Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 221334 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 934 AM EDT Sat Oct 22 2016 .SYNOPSIS... Low pressure along coastal New England this morning will continue to track northward today and intensify. This will result in windy and much cooler conditions across our area through tonight. Another cold front arrives Sunday night, then high pressure gradually builds in through mid week. A warm front is expected to lift north over our area at the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The water vapor imagery shows a well defined upper-level trough that is taking on a negative tilt across the Mid Atlantic and into the Northeast (even closing off). This is driving an intensifying surface low along the New England coast this morning. This storm will continue to lift northward through the day, with a tight pressure gradient across our area. A ribbon of stronger lift continues to shift northeastward and is clearing our northern zones. Associated with the strong trough aloft, showers are remaining across much of the area. Based on trends, the POPs were adjusted with the these decreasing from south to north through the day. The cyclonic flow around this storm will result in much cooler conditions and some residual showers should continue through the afternoon especially across the northern portions of the area. As this storm intensifies, windy conditions will be in place across the area. The 12z Sterling, VA RAOB sampled winds to 40 knots up to 850 MB where an inversion is located. Some of this will mix down to the surface, initially with the continued cold air advection surge this morning, then through the afternoon as the low-level lapse rates steepen a bit more. It appears that peak wind gusts should be to around 40 mph, therefore we will continue with no wind advisory at this time. The wind on top of the much cooler temperatures will add a wind chill factor. High temperatures were lowered some, especially across the northern areas where more cloud cover and even some showers will linger the longest. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... Any lingering precip acrs nrn sections shud come to an end erly tonight, then clouds will decrease as the upr flow becomes more zonal, the sfc low moves away and high pres builds slowly in from the s. The wind will slowly begin to subside but will remain gusty. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Sunday...low will continue to lift NE away from the region. As it does so, we should see the pressure gradient across the region slowly decrease. However, low and mid level height gradients will remain quite large through the day time hours, so depending on how deep the mixing is, we could continue to see windy conditions, though still not as windy as what we are expecting today. Sunday night...A secondary surface cold front slides through the region late (after midnight). As mentioned by the previous shift, a tight band of frontogenetic forcing along and just ahead of this front could lead to some showers. However, limited synoptic scale lift means that coverage should be quite limited across our region. Monday and Tuesday...A robust northwest flow pattern sets up to start the work week, resulting in continued cold air advection. In fact, a few models even depict small QPF values across the NW portions of the area in what looks like a lake effect pattern. However, given that this is still a climatologically unlikely time to see any lake effect precip, have kept the forecast dry. Wednesday and Thursday...though the high associated with the polar air mass builds closer to the region through this time, we should actually see temperatures moderate a bit thanks to low level flow shifting from northwesterly to westerly and possibly southwesterly. Having said that, latest model runs backed off on southerly return flow developing, so think that through the day on Thursday we will continue to see slightly below normal temperatures. Friday and Saturday...there are big differences both between models and run to run with how to handle the next upper level low at the end of the week. The GFS depicts the upper level low digging into the deep South with essentially no reflection of a low in the surface pattern. The ECMWF on on the other hand, shows a well defined extra tropical cyclone sliding across the Great Lakes region resulting in first a warm front lifting over our region and then a cold front sweeping through at the very end of the forecast period. Given the uncertainty, have stayed close to the previous forecast for now. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of Today...Ceilings are mostly VFR this morning with some local MVFR still remaining at times. Overall, the ceilings are expected to remain at VFR through the day. Showers will become less numerous and shift northward through the afternoon. Much of the shower activity is on the light enough side, resulting in VFR visibilities. However localized/brief MVFR visibilities can occur through the remainder of the morning. Northwest winds will continue to increase to 15-20 knots with gusts to about 35 knots, with the more widespread higher gusts especially later this morning and this afternoon. Tonight...VFR. West-northwest winds 15-20 knots with gusts up to 35 knots should diminish some through the night. The wind gusts should become less frequent through the night. Outlook... Sunday...VFR conditions expected. Breezy westerly winds continue. Sunday night...Mostly VFR conditions expected but there is a small chance of MVFR with showers after midnight primarily for TAF sites north of KPHL. Monday through Wednesday...Mostly VFR conditions expected. && .MARINE... The Gale Warning for the coastal waters and Delaware Bay will remain in effect unchanged. Gale force gusts have already occurred across the southern waters into Delaware Bay, and this will spread northward through the day as low pressure in New England intensifies. By late tonight, it is expected that the Gale Warning will come down on the Bay but that will be reviewed later today. Outlook... Sunday...winds will diminish slightly on Sunday, and should drop below gale conditions by late afternoon on the coastal waters. However, SCA conditions will continue into Sunday night. Monday and Tuesday...SCA conditions are expected to continue as winds should continue gusting above 25 kt (though seas may drop off below 5 ft. Wednesday...winds are expected to subside below SCA criteria early in the day. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Warning until noon EDT Sunday for ANZ452>455. Gale Warning until 6 PM EDT Sunday for ANZ450-451. Gale Warning until 2 AM EDT Sunday for ANZ430-431. && $$ Synopsis...Gorse/Johnson Near Term...Gorse Short Term...Nierenberg Long Term...Johnson Aviation...Gorse/Johnson Marine...Gorse/Johnson/Nierenberg is the U.S. government's official web portal to all federal, state and local government web resources and services.