An upper level system moved through the region, triggering showers and storms. Some of the storms became severe producing damaging winds.
Every event with a place to put it. Tap one for its entry below.
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.
An upper level system moved through the region, triggering showers and storms. Some of the storms became severe producing 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 Aug 8, 11:39 AM CST, 2 hours 39 minutes earlier.
Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1239 PM CDT Sun Aug 8 2021 .SHORT TERM... (Through Late Monday Afternoon) Issued at 310 AM CDT Sun Aug 8 2021 Key messages through Monday afternoon: 1) The potential for strong to severe thunderstorms remains elevated across most of the area this afternoon and evening. Damaging wind and large hail are the predominant threats, but flash flooding could also be of concern. 2) Humidity will continue to build across the region Monday, which could result in heat indices over 100F if lingering clouds and convection do not hinder temperatures. An upper-level trough, currently providing synoptic support to a decaying MCS in eastern KS/western MO, will continue to propagate east overnight and provide the focus for thunderstorms today. Latest surface analysis shows a warm, humid airmass across most of the Mississippi Valley, with sub-65F dewpoints at a premium. Southerly low-level flow is beginning to strengthen in advance of the MCS and amidst a tightening surface pressure gradient. Lingering clouds from this morning's convection will work to restrict our high temperatures today, despite stronger low-level winds, but we should still reach the upper 80s/low-90s. CAMs differ on the timing of CI and convective evolution, but it appears that the majority of the storms should develop with the passage of a vortmax through the CWA early this afternoon. There are some indication of isolated CI ahead of the synoptic mid-level forcing during the late morning, which may serve to destabilize the cap in advance of the stronger storms. Most guidance continues to produce elevated surface dewpoints and does not properly handle diurnal mixing, but it is clear that more-than-sufficient SBCAPE will be available to the forcing to produce scattered strong/severe thunderstorms during the afternoon. 0-6km bulk shear appears slightly weaker among the current suite of deterministic and HREF guidance, which could serve to limit organized storm development and favor quick upscale growth. Mid- level lapse rates of 6.5-7.0C/km, combined with the robust updrafts expected from even a conservative CAPE estimate, could pose an initial threat of both large hail and damaging wind. However, with weak deep-layer shear, upscale growth should occur quickly and the threat shifts more to damaging wind. This threat extends across eastern MO and western IL, but the greatest concern remains across central/northeast MO and west-central IL during the afternoon and early evening. As the initial synoptic forcing moves east and the base of the shortwave crosses the CWA, the threat for severe storms should transition to one for flash flooding. Guidance continues to indicate that an outflow boundary will set up across part of the area and provide the focus for training thunderstorms to cause heavy rain for several hours. HREF probability-matched mean 3-hr QPF highlight southeast MO for potentially 1"+/hr rain rates Sunday evening through early Monday morning. However, there is uncertainty as to where this boundary sets up, which could shift this axis of heavy rain north or south accordingly. With IVT values still expected to exceed the 90th climatological percentile, aided by a 30- 35kt LLJ, plentiful moisture could interact with this boundary and produce instances of flash flooding for some across the area, with focus on southeast/south- central MO. The upper-level shortwave will begin to exit the area Monday morning, pulling synoptic support for precipitation with it. Some guidance is more sluggish in clearing the shortwave, and if convective activity can sustain itself through the night along the nose of the LLJ, it could help reinvigorate showers and storms Monday. While bulk shear looks a bit more robust later Monday morning across southwest/west-central IL, the quality of the airmass is in question after the activity overnight. Given this, while an isolated strong storm cannot be ruled out before the system exits the CWA, most of the robust convection should be east of us. Decreasing clouds from west to east will help central MO warm a degree or two higher than eastern MO and western IL, but we should still reach at least the upper 80s areawide. At this point, the greatest chance for 100F+ heat indices rests in central/northeast MO, where warmer temperatures and higher humidity will overlap. MRB .LONG TERM... (Monday Night through Saturday) Issued at 310 AM CDT Sun Aug 8 2021 Key messages through the extended forecast period: 1) Elevated heat and humidity is possible through Thursday, with the potential for dangerous heat indices across most of the area Tuesday. 2) Several rounds of energy, which should help spur daily threats for thunderstorms, may eventually help push a weak cold front through the area. This could bring a brief, but welcomed, respite from heat concerns. Upper-level ridging will build into the region Monday night, setting up Tuesday to potentially be the warmest and most humid day of the week. NAEFS and GEFS guidance point to 850mb temperatures near the 90th percentile, but surface humidity could help push heat indices into the triple digits. However, Tuesday could also see convective activity which would act against warmer temperatures. Deterministic models are in agreement that a subtle shortwave will traverse the northern portion of the area, which could spark thunderstorms. Several sources of uncertainty remain, namely whether or not this consensus of such a subtle feature is accurate and whether the storms would occur after peak heating. With several consecutive days featuring heat indices over 100F, a Heat Advisory is certainly possible. However, my confidence regarding marginally- high heat indices is low given the potential for convection to restrict temperatures, as such no Heat Advisory was issued. Several rounds of shortwave impulses traversing the base of a longwave trough, modeled to set up across southern Canada, will help to gradually push a boundary through the region later this week. As such, the chance for precipitation remains non-zero during the afternoon each day of the extended period as this energy interacts with moisture on the warmer side of the boundary. WPC Cluster Analysis depicts the uncertainty that exists with respect to the upper-level flow pattern late this week. One cluster, which represent nearly one-third of the members, has a more expansive ridge across most of the CONUS, restricting cooler air to the north. As of now, the forecast reflects a gradual but notable cooldown compared to recent conditions. MRB && .AVIATION... (For the 18z TAFs through 18z Monday Afternoon) Issued at 1224 PM CDT Sun Aug 8 2021 Thunderstorms are expected to develop across the region this afternoon and will likely affect all of the terminals between 20-24Z with IFR visibilities in heavy rainfal, MVFR or IFR ceilings, wind gusts to 35 knots or higher, and possibly some hail. Thunderstorms will continue into the evening hours before diminshing overnight with generally dry and VFR conditions expect late tonight into Monday morning. Only exception will be at KUIN where low ceilings are expected to linger. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && WFO LSX
Hazardous Weather Outlook National Weather Service Saint Louis MO 302 PM CDT Sun Aug 8 2021 ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027- 034>036-041-042-047>052-059>065-072>075-084-085-099-092015- 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- 302 PM CDT Sun Aug 8 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 through tonight. A few of the thunderstorms through this evening could be severe, with large hail and damaging winds being the main threats. Locally heavy rainfall will also be possible this afternoon into tonight, which could result in isolated instances of flash flooding. .DAYS TWO THROUGH SEVEN...Monday through Saturday. Heat index readings will be in the 100 to 110 degree range over parts of the area during the afternoon and early evening hours from Monday into Thursday. A heat advisory is now in effect for much of the area on Monday. There is a chance for thunderstorms over portions of the area from Monday through Saturday. .SPOTTER INFORMATION STATEMENT... Spotter activation will likely be needed through tonight. Britt
The St Louis radar (KLSX), 40 km away, was scanning. The volume nearest the first event began at 20:18 UTC.
5 thunderstorm wind. Local standard time, as filed.
Thunderstorm winds blew down several trees and tree limbs.
Thunderstorm winds blew down several power lines between Hopewell and Marthasville.
Thunderstorm winds blew down several large tree limbs.
Thunderstorm winds blew down a tree onto power lines.
A swath of damaging winds moved across the central portions of St. Louis County. Several trees were blown down N. Forty Drive just north of Frontenac. Also, several large tree limbs were blown down in Overland and St. Ann, as well as, Hazelwood.
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, 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: 979061, 979062, 979063, 979064, 979065.