An area of low pressure over eastern Iowa produced showers and thunderstorms with heavy rain. One of these thunderstorms produced a brief tornado in Clinton County that caused damage to trees along a half mile path.
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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 DVN wrote it up.
An area of low pressure over eastern Iowa produced showers and thunderstorms with heavy rain. One of these thunderstorms produced a brief tornado in Clinton County that caused damage to trees along a half mile path. In addition, heavy rain fell along and north of a Fairfield to Burlington line, with widespread 1 to 2 inch amounts and isolated reports of 2 to 5 inches north of a Cedar Rapids to Clinton County line.
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, 1:22 PM CST, 1 hour 27 minutes earlier.
Area Forecast Discussion National Weather Service Quad Cities IA IL 222 PM CDT Mon Aug 20 2018 .SYNOPSIS... Issued at 215 PM CDT Mon Aug 20 2018 As of 200 PM: A seasonably strong upper level low was located along the Iowa and Missouri border to the south of Des Moines. Bands of scattered showers and isolated thunderstorms were spiraling around the low and affecting parts of eastern Iowa and northwestern Illinois. Instability per the SPC Mesoanalysis has increased to 1000-1500 J/kg of MLCAPE, and with high PWATs near 1.7 inches, the atmosphere is supportive of localized heavy downpours. Across the forecast area, temperatures were in the mid 70s on average, and it was very humid with dewpoints near 70 F. && .SHORT TERM...(This Evening through Tuesday) ISSUED AT 215 PM CDT Mon Aug 20 2018 This Afternoon through Tonight Scattered showers and thunderstorms will continue through this evening. The main impact will be the brief heavy downpours. Monitoring satellite trends through the day, a brief window of clearing is most probably over the eastern and northeast sections of the CWA. Due to moderate low-level shear with 0-1 km values between 15-20 kts, and low LCLs and LFCs, isolated severe storms are possible. The Storm Prediction Center has outlined areas mainly along and north of I-80 for a marginal severe weather threat. If we were to get a few severe storms, the primary risks would be strong wind gusts and brief spin-up tornadoes. Latest HRRR model runs develop the strongest storms over the far east and in the northeast CWA, where there are more significant breaks in the cloud cover. We'll have to continue to monitor conditions and radar trends through the evening. Additional rainfall will vary considerably across the forecast area, but because of the slow storm motion and high PWATs, isolated locations north of I-80 could pick up another 1-2 inches before it winds down early tonight. Tuesday After residual showers in the morning, dry weather and high pressure return for the afternoon along with seasonable temperatures. Uttech .LONG TERM...(Tuesday Night through Monday) ISSUED AT 215 PM CDT Mon Aug 20 2018 Wednesday and Thursday The high pressure system that begins to move in Tuesday will linger over the Midwest through Thursday. Expect highs in the 70s to near 80F and lows in the 50s. The cool overnight temperatures may lead to shallow fog formation in favored low-lying areas, but did not include fog in the forecast yet. Uttech Friday On Models bring a shortwave through Iowa and Illinois late in the week. The model blend has increased rain chances into the 50-70% range, which would come in the form of scattered showers and isolated thunderstorms. This is not a strong system, so the threat for widespread significant rainfall is low. Hot and humid conditions are likely by next weekend as the mid- level flow becomes southwesterly and forecast 850mb temperatures eclipse 20 C. The model blend has our area in the mid 80s to near 90 F with dewpoints near 70 F -- summer will be in full force heading into the final week of August. There is also a chance for thunderstorms Sunday and Sunday night with a potential shortwave tracking along an instability gradient. Confidence on the details is low this far out. Uttech && .AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon) ISSUED AT 1217 PM CDT Mon Aug 20 2018 Rain showers and scattered thunderstorms associated with low pressure and a warm front will continue to produce MVFR and brief IFR conditions across all terminals this afternoon. There is low risk of severe thunderstorms at KMLI, KCID and KDBQ late this afternoon, but confidence is low on occurrence. Shower and storm coverage will decrease this evening, leaving mainly MVFR conditions through early tonight. Low clouds behind the eastward moving low pressure may bring IFR conditions at all terminals after midnight. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && SYNOPSIS...Uttech SHORT TERM...Uttech LONG TERM...Uttech AVIATION...Speck
Hazardous Weather Outlook National Weather Service Quad Cities IA IL 401 AM CDT Mon Aug 20 2018 IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007- 009-015>018-024>026-034-035-MOZ009-010-210915- 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- 401 AM CDT Mon Aug 20 2018 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 Thunderstorms are likely across the outlook area today through this evening. There is a low potential for severe thunderstorms, especially along a warm front that will extend across northwest Illinois in the afternoon. The main severe weather threats will be damaging wind and isolated tornadoes. Heavy rainfall will also be possible with thunderstorms over the entire outlook area today. This may lead to minor urban flooding. .DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY There is a chance for thunderstorms Friday. It is too soon to determine the potential for severe weather. .SPOTTER INFORMATION STATEMENT... Spotter activation may be needed this afternoon and evening. Sheets
The Quad Cities radar (KDVN), 43 km away, was scanning. The volume nearest the first event began at 20:51 UTC.
1 tornado. Local standard time, as filed.
An EF-0 tornado caused damage to soybeans and trees along its half mile path. A trained spotter report and videos were used to determine the time of the tornado. The peak estimated winds were 65 MPH.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2018Every state in 2018This day in weather historyThe tornado archive for Iowa, 2018Warnings in Iowa, August 2018
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: 782089.