Remnants of tropical cyclone Nicholas over Louisiana promoted a humid air mass and diurnal convection that produced heavy rains over and near the southern Plateau.
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The episode as NWS MRX wrote it up.
Remnants of tropical cyclone Nicholas over Louisiana promoted a humid air mass and diurnal convection that produced heavy rains over and near the southern Plateau.
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 Sep 18, 11:38 AM CST, 1 hour 34 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Morristown TN 138 PM EDT Sat Sep 18 2021 .UPDATE... FOR 18Z AVIATION. && .DISCUSSION... Radar shows weak convection on the east side of the inverted surface trough to our west, and this convection has been impacting parts of our area mainly along the Plateau. Still looks like the western/southern parts of our area will be the focus for precipitation, and plan to beef PoPs up to likely for all of this area. With the abundant moisture, weak flow, and high freezing levels there remains a threat for isolated flooding as highlighted in the HWO. Will tweak temps up northeast where best insolation will occur, and make a few tweaks to sky as well with this update. Otherwise, previous forecast looks to be on track. && .AVIATION... 18Z TAF DISCUSSION. Convection will continue to show the most coverage south, but activivity will wane overnight before increasing again late in the period. Will try to time best chances for thunder with tempo and prob30 groups at CHA/TYS but no more than VCTS at TRI this afternoon. MVFR, possibly briefly lower, conditions are possible with heavier showers/t-storms. May also see conditions lower to at least MVFR at CHA in fog/low cigs later tonight, and in fog at TRI toward sunrise, but confidence is low on the details. Winds will generally be light. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 70 79 69 78 69 / 50 80 80 60 50 Knoxville McGhee Tyson Airport, TN 68 83 68 77 67 / 30 40 80 70 30 Oak Ridge, TN 68 83 68 76 66 / 30 60 80 70 40 Tri Cities Airport, TN 65 85 66 78 65 / 20 20 30 50 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. &&
Hazardous Weather Outlook National Weather Service Morristown TN 1029 AM EDT Sat Sep 18 2021 NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002- 005-006-008-191430- 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- 1029 AM EDT Sat Sep 18 2021 /929 AM CDT Sat Sep 18 2021/ This Hazardous Weather Outlook is for portions of southwest North Carolina...east Tennessee and southwest Virginia. .DAY ONE...Today and Tonight Scattered to numerous showers and thunderstorms can be expected today, especially in areas along the Northern Plateau and also south of Interstate 40. These storms could cause isolated flash flooding of low lying and poor drainage areas. .DAYS TWO THROUGH SEVEN...Sunday through Friday Periods of heavy rainfall will be possible at times from Sunday afternoon through Monday morning, mainly across the southern Tennessee Valley and Cumberland Plateau. Another round of heavy rains will be possible area-wide Tuesday afternoon and night. Localized flooding will be possible in areas that typically see flooding, and in areas that receive heavy rainfall today and tonight. .SPOTTER INFORMATION STATEMENT... Spotter activation is not needed at this time.
The Northeast Alabama radar (KHTX), 102 km away, was scanning. The volume nearest the first event began at 19:14 UTC.
4 flash flood. Local standard time, as filed.
Flash flooding was reported in several parts of the county.
Some evacuations were occurring primarily along Branch Road.
Flooding, especially near Branch Road, was ongoing but improving.
Gunbarrel Road closed due to flooding.
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, September 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: 987539, 987544, 987546, 987550.