An ideal setup was seen across northern and central Iowa for repeated rounds of heavy rainfall and severe weather. A weak warm frontal boundary stalled out across the area as it transitioned to a stationary boundary and allowed multiple rounds of storms to initiate on the 21st and well into the 22nd.
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.
An ideal setup was seen across northern and central Iowa for repeated rounds of heavy rainfall and severe weather. A weak warm frontal boundary stalled out across the area as it transitioned to a stationary boundary and allowed multiple rounds of storms to initiate on the 21st and well into the 22nd. Primarily heavy rainfall and flooding was seen, however a couple of hail and a handful of damaging wind reports were received as well. The hardest hit areas were from roughly Forest City on southeast towards Mason city and Waverly. Rainfall amounts of 4 to 6 plus inches were seen, with greatest amounts just outside of the Des Moines county warning area in and around Charles City.
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 21, 3:12 AM CST, 1 hour 48 minutes earlier.
AREA FORECAST DISCUSSION National Weather Service Des Moines IA 412 AM CDT Wed Sep 21 2016 .SHORT TERM.../Today/ Issued at 405 AM CDT Wed Sep 21 2016 Thunderstorms have remained north and northeast of the forecast area early this morning and just north of a warm front that is currently near the IA/MN border. The lower res solutions such as the GFS/ECMWF/NAM all tried to drive this convection down the instability gradient and into central Iowa this morning. The CAMs are much more in tune with the current situation generally keeping convection out of the forecast area until mid to late afternoon. The exception is potential for a few sprinkles/light showers over the far north where high level theta-e advection has commenced. A broad cirrus shield is currently moving into western IA and may play a role in limiting convective development today. Good elevated mixed layer in place this morning with steep lapse rates and good instability aloft. Convective temperatures in the upper 80s to low 90s may difficult to reach today though if the cirrus deck is thicker than expected. In addition the moisture advection and first wave of energy associated with tropical storm Paine will not arrive over northern Iowa until late this afternoon. Overall have backed off PoPs today before increasing across the north late this afternoon. The EML should hold most of the day and may not have much convective development until the low level jet strengthens this evening. Deep layer shear will remain weak into this afternoon therefore it will be difficult for organized storms to develop through 7 pm however given the amount of instability any surface based storm that does develop will have the potential of damaging wind gusts and localized hail along with locally heavy rainfall. The flash flood watch remains in effect for the far north though areal coverage of storms should remain limited. PWAT values by this afternoon will be nearing 2 inches or over 200 percent of normal. .LONG TERM.../Tonight through Tuesday/ Issued at 405 AM CDT Wed Sep 21 2016 The main forecast concern was focused on heavy rain potential tonight into Thursday across western to northern Iowa. Models remain in fairly good agreement with the location and timing of convection and leaned toward a blend of the NAM/GFS/ECMWF tonight into tomorrow and then closer to the GFS through the remainder of the forecast. Tonight into Friday...Very impressive moisture plume evident on Water Vapor Satellite will continue to pump significant tropical moisture into the state tonight into Thursday. Stationary front looks to remain planted along the Minnesota/Iowa border tonight and possibly get shifted northward slightly with the strong WAA throughout the day into this evening. Iowa remains entrenched within west to southwest flow aloft with several shortwaves training across the state tonight into Thursday evening. The strongest push of Theta- E advection looks to be between 03z and 12z Thursday and have highest pops going across northern Iowa during this time. Plenty of moisture transport into the forecast area with PWATs ranging from 1.6 to 1.9 inches, which is roughly 200-250% of normal or +2-3 sigma for this time of year. Even surface dew points remain near 70 tonight, but there is some mid-level dry air tonight that will ward off the heavy rain until after 03z Thursday when the column becomes deeply saturated over northern Iowa. Warm layer cloud depths are around 3500 meters with weak Corfidi vectors generally oriented with the storm motion vectors tonight into Thursday morning, and thus efficient rain producers and training are likely over northern Iowa. Therefore, no changes to the ongoing Flash Flood Watch. Another shortwave combined with weak Theta-E advection in the vicinity of the surface boundary draped over western to north- central Iowa Thursday night will lead to another round of storms over northern Iowa. Similar PWATs and slightly higher warm layer cloud depths but weaker moisture transport into the state and a bit stronger Corfidi vectors, so not the best set up for training heavy rain producers but still the threat exist. Depending how tonight into Thursday shapes up, another Flash Flood Watch might be needed over northern Iowa. Some lingering storms are possible Friday morning over northern Iowa, but overall Friday looks to be dry for much of central Iowa with a strong ridge building into the region. Saturday through Tuesday...Very deep and strong upper level trough digs into the western CONUS at the beginning of the weekend and slowly transitions eastward and pushes a cold front through the state Saturday night into Sunday. Yet another round of storms and heavy rain potential for Iowa during this time. Storms linger across the east Sunday night, but much of the precip looks to further east by early Monday. However, GFS and even the ECMWF are suggesting the low to strengthen and become cutoff or remain stationary across the central CONUS through late next week. Thus, providing focus for periods of showers, cloudy skies, and cooler temperatures into the state by Monday and lasting for much of the week. 850 mb temperatures drop to +2C by mid-week. && .AVIATION.../For the 06Z TAFS through 06Z Wednesday night/ Issued at 1151 PM CDT Tue Sep 20 2016 Storms have fired across southern MN and may trickle southeastward toward KMCW and KALO. Current trends expect the storms to slide just east of the CWA, but will have to monitor. Still left the VCTS for the possibility. Otherwise southerly winds picking up again during the day Tuesday. Additional storm activity expected late Wednesday. May end up being beyond the current forecast period, so have not included in the TAF currently. && .DMX WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Thursday evening for IAZ004>007- 015>017. Flash Flood Watch from this evening through Thursday evening for IAZ023>028-033>039-044>048. && SHORT TERM...Donavon LONG TERM...Podrazik AVIATION...Beerends
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE DES MOINES IA 539 AM CDT WED SEP 21 2016 IAZ004>007-015>017-023>028-033>039-044>048-221045- EMMET-KOSSUTH-WINNEBAGO-WORTH-PALO ALTO-HANCOCK-CERRO GORDO- POCAHONTAS-HUMBOLDT-WRIGHT-FRANKLIN-BUTLER-BREMER-SAC-CALHOUN- WEBSTER-HAMILTON-HARDIN-GRUNDY-BLACK HAWK-CRAWFORD-CARROLL-GREENE- BOONE-STORY- 539 AM CDT WED SEP 21 2016 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT A SLIGHT RISK FOR SEVERE STORMS IS FORECAST TONIGHT INTO THURSDAY MORNING. THE MAIN THREAT WILL BE DAMAGING WINDS AND LARGE HAIL. HEAVY RAIN IS ALSO ANTICIPATED AND A FLASH FLOOD WATCH REMAINS IN EFFECT FOR THE AREA THROUGH THURSDAY EVENING. PLEASE REFER TO THE NATIONAL WEATHER SERVICE WEBSITE AT WEATHER.GOV/DESMOINES FOR FURTHER DETAILS. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY ADDITIONAL THUNDERSTORMS WITH HEAVY RAIN AND ISOLATED SEVERE WEATHER ARE EXPECTED ON THURSDAY INTO THURSDAY EVENING. THE NEXT POTENTIAL FOR STORMS IS FORECAST SATURDAY NIGHT INTO SUNDAY. THE PREDICTABILITY FOR SEVERE WEATHER REMAINS TOO LOW AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED AT TIMES THIS AFTERNOON THROUGH THURSDAY. IAZ049-050-057>062-070>075-081>086-092>097-221045- MARSHALL-TAMA-AUDUBON-GUTHRIE-DALLAS-POLK-JASPER-POWESHIEK-CASS- ADAIR-MADISON-WARREN-MARION-MAHASKA-ADAMS-UNION-CLARKE-LUCAS- MONROE-WAPELLO-TAYLOR-RINGGOLD-DECATUR-WAYNE-APPANOOSE-DAVIS- 539 AM CDT WED SEP 21 2016 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL IOWA. .DAY ONE...TODAY AND TONIGHT A CHANCE OF THUNDERSTORMS IS FORECAST OVERNIGHT TONIGHT INTO THURSDAY MORNING. THE SEVERE WEATHER POTENTIAL REMAINS LOW AT THIS TIME. LOCALLY BRIEF HEAVY RAIN IS POSSIBLE. .DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY THUNDERSTORMS WITH LOCALLY HEAVY RAIN AND ISOLATED SEVERE WEATHER ARE POSSIBLE ON THURSDAY INTO THURSDAY EVENING. THEN, THE NEXT POTENTIAL FOR STORMS IS FORECAST SATURDAY NIGHT INTO SUNDAY. HOWEVER, THE PREDICTABILITY FOR SEVERE WEATHER REMAINS TOO LOW AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION MAY BE NEEDED AT TIMES THIS AFTERNOON THROUGH THURSDAY. KLP
The Des Moines radar (KDMX), 153 km away, was scanning. The volume nearest the first event began at 11:00 UTC.
31 heavy rain, 7 thunderstorm wind, 7 flash flood, 6 flood, 5 hail. Local standard time, as filed.
CoCoRaHS observer in Britt recorded heavy rainfall of 2.45 inches over the last 24 hours.
CoCoRaHS observer in Lake Mills recorded heavy rainfall of 2.07 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 3.15 inches, over a duration of 36 hours.
Mason City ASOS recorded heavy rainfall of 2.53 inches over the last 24 hours.
Forest City AWOS recorded heavy rainfall of 2.19 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.3 inches over the last 24 hours.
Coop observer KIOW Radio recorded heavy rainfall of 3.05 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.1 inches over the last 24 hours.
Mason City ASOS recorded heavy rainfall of 2.53 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.25 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 4.13 inches over the last 24 hours.
Public reported heavy rainfall of 2.88 inches over the last 24 hours.
Public reported heavy rainfall of 4.00 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.26 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.35 inches over the last 24 hours.
Coop observer KIMT TV recorded heavy rainfall of 2.38 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 4.13 inches over the last 24 hours.
CoCoRaHS observer in Swaledale recorded heavy rainfall of 2.4 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.1 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.61 inches over the last 24 hours.
Coop observer recorded heavy rainfall of 2.30 inches over the last 24 hours.
CoCoRaHS observer recorded heavy rainfall of 2.30 inches over the last 24 hours.
Mesonet station recorded heavy rainfall of 2.10 inches over the last 24 hours.
Mesonet station recorded heavy rainfall of 2.27 inches over the last 24 hours.
Mesonet station recorded heavy rainfall of 2.37 inches over the last 24 hours.
Mesonet station recorded heavy rainfall of 2.15 inches over the last 24 hours.
Mesonet station recorded heavy rainfall of 4.21 inches over the last 24 hours.
Public reported storm total heavy rainfall of 3.03 inches.
Trained spotter reported quarter sized hail.
Trained spotter reported 3 inch tree branches down along with quarter sized hail.
Green fire department reported heavy rainfall of 7.50 inches storm total.
Greene fire department reported a storm total rainfall since beginning Wednesday of 10.40 inches. Total rainfall since last report, 7.5 inches through 10:47pm previous night, was 2.9 inches. Relayed by Butler County Emergency Manager.
Public reported heavy rainfall of 6.25 inches from yesterday evening through this morning.
Amateur radio operator reported tree limbs approximately 3 inches in diameter down.
Trained spotter reported hail lasted for around 10 minutes, starting out as pea sized and gradually got bigger to around half dollar size.
Public reported a large tree downed, estimated 1 foot or more in diameter.
Trained spotter reported creek in pasture out of banks and rising. Location estimated.
Observed tree damage in storm chaser live video stream. Multiple large tree limbs down.
Emergency manager reported trees down on roofs and power lines. Extent of damage unknown at the time. Time estimated from radar.
Emergency manager reported widespread tree damage throughout town, including several trees on houses.
Trained spotter reported penny sized hail.
DOT reported county roads flooded near Rockwell. Delayed report.
Public reported quarter sized hail.
Emergency manager reported quarter sized hail.
Cerro Gordo County dispatch noted that East Park had been fully closed due to flooding.
Emergency Manager reported many roads closed throughout the northern fourth of Butler county. The Shell Rock river reported beginning to leave its banks and moving toward businesses in downtown Greene. Sandbagging ongoing in Green and Clarksville.
Emergency manager reported multiple homes in Greene now being impacted by floodwaters from the rapidly rising Shell Rock river. Also estimated that the river is near the level it reached in 2008.
Law enforcement reported evacuations occurring in Greene due to flash flooding.
Public reported damage to several large trees. Time estimated.
Law enforcement reported barricades put up due to street flooding along Highway 65 near Rockwell.
Law enforcement reported street flooding along 130th in Plainfield, along with several other roads in the Plainfield area.
Emergency manager reported most roads closed in and around Greene. The only way to access the town is via Highway 14. Delayed report.
Public reported water over the road on Highway 188 just south of Clarksville.
Iowa DOT reported US Highway 63 closed to southbound traffic due to flooding. Detour in place.
Iowa DOT reported Highway 188 closed in both directions due to flooding. Detour in place.
Emergency Manager reported levee on the west side of Clarksville along the Shell Rock river failed and the southwest side of town is flooding. Residents being evacuated.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2016Every state in 2016This day in weather historyWarnings in Iowa, September 2016
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: 659360, 659361, 659395, 659364, 659365, 659366, 659367, 659368, 659369, 659370, 659371, 659372, 659373, 659374, 659375, 659376, 659377, 659378, 659379, 659380, 659381, 659382, 659384, 659385, 659386, 659387, 659388, 659391, 659341, 659342, 659356, 659394, 659389, 659343, 659344, 659345, 659346, 659347, 659348, 659349, and more.