A line of strong to severe thunderstorms impacted much of eastern Iowa, northwest Illinois, and northeast Missouri during the early morning of August 20. This line of storms produced wind gusts to 70 MPH and several reports of wind damage.
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 DVN wrote it up.
A line of strong to severe thunderstorms impacted much of eastern Iowa, northwest Illinois, and northeast Missouri during the early morning of August 20. This line of storms produced wind gusts to 70 MPH and several reports of wind damage. Several trees and power lines were taken down in Mediapolis, Monmouth and Roseville.
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 Quad Cities, IA wrote its last area forecast discussion before the first event at Aug 20, 5:43 AM CST, 1 hour 37 minutes earlier.
Area Forecast Discussion National Weather Service Quad Cities IA IL 643 AM CDT Tue Aug 20 2019 ...AVIATION UPDATE... .SYNOPSIS... Issued at 300 AM CDT Tue Aug 20 2019 High pressure beginning to shift into the Western Great Lakes has led to return flow and increasing theta-e advection through western and central Iowa. Over the last few hours, IR imagery has shown explosive development of elevated convection across western Iowa in a region of low-level jet induced isentropic lift and convergence. MUCAPE is this area is around 4000 J/kg. Locally, for eastern Iowa and northwest Illinois, it has been a muggy but dry night with temps and dewpoints in the mid 60s to low 70s. && .SHORT TERM...(Today and Tonight) ISSUED AT 300 AM CDT Tue Aug 20 2019 Today Thunderstorm Potential: There is an Enhanced risk for severe thunderstorms this morning roughly in the counties along and south of I-80. An organized MCS or squall line is expected to quickly move through about the SW half of the forecast area. The stratiform comma-head precip shield with embedded thunder will likely extend into parts of the northern CWA. The primary threat is damaging straight- line winds of 50-70+ mph with the highest gusts from bowing segments or surges in the line. Large hail is also possible in embedded supercell structures. The HRRR seems to be a little too far north with the track of the MCS compared to the 3 km NAM and other HREF members. Timing: The most likely timing for the MCS to reach the western counties is between 5-8 AM, the Mississippi River corridor between 7-10 AM, and then areas to the SE in the 8-11 AM window. Environmental Setup: The atmosphere will become primed for a severe thunderstorm complex to track from central Iowa into west-central Illinois this morning. Storm clusters will initially form in a region of elevated instability across central Iowa on the periphery of a 30 kt low-level jet early this morning. Continual theta-e advection manifest as a surge in both surface- based and elevated CAPE, will provide the fuel to sustain a mature MCS into parts of E Iowa/NW Illinois. While the deep layer shear isn't terribly strong (at 30 kts or less), moderate to high instability and more than sufficient 0-1 km shear of 20-25 kts will foster robust convection and a sustained/balanced cold pool. For storm motion, the instability gradient, 1000-500mb thickness contours, and forward-propagating Corfidi vectors all support an ESE trajectory with the line. The tornado risk is low because 0-1 km shear vectors are below 30 kts, but an isolated spin up tornado is possible. Again, this is mainly a wind threat event, with some opportunity for large hail especially across the western CWA where residual supercellular structures may still be intact. Rainfall amounts shouldn't get too out of hand given storm motion of 40-50+ mph. However, PWATs around 2 inches will lead to extremely heavy downpours with hourly rates over 2 inches a possibility. For event totals, thinking 0.50 to 1.50 inches for most areas that get impacted by the MCS. Lower amounts are possible across the north and northeast. After the MCS shifts east by late morning to midday we may have to watch for a period of strong winds on the backside of the MCS due to a wake low/meso high tight pressure gradient. It will be very warm and humid during the afternoon with peak heat indices in the 90s across the west and south. Tonight Majority of the night will be quiet, but another complex of storms may develop to our west across eastern Nebraska and western Iowa and then track to the ESE. Models varying quite a bit on the timing of this round of storms, which could hit the SW forecast area prior to 6-7 AM. Right now the consensus is near or after 7-8 AM. This time tracking a little more to the southwest than this morning's round. Uttech .LONG TERM...(Wednesday through Monday) ISSUED AT 300 AM CDT Tue Aug 20 2019 There are timing and placement issues through the long term period. The main forecast concerns are chances of precipitation through the period. The long term period is dominated by a progressive zonal flow across the northern CONUS. The long term period opens 12 UTC on Wednesday as a piece of shortwave energy dig southward into the base of a trough over southeastern Canada that digs into the northeast US. This energy will phase with another shortwave moving eastward across Iowa and drive a cool front across the area Wednesday morning. The NAM has come in wetter and farther to the north with the latest run which has expanded POPs northward across the area in the forecast. THe GFS, ECWMF, and Canadian limit convection to south of I-80 during the day on Wednesday. Disagreement between the models on the Thursday to Friday time frame as to how far south the Wednesday cool front sinks into Missouri. The GFS pushes the front south of Interstate 80 with any precipitation in the region closer to the frontal boundary while the Canadian and ECWMF keep the front further to the north and lingers precipitation across northern Missouri and southern Iowa through the day on Thursday. The Canadian and ECWMF solution seems to be more likely as the front will be parallel to the the winds aloft and that will slow its southward progression. This will help to keep the chance of showers and thunderstorms across southern Iowa and northern Missouri into Thursday. Lowered chances of showers and storms on Friday and Saturday as models showing high pressure lingering over the Great Lakes with high temperatures in the upper 70s and dewpoints in the upper 50s to lower 60s. Friday and Saturday look to be pleasant days. Another 500 HPA trough will move into the Canadian Prairie Provinces and Upper Midwest during the day on Sunday. At this point, the GFS develops northwesterly flow aloft as a ridge builds in the Pacific Northwest while the ECWMF leaves the ridge off shore and develops a zonal flow across the region. Either solution results in several prices of shortwave energy moving across eastern Iowa, northwest Illinois, and far northeast Missouri. This will result in daily chances of precipitation with the best chances on Sunday. Monday through Tuesday will usher in temperatures warming into the mid 80s with dewpoints back into the mid 60s. && .AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning) ISSUED AT 634 AM CDT Tue Aug 20 2019 A complex of thunderstorms will dive southeastward across eastern Iowa this morning through 15 UTC. This will being mvfr ceilings and visibilties to KCID, KBRL, KMLI, and KDBQ with periods of IFR ceilings and visibilties in the strongest storms. Strongest winds with these storms are expected near KCID and KBRL this morning. Thunderstorms are expected to exit by 16 UTC with conditions quickly improving to VFR and expected to remain there through the TAF period. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && SYNOPSIS...Uttech SHORT TERM...Uttech LONG TERM...Cousins AVIATION...Cousins
Hazardous Weather Outlook National Weather Service Quad Cities IA IL 418 AM CDT Tue Aug 20 2019 IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007- 009-015>018-024>026-034-035-MOZ009-010-210930- Buchanan-Delaware-Dubuque-Benton-Linn-Jones-Jackson-Iowa-Johnson- Cedar-Clinton-Muscatine-Scott-Keokuk-Washington-Louisa-Jefferson- Henry IA-Des Moines-Van Buren-Lee-Jo Daviess-Stephenson-Carroll- Whiteside-Rock Island-Henry IL-Bureau-Putnam-Mercer-Henderson- Warren-Hancock-McDonough-Scotland-Clark- 418 AM CDT Tue Aug 20 2019 This Hazardous Weather Outlook is for portions of north central Illinois...northwest Illinois...west central Illinois...east central Iowa...northeast Iowa...southeast Iowa and northeast Missouri. .DAY ONE...TODAY AND TONIGHT There is an Enhanced risk for severe thunderstorms this morning in the counties along and south of Interstate 80 and a slight risk further north. The main threat is damaging winds as a fast moving squall line crosses through parts of the outlook area. The strongest cells within the line could produce gusts up to 70 mph. Torrential rainfall rates could lead to ponding of water on roadways and very low visibilities. There is a low threat for an isolated spin up tornado and large hail. For timing, the line of storms should reach the western counties between 6 to 9 AM, along the Mississippi River corridor between 7 to 10 AM, and into the southeast counties between 8 to 11 AM. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY An active weather pattern is forecast through the long term period with chances of showers and thunderstorms Wednesday and Thursday and again Sunday through Tuesday. There is still some uncertainty on Wednesday but there is the potential for at least isolated severe thunderstorms in far southeastern Iowa, northeast Missouri and west central Illinois during the day. Severe thunderstorms are not anticipated on Thursday. It is still too early to determine the severe thunderstorm threat for Sunday through Monday. .SPOTTER INFORMATION STATEMENT... Spotter and amateur radio activation will be needed this morning. Uttech/Cousins
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
743 AM CDT TUE AUG 20 2019
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0743 AM HEAVY RAIN KEYSTONE 42.00N 92.20W
08/20/2019 M3.72 INCH BENTON IA PUBLIC
SPOTTER REPORT RELAYED FROM BROADCAST MEDIA.
TOTAL RAINFALL SO FAR.
&&
PSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
745 AM CDT TUE AUG 20 2019
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0744 AM TSTM WND GST NEW LONDON 40.93N 91.41W
08/20/2019 M70 MPH HENRY IA TRAINED SPOTTER
SPOTTER REPORT RELAYED BY EMERGENCY
MANAGEMENT.
&&
PSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
746 AM CDT TUE AUG 20 2019
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0743 AM HEAVY RAIN KEYSTONE 42.00N 92.20W
08/20/2019 M3.72 INCH BENTON IA TRAINED SPOTTER
CORRECTS PREVIOUS HEAVY RAIN REPORT FROM
KEYSTONE. SPOTTER REPORT RELAYED FROM
BROADCAST MEDIA. TOTAL RAINFALL SO FAR.
&&
PSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
752 AM CDT TUE AUG 20 2019
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0752 AM HEAVY RAIN PARNELL 41.58N 92.01W
08/20/2019 M1.40 INCH IOWA IA TRAINED SPOTTER
RAINFALL TOTAL SO FAR THIS MORNING.
&&
PSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
756 AM CDT TUE AUG 20 2019
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0755 AM TSTM WND GST MIDDLETOWN 40.83N 91.26W
08/20/2019 E65 MPH DES MOINES IA TRAINED SPOTTER
&&
PSPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
809 AM CDT TUE AUG 20 2019
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0650 AM TSTM WND DMG SIGOURNEY 41.33N 92.21W
08/20/2019 KEOKUK IA BROADCAST MEDIA
REPORT OF TREE AND POWER LINE DAMAGE IN
SIGOURNEY RELAYED FROM BROADCAST MEDIA. TIME
ESTIMATED FROM RADAR.
&&
PSThe Quad Cities radar (KDVN), 78 km away, was scanning. The volume nearest the first event began at 13:22 UTC.
3 thunderstorm wind. Local standard time, as filed.
Law enforcement reported both trees and power lines down in Monmouth and just north of the city.
Several 8 inch diameter tree branches were blown down.
A large tree limb was reported blown down at 12th Street and 25th Avenue in Moline.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Illinois in 2019Every state in 2019This day in weather historyWarnings in Illinois, August 2019
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: 849403, 849404, 849405.