Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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387 FXUS61 KPHI 211248 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 848 AM EDT Wed Mar 21 2018 .SYNOPSIS... A major Nor`easter just east of the Mid-Atlantic coast today will track northeastward tonight, then will be located off the New England coast Thursday morning. High pressure builds southward to start the weekend, as low pressure slides to our south Saturday night and Sunday. High pressure should then build back in for early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 8 AM checkin. STS snow grid as posted on PHI web site and in briefing pkgs conts as is and is from 8AM today through 8 AM Thursday and does NOT include what occurred between 8 AM ydy and 8AM this morning. No further briefing pkgs today but we will update the STS as it becomes apparent to us that amounts will differ more 2 inches from our fcst. Will we get 10-12" in PHL? Possibly not but its going to be quite a mess. We already have a widening areas of MDT snow developing eastern PA and nw NJ just west of the I95 corridor and its only 12z with many reports coming in now of 2" snowfall in the last several hours. Also fwiw...temps rose into the upper 30s overnight in the I95 corridor when pcpn quit and still the ice/snow mix held strong. Ground has been cooled. We will be issuing LSR`s only for 1/hr snowfall accumulations and glaze reports elsewhere that totaled 0.1 or greater. Lets continue sending those reports to us via our skywarn or social media accts. Both the glaze overnight and the storm total snow and lets us know how the roads are doing and if any power outages. Collapsing thicknesses as pcpn now is changing to sleet and then snow most of our I95 area except the coast this morning. Synoptically: no chg from pattern recognition. A big event is unfolding and we just need to be patient. Significant nearly stationary banding now evident N central MD to eastern Berks western Bucks County to near NYC. EVERYONE will share in snow but the main axis of the S+ should be vcnty MQS-CKZ-SMQ. Higher amts than forecast are possible in the NNJ part of our fcst, particularly Northampton, Warren, Hunterdon, Morris, Somerset but we`re not raising at this time until we know for sure what we already have at 230 PM. If we will be STS only and posted to our office winter wx web page and also SM. Inverted trough developing from the developing primary coastal low through through Ches Bay and that can aid lift to its northeast. Monitoring. Regardless of snow amounts, SUBSTANTIAL impacts, including power outages and additional tree damage, are likely due to a combination of heavy snow, strong winds, blowing and drifting snow. Mesoscale wise: please note we are aware of a typical Berks county downslope shadow in western Berks. I can see storm totals ranging 7" western Berks to 15" near Huffs Church in the high terrain far eastern Berks. No changes yet but we are aware of the potential. Snow ratios: in 3 hr increments 12z tdy-07z tonight. PHL 9,10,11,12,12,12 to 1 using snow ratio blender. In the cldr ptn of storm e PA/NNJ vcnty I78 10,12,12,12,12,12 to 1 with Poconos slightly higher snow ratio. So even if qpf were to decrease this aftn, snow ratios will permit greater hourly accums. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... The low will begin to move northeast away from the region, bringing a gradual end to the snow but still expect an easy 1-3" after 8 PM. For the most part, expect any significant accumulations to be over with around 2 AM. Light snow showers may linger into the early morning hours, especially across northern NJ. For low temperatures, have gone on the lower side of guidance in anticipation of a widespread snow pack by that time. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Summary...Brisk and chilly Thursday and Friday; low pressure should slide to our south late Saturday and Sunday; some moderating of the temperatures should occur during early next week. Synoptic Overview...A significant closed low off the New England coast Thursday will take the Nor`easter with it. A significant short wave in the form of a closed mid level feature then drops southeastward across the Northeast and northern Mid-Atlantic Thursday night through Friday. The associated larger trough may linger through the weekend across the Northeast, helping to force low pressure to our south. There is some potential for an expansive closed low to evolve somewhere off the East Coast early next week while a ridge tries to shift eastward from the Great Lakes and Tennessee Valley. Given the major Nor`easter expected today, no major changes were made to the long term and much of the following is from yesterday`s day shift. For Thursday and Friday...Blustery and cold with northwest winds gusting to 35 mph during the day and a little less at night. Blowing snow in open areas depending on the amount of melting of the top layer of the expected snow pack. The snow pack could limit day time heating, so went with the lower side of guidance for highs each day. A southeastward moving mid level closed low crosses our area and should produce some rain/snow showers and perhaps a heavier snow shower. For Saturday through Monday...The mid-level large scale features include additional energy digging into the western states trough, which amplifies a downstream ridge over the central U.S., while high latitude blocking in the vicinity of the Davis Straits continues to trend down. This continues to influence the axis and amplitude of the trough across the Northeast U.S. and Southeast Canada, and the short wave disturbances moving through this feature as it gradually closes off well south of Nova Scotia early next week. There remains disagreement in the deterministic and ensemble solutions regarding low pressure tracking from the Great Planes on Saturday, with redevelopment off the Mid-Atlantic coast Sunday. The trend has been to suppress the low further to the south, yet the extent of dry air associated with a high pressure located east of the Appalachian Mountains remains in question, and therefore the northward extent of overunning precipitation associated with this system. While a focus for some precipitation would be across portions of eastern Pennsylvania and Delmarva from late Saturday into at least Sunday, it could certainly be more widespread across the remainder of the area, however this is uncertain and PoPs remain on the low side. Northeasterly low-level flow sets up once again later in the weekend and early next week, and we may have to monitor the potential for some renewed coastal flooding however this will depend on the strength and duration of the onshore flow. For Tuesday, the pattern is favoring a return to improved weather with temperatures moderating to closer to average. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...IFR/LIFR developing in snow, some of it mdt to 1/4S+. The sleet/freezing rain snow mix I95 TAF sites changing to all snow by 1330z. MIV and ACY take several more hrs, but probably go to all snow around 16z. Plowing ops will be needed at all TAF sites today and tonight. Drifting snow will develop at most if not all TAF sites by late this aftn. NE wind with occasional gusts 20-30 kt except gust 35-40 kt possible KACY. Winds trend N late today. Tonight...IFR conds in snow 00z-03z/22 becoming VFR as nw winds gust 20-30 with drifting snow and blowing snow at some of the TAF sites. Storm total accums 8 AM today through 5AM Thursday as of our current fcst. Amounts should be accurate to within 3". RDG 6 ABE 10 TTN 13 PNE 12 PHL 11 ILG 10 ACY 5 GED 4 Outlook... Thursday and Friday...VFR overall, however a few rain or snow showers possible Friday afternoon. Northwest winds near 15 knots with gusts up to 30 knots, then diminishing some Thursday night and Friday. Saturday and Sunday...VFR during the day Saturday, then possible MVFR conditions Saturday night and Sunday with a chance rain/snow. Northwest winds around 10 knots, becoming north to northeast 10-20 knots late Saturday into Sunday. Low confidence. && .MARINE... Winds should continue to increase through the morning hours. We haven`t gotten to storm force yet, but think that remains likely, at least through a few hour window during the day today, so have kept the storm warning going for the coastal waters and lower Delaware Bay. Along the upper Delaware Bay, gale conditions are expected. Seas are already observed over 11 feet, and those should continue to increase through at least the first half of the day. By early this evening, expect winds to begin to diminish as the storm moves away from the region. However, we may still see gale conditions for much of the night especially on the coastal waters. Outlook... Thursday and Friday...Small Craft Advisory conditions expected within a northwest flow. Saturday and Sunday...Small Craft Advisory conditions expected within a northwest flow Saturday, then continuing into Sunday as winds becoming northeasterly. && .TIDES/COASTAL FLOODING... Tide fcst still looks to be close to target at 730AM. A strong northeast wind continued along the coasts of New Jersey and Delaware during the night. The surge around the nighttime high tide was about 1.0 to 1.5 feet north of Barnegat Inlet and around 1.5 to 2.0 feet to the south. Minor flooding took place along the coast from Long Beach Island, New Jersey down to Sussex County, Delaware around the time of high tide. We have not made much change to the total water level forecasts for our tidal areas. We continue to favor the more robust ETSS due to the strength of the coastal storm. The ETSS has remained rather consistent from run to run over the past couple days. The Coastal Flood Warning for the New Jersey counties of Ocean, southeastern Burlington, Atlantic, Cape May and Cumberland, and for the Delaware counties of Sussex and Kent remains in effect until 5:00 AM Thursday. It covers the next two high tide cycles. The Coastal Flood Advisory for Monmouth County and Middlesex County remains in effect from 9:00 AM today until 5:00 AM Thursday. The surge will continue to lag a bit along the northern part of the New Jersey coast. The across-water fetch there is limited by Long Island and southern New England. Monmouth County and Middlesex County are forecast to experience widespread minor flooding, falling short of the warning threshold which is defined by moderate flooding. The surge is forecast to push up Delaware Bay and into the far lower Delaware River, impacting the high tides there this afternoon and tonight. A Coastal Flood Advisory is in effect for New Castle County and Salem County from noon today until 5:00 AM Thursday. The surge along the coast for today`s high tide is forecast to be around 2.0 feet in the far north and in the 2.5 to 3.0 foot range elsewhere. It is expected to produce minor to moderate coastal flooding along much of the New Jersey coast, the Delaware coast and Delaware Bay. Also, minor flooding should reach the the far lower part of the Delaware River. The wind is forecast to transition from north to northwest tonight. However, water is expected to remain trapped along our coast and we are anticipating another round of surge levels in the 2.0 to 3.0 foot range. The degree of flooding is expected to be similar to that of today. 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. && .CLIMATE... 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 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 chance of cracking top 10. We`ll update again at 5 PM Wednesday once we know whats occurred and whats coming. 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 end up closer to 15 inches or more... this would put northern NJ by Thursday morning 8 AM as the highest ever in our recorded history. Right now the average is 18.9 there and we expect it to rise to ~25 or 30" by 8AM Thursday (this has yet to happen), which would propel us to the snowiest March on record in NNJ. 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, above those records...we just dont know yet but by this time! We`ll let the reality determine the outcome. This is all stated to place some perspective on what we think this upcoming event can produce for us. 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 Daily Record Rainfall Site 3/20 3/21 3/22 ---- ---- ---- ---- PHL 1.76" (1958) 2.24" (2000) 1.90" (1977) ACY 2.56" (1958) 1.98" (2000) 1.54" (1903) ILG 1.99" (1913) 3.21" (2000) 2.22" (1977) ABE 2.12" (1958) 1.42" (1983) 2.49" (1977) RDG 3.03" (1958) 1.57" (1890) 2.70" (2000) TTN 1.74" (1958) 2.02" (1980) 2.25" (1977) GED 2.12" (1975) 1.94" (2001) 1.20" (1964) MPO 2.13" (1975) 1.28" (1950) 2.74" (1980) && .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 from noon today to 5 AM EDT Thursday for NJZ016. Coastal Flood Advisory until 5 AM EDT Thursday for NJZ012>014. 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 from noon today to 5 AM EDT Thursday for DEZ001. MD...Winter Storm Warning until 2 AM EDT Thursday for MDZ008-012- 015-019-020. MARINE...Storm Warning until 6 PM EDT this evening for ANZ431-451>455. Storm Warning until 7 PM EDT this evening for ANZ450. Gale Warning until midnight EDT tonight for ANZ430. && $$ Synopsis...Gorse Near Term...Drag/Johnson 847 Short Term...Drag/Johnson 847 Long Term...Drag/Gorse Aviation...Drag/Gorse/Johnson 847 Marine...Drag/Gorse/Johnson 847 Tides/Coastal Flooding...847 Climate...847 is the U.S. government's official web portal to all federal, state and local government web resources and services.