A marginally severe environment characterized by low to mid-60s dewpoints and 1500-2000 J/kg of skinny SBCAPE resulted in scattered, disorganized thunderstorms across portions of eastern Missouri and southern Illinois. One of these thunderstorms produced a microburst, causing isolated severe wind damage in southern Illinois.
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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.
A marginally severe environment characterized by low to mid-60s dewpoints and 1500-2000 J/kg of skinny SBCAPE resulted in scattered, disorganized thunderstorms across portions of eastern Missouri and southern Illinois. One of these thunderstorms produced a microburst, causing isolated severe wind damage in southern Illinois.
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 21, 6:01 PM CST, 1 hour 9 minutes earlier.
Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 701 PM CDT Thu Sep 21 2023 .SHORT TERM... (Through Late Friday Night) Issued at 227 PM CDT Thu Sep 21 2023 Our attention is slowly turning away from the low that tracked across our area yesterday and has boomeranged across Illinois and back into Iowa today. We've been enjoying subsident flow on the back side of this low today which has led to the sunnier and warmer conditions. Our attention is gradually shifting toward the Plains where low level moisture return has begun beneath a southwesterly flow aloft. This southwesterly flow creates a lee surface trough over the western Plains and aids in the development of south/southeast flow over the Plains, sucking in Gulf of Mexico moisture. This moisture surge will be greater to our west and this is where most of the action will be over the next day or two as that moist flow increases the instability beneath a slowly advancing trough aloft. In our area the moisture return is weaker and more subtle, and as a result, is not as likely to produce significant rainfall. As of this afternoon, a moisture gradient exists in the low levels across our area with drier air to the north beneath that subsident flow while more moist air exists across the south within a band of moisture rotating around the retrograding low. Within this belt of greater moisture a few showers have been noted through the day, and we cannot rule out a shower or thunderstorm popping up through the afternoon and evening, mainly focused within this area of moisture. As we go through the evening, the flow aloft becomes more southerly as the low to our north moves further away and the pressure gradient becomes more oriented in response to the lee trough to our west. The area of higher moisture across the southern forecast area this afternoon will then get pulled northward overnight, and this moist advection could be the trigger for a few showers and thunderstorms overnight mainly across the central and northern portion of the forecast area where that moist advection is greatest. Instability is rather weak with a skinny CAPE profile on soundings, so we're not expecting significant thunderstorms or severe weather. Meanwhile to our west, multiple clusters of thunderstorms are expected to form across the Plains of Kansas and Nebraska this evening and overnight with their movement generally to the east southeast. It's unclear which of these clusters may eventually make its way far enough east to affect our area, but we may be dealing with a remnant thunderstorm cluster by Friday morning, possibly aiding some redevelopment during the day. This remains fairly unclear at this point, though, and overall rain chances remain somewhat low (40 percent or less). Confidence in this time period will likely increase once we see how thunderstorms initiate and evolve to our west this evening. Either way we should see more cloud cover on Friday spilling over from the storms to our west which will result in lower temperatures. Kimble .LONG TERM... (Saturday through Next Thursday) Issued at 227 PM CDT Thu Sep 21 2023 The primary upper trough moves out over the Northern Rockies and into the Northern Plains on Saturday. This sets the stage for the final and most focused threat for thunderstorms of this pattern. Low level moisture maximizes to the east of the lee trough/dryline over eastern Kansas and Oklahoma on Saturday. This focuses the instability axis to our west during the day, with thunderstorms most likely to form along and east of that trough/dryline during the afternoon and evening. NBM PoP has finally come around to the idea that our area will largely be dry on Saturday, with the better rain chances coming through Saturday night into Sunday when what's left of those thunderstorms to our west finally track through. There's still some uncertainty on where they will form and track, but a new consensus may be developing which favors storms forming near the Kansas City area and tracking southeast from there, potentially affecting the southwest portion of our area. It's still possible portions of our area remain dry even as the primary trough axis moves by. While there is definitely a severe weather threat on Saturday afternoon and evening, we think that threat remains to our west within that corridor of greater instability over the Plains and we continue to not message a severe weather threat at this time. Considerable uncertainty exists beyond Saturday as models diverge on how to handle what's left of the upper trough in the Northern Plains. It may become cut off from the upper flow or get pulled gradually northward into Canada. Either way the relevant surface and upper level features become weak and nebulous across our area leading to less confidence particularly in the forecast precipitation chances. Generally speaking we'll be on the northeast side of a ridge axis to our west which favors subsident flow and dry conditions with temperatures dependent on how deeply we mix each day and how close the ridge gets. But subtle disturbances in that flow (or the meandering upper trough itself) could lead to areas of showers as well. At the moment the NBM PoP forecast was accepted which shows PoP generally fading out after Sunday but never really going to zero. Interquartile range of NBM temperature probabilities gets large from about Sunday onward with the difference being whether we stay in the 70s in a cooler easterly low level flow or whether we mix into some warmer air within the ridge and warm into the 80s. Kimble && .AVIATION... (For the 00z TAFs through 00z Friday Evening) Issued at 645 PM CDT Thu Sep 21 2023 Scattered showers and thunderstorms will affect the St. Louis area terminals through 01-02Z before diminishing, and have included VCTS during this time period. There will be a low chance of showers and thunderstorms during the rest of the period at all of the terminals, but the chance is too low to include in the TAFs at this time. Fog may develop late tonight into tomorrow, particularly in the river valleys, and have maintained 2SM FG at SUS between 9-13Z for this. Otherwise, mainly light winds are expected outside of thunderstorms. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && WFO LSX
Hazardous Weather Outlook National Weather Service St Louis MO 228 PM CDT Thu Sep 21 2023 ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027- 034>036-041-042-047>052-059>065-072>075-084-085-099-221930- Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL- Marion IL-Washington IL-Randolph IL-Adams IL-Brown IL-Pike IL- Calhoun IL-Jersey IL-Madison IL-Saint Clair IL-Monroe IL-Knox MO- Lewis MO-Shelby MO-Marion MO-Monroe MO-Ralls MO-Pike MO-Boone MO- Audrain MO-Moniteau MO-Cole MO-Osage MO-Callaway MO-Montgomery MO- Lincoln MO-Gasconade MO-Warren MO-Saint Charles MO-Franklin MO- Saint Louis MO-Saint Louis City MO-Jefferson MO-Crawford MO- Washington MO-Saint Francois MO-Sainte Genevieve MO-Iron MO- Madison MO-Reynolds MO- 228 PM CDT Thu Sep 21 2023 This Hazardous Weather Outlook is for portions of eastern and central Missouri as well as west central and southwest Illinois. .DAY ONE...Tonight. Showers and a few thunderstorms are possible but severe weather is not expected. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Thunderstorms are possible Friday through Sunday, with the best chance being Saturday night into Sunday. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time. Kimble
The St Louis radar (KLSX), 95 km away, was scanning. The volume nearest the first event began at 01:11 UTC.
2 thunderstorm wind. Local standard time, as filed.
Broadcast media reported that trees and power lines were knocked down in and around Marissa, with the most damage occurring on the southeast side of town. No information was given on the details of the trees.
Two campers were rolled over and multiple more campers were damaged at the World Shooting Complex north of Sparta as a result of severe microburst winds.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2023Every state in 2023This day in weather historyWarnings in Illinois, September 2023
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: 1148676, 1148677.