Early morning convection anchored over a ridgetop and produced a localized area of heavy rainfall. The run off produced flash flooding downstream to the northeast of Elizabethton.
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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 MRX wrote it up.
Early morning convection anchored over a ridgetop and produced a localized area of heavy rainfall. The run off produced flash flooding downstream to the northeast of Elizabethton.
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 Morristown, TN wrote its last area forecast discussion before the first event at Aug 20, 2:32 AM EST, 3 hours 28 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Morristown TN 332 AM EDT Fri Aug 20 2021 .SHORT TERM (Today and Tonight)... Key Messages: 1. Isolated to scattered showers and thunderstorms are most likely in southeast Tennessee and southwest North Carolina. 2. Highs will be in the 80s for most with lows in the 60s to near 70. Today Currently, a mid/upper shortwave is centered along eastern portions of the area with an upstream 60+ kt jet streak. Upper divergence continues to be noted in the left-exit region of the jet streak due to indirect ageostrophic circulations. This has and will continue to allow for isolated shower activity across the area. During the daytime, the shortwave will progress eastward with northerly flow remaining in place down into the lower levels. Diurnal heating will allow for convective development with a focus on southwestern portions of the area where more notable overall and boundary layer moisture is noted. ML instability will be fairly marginal for this time of year at generally 1,000 to 1,500 J/kg. This is also coupled with indications for deep-layer shear of 20 to 25 kts. With these considerations and indications for notable DCAPE above 1,000 J/kg, locally gusty winds from a stronger storm or two can't be ruled out. Also, with recent heavy rainfall, isolated flooding is possible where repeated rainfall occurs. Tonight Heading into tonight, the shortwave will continue to move off to the east with a weak upper low forming west of the Mid-Atlantic region. This comes ahead of a shortwave ridge to the west. With generally weak forcing locally, much of the area will likely remain dry outside of some showers/storms possibly lingering. Model guidance does indicate potential for additional development into the morning hours on the eastern periphery of the ridge, but these indications are largely west of our area. BW .LONG TERM (Saturday through Friday)... Key Messages: 1. Troughing and NW flow this weekend will bring cooler temperatures and a defined moisture gradient across the area with precipitation being most probable across southeast TN. 2. Broad ridging will prevail to start next week with more diurnal convective trends favored amidst warming temperatures. Discussion: This weekend will be characterized by an upper level trough across the Central Appalachians with ridging building across the Great Plains. This will lead to NW flow aloft across the forecast area with subsidence strongest across NE TN and SW VA. This will result in a drier airmass and lower than normal PW values. Models show a tight moisture gradient across the region with higher PW values near 1.8 inch across portions of SE TN near Marion and Hamilton Counties with a tight gradient of drier values to the northeast near Knoxville and the Tri-Cities. This will result in highest PoPs on Saturday and Sunday being across the southwest zones of our forecast area with mostly dry conditions forecast further north and east of Knoxville. Cooler temperatures are also forecast with the lower heights across the forecast area, especially across NE TN and SW VA. Moving into the workweek, upper ridging to across the Great Plains expands eastward with 500mb heights increasing to 591 to 594 dam by midweek. This will lead to a warming trend and a more diurnal trends on convection. Isolated to scattered convection will be possible most afternoons along the mountains and plateau due to differential heating along the higher terrain. This trends is expected to continues through the week. JB && .AVIATION... 06Z TAF DISCUSSION. A relatively quiet TAF period is expected with reductions to MVFR or less likely at all TAF sites in the early morning hours. This will be from potential for fog and lower ceilings. Otherwise, MVFR is likely to prevail during the day and through the evening with TSRA more likely at or near CHA than TYS and TRI. BW && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 85 70 86 72 89 / 60 30 50 20 30 Knoxville McGhee Tyson Airport, TN 85 68 88 71 90 / 20 10 30 10 20 Oak Ridge, TN 86 68 87 69 89 / 20 10 30 20 20 Tri Cities Airport, TN 85 64 87 66 88 / 20 10 10 10 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. &&
Hazardous Weather Outlook National Weather Service Morristown TN 332 AM EDT Fri Aug 20 2021 NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002- 005-006-008-210745- Cherokee-Clay-Scott-Campbell-Claiborne-Hancock-Hawkins-Sullivan- Johnson-Morgan-Anderson-Union-Grainger-Hamblen-Northwest Cocke- Cocke Smoky Mountains-Northwest Greene-Southeast Greene- Washington-Unicoi-Northwest Carter-Southeast Carter-Roane-Loudon- Knox-Jefferson-Northwest Blount-Blount Smoky Mountains- North Sevier-Sevier Smoky Mountains-Sequatchie-Bledsoe-Rhea-Meigs- McMinn-Northwest Monroe-Southeast Monroe-Marion-Hamilton-Bradley- West Polk-East Polk-Lee-Wise-Russell- 332 AM EDT Fri Aug 20 2021 /232 AM CDT Fri Aug 20 2021/ This Hazardous Weather Outlook is for portions of southwest North Carolina...east Tennessee and southwest Virginia. .DAY ONE...Today and Tonight The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Saturday through Thursday The probability for widespread hazardous weather is low. .SPOTTER INFORMATION STATEMENT... Spotter activation is not needed at this time.
The Knoxville radar (KMRX), 113 km away, was scanning. The volume nearest the first event began at 10:58 UTC.
2 flash flood. Local standard time, as filed.
Several roads were closed due to high water or fast moving water in the Stoney Creek area northeast of Elizabethton.
Video depicted fast moving water on a homeowners property on Grindstaff Hollow Road near Sadie.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Tennessee in 2021Every state in 2021This day in weather historyWarnings in Tennessee, August 2021
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: 983700, 983701.