Runoff from snow melt in late March worked through the upper and middle portions of the Little Sioux River, resulting in minor and mainly agricultural land flooding.
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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 FSD wrote it up.
Runoff from snow melt in late March worked through the upper and middle portions of the Little Sioux River, resulting in minor and mainly agricultural land flooding.
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 Sioux Falls, SD wrote its last area forecast discussion before the first event at Mar 31, 9:38 PM CST, 2 hours 22 minutes earlier.
Area Forecast Discussion National Weather Service Sioux Falls SD 1038 PM CDT Sat Mar 31 2018 .SHORT TERM...(This evening through Sunday) Issued at 330 PM CDT Sat Mar 31 2018 Arctic high pressure has settled over the area today with very cold air persisting through the work week. Breezy northwest winds of 20 to 30 mph will gradually decrease around sunset, as the strong pressure gradient moves out of the region. Winds will calm down, but very cold temperatures will stay around. A cold night is expected with lows struggling to reach the upper teens. Areas along and north of I-90 could see temperatures in the single digits to lower teens. Areas along the Missouri River could see temperatures in the upper teens, where mostly cloudy skies will stick around for most of the night. As the center of the high pressure moves overhead, a very chilly Easter morning is expected. Wind chill values in the single digits will persist in the morning, with below zero values possible along and north of Highway 14. Clouds will be decreasing Sunday morning from north to south, giving way to partly sunny skies in the afternoon. Daytime temperatures 10 to 15 degrees colder than average are expected with highs reaching the 30s and lower 40s. .LONG TERM...(Sunday night through Saturday) Issued at 330 PM CDT Sat Mar 31 2018 West-northwest flow aloft prevails for the first half of the extended allowing multiple impulses of energy across the region; therefore bringing chances of precipitation. By Sunday night, a surface low will be located over the Northern Rockies with an inverted trough extending across west-central Dakotas. With decent moisture, south winds on the backside of the departing surface high and upper level jet support, cannot rule out light precipitation, mainly west of the James River, then spreading east early Monday morning. The main impact will occur Monday into Tuesday as the aforementioned low and upper wave approach the region. This will likely be the next snow-maker system, bringing measurable rain and snow across the CWA. Deterministic models are in good agreement in bringing this system close to the CWA, but still diverge a bit in phase/timing. The GFS/ECMWF bring the first round of precipitation 12Z Monday while NAM remains dry. Later through the day there is better consensus between models, bringing better chances of precipitation by Monday night, mainly along and east of the James river. In terms of precipitation type, model soundings show periods of rain developing through the day, then changing all to snow Monday evening into Tuesday. While there could be brief periods of mix precipitation, accumulating snow is possible with 2 to 4 inches, mainly east of the I-29 corridor. Definitely a system to keep an eye on. After Tuesday, an Arctic airmass is expected to reinforce very cold temperatures that could be as low as 15 to 20 degrees below average. Overnight temperatures could reach the single digits to lower teens across the entire CWA Tuesday night into Wednesday. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) Issued at 1038 PM CDT Sat Mar 31 2018 VFR conditions are expected through the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && SHORT TERM...05 LONG TERM...05 AVIATION...
Hazardous Weather Outlook National Weather Service Sioux Falls SD 524 AM CDT Sat Mar 31 2018 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ038>040-050-052>071-011030- Lyon IA-Osceola-Dickinson-Sioux-O'Brien-Clay IA-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln MN-Lyon MN-Murray-Cottonwood- Nobles-Jackson-Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury- Brookings-Gregory-Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora- Davison-Hanson-McCook-Minnehaha-Charles Mix-Douglas-Hutchinson- Turner-Lincoln SD-Bon Homme-Yankton-Clay SD-Union- 524 AM CDT Sat Mar 31 2018 This Hazardous Weather Outlook is for portions of northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, central South Dakota, east central South Dakota, south central South Dakota, and southeast South Dakota. .DAY ONE...Today and Tonight Minor flooding is occurring on portions of the Big Sioux and Little Sioux rivers, as well as a few small streams because of recent rainfall and melting snow. Northwest winds will gust to around 45 to 50 mph this morning, before gradually diminishing by afternoon. .DAYS TWO THROUGH SEVEN...Sunday through Friday Additional chances for accumulating snowfall, possibly with areas of wintry mix, will occur between Sunday night and Tuesday. Minor river flooding currently occurring on local rivers may continue into next week. .SPOTTER INFORMATION STATEMENT... Spotter activation will not be needed.
The national radar mosaic for the moment the first event began.
6 flood. Local standard time, as filed.
A continuation of flooding from March 2018, the river crested at minor flood level at Milford (gage site MIFI4) 0.9 feet above flood stage on April 1.
A continuation of flooding from March 2018, the river crested at minor flood level at Milford (gage site MIFI4) 0.9 feet above flood stage on April 1.
Minor flooding continued from March 2018, with the river at Spencer (gage site SPWI4) returning below flood stage on April 4.
A continuation of flooding from March 2018, the river crested at minor flood level at Linn Grove (gage site LNNI4) 0.6 feet above flood stage on April 1.
A continuation of flooding from March 2018, the river crested at minor flood level at Linn Grove (gage site LNNI4) 0.6 feet above flood stage on April 1.
A continuation of flooding from March 2018, the river crested at minor flood level at Linn Grove (gage site LNNI4) 0.6 feet above flood stage on April 1.
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, April 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: 771724, 771725, 771726, 771727, 771728, 771729.