Heavy rainfall across northern Iowa through early September resulted in many rivers going into flood through the early to middle portion of September. The flooding impacted the basins of the Cedar, Iowa, and Shell Rock Rivers, and also Black Hawk Creek at Hudson.
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.
Heavy rainfall across northern Iowa through early September resulted in many rivers going into flood through the early to middle portion of September. The flooding impacted the basins of the Cedar, Iowa, and Shell Rock Rivers, and also Black Hawk Creek at Hudson.
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 2, 6:03 AM CST, 3 hours 12 minutes earlier.
Area Forecast Discussion National Weather Service Des Moines IA 703 AM CDT Sun Sep 2 2018 .DISCUSSION.../Today through Saturday/ Issued at 415 AM CDT Sun Sep 2 2018 Overall upper level pattern will change little for the foreseeable future. High pressure over the East Coast with a trough out west will keep our area in a southwest flow with little alteration to this through much of this week. Numerous shortwaves of varying intensity move through this flow across Iowa. Additionally, at the surface, a frontal boundary will reside across the state and waffle little for the next several days. We will keep abundant instability and shear over the state for some time. Forcing and periodic waves of theta-e advection will push across Iowa giving periodic chances for storms. A bigger factor in the forecast will be the continued development of a low level jet in the evening/overnight hours and it's interaction with the boundary. Soundings continue to show deep warm cloud depths and PWATS in excess of 2 inches. This will likely keep our pattern of late day/overnight thunderstorms in the forecast. The most likely areas for the heavy rain and marginally severe storms will reside in the vicinity of the frontal boundary and either be enhanced by the shortwaves or precip will expand in the areas that these waves pass. For today...storms have developed along a boundary across southern Iowa along with a 30kt low level jet. This boundary will lift north and storms will weaken through the morning and end by mid morning. Focus will then shift to a cold front that will move into northwest Iowa. Peak heating will bring an increased threat for redevelopment of storms. Similar to the past few days, the storms will initially have a hail threat with them then evolve in a cluster with damaging wind becoming more favorable before evolving into a heavy rain complex. The potential for flooding/flash flooding will again be possible mid evening through tonight. The area of heavy rainfall for tonight will depend on frontal position and where the next wave comes across. Additional flash flood headlines will undoubtedly occur for tonight and in the next few days but it was collaborated with neighbors to have the day shift look at a model run or two more to best determine the area of heavy rainfall. Depending on which model you believe, mid to late week the trough out west finally lifts out and the high to the east shifts putting our area in a more zonal flow. The Euro keeps a parade of shortwaves coming across the region but the GFS and the Canadian do finally dry us out. For now model blends keep chance or higher PoPs going through the forecast period and with the model uncertainty I am hesitant to pull these until there is a stronger signal on which period appears to be most likely to be dry. && .AVIATION.../For the 12Z TAFS through 12Z Monday morning/ Issued at 703 AM CDT Sun Sep 2 2018 Mainly VFR conditions with ocnl MVFR/IFR in SHRA and TSRA. Patchy fog also possible which may produce MVFR/IFR vsbys through 14Z. Current precip expected to end mid morning then redevelop...possibly further north later this afternoon bringing back MVFR conditions. Sfc winds to remain south or southeast around 10kts then diminish aft 00Z. && .HYDROLOGY... Issued at 415 AM CDT Sun Sep 2 2018 With a very stagnant weather pattern in place for the next several days and daily rainfall amounts of 1 to 3 inches with locally higher amounts expected the need for additional flash flood watches will be likely. Latest flash flood guidance has most counties in the forecast area with rainfall of an inch and a half in an hour and around 2 inches in 3 hours. These kinds of amounts have been easily attained of late and forecast soundings show PWATs of 2+ inches through Tuesday. We are in a moderate risk of excessive rainfall for the Day 1 and Day 3 period. Confidence is high at least for the next few days that we will see heavy rainfall over the forecast area. However with subtle shifts in where the heavy rain will occur, watch locations will change some daily and new flash flood watches will likely be issued during the day for evening/overnight storms...once a better handle on location can be obtained.&& .DMX WATCHES/WARNINGS/ADVISORIES... NONE. && DISCUSSION...FAB AVIATION...FAB HYDROLOGY...FAB
Hazardous Weather Outlook National Weather Service Des Moines IA 454 AM CDT Sun Sep 2 2018 IAZ004>007-015>017-023>028-033>038-044>047-050-057>059-070>075- 081>086-092>097-031000- Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo- Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun- Webster-Hamilton-Hardin-Grundy-Crawford-Carroll-Greene-Boone-Tama- Audubon-Guthrie-Dallas-Cass-Adair-Madison-Warren-Marion-Mahaska- Adams-Union-Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur- Wayne-Appanoose-Davis- 454 AM CDT Sun Sep 2 2018 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight Thunderstorms will diminish this morning then redevelop late day and persist through tonight. There is a marginal risk of severe storms with large hail and damaging wind possible. Heavy rainfall is also a threat. Flash flood headlines may become necessary later today for areas where heavy rainfall becomes focused. .DAYS TWO THROUGH SEVEN...Monday through Saturday Periods of thunderstorms, especially during the overnight hours through the period. Widespread severe weather is not likely but a few storms from time to time may be strong to severe. Damaging winds will likely be the main threats with any stronger storms. Heavy rainfall will be possible with any thunderstorm. River flooding and flash flood threats are possible with any storm and future flash flood headlines will be possible for periods when the heaviest rainfall is expected. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected though severe weather and rainfall reports are appreciated. IAZ039-048-049-060>062-031000- Black Hawk-Story-Marshall-Polk-Jasper-Poweshiek- 454 AM CDT Sun Sep 2 2018 This Hazardous Weather Outlook is for portions of central Iowa. .DAY ONE...Today and tonight An areal flood warning is in effect for the area. Please refer to the National Weather Service website at weather.gov/desmoines for further details. Thunderstorms will diminish this morning then redevelop late day and persist through tonight. There is a marginal risk of severe storms with large hail and damaging wind possible. Heavy rainfall is also a threat. Flash flood headlines may become necessary later today for areas where heavy rainfall becomes focused. .DAYS TWO THROUGH SEVEN...Monday through Saturday Periods of thunderstorms, especially during the overnight hours through the period. Widespread severe weather is not likely but a few storms from time to time may be strong to severe. Damaging winds will likely be the main threats with any stronger storms. Heavy rainfall will be possible with any thunderstorm. River flooding and flash flood threats are possible with any storm and future flash flood headlines will be possible for periods when the heaviest rainfall is expected. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected though severe weather and rainfall reports are appreciated. FAB
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
746 AM CDT SUN SEP 2 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0700 AM HEAVY RAIN 2 WSW GRINNELL 41.73N 92.75W
09/02/2018 M4.54 INCH POWESHIEK IA CO-OP OBSERVER
&&
BFPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
747 AM CDT SUN SEP 2 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0700 AM HEAVY RAIN 2 WSW GRINNELL 41.73N 92.75W
09/01/2018 M3.00 INCH POWESHIEK IA CO-OP OBSERVER
LATE REPORT.
&&
BFPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
814 AM CDT SUN SEP 2 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0800 AM HEAVY RAIN AMES 42.03N 93.63W
09/02/2018 E2.10 INCH STORY IA PUBLIC
VIA SOCIAL MEDIA. REPORT WAS FOR THE
NORTHERN END OF AMES.
&&
BFPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
836 AM CDT SUN SEP 2 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0700 AM HEAVY RAIN 1 NNW ZEARING 42.17N 93.31W
09/02/2018 M1.17 INCH STORY IA CO-OP OBSERVER
&&
BFPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
931 AM CDT SUN SEP 2 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0900 AM HEAVY RAIN 2 NNE GRANGER 41.79N 93.80W
09/02/2018 E3.44 INCH POLK IA COCORAHS
&&
BFPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DES MOINES IA
933 AM CDT SUN SEP 2 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0900 AM HEAVY RAIN 4 SSW KELLOGG 41.66N 92.94W
09/02/2018 E7.50 INCH JASPER IA TRAINED SPOTTER
&&
BFThe national radar mosaic for the moment the first event began.
6 flood. Local standard time, as filed.
The Cedar River at Cedar Falls crested twice through the period of flooding with the first crest at 91.54 feet on 4 September 2018 at 0745 UTC, and the second crest at 93.74 feet on 7 September 2018 at 1530 UTC.
Black Hawk Creek at Hudson crested at 16.82 feet on 5 September 2018 at 1345 UTC.
The Cedar River at Waterloo crested at 13.62 feet on 4 September 2018 at 0800 UTC.
The Iowa River at Tama Highway E49 crested at 13.04 feet on 6 September 2018 at 0430 UTC.
The Cedar River at Waterloo crested at 16.45 feet on 7 September 2018 at 1815 UTC.
The Shell Rock River at Shell Rock crested at 14.49 feet on 6 September 2018 at 1415 UTC.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Iowa in 2018Every state in 2018This day in weather historyWarnings 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: 785675, 785676, 785673, 785678, 785674, 785677.