Dewey County, South Dakota

What hazards hit Dewey County most?

The most frequent records are hail reports: 265 since 1957. 66% of its hail reports since 1957 fell in June and July. The rank column places the county among South Dakota's counties by days with a record per 1,000 square miles of land over each hazard's complete period.

Source: NOAA NCEI Storm Events Database (county and forecast-zone records attributed to the county; a zone record shows its own totals on each county it covers). Days: dates with at least one record of the hazard in the county. Ranks: days with a record per 1,000 square miles of land (Census Bureau 2024 Gazetteer), since 1950 for tornadoes, 1955 for hail and thunderstorm wind, 1996 for the rest.

How many tornadoes has Dewey County had?

NOAA records 27 tornadoes in Dewey County from 1953 to 2014, the strongest rated EF2, with 0 deaths and 1 injury recorded in the county. A tornado that crossed a county line is counted in each county it touched, with the length of its path inside the county.

Counted as whole tornadoes rather than county records, the Storm Prediction Center's database holds 28 tornadoes whose track touched Dewey County since 1950 (NOAA's county records number 27: they file a crossing tornado once per county segment, and the two databases differ on some tracks); along their whole tracks they killed 0 people.

Map of the strongest tornado tracks in South Dakota.

Source: NOAA NCEI Storm Events Database, tornado records by county (path length in the county, maximum width); ratings as published: F scale before February 1, 2007, EF scale after. Whole-track figures: NOAA Storm Prediction Center tornado database (1950-2025). SPC severe weather database.

When was the last damaging storm in Dewey County?

The most recent record with damage, injuries or deaths is the January 12, 2024 extreme cold/wind chill (1 death).

Expansive high pressure out of Canada followed a clipper system resulting in high winds, arctic cold and dangerous wind chills on January 11th. A second system from the south followed close behind enhancing winds overnight January 12th into the 13th. Extreme cold with dangerous wind chills lingered through January 15th after which temperatures began to moderate. Record cold high temperatures were set at Pierre, with a high on January 12th of 1 degree below zero, and on January 13th with a high of only 9 degrees below zero. For Aberdeen, Sisseton and Watertown, the temperature remained below zero between the 13th through the 15th, while for Mobridge, the high temperature failed to exceed zero from the 12th through the 15th. …
National Weather Service event narrative, NOAA Storm Events Database (search the full record, event 1152314)

Source: NOAA NCEI Storm Events Database; every record of 2025-2026 is listed, earlier ones when they caused deaths, injuries or $250,000 of damage (2025 dollars), and every tornado.

The deadliest and costliest records

Source: NOAA NCEI Storm Events Database: deaths and injuries direct and indirect; damage is property plus crops as estimated by the National Weather Service, converted to 2025 dollars.

Is it getting more frequent?

Records per decade for Dewey County's most frequent hazards. Counts rose everywhere after 1996, when NOAA began recording every event type, so compare decades within a hazard's complete period only (the shaded cells come before it).

Extreme cold in the 2010s: 17 records against 5 in the decade before, 17 of them forecast-zone records. Cells marked z rose mostly through zone records. The local National Weather Service office files these once per forecast zone, so a change in how it draws its zones or splits a storm into records moves this count as much as the weather does; read it beside the Dewey County days with a record above.

Source: NOAA NCEI Storm Events Database, records per calendar decade; zone records from the CZ_TYPE field (Z).

What time of year?

66% of its hail reports since 1957 fell in June and July. The two busiest months are in violet.

Source: NOAA NCEI Storm Events Database, records by the month they began.

Federal disaster declarations for Dewey County

FEMA's register lists 16 declarations that include Dewey County: 13 major disasters, 3 emergencies and 0 fire management assistance declarations. Most were for severe storm (7) and flood (3).

Source: FEMA OpenFEMA Disaster Declarations Summaries (v2), declarations through October 2, 2026; one declaration is counted once however many areas it names. OpenFEMA dataset page.

FEMA's modeled risk for Dewey County

FEMA's National Risk Index rates Dewey County Relatively Low overall, with an expected annual loss of $22.1 million. These are FEMA's model estimates of future loss from 18 hazards, not a count of what happened; they can differ from the record above.

Source: FEMA National Risk Index, county table, December 2025 release. FEMA's National Risk Index map.

Counties that share a border with Dewey County

1. Corson County 939
2. Haakon County 843
3. Dewey County 814
4. Ziebach County 738
5. Stanley County 703
6. Walworth County 663
7. Potter County 559
8. Sully County 525

Source: U.S. Census Bureau county adjacency file; NOAA NCEI Storm Events Database, records since 1950. The Census Bureau's adjacency file.

Next

• Tornadoes in South DakotaEvery South Dakota tornado since 1950 and the counties with the most per square mile
• Hail in South DakotaThe state's hail reports, by county, year and month
• The South Dakota recordEvery hazard in the state, its deadliest events and its federal declarations
• FEMA's risk rating for each hazard in Dewey CountyThe hazard risk calculator: 18 hazards beside the county's record
• Download Dewey County's FEMA declarations (CSV)16 rows: every declaration that named the county, for your own analysis