A frontal boundary stalled over the mid-Atlantic on the overnight of September 2 and lifted northward slightly during the day on September 3. A robust shortwave trough was also approaching during the day.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS PHI wrote it up.
A frontal boundary stalled over the mid-Atlantic on the overnight of September 2 and lifted northward slightly during the day on September 3. A robust shortwave trough was also approaching during the day. This combination caused a high shear environment to develop, with good moisture also present. However, instability was marginal due to considerable cloud cover over the area. In addition, multiple rounds of storms associated with different sources of lift tended to work against each other, as storms generally struggled to organize and become dominant. However, given the high shear some storms still became strong to severe and produced instances of damaging wind.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Sep 3, 1:20 PM EST, 4 hours 10 minutes earlier.
Area Forecast Discussion National Weather Service Mount Holly NJ 220 PM EDT Thu Sep 3 2020 .SYNOPSIS... Another cold front is expected tonight into tomorrow morning. In the wake of that cold front, high pressure is expected to build in from the north, brining tranquil conditions through at least the weekend. Heat and humidity could build again next week as a low lifts across the Great Lakes region. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Expect an active evening of weather tonight as showers and thunderstorms impact the Mid Atlantic region. We anticipate some of these storms will have the potential to become severe and there is a risk that some of the storms will have the potential to produce tornados. Based on an analysis of current observations and satellite we can see plenty of clear skies across portions of DelMarVa and southern New Jersey with what amounts to a warm front lifting north. The front is generally aligned across the border of MD/PA and then and then curves north towards central NJ. North of the front clouds are filtering in from the west and are causing a slight decrease in overall potential instability. South of the warm front we are seeing rich theta-e advection and instability should increase throughout the rest of the afternoon. Across portions of southern DelMarVa we already have upwards of 1500-2000 J/kg of MUCAPE with the expectation that area of instability will continue pushing north. The storms this evening will be the result of an approaching cold front with an upper level shortwave which will provide the needed surface convergence and lift to get storms developing. The challenge will be where the greatest chance for severe thunderstorms materializes and how much potential rainfall do we see from them. Nothing in the 12z or subsequent hourly rapid updating HRRR/RAP seems to indicate a difference in timing with the thought that showers with embedded thunderstorms will be moving into the region between 4-5PM this evening. As typical for the region we anticipate mixed mode storms. We'll likely see clusters of cells develop that with time as they move closer to the coastal will merge into line segments or even perhaps become a qlcs as the bulk shear is off the boundary but the anvil relative flow will be boundary parallel and become stronger towards the coast. We think as the storms move towards the region there will likely be a split, or delineation of the highest thunderstorms potential across where the warm front stalls. We've indicated that in the forecast by mentioning numerous showers with scattered thunderstorms moving through the Lehigh Valley into central and northern NJ while across DelMarVa we are using numerous showers and thunderstorms in the forecast. The main threat today will be damaging winds as 40 to 50 kt winds will be possible between 2-4 km above the surface and DCAPE values are forecast to increase through the afternoon, so it won't take much to mix down stronger winds. Tornados can not be ruled out as there is 0-1 cyclonic shear with helicity values increasing to 200-300 this evening. The tornado threat is maximized from roughly Cecil County MD through New Castle DE north to Chester, Eastern Montgomery, Philadelphia counties in PA and then across southern NJ from Burlington and southern Ocean county all the way to Cape May. This is where LCL's should be low enough that even as the storms become linear there will still be enough rotational potential to develop tornados. As the previous forecaster mention, heavy rain is a threat this afternoon and evening. PWAT's based on a blend of satellite data are increasing towards 1.7" to 1.8" this evening over DelMarVa. With a deep warm cloud layer there should be efficient warm cloud processes to cause high rainfall rates especially just south of the warm front. So heavy rain will be possible, even as storm motions are anticipated to be relatively fast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Storms should be shifting off shore and out of the region by or shortly after midnight. The cold front should be trailing shortly behind the storms during the overnight hours, but it the strongest cold air advection is not expected to develop until during the day on Friday. Thus, expect little change in lows tonight as compared to Thursday morning. Lows should generally be in the 60s and 70s. Strong cold air advection does indeed start pushing into the region on Friday as a more significant front moves through early Friday morning. We cloud see a shower or two mainly across southern DelMarVa as there does seem to be a weak short wave that tracks across late in the day. Rainfall totals would be low at best but the potential is there so we've indicated a slight chance for some showers or isolated thunderstorms. Highs will be tricky because even as there's cold air advection aloft the skies will be mostly clear so we should reach peak heating during the day. Highs generally will be in the low 80s with mid to upper 80s possible along the coastline. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Overview: For once, rather tranquil conditions are forecast through much of the long term. Details: Friday Night through Sunday...Cold advection pattern continues Friday night and by Saturday, most of the region should see highs staying in the 70s. On Sunday, the center of the surface high will have shifted offshore, so low level southwesterly flow is expected to develop. Consequently, we'll see a modest warming trend on Sunday, with highs mostly in the lower 80s. Monday and Tuesday...Most guidance keeps an upper level trough and associated surface low through the Great Lakes region well west of our area through this period. With this solution, our region should stay mostly dry through Tuesday. There should also be a slow warming trend through this period with much of the area seeing highs by Tuesday back into the mid 80s along with dew points starting to creep up as well. Wednesday and Thursday...By this timeframe the combination of a moist southerly flow and an approaching system from the west may bring a return to some showers and storms but there is uncertainty on this at this time range. We stayed close to the blended model guidance which brings in a chance for showers and storms for both days. Temperatures look to remain near to slightly above average for this time of year. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Mostly VFR conditions through the majority of the day. Another round of showers and storms is expected though by the late afternoon / evening time frame (mostly after 21z) and these will likely bring brief restrictions as low as IFR. The storms could even be severe and produce very strong winds. Winds will be shifting from northwesterly to southwesterly through the day. Moderate confidence on the overall pattern, but low confidence on the exact timing of storms. Tonight...Once the storms shift off shore, guidance is depicting MVFR ceilings and/or visibilities developing across much of the region. I think this will be highly dependent on which areas get heavy rain earlier in the evening. A cold front after 06Z will bring an abrupt shift to northwesterly winds of 5 to 15 kt. Low confidence. Outlook... Friday through Tuesday...VFR conditions are expected through this period. Northwesterly winds 5 to 15 kt through Saturday, becoming southwesterly and southerly 5 to 10 kt Sunday and Monday and eventually southeast around 5 knots by Tuesday. Moderate confidence. && .MARINE... Winds and seas are expected to be below Small Craft Advisory conditions through tonight though storms possible this evening could result in locally strong winds and higher waves. Outlook... Winds and seas should stay below SCA criteria through Tuesday. However, gusts near 20 kt are possible Friday night into Saturday morning. Rip currents... A moderate risk for the formation of dangerous rip currents is expected to continue through this evening. By tomorrow, wave height should decrease slightly, bringing a return of a low risk of rip currents. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && Synopsis...Johnson Near Term...Deal Short Term...Deal Long Term...Fitzsimmons/Johnson Aviation...Deal/Fitzsimmons/Johnson Marine...Deal/Fitzsimmons/Johnson
Hazardous Weather Outlook National Weather Service Mount Holly NJ 347 PM EDT Thu Sep 3 2020 NJZ001-008-PAZ054-055-042000- Sussex-Morris-Carbon-Monroe- 347 PM EDT Thu Sep 3 2020 This Hazardous Weather Outlook is for northern New Jersey and northeast Pennsylvania. .DAY ONE...This afternoon and tonight. Showers and storms will move through the region late this afternoon into this evening. The strongest storms should be just south of the area however it's possible a few storms could still produce locally damaging winds in addition to heavy rainfall. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. DEZ001>003-MDZ008-012-015-019-020-NJZ016>023-027-PAZ060-061-070-071- 101>106-042000- New Castle-Kent-Inland Sussex-Cecil-Kent MD-Queen Annes-Talbot- Caroline-Salem-Gloucester-Camden-Northwestern Burlington-Ocean- Cumberland-Atlantic-Cape May-Southeastern Burlington-Berks-Lehigh- Delaware-Philadelphia-Western Chester-Eastern Chester- Western Montgomery-Eastern Montgomery-Upper Bucks-Lower Bucks- 347 PM EDT Thu Sep 3 2020 ...TORNADO WATCH 485 IN EFFECT UNTIL 10 PM EDT THIS EVENING... This Hazardous Weather Outlook is for central Delaware, northern Delaware, southern Delaware, northeast Maryland, southern New Jersey, east central Pennsylvania and southeast Pennsylvania. .DAY ONE...This afternoon and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tornado Watch. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Please relay any information about observed severe weather to the NWS while following all local, state, and CDC guidelines. NJZ007-009-010-012-013-015-PAZ062-042000- Warren-Hunterdon-Somerset-Middlesex-Western Monmouth-Mercer- Northampton- 347 PM EDT Thu Sep 3 2020 This Hazardous Weather Outlook is for central New Jersey, northern New Jersey, northwest New Jersey and east central Pennsylvania. .DAY ONE...This afternoon and tonight. Thunderstorms are expected late this afternoon into this evening and some of these could be severe. The primary hazard is expected to be damaging winds however tornadoes will be possible as well. In addition, any storms will be capable of producing very heavy rainfall which could result in localized flash flooding. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Please relay any information about observed severe weather to the NWS while following all local, state, and CDC guidelines. NJZ014-042000- Eastern Monmouth- 347 PM EDT Thu Sep 3 2020 This Hazardous Weather Outlook is for central New Jersey. .DAY ONE...This afternoon and tonight. Some storms late this afternoon and evening could be severe. The primary hazard is expected to be damaging winds. A moderate risk for the formation of dangerous rip currents continues through this evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Please relay any information about observed severe weather to the NWS while following all local, state, and CDC guidelines. DEZ004-NJZ024>026-042000- Delaware Beaches-Atlantic Coastal Cape May-Coastal Atlantic- Coastal Ocean- 347 PM EDT Thu Sep 3 2020 ...TORNADO WATCH 485 IN EFFECT UNTIL 10 PM EDT THIS EVENING... This Hazardous Weather Outlook is for southern Delaware and southern New Jersey. .DAY ONE...This afternoon and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tornado Watch. A moderate risk for the formation of dangerous rip currents continues through this evening. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Please relay any information about observed severe weather to the NWS while following all local, state, and CDC guidelines. ANZ430-431-451>455-042000- Delaware Bay waters north of East Point NJ to Slaughter Beach DE- Delaware Bay waters south of East Point NJ to Slaughter Beach DE- Coastal waters from Manasquan Inlet to Little Egg Inlet NJ out 20 nm- Coastal waters from Little Egg Inlet to Great Egg Inlet NJ out 20 nm- Coastal waters from Great Egg Inlet to Cape May NJ out 20 nm- Coastal waters from Cape May NJ to Cape Henlopen DE out 20 nm- Coastal waters from Cape Henlopen to Fenwick Island DE out 20 nm- 347 PM EDT Thu Sep 3 2020 ...TORNADO WATCH 485 IN EFFECT UNTIL 10 PM EDT THIS EVENING... This Hazardous Weather Outlook is for Atlantic coastal waters and Delaware Bay Waters. .DAY ONE...This afternoon and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tornado Watch. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Please relay any information about observed severe weather to the NWS while following all local, state, and CDC guidelines. ANZ450-042000- Coastal waters from Sandy Hook to Manasquan Inlet NJ out 20 nm- 347 PM EDT Thu Sep 3 2020 This Hazardous Weather Outlook is for Atlantic coastal waters. .DAY ONE...This afternoon and tonight. Some storms late this afternoon and this evening will be capable of producing wind gusts above 34 kt. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed. Please relay any information about observed severe weather to the NWS while following all local, state, and CDC guidelines.
The Dover AFB radar (KDOX), 66 km away, was scanning. The volume nearest the first event began at 22:27 UTC.
3 thunderstorm wind. Local standard time, as filed.
Measured by a Tempest weather station on Bennet Point Rd.
County dispatch reported three calls for downed trees in Federalsburg. Time estimated from radar.
Wires were downed on Smithville Rd. Time estimated from radar.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Maryland in 2020Every state in 2020This day in weather historyWarnings in Maryland, September 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 910198, 910196, 910197.