A small shower near an outflow boundary produced a well developed funnel cloud that was observed from multiple locations, including the air traffic control tower at the Aurora Municipal Airport.
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 LOT wrote it up.
A small shower near an outflow boundary produced a well developed funnel cloud that was observed from multiple locations, including the air traffic control tower at the Aurora Municipal Airport.
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 19, 5:30 PM CST, 31 minutes earlier.
Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 630 PM CDT Thu Aug 19 2021 .SHORT TERM... 259 PM CDT The primary forecast concern through the short term is the potential for fog developing late tonight into early Friday morning. There also may be a couple showers or storms Friday afternoon, but of a lower potential than the past two days. Early afternoon scattered showers and storms on primarily the lake breeze (or a composite of the lake breeze and convective outflows) have largely faded in coverage. Along this boundary and immediately behind it where still some forced parcel ascent, there will continue to be a chance for isolated showers and storms. This looks to be a little more favored along/east of I-57 and along/north of the Kankakee River. Any activity should fade by sunset or a little before. A stagnant, recycled air mass remains in place going into the night presenting the likelihood of fog to return. The low-level flow remains very light and surface winds should go calm. With again there having been scattered rain activity (primarily in the metro), this also aids in the boundary layer moisture. Guidance solutions are quite dispersive so that does not add to the confidence, but relying on persistence would indicate that at least patchy fog -- some being dense -- is probable. Forecast grids have several hours of 100 percent relative humidity based on temperature and dew point forecasts, and forecast soundings certainly are supportive. So have patchy fog area-wide and the evening shift may gain confidence on where to mention some dense verbiage. For Friday, a lake breeze will expand inland again. Convergence along it actually may be a little greater than today. However, slight height rises and warming near the 700 mb layer, will likely provide more capping. Convection allowing models do indicate spotty precipitation potential along the lake breeze, and feel that is the only area where there could be a focus. Otherwise, Friday looks muggy with similar highs to today, probably adding a degree or two. MTF && .LONG TERM... 246 PM CDT Saturday through Thursday... The primary forecast concerns from this weekend onward are occasional chances for showers and thunderstorms as well as building heat and humidity. Friday night, showers and thunderstorms are expected to develop from Minnesota southward into northern Missouri along an eastward- moving cold front. As the upper-level parent trough pivots northeast Saturday morning, the remnants of the overnight activity should attempt to work eastward into northern Illinois, though likely in a weakening state as the best upper-level forcing pulls away. Depending on the amount of remnant cloud cover from the overnight activity, at least scattered redevelopment of thunderstorms appears probable along the cold front during the afternoon hours (mainly along and southeast of I-55?). Forecast meager mid-level lapse rates of ~6 K/km, MLCAPE of 1500 J/kg, modest cloud-layer shear of 25-30 kt, and forecast PWATs of 1.7+ inches point to threats of gusty winds strong enough to down small tree limbs, healthy downpours, and occasional lightning strikes with the strongest storms all in all consistent with a level 1/5 severe weather threat. Anyone with outdoor plans Saturday evening are encouraged to stay up to date with the forecast. Highs Saturday will top off in the mid to upper 80s with peak heat indices in the low to mid 90s. In the wake of the cold front, Sunday will be dry and noticeably less humid with highs in the low to mid 80s. An onshore breeze from Lake Michigan will hold lakeshore locations in the upper 70s. As an upper-level ridge builds into the Great Lakes Monday onward, temperatures and humidity levels will rise once again. Forecast highs Monday onward are expected to reach the lower 90s with dew points in the lower 70s making it feel closer to 100. Peak forecast wet bulb globe temperatures (which takes into account sun angle and cloud cover in addition to temperature and humidity levels) top off around 90 along and south of I-80 Monday and Tuesday, suggesting that heat-preventative measures may need to be taken. With building heat and humidity levels will come increasing chances for gusty thunderstorms not dissimilar from the pattern last week. At this point, identifying when thunderstorms will occur is futile, so will stick to the message of rising heat, humidity, and thunderstorm chances. Borchardt && .AVIATION... For the 00Z TAFs... Aviation Forecast Concerns: * Isolated convection mainly vicinity KRFD early this evening. * Potential for IFR fog late tonight into early Friday (most likely MVFR for ORD/MDW). * East to southeast winds Friday with another lake breeze. Isolated thunderstorms had developed along the lake breeze earlier today. Combined outflow/lake breeze boundary has spread well west and south of the Chicago metro terminals as of early this evening, and convection is not expected in the immediate vicinity. The exception to this is at KRFD, where some weak convective cells have been festering 5-10 miles north of the field along an outflow boundary. One or more of these weak cells may drift south- southwest across the airfield in the next hour along a southwestward morning outflow boundary, but should eventually dissipate with sunset. These cells have not produced lightning as of 2320Z, though it can't be completely ruled out over the next hour or so. Otherwise, the main aviation weather concern is a repeat of diurnal fog development overnight in our moist low level air mass. Confidence in IFR (and potentially even brief LIFR) visibility remains fairly high for our outlying sites (GYY, DPA, RFD), with high confidence in MVFR (but low for IFR vis) for ORD and MDW. Light east-southeast surface winds on Friday will again support a lake breeze moving through ORD/MDW during the early afternoon hours. Strengthening ridge aloft will make for less favorable conditions for diurnal TSRA development (warmer mid-level temps and a fairly dry column above the boundary layer), though there is still a low-probability (below mention in TAF) potential for isolated convective SHRA/TSRA to develop along the lake breeze boundary. If this does occur, coverage should be more limited than it was today, and likely with weaker cells overall. Ratzer && .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 257 PM CDT Thu Aug 19 2021 ILZ003>006-008-010>013-019>021-023-032-033-039-103>108-INZ001-002- 010-011-019-202000- 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- 257 PM CDT Thu Aug 19 2021 /357 PM EDT Thu Aug 19 2021/ This Hazardous Weather Outlook is for portions of North Central Illinois...Northeast Illinois and Northwest Indiana. .DAY ONE...Tonight. Weather hazards expected... Limited Thunderstorm Risk. Limited Fog Risk. DISCUSSION... Isolated thunderstorms may continue through early evening, though almost all areas will remain dry. The greatest threats with any thunderstorm will be torrential downpours and occasional lightning strikes. Locally dense fog is likely again late tonight. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Friday... Limited Thunderstorm Risk. Limited Fog Risk. Saturday... Limited Thunderstorm Risk. Monday through Wednesday... Limited Thunderstorm Risk. Limited Excessive Heat Risk. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be necessary through tonight. GENERAL STORM MOTION OF THE DAY: Slow and erratic storm motions under 10 mph. LMZ740>745-202000- 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- 257 PM CDT Thu Aug 19 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...Tonight. Weather hazards expected... Limited Thunderstorm Risk. Limited Fog Risk. .DAYS TWO THROUGH SEVEN...Friday through Wednesday. Friday... Limited Fog Risk. Saturday... Limited Thunderstorm Risk. Monday through Wednesday... Limited Thunderstorm Risk. Borchardt 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
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
341 PM CDT THU AUG 19 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0205 PM HEAVY RAIN 1 SSE OAK FOREST 41.59N 87.74W
08/19/2021 M2.19 INCH COOK IL MESONET
USGS RAIN GAUGE AT OAK FOREST REPORTS 2.19
INCHES OF RAINFALL IN ABOUT 1 HOUR, WITH
OVER 1 INCH OCCURRING IN JUST 15 MINUTES.
0230 PM HEAVY RAIN HOMEWOOD 41.56N 87.65W
08/19/2021 M1.69 INCH COOK IL PUBLIC
PRIVATE WEATHER STATION REPORTS 1.69 INCHES
OF RAINFALL IN ABOUT 1 HOUR IN HOMEWOOD.
OVER 1 INCH OCCURRED IN 15 MINUTES.
&&Special Weather Statement
National Weather Service Chicago/Romeoville
444 PM CDT Thu Aug 19 2021
ILZ005-192230-
McHenry IL-
444 PM CDT Thu Aug 19 2021
...A strong thunderstorm will impact portions of northwestern McHenry
County through 530 PM CDT...
At 443 PM CDT, Doppler radar was tracking a strong thunderstorm near
Woodstock. This storm was nearly stationary.
HAZARD...Winds in excess of 40 mph and pea 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...
Woodstock, Wonder Lake and Greenwood.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
&&
LAT...LON 4238 8860 4248 8851 4238 8836 4228 8855
TIME...MOT...LOC 2143Z 320DEG 3KT 4238 8851
MAX HAIL SIZE...0.25 IN
MAX WIND GUST...40 MPH
RATZERThe Chicago radar (KLOT), 71 km away, was scanning. The volume nearest the first event began at 00:01 UTC.
1 funnel cloud. Local standard time, as filed.
A well developed funnel cloud formed between Lee and Shabbona and was observed from multiple locations, including the air traffic control tower at the Aurora Municipal Airport.
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: 979475.