016 .SYNOPSIS... High pressure will remain over the area this weekend before moving off the coast Sunday night and Monday. A cold front will move through the area Tuesday afternoon into Tuesday night. The front will stall off the coast and to our south through the end of the week while high pressure builds in from the west. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pres will be located over the region today. After mrng low clouds, clearing will take place and expect a mostly sunny and pleasant day. Temps will be pleasant with low relative humidity values. Temperatures are currently running a few degrees warmer than modeled across the northern half of the region. Given the dry conditions and boundary layer temperatures near 20C have added about three degrees to the highs across the Lehigh Valley and Northern NJ with the 9:30 am update. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... The aforementioned high will remain parked over the region tonight, so a clear sky and light wind will prevail. Some patchy fog is psbl. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Sunday and Sunday night, the mid-Atlantic region will remain situated on the western periphery of high pressure that will be centered off the east coast. A southerly return flow pattern will develop around the backside of the surface high. Initially, WAA within the boundary layer appears negligible with the low-level ridge axis directly overhead. Accordingly, we are not expecting a notable warming trend heading into Sunday. The one exception to the above may be our far northern and western zones where there is a possibility the ridge axis progresses downstream early enough on Sunday for WAA to ensue by afternoon. The warmest conditions are forecast to reside west of I-95 on Sunday where highs are in the upper 80s (which would be 3-5F higher than what is forecast for today). Low temperatures Sunday night will generally be in the 60s with a few 50s possible in the Pine Barrens and the sheltered valleys of northeast PA/northwest NJ. A cold front will move into the Great Lakes-Midwest region on Monday while a pre-frontal trough approaches from the Ohio Valley. High clouds well ahead of this system will increase across the forecast area during the day. Went a few degrees above guidance for high temps, especially along and east of I-95, where it appears the arrival of the thicker cloud deck ahead of the pre-frontal trough should hold off until late in the day, allowing for strong heating to take place. Models indicate a band of precip associated a leading shortwave disturbance aloft moving into eastern PA during the afternoon and the rest of the area Monday night. Went against climo and kept thunderstorms out of the forecast for Monday as modified forecast soundings (i.e., modified to account for the cool surface temperature bias that we are expecting models to exhibit for Monday) depict a rather stable environment over the area. We could potentially see isolated thunderstorms move in from the west Monday night when some elevated instability with the pre-frontal trough could arrive. The cold front is forecast to be located in western NY and the Ohio Valley by Tuesday morning. The front may then jump to the pre- frontal surface trough on the lee side of the Applachians during the day. There is still some uncertainty with how quickly the front arrives into our western zones and subsequently moves off the coast since downstream blocking over the western Atlantic Ocean should slow down the movement of the front as it approaches the eastern seaboard. The latest forecast advertises the highest PoPs in the period for late Tuesday afternoon when the front should be at least on our western doorstep and Tuesday night when the front will likely be somewhere in the forecast area. There is a potential that we may see a few strong to severe storms if the arrival of the synoptic lift from the front and upper shortwave trough coincides with peak heating Tuesday afternoon-early evening (per 00Z GFS solution). Other guidance, including the ECMWF/Canadian depict a less favorable setup for severe storms across our area with the best forcing arriving at night. Kept low chances in the forecast for Wednesday morning if the front slows down or stalls over the area as indicated by the past several runs of the ECMWF. The frontal boundary is forecast to remain just off the coast and also to our south during the second half of the work week. Meanwhile, high pressure over the Great Plains and Midwest will will build into our region. Expect a mainly dry period late Wednesday through early Friday. A few showers may develop Friday afternoon, particularly across our southern zones with the frontal boundary starting to lift slowly northward back toward the region. Near normal temperatures are expected during this time. && .AVIATION /13Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. IFR/LIFR conds, mainly for low clouds prevail erly this mrng. However, after daybreak, conds shud become VFR. Then expect VFR to dominate thru the day and into tonight. Some fog is again possible late tonight with lcl vsby restrictions. Light wind erly will become more ne to e during the day with speeds less than 10 kts. By evening a more s to se flow is expected. Overnight, the wind is expected to be calm to less than 5 kts before increasing to less than 10 kts on Sunday. Outlook... Sunday and Sunday night...VFR with light southerly winds Monday through Tuesday night...VFR outside of heavier showers and storms. Expect coverage of showers to be scattered early in the week. Thunderstorm chances looks minimal on Monday, then increases Tuesday afternoon and evening. Wednesday...Winds shift to northwesterly in wake of fropa. VFR. && .MARINE... There could be marginal sca conds erly today due to the NE to E flow, but confidence is not high enough for sca issuance. Seas are still around three feet with the 9:30 am update making it even less likely to reach five feet with the change in wind direction to more southeasterly later today. Outlook... Sunday through Wednesday...Winds and seas should remain below SCA criteria. Thunderstorms could produce locally gusty winds over the waters Tuesday late afternoon and night. RIP CURRENTS... Moderate risk for rip currents today with the onshore flow. The risk appears to lower by Sunday as winds and seas diminish. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Klein Near Term...Gaines/Nierenberg Short Term...Nierenberg Long Term...Klein Aviation...Klein/Nierenberg Marine...Gaines/Klein/Nierenberg

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