Boulder County

Every recorded tornado

1. Injuries and deaths are for the tornado’s whole path, which may extend beyond the county. Deaths recorded within Boulder County: 0.
2. Weak tornadoes were under-recorded before Doppler radar coverage became national in the early 1990s, so earlier decades read low. Ratings use the Fujita scale before February 2007 and the Enhanced Fujita scale after.

Storm Prediction Center severe weather database, 1950 to 2025.

Every large fire

1. Large fires mapped by the Monitoring Trends in Burn Severity program since 1984: 1,000 acres or more in the West, 500 or more in the East. Prescribed burns are excluded. Acres here are the part of each perimeter inside this place.

Monitoring Trends in Burn Severity (USGS and U.S. Forest Service), 1984 to 2026.

Smoke overhead

1. A smoke day is a date on which a smoke plume traced by NOAA Hazard Mapping System analysts from satellite imagery covered this place's point (the county's population centre or the city centre). Counts here are of medium or heavy smoke. Since 2018 analysts have often drawn light smoke as one area over most of the continent, so light-smoke counts are not comparable from year to year. The plumes show smoke anywhere in the air above, not air quality at the ground, and smoke hidden by cloud is missed.

NOAA Hazard Mapping System smoke analysis, 2011 to 2026, retrieved October 30, 2026.

Claims by ZIP code

This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).

OpenFEMA NFIP Redacted Claims v3, refreshed August 4, 2026. NOAA Storm Events through 2026.

River crests

River gauges

1. Crests are the highest and the recent crests the National Weather Service lists for each river gauge in the county that has a flood stage, not every flood. Flood categories use each gauge's current flood stages; crests from before levees, dams or channel changes may not be comparable. Crests measured on an old datum are left out of the rankings.

NOAA National Water Prediction Service gauge records, retrieved October 30, 2026.

1. The Palmer Drought Severity Index is computed by NOAA each month from the county's average temperature and precipitation, relative to the county's own climate. Zero is normal; -3 or lower is severe drought and -4 or lower extreme drought. It describes the long-term balance of moisture, not water supply or crop losses.

NOAA NCEI nClimDiv county Palmer Drought Severity Index, 1895 to September 2026, issued October 6, 2026.

Every earthquake of magnitude 4 or more within 50 miles

1. Earthquakes of magnitude 2.5 or more in the USGS Comprehensive Catalog since 1900. Within 50 miles means the epicentre lies within 50 miles of the county boundary (or inside the county).
2. Small earthquakes were under-recorded before the modern seismic networks of the 1970s and are still missed in remote areas, so early decades read low. Magnitudes are as the catalogue reports them and mix scales (moment, local and body-wave).

USGS ANSS Comprehensive Earthquake Catalog, 1900 to present, retrieved October 30, 2026.

Volcanoes within 100 miles

1. U.S. volcanoes within 100 miles, from the USGS Volcano Hazards Program. The threat category is the USGS 2018 National Volcanic Threat Assessment, which ranks volcanoes by how hazardous their past eruptions were and how many people and how much infrastructure lie near them. It is not a forecast of eruption.

USGS Volcano Hazards Program, retrieved October 30, 2026.

Mapped landslides

Mapped by USGS CO Front Range Sept 2013 (840), CO GS (35), NASA (9), USGS Conterminous (1).

Deadly landslides

1. Landslides mapped in the USGS compilation of landslide inventories across the United States (version 3.0, 2025), rated probable or better. The compilation joins inventories made by federal and state agencies for different purposes and areas, so the number mapped in a county reflects how closely it has been surveyed as much as how often its slopes fail. An area with few records may simply not have been mapped. Deaths are as recorded in the inventories; a slide listed in two inventories is counted once.

USGS Landslide Inventories across the United States, version 3.0, retrieved October 27, 2026.

More event types since 1996

Costliest events since 1996

1. Sep 12, 2013Flood$297 million
   National Weather Service narrative

   Heavy rain, ranging from 6 to 18 inches through the storm event, caused widespread flooding along the entire drainage systems of Boulder and St. Vrain Creeks. Three vehicles were partially submerged when floodwaters undercut Dillon Road near CO287, between Lafayette and Broomfield. When the road first collapsed, several people were able to get out of the water quickly, but three were trapped in their vehicles and had to be rescued. The three drivers were taken to local hospitals for treatment. Extensive flooding was reported in Longmont and forced several road closures. Floodwaters tipped over two storage tanks containing sulfuric acid at the Longmont Brewery. Several shelters…

2. Jul 12, 1996Hail$1.0 million
   National Weather Service narrative

   Large hail, strong winds and heavy rain caused substantial damage to property in portions of Boulder and northern Jefferson Counties. Damage estimates in the Broomfield area alone were approximately $1.0 million.

3. Jul 13, 2011Flash Flood$300,000
   National Weather Service narrative

   Heavy rain produced significant flash flooding in the Fourmile burn scar.

4. Jul 17, 2011Flash Flood$300,000
   National Weather Service narrative

   Heavy rain produced extensive flash flooding.

5. May 8, 2015Flood$100,000
   National Weather Service narrative

   Heavy rain caused flooding of businesses along the Saint Vrain River in Lyons, south of Bohn Park. Several basements in Boulder County were reportedly flooded. Some flooding was also reported along Coal Creek, upstream of Erie. Road closures included the westbound lane of Arapahoe Road, between County Line Road and 119th Street.

6. Jul 30, 1997Flash Flood$100,000
   National Weather Service narrative

   Heavy rain and hail triggered a flash flood which sent a wall of water through the window of the financial aid office at the University of Colorado campus. In addition, ceiling tiles, carpets and dressing rooms were damaged at the Coors Event Center when a pipe draining rainwater broke during the downpour. In all, 10 buildings at CU received water damage causing an estimate $100,000 in damage.

7. Jun 10, 2009Lightning$25,000
   National Weather Service narrative

   Lightning struck an oil tank. The lid was partially torn off and flames shot out of the tank. The railing around the tank was also damaged.

8. Jul 7, 2012Flash Flood$25,000
   National Weather Service narrative

   Heavy rain caused rock and mudslides in central Boulder County.

9. Jun 19, 2002Lightning$25,000
   National Weather Service narrative

   Lightning struck a garage and caused a small fire. Two vehicles parked in the garage were damaged.

10. Jun 15, 2009Thunderstorm Wind$20,000
    National Weather Service narrative

    Thunderstorm winds knocked a tree on to two vehicles in Boulder. One of the two drivers was injured when the tree smashed the windshield of her car.

1. Storm Events records before 1996 cover only tornadoes, thunderstorm wind and hail. Damage figures are as reported by the National Weather Service at the time, not adjusted for inflation.

NOAA NCEI Storm Events Database, 1950 to 2026, issued October 26, 2026.

All-time high

104°F3 times, most recently Aug 3, 2026

All-time low

−33°FJan 17, 1930

Warmest night

80°FJun 24, 1954

Coldest day

−12°FFeb 4, 1989

Wettest day

9.08 inSep 12, 2013

Snowiest day

22.1 inOct 25, 1997

Hottest year

1954mean 56.1°F

Coldest year

1993mean 47.4°F

Wettest year

201334.15 in

Driest year

195410.91 in

Snowiest season

152.0 in2019-20

Station Boulder (USC00050848), 5,489 ft elevation, 6.7 miles from the population centre. Daily records from 1893 to October 26, 2026; 99.1% of days in the last 30 years are complete. Records at a single station can differ from a city’s official threaded record, which may combine several stations.

NOAA NCEI Global Historical Climatology Network Daily.

This product uses the Federal Emergency Management Agency's OpenFEMA API, but is not endorsed by FEMA. The Federal Government or FEMA cannot vouch for the data or analyses derived from these data after the data have been retrieved from the Agency's website(s).

OpenFEMA Disaster Declarations Summaries, retrieved October 30, 2026. Statewide declarations are not listed.

Neighbouring counties

• Tornadoes NOAA Storm Prediction Center severe weather database, through 2025.
• Tropical cyclones NOAA National Hurricane Center HURDAT2 (Atlantic; Northeast and Central Pacific), through 2025.
• Wildfire USGS/USFS Monitoring Trends in Burn Severity, through 2026.
• Storm events NOAA NCEI Storm Events Database, through 2026.
• Flood insurance OpenFEMA NFIP Redacted Claims v3, refreshed August 4, 2026.
• Declarations OpenFEMA Disaster Declarations Summaries v2, retrieved October 30, 2026.
• Weather records NOAA NCEI Global Historical Climatology Network Daily, station USC00050848.
• River crests NOAA National Weather Service, National Water Prediction Service river gauges, retrieved October 30, 2026.
• Drought NOAA NCEI nClimDiv county Palmer Drought Severity Index, through September 2026.
• Smoke NOAA NESDIS Hazard Mapping System smoke analysis, retrieved October 30, 2026.
• Volcanoes USGS Volcano Hazards Program, U.S. volcanoes and 2018 threat assessment.
• Landslides USGS Landslide Inventories across the United States, version 3.0 (2025).
• Earthquakes USGS ANSS Comprehensive Earthquake Catalog (ComCat), retrieved October 30, 2026.

Joins, thresholds and known limits are set out in the methodology. Found an error? Report it. Page built October 30, 2026.