Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KPHI 220019 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 819 PM EDT Wed Mar 21 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 10 PM THIS EVENING/... The storm remains at its height through about 10 PM and there could be some 8 inch amounts for parts of coastal New Jersey between from late this afternoon through 9 PM. Strong snow bands continue along the NJ shore, and the heaviest snow will be south and east of I-95 in NJ , but down towards Atlantic City-Cape May, the strongest snow bands will be in the vicinity of the Garden State Parkway. The forecast is pattern recognition and blending 12z/21 models/WPC/adjacent office considerations. The STS is from 2PM to 8AM Thursday with this storm essentially done from west to east between midnight and 5 am. So our STS does not include all the snow that occurred prior to 2 PM. We have many reports of 10+ inches now. Regardless of snow amounts, SUBSTANTIAL impacts, including power outages and additional tree damage, are likely this evening due to heavy snow. && .SHORT TERM /10 PM THIS EVENING THROUGH 6 AM THURSDAY/... Snow ends from west to east between midnight and 5 AM with not much clearing. Temps may rise several degrees after the snow quits wet bulbing. strong cold outbreak to follow but still below normal for this time of year. && .LONG TERM /THURSDAY 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. The major coastal storm affecting our region today and tonight will be pulling northeast away from the area tomorrow. The region should be precip-free by 12Z, so a dry forecast is in place. Went below guidance for highs given expected snow cover and albedo effects tomorrow (and possibly somewhat persistent partial to considerable cloud cover). Temps generally 10-15 degrees below seasonal averages. Breezy conditions expected but nothing out of hand. Given the dryness of the snow, may see a little bit of blowing snow in the higher terrain, but winds look pretty marginal so did not feel the need for inclusion in the grids anywhere. 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 /00Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Conditions slowly improve to VFR at KRDG/KABE by 06Z. Otherwise, IFR/LIFR conditions in snow will continue at KTTN/KPNE/KPHL/KILG through 08Z, and for KMIV/KACY until 10-12Z Thursday. NW winds 10-15 kt. Thursday...VFR. NW winds 10-15 kt with gusts up to 20 kt. 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... Gale force winds through tonight with elevated seas. 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 2 AM EDT Thursday for PAZ070-071- 101>106. Winter Storm Warning until 11 PM EDT this evening for PAZ054- 055-060>062. NJ...Winter Storm Warning until 2 AM EDT Thursday for NJZ001- 007>010-012>027. Coastal Flood Warning until 5 AM EDT Thursday for NJZ020>027. Coastal Flood Advisory until 5 AM EDT Thursday for NJZ012>014- 016. DE...Winter Storm Warning until 2 AM EDT Thursday for DEZ001>004. Coastal Flood Warning until 5 AM EDT Thursday for DEZ002>004. Coastal Flood Advisory until 5 AM EDT Thursday for DEZ001. MD...Winter Storm Warning until 2 AM EDT Thursday for MDZ008-012- 015-019-020. MARINE...Gale Warning until noon EDT Thursday for ANZ450>455. Gale Warning until 4 AM EDT Thursday for ANZ430-431. && $$ Synopsis...Drag Near Term...Drag/MPS Short Term...Drag Long Term...CMS Aviation...CMS/Drag Marine...CMS/Drag Tides/Coastal Flooding... Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.