Risk-assessment baseline packet. County FIPS 19143. Release 2026-10, data as of 2026-09-30.
Summary
Plan status as of 2026-09-30: Approved, expires 2027-01-17. Plan: Sioux, O'Brien and Osceola Counties Multi-Jurisdictional HM Plan (FEMA plan 107675), approved 2022-01-17.
Since the plan was approved on 2022-01-17: 1 new hazard declaration (1 incident) and 127 NOAA Storm Events records; details under "What changed since your last plan".
Highest expected annual loss (FEMA National Risk Index, modeled total; see B1-a): Inland Flooding ($1,664,599 a year), Hail ($1,197,063) and Cold Wave ($896,152).
The packet's tables are organized by the items of FEMA's Local Mitigation Plan Review Tool, Element B (B1-a to B2-c); the summaries below follow the same order.
What the packet contains
Sections in FEMA checklist order; each heading names the review item its tables support. Full tables are in the downloads above.
Supports FEMA checklist item B1-a Hazard identification
13 of the 18 National Risk Index hazards apply here.
Not applicable to this county per NRI, with no federal declaration and no Storm Events record since 1996: avalanche, coastal flooding, tsunami and volcanic activity. That is the evidence for leaving them out of the plan.
Highest expected annual loss (NRI, modeled): Inland Flooding, Hail and Cold Wave.
Not covered by NRI (local data needed): dam failure (incl. upstream dams); levee failure; flash flood as its own subtype; ice jams; debris flows; erosion (riverine and coastal); land subsidence and sinkholes; expansive soils.
The state hazard mitigation plan also lists hazards for this county; FEMA asks the plan to explain any hazard it leaves out.
Supports FEMA checklist item B1-b Hazard location
- Cold Wave, Drought, Hail, Heat Wave, Ice Storm, Lightning, Strong Wind and Winter Weather: affects the whole county; national data give no location within it.
- Earthquake, Hurricane, Landslide, Tornado and Wildfire vary within the county; the packet lists the highest-rated census tracts for each.
- Inland Flooding: the FEMA Flood Insurance Rate Map (FIRM) is the required location source for flooding. See the FEMA Flood Map Service Center (https://msc.fema.gov) for this county.
Supports FEMA checklist item B1-c Hazard extent
Storm Events records for 12 of the 20 NOAA event-type groups mapped to the 18 hazards, with the scale, observed range and worst recorded event for each; the others say which local data are needed.
Worst recorded tornado, hail and thunderstorm wind (the three event types on record since the 1950s; the packet has every group):
- Hail: 4 in hail, 1958-08-14
- Thunderstorm Wind: 96 kt (110 mph) estimated gust, Thunderstorm Wind, 2026-06-30
- Tornado: EF4 tornado, 2010-06-25, 8.47 mi within this county, 800 yd wide, $3,000,000 property; crops not reported (2010 dollars), 13 direct injuries
Supports FEMA checklist item B1-d Previous occurrences
Federal declarations for this area: 15 declarations covering 12 separate hazard incidents counted in this packet; each with type, dates and county Public Assistance dollars.
New since the last plan (approved 2022-01-17): DR-4796-IA.
5 statewide declarations listed separately.
Hazards with no Storm Events record and no federal declaration are stated as such (7 of 18).
Storm Events history: 602 records (notable ones in the PDF, all of them in the Excel file).
Supports FEMA checklist item B1-e Probability of future events
FEMA annualized frequency (modeled) for each hazard, with a descriptor from a scale defined in the packet.
- Highly likely: Hail, Lightning, Strong Wind and Winter Weather
- Likely: Cold Wave, Drought, Heat Wave, Ice Storm, Inland Flooding and Tornado
- Possible: Landslide and Wildfire
- Unlikely: Earthquake
Historical frequency by intensity band (tornado, hail, wind): 9 bands from Storm Events.
Supports FEMA checklist item B1-f Hazards that vary across jurisdictions
Range of census tract risk scores within the area for 14 of the 18 hazards (2 tracts; rated tracts only).
6 jurisdictions: plan clock, repeat-flood count, Public Assistance dollars and event records naming the place (starting figures from federal data).
County Public Assistance in B1-d also includes applicants filed under the county that are not matched to a jurisdiction row here (for example county offices and boards filed under their own names, such as a sheriff's office or a conservation board, and state agencies, special districts and nonprofits), so the jurisdiction rows add up to less.
Supports FEMA checklist items B2-a and B2-b Vulnerability and potential impacts
The packet's table gives county-level starting figures; the plan describes impacts for each jurisdiction and its own assets.
Storm Events damage since 2022-01-17: $2,851,000 in county-coded records (45 records); $2,705,000 reported for the zone (82 zone records). Data through 2026-06-30; nominal dollars.
Local data needed
To gather:
- Critical facilities and lifelines per hazard
- A problem statement per jurisdiction per hazard
- Changes in development in hazard-prone areas since the last approval, or a statement of none (E1-a)
- Future assets
Supports FEMA checklist item B2-a Vulnerability (county context)
Population 6,192; building value $2,383,715,378 and agriculture value $590,911,938 (total, not at risk).
National Risk Index rating Very Low; social vulnerability Relatively Moderate; community resilience Relatively High.
Supports FEMA checklist item B2-c Repetitive loss properties
Repetitive-loss properties, FMA definition (44 CFR 77.2): 0 repetitive loss, 0 severe repetitive loss. NFIP insurance definition: 0 and 0.
Mitigated 0; insured 0; NFIP data as of 2026-08-02. Counts by occupancy group and for each jurisdiction are in the packet.