Wet conditions continued across the state with yet another round of moderate to heavy rainfall on top of already mostly saturated conditions. A shortwave moving through the upper level flow out of the southwest, a surface front situated to the west and northwest of the state, and strong 850 mb flow were the main contributors to showers and storms.
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 DMX wrote it up.
Wet conditions continued across the state with yet another round of moderate to heavy rainfall on top of already mostly saturated conditions. A shortwave moving through the upper level flow out of the southwest, a surface front situated to the west and northwest of the state, and strong 850 mb flow were the main contributors to showers and storms.
Conditions were certainly conducive for heavy rainfall, including MUCAPE of at least 1000 J/kg and ranging up to 2000+ J/kg, precipitable water values near and in excess of 2.0 inches, and strong moisture advection into and through the state throughout the event. Additionally, conditions were relatively favorable for a funnel cloud or brief spin up or two with lifted condensation levels predominantly under 750 m, 0-3 km CAPE values around 175-200 J/kg, and 0-1 km storm relative helicity values around 100-150 m2/s2.
In the end, a couple of funnel cloud and brief tornado reports were seen across the most favorable areas in northwest Iowa, followed up by nearly exclusively heavy rainfall and flash flooding reports from southwest Iowa into central Iowa and even parts of northern Iowa. Greatest reports included multiple 3+ inch reports across northern and northwest Iowa and 2 day totals in excess of 6 inches into parts of central Iowa.
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 Des Moines, IA wrote its last area forecast discussion before the first event at Sep 4, 3:34 AM CST, 1 hour 26 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 434 AM CDT Tue Sep 4 2018 .SHORT TERM.../Today through Tonight/ Issued at 434 AM CDT Tue Sep 4 2018 Confidence: Medium to High Moisture plume still entrenched across the Central to Southern Plains today through tonight. Next upstream shortwave now tracking across the TX/OK panhandle and is expected to move northeast this afternoon and evening. As it approaches the state...showers and thunderstorms will increase across the region with especially between 18z and 00z today. H850 moisture plume again supports +15C dewpoints from Gulf all the way north to South Dakota and eventually this will turn back into the flow over Iowa this afternoon/tonight. Warm cloud depths to 4000m and precipitable water through the column to 2.0 inches for the duration of the event in the next 24 hours support efficient and heavy rainfall once again. Have issued a FFA for much of the north and central in two parts: northwest areas from 18z to 06z and northeast/central areas from 21z to 12z. Though have been quite liberal with the watch area...feel the highest threat area will be generally east of I35 north of US 20 and generally east of I35 over the remainder of the watch area which extends south to I80. As the potent upper level wave tracks northeast this afternoon a surface system will develop, lifting a warm front northeast into northern Iowa by 00z. Strong moisture transport with H850 winds of 50 kts impinging on the boundary will support rainfall rates of 2 inches or more per hour at times over the northeast during the evening hours. As the low tracks away from the area by 12z a trailing trough/wind shift may continuing some scattered thunder into the morning hours. There is some uncertainty as to overall amounts but given the available moisture, warm cloud depths, and forcing - it is very possible to see 2 to 3 inch totals with isolated 3 to 5 inch totals over the north. Farther into central Iowa from US 30 south to I80...it is more likely that slightly lesser amounts of 1 to 2 inches with locally higher totals will be possible. Despite the lower forecast south...this area has been hit harder overall with the exception of the northeast Bremer/Black Hawk Counties which saw higher totals earlier on Monday evening. It most cases, it wont take too much more rainfall to cause immediate issues. .LONG TERM.../Wednesday through Monday/ Issued at 434 AM CDT Tue Sep 4 2018 .../Wednesday through Friday/... Confidence: Medium Some uncertainty remains tomorrow with regard for additional extent of heavy rainfall. There may be need for an additional watch across the south for heavy rainfall...though timing of the trailing trough/boundary and daytime recovery will likely determine whether only the southwest portion of the forecast area west of I35/south of I80 or all of the area south of I80 will need an additional headline. None the less...rainfall of an inch or two may still be possible there tomorrow. The Euro has backed off on the lingering front over the south Wednesday night and Thursday. Consequently PoPs have been lowered and a break in precipitation over the north and most of the south is now more likely for Thursday into Friday noon. Cooler air will increase into the region for Thursday/Friday with highs in the 60s/70s and lows in the 50s/60s. .../Friday Night through Monday/... Confidence: Low to Medium The wild card of the extended remains the remnants of TS Gordon. With a widely different solution between the GFS/Euro, it will be difficult to immediately determine potential impacts of the tropical disturbance moving north toward Iowa. Currently the Euro favors a more west/northwesterly track taking a well developed low into southeast Iowa toward Davenport by 12z Saturday. On the other hand the GFS favors a more easterly/southerly track across Missouri and Illinois. The NAM with its northwest bias...is aiming for central Iowa. Much will depend on whether the tropical system is able to merge with the continental H500 trough currently situated over the central US. Given the system...anyone in its Confidence: Medium to High Moisture plume still entrenched across the Central to Southern Plains today through tonight. Next upstream shortwave now tracking across the TX/OK panhandle and is expected to move northeast this afternoon and evening. As it approaches the state...showers and thunderstorms will increase across the region with especially between 18z and 00z today. H850 moisture plume again supports +15C dewpoints from Gulf all the way north to South Dakota and eventually this will turn back into the flow over Iowa this afternoon/tonight. Warm cloud depths to 4000m and precipitable water through the column to 2.0 inches for the duration of the event in the next 24 hours support efficient and heavy rainfall once again. Have issued a FFA for much of the north and central in two parts: northwest areas from 18z to 06z and northeast/central areas from 21z to 12z. Though have been quite liberal with the watch area...feel the highest threat area will be generally east of I35 north of US 20 and generally east of I35 over the remainder of the watch area which extends south to I80. As the potent upper level wave tracks northeast this afternoon a surface system will develop, lifting a warm front northeast into northern Iowa by 00z. Strong moisture transport with H850 winds of 50 kts impinging on the boundary will support rainfall rates of 2 inches or more per hour at times over the northeast during the evening hours. As the low tracks away from the area by 12z a trailing trough/wind shift may continuing some scattered thunder into the morning hours. There is some uncertainty as to overall amounts but given the available moisture, warm cloud depths, and forcing - it is very possible to see 2 to 3 inch totals with isolated 3 to 5 inch totals over the north. Farther into central Iowa from US 30 south to I80...it is more likely that slightly lesser amounts of 1 to 2 inches with locally higher totals will be possible. Despite the lower forecast south...this area has been hit harder overall with the exception of the northeast Bremer/Black Hawk Counties which saw higher totals earlier on Monday evening. It most cases, it wont take too much more rainfall to cause immediate issues.path is likely to see a quick several inches of rainfall and potential windy conditions and this will need to be monitored closely. The system should exit the region by Sunday with lingering clouds and showers. Cooler and drier weather is expected for Monday as high pressure builds into the region. && .AVIATION.../For the 06Z TAFS through 06Z Tuesday night/ Issued at 1204 AM CDT Tue Sep 4 2018 The primary concerns will be fog and stratus trends early this morning and then precip/thunder trends later today and this evening. The current IFR/LIFR conditions over northern IA should persist for several more hours and then gradually improve to VFR by morning as the warm front continues lifting northward. Precip chances will then increase north and west by afternoon and evening, mainly affecting KFOD/KMCW/KALO. Thunder is certainly possible, but have omitted wording with VFR showers until confidence increases. && .HYDROLOGY... Issued at 434 AM CDT Tue Sep 4 2018 With additional locally heavy rainfall possible over much of the area...a Flash Flood Watch has been issued for much of the region today through tonight. The area of higher threat will be from I35 east and US 30 north. Additional concerns due to either previous heavy rainfall from south of US 30 and east of I35 to potentially heavier rainfall in the northwestern areas resulted in an expanded threat for today/tonight. Rivers continue to be stressed... particularly the Iowa River basin east of I35 and the Cedar River basin near Cedar Falls and the Black Hawk Creek at Hudson which are already at moderate flood stage. The bulk of the rain in the next 24 hours will affect the Iowa, Cedar, and Des Moines river basins with the Cedar/Iowa probably receiving the bulk of additional water. Streams and smaller rivers will also be stressed over the northeast and east. Farther south some streams may again see brief rapid rises due to already saturated ground and quick runoff in any heavier periods of rainfall. && .DMX WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch from 4 PM CDT this afternoon through Wednesday morning for IAZ006-007-016-017-025>028-036>039-047>050-059>062. Flash Flood Watch from 1 PM CDT this afternoon through late tonight for IAZ004-005-015-023-024-033>035. && SHORT TERM...REV LONG TERM...REV AVIATION...Small HYDROLOGY...REV
Hazardous Weather Outlook National Weather Service Des Moines IA 359 AM CDT Tue Sep 4 2018 IAZ004>007-015>017-023>028-033>039-047>050-059>062-051000- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Black Hawk-Boone-Story-Marshall- Tama-Dallas-Polk-Jasper-Poweshiek- 359 AM CDT Tue Sep 4 2018 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight A Flash Flood Watch is in effect for the area today through late tonight. Also, river flooding warnings are in effect for portions of the Cedar River and Iowa River basins. Please refer to the National Weather Service website at weather.gov/desmoines for further details. Widespread thunderstorms are forecast by around midday today and look to continue through late tonight into early Wednesday morning. Heavy rain at times may lead to localized flash flooding. There is also the potential for a few strong to potentially severe storms with the threat of large hail, damaging wind and a tornado or two. .DAYS TWO THROUGH SEVEN...Wednesday through Monday The very active weather pattern persist throughout the rest of the work week and into the weekend. Heavy rain potential continues to be the main concern and with many swollen rivers and streams as well as very saturated grounds, this combination may lead to additional river flooding and flash flooding Wednesday through Saturday. .SPOTTER INFORMATION STATEMENT... Spotters might be needed today into tonight for flash flood and severe weather potential. Spotters may also be needed at times throughout the rest of the week. IAZ044>046-057-058-070>075-081>086-092>097-051000- Crawford-Carroll-Greene-Audubon-Guthrie-Cass-Adair-Madison-Warren- Marion-Mahaska-Adams-Union-Clarke-Lucas-Monroe-Wapello-Taylor- Ringgold-Decatur-Wayne-Appanoose-Davis- 359 AM CDT Tue Sep 4 2018 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Isolated to scattered thunderstorms are possible today into tonight. Although the severe weather threat is low, a brief stronger storms with hail and gusty winds cannot be ruled out. Localized heavy rain is also possible. .DAYS TWO THROUGH SEVEN...Wednesday through Monday The very active weather pattern persist throughout the rest of the work week and into the weekend. Heavy rain potential continues to be the main concern and with many swollen rivers and streams as well as very saturated grounds, this combination may lead to river flooding and flash flooding at times Wednesday through Saturday. .SPOTTER INFORMATION STATEMENT... Spotters might be needed today into tonight and at times through the rest of the week. KLP
Special Weather Statement National Weather Service Des Moines IA 407 AM CDT Tue Sep 4 2018 IAZ004>007-015>017-041300- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Including the cities of Estherville, Algona, Forest City, Lake Mills, Northwood, Manly, Emmetsburg, Garner, Britt, Kanawha, Mason City, and Clear Lake 407 AM CDT Tue Sep 4 2018 ...Dense Fog over Northern Iowa... Areas of dense fog look to continue over portions of northern Iowa. Visibility restrictions of less of one half mile at times have been observed and are anticipated to continue through 8 AM this morning. Travelers should use low beam headlights and slow down in foggy conditions. KLP
The Minneapolis radar (KMPX), 171 km away, was scanning. The volume nearest the first event began at 11:02 UTC.
25 heavy rain, 9 flash flood, 7 flood, 1 tornado, 1 funnel cloud. Local standard time, as filed.
CoCoRaHS observer recorded heavy rainfall of 3.2 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 3.36 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 3.00 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.71 inches over the last 24 hours.
Algona Municipal Airport recorded heavy rainfall of 2.06 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.04 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.00 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 3.75 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 3.70 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.50 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.04 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.00 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.08 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 4.01 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 4.02 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.85 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.41 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.34 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.44 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.01 over the last 24 hours.
Trained spotter reported heavy rainfall of 5.8 inches with the afternoon activity.
Brief tornado occurred to the west of Algona producing roof damage to a hog confinement building. The remainder of the path was in rural agricultural land.
Family members of a trained spotter sent in a video of a funnel cloud.
Public reported over 4 inches of rain near Coldwater Creek overnight. Water reported to be moving into fields. Location estimated.
Local media reported 3 hour heavy rainfall total of 3.6 inches.
Iowa DOT reported road closure between County Highway B55 and US 18 due to water over the road.
Public reported heavy rainfall of 1.63 inches since midnight and 3.89 inches since Friday.
Public reported heavy rainfall of 3.11 inches since midnight and 6.06 inches since Friday.
Emergency manager reported several road closures due to water over the roadways.
Emergency manager reported several road closures due to water over the roadways.
Emergency manager reported several road closures due to water over the roadways across the county with the worst area near Dumont.
Emergency manager reported several road closures due to water over the roadways.
Emergency manager reported several county roads under water, with one state highway closed due to flooding. Several basements were also reported flooding. This is a delayed report.
Local law enforcement reported water over the road.
Law enforcement reported water over the road.
Law enforcement reported water over the road.
Law enforcement reported water over the road.
Emergency manager reported road closure due to flooding on 275th Street near Yucca Ave. Time and location estimated from radar. This is a delayed report.
Emergency manager reported flooding in and around town.
Emergency manager reported flooding in areas around town.
Emergency management reported widespread road closures due to flooding or being washed out across much of the county.
Emergency management reported widespread road closures due to flooding or being washed out across much of the county.
Emergency manager reported road closure at 250th and 270th in Ringgold County due to water over the road.
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, September 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: 780249, 780250, 780251, 780252, 780253, 780254, 780255, 780256, 780257, 780259, 780260, 780262, 780263, 780264, 780265, 780266, 780267, 780268, 780269, 780270, 780247, 784974, 780243, 780272, 780248, 780246, 780284, 780285, 786293, 786294, 786299, 786300, 780276, 780277, 780279, 780280, 780281, 780282, 780283, 780286, and more.