Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 220745 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 345 AM EDT Thu Mar 22 2018 .SYNOPSIS... In the wake of the departing Nor`easter, high pressure in Canada will slowly build south towards our region through the end of the week. A low pressure system propagating from the southern Plains to the southeastern U.S. should remain south of our region late this weekend. High pressure builds over our region early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Remainder of the winter storm warning has been canceled as only areas of light snow remain in the northeastern portions of the region. No significant additional accumulation is expected, and we should see snow continue to diminish across our region. In the wake of the departing low, should have a relatively tranquil, albeit cold day. Thanks to the northwesterly flow, cold air advection, and fresh snow pack, temperatures will be 10 to 15 degrees below normal, with highs forecasted between the lower 30s in the Poconos and mid 40s elsewhere. This is slightly below MOS guidance as that tends to have a warm bias immediately following a snow event. While there will be some melting thanks to the temperatures above freezing, expect much of the region will keep a substantial snowpack going into this evening. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... Thanks to clearing skies, temperatures tonight are expected to be lower than what we saw this morning, with lows tonight forecasted to be generally in the 20s across the region. As a result, any water on the roads from snow melt during the day could freeze leading to slippery conditions on area roads tonight into early Friday morning. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Friday...clearing skies on Thursday night will be short lived as a mid and upper level low, digs quickly southeast over the region through the day. This will result not only in increasing clouds, but also possibly some rain and snow showers, especially along and north of the I-78 corridor through the day. As noted in the previous forecast, the ECMWF continues to show dry conditions this day, and moisture could be very limited with little chance for moisture advection before this event. However, lower resolution models tend to underforecast precip with these types of clipper systems, so kept PoPs close to the previous forecast. Did not spend much time on the forecast beyond Friday to focus on wrapping up the winter storm event. From the previous discussion...Another strong vort max moves southward from eastern Canada on Saturday as a separate vort max moves west- to- east through the central U.S. and interacts with the digging perturbation. Attendant surface low in the central plains Saturday looks to be shunted southward somewhat as it tracks into the Ohio/Tennessee Valleys. Just how far south is a challenging question, with considerable disagreement among the operational guidance. The GFS looks especially suspicious, though, given its very progressive evolution of the northern- stream vort max. The 12Z CMC/ECMWF are slower and (as a result) have the track of the southern- stream system a little farther north. This may give the Delmarva Peninsula a chance for some precipitation Saturday night and Sunday. Additionally, there are some indications that as the surface low intensifies off the coast that wraparound (light) precipitation may affect the eastern CWA on Sunday (aided by the passage of the main northern-stream vort max). Cannot discount chances of rain and/or snow for much (if any) of the area during this period, so kept slight-chance PoPs in the grids. If the southward- deflection of the southern-stream system occurs later than anticipated, this may bring somewhat heavier precipitation into the area (especially Delmarva). A low- confidence forecast exists for this period, to be sure. Strong ridging develops early next week as the strong cyclonic vortex meanders eastward off the Atlantic coast. This should bring a prolonged dry period to the area along with a warming trend. A system may affect the region by mid to late week, but models have large timing differences. Generally included slight-chance to low- chance PoPs on Wednesday for now, but temperatures fortunately look more seasonal by then. && .AVIATION /07Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR conditions expected. NW winds 10-15 kt with gusts up to 20 kt. High confidence. Tonight...VFR conditions expected with only high clouds (15000 AGL or higher). Northwesterly winds near or below 10 KT. High confidence. Outlook... Friday: Potential for MVFR or low VFR CIGs and rain/snow showers, especially north of ABE-TTN. Northwest winds 5 to 15 kts with potential for gusts to 20 kts or so. Moderate confidence. Friday night and Saturday: VFR with northwest winds 5 to 15 kts, potentially lighter during the night. High confidence. Saturday night and Sunday: Some potential for sub-VFR conditions with light rain and/or snow. Winds north to northeast under 10 kts Saturday night and 10 to 20 kts on Sunday. Very low confidence. && .MARINE... Winds continue to diminish, but expect to see gale force conditions continue through at least sunrise on the lower Delaware Bay and the coastal waters. On the upper Delaware Bay, small craft advisory conditions will continue towards sunrise. Today and tonight...winds and seas will continue to subside, but expect SCA conditions to continue on the coastal waters for much of this period. On the Delaware bay, winds and waves will likely subside below SCA criteria by mid day. Outlook... Friday and Friday night: May see a lull in winds on Friday morning, but they should increase again by afternoon evening to advisory criteria. Saturday and Saturday night: Sub-advisory winds/seas expected. A slight chance of rain and/or snow late, especially near/south of Delaware Bay. Sunday: Advisory-level northeast winds expected, with some potential for gales (though this is low confidence). Some potential for rain and/or snow. && .TIDES/COASTAL FLOODING... Going through what should be the last high tide of concern right now. Once tide levels drop on the back bays, the coastal flood headlines will be allowed to expire. && .CLIMATE... There were several record daily maximum snowfalls set yesterday, March 21st. This occurred at Philadelphia, Wilmington and Allentown (which smashed their daily record). Atlantic City just missed the daily snowfall record. Location Record for 3/21 Actual Snowfall 3/21/18 -------- --------------- ----------------------- PHL 4.7" (1932) 6.7" ACY 5.9" (1889) 5.7" ILG 5.4" (1964) 6.7" ABE 4.3" (1964) 13.2" && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Coastal Flood Warning until 5 AM EDT early this morning for NJZ020>027. Coastal Flood Advisory until 5 AM EDT early this morning for NJZ012>014-016. DE...Coastal Flood Warning until 5 AM EDT early this morning for DEZ002>004. Coastal Flood Advisory until 5 AM EDT early this morning for DEZ001. MD...None. MARINE...Gale Warning until noon EDT today for ANZ450>455. Small Craft Advisory until 8 AM EDT this morning for ANZ430. Gale Warning until 6 AM EDT early this morning for ANZ431. && $$ Synopsis...Johnson Near Term...Johnson Short Term...Johnson Long Term...CMS/Johnson Aviation...CMS/Johnson Marine...CMS/Johnson Tides/Coastal Flooding...Johnson Climate...Gorse is the U.S. government's official web portal to all federal, state and local government web resources and services.