As a cold front moved through the region, showers and storms developed. Some of the storms produced damaging winds.
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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 LSX wrote it up.
As a cold front moved through the region, showers and storms developed. Some of the storms produced 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 St. Louis, MO wrote its last area forecast discussion before the first event at Sep 20, 5:43 PM CST, 2 hours 43 minutes earlier.
Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 643 PM CDT Mon Sep 20 2021 .SHORT TERM... (Through Late Tuesday Night) Issued at 240 PM CDT Mon Sep 20 2021 The main concern for tonight is the thunderstorm/severe weather potential and then the extent of any precipitation Tuesday/Tuesday night. The latest model runs continue to indicate a broad upper trof currently moving into the northern/central Plains will move eastward tonight through Tuesday night impacting our region. This progressive and deepening trof will drive a cold front through our area, with the front entering the western CWA this evening, and exiting the CWA by midday on Tuesday. Current anticipation is that a line of showers and storms will develop along the front in NW MO later this afternoon with the line expanding with time and entering western portions of the LSX CWA around 01-02z and moving eastward across central and eastern MO and into western IL through the night. There appears to be a roughly 3-4 hour window or so of severe weather potential with this line, mainly across parts of central and northeast MO into west central IL this evening. During this time frame deep layer shear and 0-3 km shear along and just ahead of the frontal zone will be in the 25-30 kt range, the shear vectors will have a good orthogonal component to the front, and MLCAPE will range from 1000-1500 J/KG. The linear forcing along with this CAPE/shear space would support potential for a few bowing line segments with wind damage the main threat and possibly a short-lived tornado. Overnight large scale forcing becomes greater in the wake of the front and deep shear weakens quite a bit ahead of the front as the shear vectors back. Cumulatively this along with weakening MLCAPE would suggest that the surface-based convection with the advancing cold front will lose organization and weaken, and elevated post-frontal precipitation will become more dominant through the overnight hours as the front moves eastward. The upper trof will continue to dig into the region on Tuesday and into Tuesday night with an upper low eventually evolving over southern IL early Wednesday morning. The bulk of lingering precipitation on Tuesday should be centered in the morning hours from east-central and southeast MO into southwest IL associated with large scale forcing attendant with the deepening trof and low-mid level frontogenetic forcing. This cold front will bring much cooler temperatures and our first real taste of fall with highs on Tuesday some 15-20 degrees cooler than today. Glass .LONG TERM... (Wednesday through Next Monday) Issued at 240 PM CDT Mon Sep 20 2021 Model guidance is in general agreement that a rather deep trof and embedded upper low will be the dominate weather features Wednesday-Thursday with the upper trof meandering eastward through the eastern U.S. The biggest model differences revolve around how quickly the upper closed low will evolve, it's position and impact on the sensible weather in the LSX CWA including lingering showers. Given the aforementioned evolution of the closed low in the vicinity of southern IL early Wednesday morning, there could be lingering showers in the eastern CWA in the morning. Otherwise the trof will maintain an expansive and cool surface/low level anticyclone across the region Wednesday and Thursday which will result in below normal but seasonably cool temperatures. Late Thursday into Friday, the eastern U.S. upper trof weakens and is kicked northeastward in response to a new upper trof digging into the middle/upper MS Valley. This results in a short-lived period of low level WAA as the aforementioned anticyclone retreats and before the next cold front arrives. This new digging upper trof will send a cold front through the area late Friday into early Saturday and potentially another reinforcing cold front late Saturday/Saturday night. Weak forcing with the trof and cold front itself could end up producing a few light showers with the fropa, but at this time the moisture appears rather limited due to the early week fropa and thus the current forecast is dry. There is growing agreement with the deterministic and ensemble guidance with continued deepening and residence of the upper trof in the eastern U.S. for the coming weekend. This should at least result in another period of seasonably cool temperatures on Saturday, but the longevity into Sunday is a bit more uncertain at this time. Glass && .AVIATION... (For the 00z TAFs through 00z Tuesday Evening) Issued at 626 PM CDT Mon Sep 20 2021 A line of showers and thunderstorms have developed along and just ahead of a cold front over northwestern Missouri that will move through the region tonight. This activity will move into central/northeast Missouri and west central Illinois this evening, by 02z. So MVFR/IFR flight conditions expected with onset of activity at KUIN, KCOU and KJEF between 02z and 07z Tuesday. Once front moves through by 07z Tuesday, gusty south to southwest winds will veer to the northwest. Ceilings will lift back to VFR by 17z Tuesday. As for St. Louis metro area TAFs, showers and storms will not move in til after 06z-07z Tuesday. VFR flight conditions will persist this evening before lowering to MVFR/IFR with onset of showers and storms. South to southwest winds will veer to the northwest with frontal passage by 11z Tuesday. Despite frontal passage, expect some lingering post frontal showers in the St. Louis metro area til midday. Then VFR flight conditions will return to the area by 21z Tuesday. Byrd && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && WFO LSX
Hazardous Weather Outlook National Weather Service Saint Louis MO 255 PM CDT Mon Sep 20 2021 ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027- 034>036-041-042-047>052-059>065-072>075-084-085-099-212000- Adams IL-Audrain MO-Bond IL-Boone MO-Brown IL-Calhoun IL-Callaway MO- Clinton IL-Cole MO-Crawford MO-Fayette IL-Franklin MO-Gasconade MO- Greene IL-Iron MO-Jefferson MO-Jersey IL-Knox MO-Lewis MO-Lincoln MO- Macoupin IL-Madison IL-Madison MO-Marion IL-Marion MO-Moniteau MO- Monroe IL-Monroe MO-Montgomery IL-Montgomery MO-Osage MO-Pike IL- Pike MO-Ralls MO-Randolph IL-Reynolds MO-Saint Charles MO- Saint Clair-Saint Francois MO-Saint Louis City MO-Saint Louis MO- Sainte Genevieve MO-Shelby MO-Warren MO-Washington IL-Washington MO- 255 PM CDT Mon Sep 20 2021 This Hazardous Weather Outlook is for portions of eastern and central Missouri as well as west central and southwest Illinois. .DAY ONE...Tonight. Thunderstorms are likely over much of the area tonight. A few severe thunderstorms are possible, mainly across central and northeast Missouri and west central Illinois. Damaging winds are the primary severe weather threat with any severe storms. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. There is a chance of thunderstorms across southeast and east central Missouri and southwest Illinois on Tuesday morning. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this evening. Glass
The St Louis radar (KLSX), 176 km away, was scanning. The volume nearest the first event began at 02:27 UTC.
2 thunderstorm wind. Local standard time, as filed.
Thunderstorm winds blew down several large trees as well a a couple of power poles around town.
Thunderstorm winds blew a tree down onto an unoccupied car causing moderate damage.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Missouri in 2021Every state in 2021This day in weather historyWarnings in Missouri, 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: 984534, 984536.