Automated baseline from FEMA and NOAA data, release 2026-10.

Walworth County, SD

Risk-assessment baseline packet. County FIPS 46129. Release 2026-10, data as of 2026-09-30.

Summary

Plan status as of 2026-09-30: Approved, expires 2030-01-15. Plan: Warhawk District, SD Hazard Mitigation Plan 2025 (FEMA plan 110116), approved 2025-01-16.

Since the plan was approved on 2025-01-16: no new hazard declaration and 47 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): Cold Wave ($5,252,762 a year), Inland Flooding ($3,395,034) and Tornado ($366,781).

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.

Download the packet

Full packet as a web page. File manifest (checksums, source versions).

Plan clock

Approved, expires 2030-01-15

Plan:
Warhawk District, SD Hazard Mitigation Plan 2025 (FEMA plan 110116)
Approved:
2025-01-16
Days to expiry:
1,203

What changed since your last plan (approved 2025-01-16)

New federal declarations:
none
Storm Events records since approval:
47 records (data through 2026-06-30)
Repetitive loss now:
FMA RL 0, SRL 0 (44 CFR 77.2); any definition: 0
Repeat-flood change:
this release sets the baseline count.

Plan status for every jurisdiction listed in this county

2 jurisdictions. Each row is that jurisdiction's own plan clock.

JurisdictionTypeStatusPlanApprovedExpiresDays to expirynegative = days since expiry
Walworth CountyCountyApproved, expires 2030-01-15Warhawk District, SD Hazard Mitigation Plan 2025 (FEMA plan 110116)2025-01-162030-01-151,203
Mobridge cityCityApproved, expires 2030-01-15Warhawk District, SD Hazard Mitigation Plan 2025 (FEMA plan 110116)2025-01-162030-01-151,203

Plan 110116 covers 5 other participants: Campbell County; Corson County; Dewey County; McLaughlin city (Corson County); Ziebach County.

State plan status and tribal plans in this state: see the state page.

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): Cold Wave, Inland Flooding and Tornado.

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 11 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: 3 in hail, 2018-08-23
  • Thunderstorm Wind: 87 kt (100 mph) measured gust, Thunderstorm Wind, 2018-06-05
  • Tornado: F3 tornado, 1968-06-20, 8.8 mi path length (whole path, pre-1996), 200 yd wide, damage not recorded (pre-1996 record); same rating, casualties and property damage also recorded on 1968-06-20

Supports FEMA checklist item B1-d Previous occurrences

Federal declarations for this area: 12 declarations covering 9 separate hazard incidents counted in this packet; each with type, dates and county Public Assistance dollars.

New since the last plan (approved 2025-01-16): none.

3 statewide declarations listed separately.

Hazards with no Storm Events record and no federal declaration are stated as such (8 of 18).

Storm Events history: 656 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 and Strong Wind
  • Likely: Cold Wave, Drought, Heat Wave, Ice Storm, Inland Flooding, Landslide, Tornado and Winter Weather
  • Possible: Wildfire

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).

2 jurisdictions: plan clock, repeat-flood count, Public Assistance dollars and event records naming the place (starting figures from federal data).

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 2025-01-16: $0 in county-coded records (23 records); $0 reported for the zone (24 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 5,315; building value $1,803,454,913 and agriculture value $112,058,365 (total, not at risk).

National Risk Index rating Very Low; social vulnerability Relatively High; community resilience Very 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.

Releases

Each release is dated; this is release 2026-10. It was first published 2026-09-30; its files do not change. Later releases will be listed here with what changed between them. All releases.

Cite this

Hazard Plain (2026). Walworth County, SD: risk-assessment baseline packet, release 2026-10 (data as of 2026-09-30; County FIPS 46129). Automated baseline. https://hazardplain.org/sd/46129/ Built from FEMA OpenFEMA, the FEMA National Risk Index and NOAA NCEI Storm Events; source versions in the packet's Sources list.

Source citations for the plan's bibliography (8)

How this packet is built: methods and sources