A warm front lifted through the mid-Atlantic on the morning of August 23, bringing some showers with it. After a midday lull in precipitation, a lee side surface trough helped to initiate some thunderstorms in a moist and moderately unstable environment.
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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 warm front lifted through the mid-Atlantic on the morning of August 23, bringing some showers with it. After a midday lull in precipitation, a lee side surface trough helped to initiate some thunderstorms in a moist and moderately unstable environment. The relatively weak forcing and limited shear prevented much storm organization, but a few storms did become strong to severe with a few instances of damaging winds.
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 Aug 23, 2:42 PM EST, 1 hour 11 minutes earlier.
Area Forecast Discussion National Weather Service Mount Holly NJ 342 PM EDT Sun Aug 23 2020 .SYNOPSIS... A surface trough will remain near the Mid Atlantic states through early next week. A cold front is forecast to approach the area later Tuesday into Tuesday night. This front will lift back northward as a warm Front Wednesday night into Thursday, then another surface trough is forecast to develop across the Mid Atlantic states Thursday. This trough will likely remain near the Mid Atlantic region into the weekend until another cold front possibly moves across the area around Saturday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... A surface warm front lifting northward through our region, and an impulse traveling in the west southwest mid level flow set off some showers in northeastern Maryland and Delaware this morning. The showers expanded northward into the Philadelphia metropolitan area and southern New Jersey. Daytime heating and the resulting increase in instability caused the showers to build into thunderstorms this afternoon. The availability of abundant low level moisture led to locally heavy downpours with some spots picking up around 2 inches of rain in a short amount of time. At mid afternoon, the showers and thunderstorms were weakening a bit in parts of our region. There was a well defined outflow boundary spreading outward from the complex of showers and thunderstorms. We continue to expected scattered showers and thunderstorms into this evening, especially in southeastern Pennsylvania, southwestern New Jersey, northern Delaware and far northeastern Maryland. Those areas should be the focus of the best instability in our region. Also, there will likely be lingering outflow boundaries to help trigger additional convection. The loss of daytime heating this evening should cause any lingering showers and thunderstorms to weaken and dissipate before midnight. We are anticipating a partly cloudy sky overnight with patchy fog possible, especially in areas that received rain today. Low temperatures will favor the upper 60s and lower 70s with a light and variable wind. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... Monday should be another very warm and humid day in our region. Dew point readings are expected to be in the lower 70s with maximum temperatures near 90 in many spots. We are anticipating that a mid level impulse will pass overhead around midday with another one approaching from the west late in the day. Mixed layer CAPE values are forecast to rise into the 1000 to 1500 J/KG range. As a result, we are expecting another round of scattered showers and thunderstorms. Precipitable water values should be near 2 inches, so locally heavy rainfall is again possible. The wind is forecast to be from the southwest and west around 5 to 10 MPH. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... Several periods of warm and unsettled weather are expected during the long term forecast, with one nice day for the middle of the week. The lee-side/thermal surface trough that have been in place across the Mid Atlantic region Sunday and Monday will still be near the area on Tuesday. But it will finally get pushed out of the area as a cold front is expected to move across the area later Tuesday into Tuesday night. There will be a chance of showers and thunderstorms in the morning as a short wave/vorticity impulse is forecast to move through early in the day and may interact with the surface trough and create a few showers and thunderstorms. However, a stronger short wave/vorticity impulse will move across the area later in the day into Tuesday evening when there will be greater instability with CAPE values of 1000+ J/kg. Meanwhile, 0-6 km shear values increase to 30+ knots as the mid-level winds increase to 35-45 knots as the flow turns northwest. Strong to damaging winds are expected to be the main threat with, especially if a squall line forms. Freezing levels/wet bulb 0 heights are pretty high at 13,000-14,000 feet, so hail is not expected to be a big threat, although cannot be ruled out for taller storms. Even outside of thunderstorms, Sunday-Tuesday will have gusty afternoon winds of 20-25 mph possible. The front will continue to move across the area Tuesday evening, and as the front passes eastward, shower/thunderstorm activity will dissipate through the night. The front will be south of the area by Wednesday morning, and a dry and not as warm day is expected. Temperatures are still forecast to be above normal, but mostly in the low-mid 80s. No precipitation is expected as PW values will 1 inch or less for much of the day and dewpoints will be int he low to mid 60s. However, this begins to change by Wednesday evening and overnight. PW values return to 1.5+ inches as the front to the south returns back northward as a warm front overnight. Another surface trough is expected to develop across the Mid Atlantic later Thursday and remain across the Mid Atlantic region into Friday. This will lead to above normal temperatures, and with several short waves/vorticity impulses, there will be a few rounds of showers and thunderstorms possible. Another front is expected to approach the area later Friday into Saturday which could also bring with it moisture from the remnants of what is currently Tropical Storm Laura. There are timing and placement differences between the long term guidance, but they all do show some effects from the front and moisture from Laura late Friday into Saturday. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Into this evening...Mainly VFR. Scattered showers and thunderstorms may bring conditions briefly to MVFR/IFR. Variable wind 5 to 10 knots. Medium to high confidence. Overnight...Mainly VFR. Local MVFR/IFR conditions in low clouds and patchy fog after 06Z. Variable wind 6 knots or less. Medium to high confidence. Monday...Mainly VFR. Scattered showers and thunderstorms may bring conditions briefly to MVFR/IFR. Southwest to west wind 5 to 10 knots. Medium to high confidence. Outlook... Tuesday-Tuesday night...Generally VFR conditions expected. Chance of showers and thunderstorms which may temporarily lead to localized lower conditions, especially Tuesday afternoon and evening. West winds 5-10 knots, become northwest then north behind the front Tuesday evening and overnight. Gusts each afternoon could reach 15- 20 knots. Gusts could reach 15-20 knots during the afternoon. Wednesday-Wednesday night...VFR conditions expected. Northwest wind 5-10 knots, with gusts 15-20 knots possible during the afternoon, becoming light and variable during the evening and overnight. Thursday-Friday...Generally VFR expected. A chance of showers and thunderstorms which may temporarily lead to lower conditions. West to southwest winds 5-10 knots, with gusts of 15-20 knots during the daytime. && .MARINE... A southwest to west wind around 10 knots is expected to continue into Monday. Wave heights on our ocean waters should range from 2 to 3 feet. Waves on Delaware Bay are forecast to be 2 feet or less. OUTLOOK... Monday night-Friday...Conditions expected to remain below Small Craft Advisory levels through the period, although winds could gust around 20 knots at times, and seas could build to 3-4 feet. There is a chance of showers and thunderstorms each day, especially Monday and Tuesday, and Thursday and Friday which could lead to locally higher winds and waves. Rip currents...There is a low risk for the development of dangerous rip currents into this evening. A southerly wind around 10 MPH is expected. Breaking waves should be less than 2 feet with a medium period swell from the southeast. The low risk is forecast to continue on Monday. The wind should be from the south around 10 MPH. Breaking waves are expected to be 2 feet or less with a medium period swell from the southeast and south. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && Synopsis...Robertson Near Term...Iovino Short Term...Iovino Long Term...Robertson Aviation...Iovino/Robertson Marine...Iovino/Robertson
Hazardous Weather Outlook National Weather Service Mount Holly NJ 344 PM EDT Sun Aug 23 2020 DEZ001>003-MDZ008-012-015-019-020-NJZ001-007>010-012-013-015>023-027- PAZ054-055-060>062-070-071-101>106-241945- New Castle-Kent-Inland Sussex-Cecil-Kent MD-Queen Annes-Talbot- Caroline-Sussex-Warren-Morris-Hunterdon-Somerset-Middlesex- Western Monmouth-Mercer-Salem-Gloucester-Camden- Northwestern Burlington-Ocean-Cumberland-Atlantic-Cape May- Southeastern Burlington-Carbon-Monroe-Berks-Lehigh-Northampton- Delaware-Philadelphia-Western Chester-Eastern Chester- Western Montgomery-Eastern Montgomery-Upper Bucks-Lower Bucks- 344 PM EDT Sun Aug 23 2020 This Hazardous Weather Outlook is for central Delaware, northern Delaware, southern Delaware, northeast Maryland, central New Jersey, northern New Jersey, northwest New Jersey, southern New Jersey, east central Pennsylvania, northeast Pennsylvania and southeast Pennsylvania. .DAY ONE...This afternoon and tonight. There is a low probability for widespread hazardous weather. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Scattered showers and thunderstorms are anticipated to move through the region on Tuesday. Some of these storms could become strong to severe with the most likely threat being isolated swaths of damaging wind gusts. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. DEZ004-NJZ014-024>026-241945- Delaware Beaches-Eastern Monmouth-Atlantic Coastal Cape May- Coastal Atlantic-Coastal Ocean- 344 PM EDT Sun Aug 23 2020 This Hazardous Weather Outlook is for southern Delaware, central New Jersey and southern New Jersey. .DAY ONE...This afternoon and tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Monday through Saturday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. ANZ430-431-450>455-241945- 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 Sandy Hook to Manasquan Inlet NJ out 20 nm- 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- 344 PM EDT Sun Aug 23 2020 This Hazardous Weather Outlook is for Atlantic coastal waters and Delaware Bay Waters. .DAY ONE...This afternoon and tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Monday through Saturday. The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
338 PM EDT SUN AUG 23 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0300 PM FLOOD 1 SE ELAM 39.85N 75.53W
08/23/2020 DELAWARE PA PUBLIC
SEVERAL ROADS FLOODED IN BETHEL TOWNSHIP
INCLUDING NAAMANS CREEK ROAD BETWEEN EBRIGHT
ROAD AND ROUTE 202.
&&
GORSESpecial Weather Statement
National Weather Service Mount Holly NJ
344 PM EDT Sun Aug 23 2020
NJZ016-017-021-022-232015-
Salem-Cumberland-Atlantic-Gloucester-
344 PM EDT Sun Aug 23 2020
...A LINE OF STRONG THUNDERSTORMS WILL AFFECT WEST CENTRAL
ATLANTIC...NORTHERN CUMBERLAND...CENTRAL SALEM AND SOUTHEASTERN
GLOUCESTER COUNTIES...
At 342 PM EDT, radar indicated strong thunderstorms were located
roughly along a line extending from Newfield to near Rosenhayn to
near Elmer to Port Penn. Movement was southeast at 5 mph. There are
three separate strong thunderstorms along this line, with the one
heading into western Atlantic County being the strongest.
Wind gusts up to 40 mph and pea size hail are possible with these
storms.
Locations impacted include...
Vineland, Millville, Bridgeton, Salem, Buena, Alloway, Weymouth,
Quinton, Newfield, Elmer, Shiloh, Franklinville, Olivet, Malaga,
Hancocks Bridge, Hope Creek, Mizpah, Seabrook Farms, South Vineland
and Rosenhayn.
This includes Atlantic City Expressway between mile markers 22 and
24.
Frequent cloud to ground lightning is expected at times with these
storms. Lightning can strike 10 miles away from a thunderstorm. Seek
a safe shelter inside a building or vehicle.
LAT...LON 3941 7485 3946 7558 3951 7558 3953 7557
3957 7557 3962 7527 3963 7510 3958 7475
3949 7471
TIME...MOT...LOC 1942Z 320DEG 6KT 3954 7499 3952 7510 3957 7523 3953
7557
GorsePRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
350 PM EDT SUN AUG 23 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0320 PM HEAVY RAIN 1 SE ELAM 39.84N 75.52W
08/23/2020 M4.65 INCH DELAWARE PA PUBLIC
4.65 INCHES OF RAIN MEASURED IN ABOUT 90
MINUTES BY A PERSONAL WEATHER STATION IN
BETHEL TOWNSHIP.
&&
GORSESpecial Weather Statement National Weather Service Mount Holly NJ 410 PM EDT Sun Aug 23 2020 NJZ016-021-232045- Salem-Cumberland- 410 PM EDT Sun Aug 23 2020 ...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN CUMBERLAND AND SOUTHERN SALEM COUNTIES... At 409 PM EDT, a strong thunderstorm was located near Newport Meadows, or 9 miles west of Bridgeton, moving east at 15 mph. Wind gusts up to 40 mph and pea size hail are possible with this storm. Locations impacted include... Bridgeton, Alloway, Quinton, Greenwich, Shiloh, Olivet, Hancocks Bridge, Newport Meadows, Fairton, Cedarville, Seabrook Farms, Rosenhayn and Centerton. Torrential rainfall is also occurring with this storm, and may cause localized flooding. Do not drive your vehicle through flooded roadways. Frequent cloud to ground lightning is occurring with this storm. Lightning can strike 10 miles away from a thunderstorm. Seek a safe shelter inside a building or vehicle. LAT...LON 3944 7553 3955 7547 3956 7511 3925 7524 TIME...MOT...LOC 2009Z 289DEG 15KT 3948 7539 Gorse
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
414 PM EDT SUN AUG 23 2020
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0410 PM HEAVY RAIN NEWFIELD 39.55N 75.02W
08/23/2020 M1.93 INCH GLOUCESTER NJ TRAINED SPOTTER
STREET FLOODING REPORTED.
&&
CMSSpecial Weather Statement
National Weather Service Mount Holly NJ
445 PM EDT Sun Aug 23 2020
NJZ021-232115-
Cumberland-
445 PM EDT Sun Aug 23 2020
...A STRONG THUNDERSTORM WILL AFFECT CENTRAL CUMBERLAND COUNTY...
At 444 PM EDT, a strong thunderstorm was located over Fairton, or
over Bridgeton, moving southeast at 20 mph.
Wind gusts up to 45 mph and pea size hail are possible with this
storm.
Locations impacted include...
Vineland, Millville, Bridgeton, Laurel Lake, Greenwich, Shiloh,
Newport, Dividing Creek, Fairton, Cedarville, Fortesque, South
Vineland, Rosenhayn and Seabrook Farms.
Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.
Frequent cloud to ground lightning will occur at times with this
storm. Lightning can strike 10 miles away from a thunderstorm. Seek
a safe shelter inside a building or vehicle.
LAT...LON 3918 7514 3939 7545 3940 7544 3939 7542
3940 7541 3941 7542 3951 7519 3950 7515
3946 7508 3949 7507 3947 7493
TIME...MOT...LOC 2044Z 299DEG 19KT 3939 7524
GorseThe Dover AFB radar (KDOX), 70 km away, was scanning. The volume nearest the first event began at 20:50 UTC.
2 thunderstorm wind. Local standard time, as filed.
Trees were reported down in Hopewell Twp and the Bridgeton area, including near Greenwood Dr and Osborn Ln. Time estimated from radar.
Power lines were downed near Victory Rd. Time estimated from radar.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in New Jersey in 2020Every state in 2020This day in weather historyWarnings in New Jersey, August 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: 909983, 909984.