Scattered thunderstorms moved across portions of northwest Illinois during the afternoon of August 23rd producing localized wind damage.
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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 LOT wrote it up.
Scattered thunderstorms moved across portions of northwest Illinois during the afternoon of August 23rd producing localized wind damage.
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 Chicago, IL wrote its last area forecast discussion before the first event at Aug 23, 12:24 PM CST, 1 hour 35 minutes earlier.
Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 124 PM CDT Mon Aug 23 2021 .SHORT TERM... 325 AM CDT Through Tuesday... The name of the game this week is "low predictability" as the eastern fringes of the EML plume advect perilously close to the region. Subtle low-amplitude perturbations riding the seasonably fast southwesterly upper-level flow will each have a potential to spark convection with one or several potential MCSs resulting for cell mergers/upscale growth, but narrowing down specific timing or location remains challenging to say the least. A significant bust potential on high temperatures exists on Tuesday--a totally dry day with sunny skies would likely result in widespread Heat Advisory conditions (Heat Indices 105+), while convective episodes would result in significantly lower values. In the immediate short term, light winds, clear skies, and lingering near-surface moisture will create an environment conducive for fog development--some of which could be dense at least on a localized basis south and west of I-90/94. We'll keep an eye on trends this morning for any fog headlines. First precipitation issue to contend with this morning is what happens with the developing/ongoing convection across northeast Iowa. This activity seems to be developing behind an earlier outflow boundary and within a zone of better isentropic upglide on the 310 K theta surface (or thereabouts). This warm advection is being modeled universally across the guidance suite, but the magnitude of saturation is not--with varying degrees of dry air noted in forecast soundings near 700 mb. The NAM/NAMNest duo seem to be matching reality in this regards better than anything else given surface observations of cloud ceilings now down to around 5 kft across NE Iowa. We'll usher in some chance PoPs after 7 AM into our western locales to account for this elevated convection. With an increasingly dry airmass in place with eastward extent, and with diurnally-waning WAA, do think precip chances will remain pretty minimal into the Chicago area later this morning. Forecast soundings look generally capped this afternoon to surface-based convection. High temperatures today should rise into the upper 80s/low 90s area-wide. Tonight's forecast gets pretty muddled given the overall subtle nature to the forcing. However, concerned a bit given the progged eastward advance of the EML plume, with 800-550 mb lapse rates forecast to steepen towards 7.5-8 C/km, in time to be intercepted by another diurnally-intensifying low-level jet. Recent guidance has shifted perhaps a bit north with the northern terminus of the attendant warm advection, meaning incipient convection could develop pretty far removed from our forecast area across southern Minnesota. The thickness and instability gradient though portend a southeast motion to any upscale-growing MCS, and so we'll continue to advertise a pretty broad region of chance PoPs very late tonight and into Tuesday with confidence on these mesoscale details just way too low to get more specific than this at this time. Deep shear should remain generally modest, but instability would be sufficient to foster at least a gusty wind threat with a (decaying) MCS. The potential for additional rounds of convection exist through the day on Tuesday--pending how things evolve during the morning. Bigger issue for Tuesday is that if we remain clear through peak heating, the combination of mid 70s dewpoints and temperatures climbing possibly into the mid-upper 90s would easily result in Heat Advisory conditions across a broad swath of the forecast area. For now, there's too much uncertainty here for any headlines with the current thinking that we'll have to contend with at least some convection during the day on Tuesday. Carlaw && .LONG TERM... 325 AM CDT Tuesday night through Sunday... The upper ridge remains locked in place over the central CONUS this week. Wednesday still looks the warmest of the extended period where the axis of warmest 850 temps (just above 20C) will be overhead. Guidance has this axis of warmer 850 temps shift slightly to the west for the latter half of the week which should help temps ease a few degrees along with whether any organized convection can help shift the front south of the area providing some northerly flow off of Lake Michigan. Dewpoints will generally remain elevated in the 70s, however, so it will likely still feel muggy. Those spending prolonged periods of time outdoors this week should take frequent breaks and drink plenty of water. This may sound like a broken record... but given the generally weaker flow south of the upper ridge and subtle disturbances moving through it, pinpointing specific timing and placement of various convective complexes that develop and move through the region remains rather fruitless. So have maintained precip chances nearly every period. There are signs the ridge tries to break down sometime next week with the flow turning more meridional which could help us get out of this warmer pattern. Petr && .AVIATION... For the 18Z TAFs... Aviation Weather Concerns: Primary concern will be possible early morning showers and thunderstorms Tuesday morning, with a second round possible late Tuesday afternoon. An area of thunderstorms west of I-39 this morning kicked off a line of showers that is now dying out south and east of I-80, but a few showers may linger into the late afternoon, especially in my southern counties. IFR to LIFR CIGs/VIS from this morning have lifted or dissipated to VFR conditions, which will remain VFR throughout the rest of Monday into Monday evening. Overall wind flow is from the south to southwest, with a few locations gusting to around 16 kt. Overall flow will remain from the south through Tuesday afternoon. A short-wave and associated convection is expected Tuesday morning, bringing showers and thunderstorms, and some MVFR visibilities and ceilings. Model guidance is a bit scattered in location and timing, but enough of a hint exists, and has existed for the past couple of days that we believe convection will occur, most likely between 10 and 15Z on Tuesday. Presently conditions do not appear to be severe, but some gusty winds and heavy rainfall is possible with these storms. After this area of convection moves out late morning Tuesday, there is a possibility for a second wave of convection occurring around 00Z Tuesday evening, but only a few models have indicated this possibility, so did not reflect this second wave of convection in my TAFs. If it occurs it could be as early as 23Z, and last into Tuesday evening. BKL && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && Visit us at weather.gov/chicago Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSChicago www.twitter.com/NWSChicago www.youtube.com/NWSChicago
Hazardous Weather Outlook National Weather Service Chicago/Romeoville IL 1153 AM CDT Mon Aug 23 2021 ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002- 010-011-019-241700- Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-De Kalb-Kane-DuPage- La Salle-Kendall-Grundy-Kankakee-Livingston-Iroquois-Ford- Northern Cook-Central Cook-Southern Cook-Northern Will- Southern Will-Eastern Will-Lake IN-Porter-Newton-Jasper-Benton- 1153 AM CDT Mon Aug 23 2021 /1253 PM EDT Mon Aug 23 2021/ This Hazardous Weather Outlook is for portions of North Central Illinois...Northeast Illinois and Northwest Indiana. .DAY ONE...This Afternoon and Tonight. Weather hazards expected... Limited Thunderstorm Risk. Limited Flooding Risk. Limited Excessive Heat Risk. DISCUSSION... A few isolated thunderstorms are possible this afternoon near and west of I-39. Additional thunderstorms may develop over the area overnight, posing a threat for gusty winds. Heavy downpours may cause ponding on some roads. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday and Wednesday... Limited Thunderstorm Risk. Limited to Excessive Heat Risk. Thursday through Sunday... Limited Thunderstorm Risk. Limited Excessive Heat Risk. DISCUSSION: Hot and humid conditions are expected through at least Wednesday with heat indices over 100 possible Tuesday and Wednesday. Periodic thunderstorms will occur as well, though many hours will stay dry. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be necessary through tonight. GENERAL STORM MOTION OF THE DAY: Moving toward the east and southeast at 10 to 20 mph. LMZ740>745-241700- Winthrop Harbor to Wilmette Harbor IL- Wilmette Harbor to Northerly Island IL- Northerly Island to Calumet Harbor IL- Calumet Harbor IL to Gary IN-Gary to Burns Harbor IN- Burns Harbor to Michigan City IN- 1153 AM CDT Mon Aug 23 2021 This Hazardous Weather Outlook is for portions of the Illinois nearshore waters of Lake Michigan and the Indiana nearshore waters of Lake Michigan. .DAY ONE...This Afternoon and Tonight. Weather hazards expected... Limited Thunderstorm Risk. .DAYS TWO THROUGH SEVEN...Tuesday through Sunday. Tuesday through Sunday... Limited Thunderstorm Risk. Castro Visit us at http://weather.gov/chicago Follow us on Facebook, Twitter, and Youtube at: www.facebook.com/nwschicago www.twitter.com/nwschicago www.youtube.com/nwschicago
Special Weather Statement
National Weather Service Chicago/Romeoville
252 PM CDT Mon Aug 23 2021
ILZ008-010-232030-
Ogle IL-Lee IL-
252 PM CDT Mon Aug 23 2021
...A strong thunderstorm will impact portions of western Lee and
southwestern Ogle Counties through 330 PM CDT...
At 252 PM CDT, Doppler radar was tracking a strong thunderstorm near
Dixon, moving southeast at 30 mph.
HAZARD...Wind gusts up to 50 mph and penny size hail.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects. Minor damage to outdoor objects is
possible.
Locations impacted include...
Dixon, Polo, Lost Nation, Grand Detour, Nelson, Harmon, Woodland
Shores, Eldena, Woosung and Nachusa.
Including the following interstate...
I-88 between mile markers 45 and 60.
This includes... Sauk Valley College.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
&&
LAT...LON 4200 8961 4188 8930 4165 8948 4176 8963
4193 8963 4193 8967
TIME...MOT...LOC 1952Z 305DEG 24KT 4188 8959
MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH
LENNINGThe Quad Cities radar (KDVN), 85 km away, was scanning. The volume nearest the first event began at 20:00 UTC.
1 thunderstorm wind. Local standard time, as filed.
Several large trees were damaged, about 100 yards east of the intersection of Penrose and Weldon Roads.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2021Every state in 2021This day in weather historyWarnings in Illinois, 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: 979472.