Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 220433 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1233 AM EDT Thu Mar 22 2018 .SYNOPSIS... A major Nor`easter located just east of the Mid-Atlantic coast this evening will track east out to sea later tonight. High pressure will attempt to build southward to start the weekend, as cold air settles into the region. A system will move through the eastern U.S. Saturday night and Sunday but may stay south of the northern Mid- Atlantic. High pressure should then build back in for early next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Current observations and radar trends depict low level dry air working in from the northwest. Thanks to dry air entrainment, snow showers especially along and west of the I-95 corridor are eroding. None the less, there are still pockets of visibility of 1 to 2 miles in these areas, so will hold off on canceling any more of the winter storm warning for now. Otherwise, temperatures will drop into the upper 20s or so, allowing for any slush or snow melt to freeze. Slippery driving conditions will likely continue through at least sunrise even after the snow ends. Power outages and additional tree damage, are possible tonight due to the buildup of heavy snow. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... Snow ends prior to daybreak Thursday. Not much clearing through the day, so expecting well below normal highs, given the cloud cover, fresh snowpack, and unseasonably cold airmass building into the region. Not much melting may occur. Highs will struggle to get out of the low 40s. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... With the ongoing winter storm, very little time was spent on the long-term forecast today. Main concerns include a chance of some rain/snow showers with a northwest-flow vort max passage on Friday and the ultimate track of a system moving through the eastern U.S. this weekend. Few changes were made to the previous forecast overall. Skies may not completely clear out Thursday night, so did not stray too far from guidance for lows...only slightly below consensus at this point. Friday`s forecast is tricky, as a potent northwest-flow vort max moves into the Northeast during the day. Its passage will be during the day, so timing is favorable for some instability showers, especially in northern/eastern portions of the area (given the track of the vort max). ECMWF is not enthused by the prospects, but coarser models tend to underforecast this threat. Some indications from GFS of this threat, and I think it is reasonable to keep slight PoPs during the afternoon for areas northeast of Allentown to Philly to Atlantic City. I did lower PoPs a little given insufficient support from longer-range hi-res guidance. Temperatures again below guidance given expected clouds and remaining snow cover (and once again 10-15 degrees below climatology). 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 /06Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Conditions are beginning to improve to VFR from the Delaware Valley and points west. At KMIV and KACY, IFR and MVFR conditions may linger through 10Z. NW winds 10-15 kt. Moderate confidence on the timing of improving conditions Thursday...VFR. NW winds 10-15 kt with gusts up to 20 kt. High confidence. Outlook... Thursday night: VFR with northwest winds 5 to 15 kts. High confidence. Friday: Potential for MVFR or low VFR CIGs and rain/snow showers, especially northeast of ABE-PHL-MIV. 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 are starting to diminish, but expect to see gale force conditions continue for at least the next few hours on all the waters. On the Delaware Bay, winds should subside below gale force well before sunrise. Outlook... Thursday: Remnant gale-force northwest gusts becoming small-craft advisory criteria during the day. Seas slowly subsiding. Thursday night: Small-craft advisory northwest winds continue. 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... Winds have shifted to the northwest, and have begun to diminish t0 10-20 mph. Although tides remain elevated tonight, they should not be as high as previously expected given that winds will not be quite as strong as forecasted. In general, expecting departures around 2 feet for northern and central NJ, 2 to 2.5 feet for southern NJ and DE zones, including land adjacent to Lower DE Bay, 1.5 to 2 feet for northern NJ, and around 1.5 feet for land adjacent to Upper DE Bay and the Tidal DE River. Coastal Flood Advisory remains in effect for northern NJ and parts of NJ and northern DE adjacent to Upper DE Bay and DE River as minor coastal flooding is expected with the upcoming high tides. The Coastal Flood Warning remains in effect for all other areas, though now anticipating widespread minor coastal flooding with areas of moderate coastal flooding, as opposed to widespread moderate coastal flooding. At this point, only spotty minor flooding is anticipated for the tidal Delaware River between the Commodore Barry Bridge and Trenton. No tidal flooding is expected for the upper eastern shore of Chesapeake Bay. Between this evening and early Thursday morning, these should be the last rounds of coastal flooding for this storm. && .CLIMATE... This section will be updated later this evening. NEAR record breaking March snowfall accumulation forecast at PHL. The record is 12 inches on March 13-14, 1993. #9 is 8.8 inches March 3-4, March 4-5 in 1981. Allentown record March two day storm total snow 19.9 inches March 19-20 1958 (close to a 60 year anniversary). # 10 is the 10.2" event of 3/29-30/1970. We have a very good chance of top 10 at ABE, barring any last minute model surprises. Wilmington record March two day storm total snow is 17.9 inches 3/19-20/1958. # 10 is 7.9" 3/2-3/1960. We have a VERY good chance of cracking top 10 list. Atlantic City record March two day storm total is 11.6 inches 3/1-2/69 and #7 is 7 inches 3/4-5/15 and 3/6-7/53. There is a good chance of cracking top 10. Also from Rutgers-Dave Robinson and Mat Gerbish at our request below. Since we think northern NJ per the Rutgers areal definition will exceed 5 inches of snow (areal average), probably 5 to 10 inches...this would put northern NJ by Thursday morning 8 AM as one of the highest ever in our recorded history. Right now the average is 18.9 there and we expect it to rise to ~25 by 8AM Thursday (this has yet to happen), which would propel us to the top 3 snowiest March on record in NNJ. Its going to take awhile before we know for sure. The monthly MARCH record for a single station in NJ to our knowledge via Rutgers is 43.0 in March 1958 at Canistear Reservoir. Oak Ridge had 42.0 and Greenwood Lake 36.8 also in 1958. This storm may drive the current Jefferson Township and Rockaway values which are near 33 inches, to near those records. We just wont know for sure until the final values post midday Thursday. This is all stated to place some perspective on what we think this upcoming event can produce for us. All climate sites will probably have record daily snowfall for March 21! See the records below. We wont know until early Thursday morning regarding specifics of the records. Our staff will post the appropriate RER at that time. Please dont call us. Our staff will still be very busy. Thank you. Daily Record Snowfall Site 3/20 3/21 3/22 ---- ---- ---- ---- PHL 9.6" (1958) 4.7" (1932) 3.0" (1914) ACY 5.0" (1914) 5.9" (1889) 2.4" (1964) ILG 10.3" (1958) 5.4" (1964) 3.0" (1943) ABE 16.5" (1958) 4.3" (1964) 2.6" (1992) Snowfall as of (3/18/18) Site March `18 Rank Since 7/1 Rank ---- --------- ---- --------- ---- PHL 7.6" 26 22.2" 56 ACY 3.5" 17 28.0" 13 ILG 6.1" 24 19.9" 48 ABE 7.5" 26 32.8" 39 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Winter Storm Warning until 6 AM EDT early this morning for PAZ060>062-070-071-101>106. NJ...Winter Storm Warning until 6 AM EDT early this morning for NJZ001-007>010-012>027. 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...Winter Storm Warning until 6 AM EDT early this morning for DEZ001>004. 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...Winter Storm Warning until 6 AM EDT early this morning for MDZ008-012-015-019-020. MARINE...Gale Warning until noon EDT today for ANZ450>455. Gale Warning until 4 AM EDT early this morning for ANZ430-431. && $$ Synopsis...Drag Near Term...Drag/Johnson/MPS Short Term...Drag Long Term...CMS Aviation...CMS/Drag/Johnson Marine...CMS/Drag/Johnson Tides/Coastal Flooding... Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.