States › Colorado › Boulder County › Flood
Flood in Boulder County, Colorado
36 floods and flash floods events in the NCEI Storm Events record, 1950 to 2026. Event types counted: Flood, Flash Flood, Coastal Flood, Lakeshore Flood.
NCEI notes that Storm Data is compiled from a variety of sources including the National Weather Service, other federal, state and local agencies, the media and the public; that property and crop damage figures are estimates; and that some events are recorded by NWS forecast zone rather than by county. FEMA notes that NFIP claim records are redacted and aggregated to protect the privacy of policyholders. Storm records through 30 Jun 2026.
NCEI records 36 flood events in Boulder County, Colorado, between 1950 and 2026, spread over 12 years.
September is the busiest month, with 17 of the recorded events. The last 20 years account for 30 events against 6 in the 20 years before, a change that reflects reporting practice as much as weather.
The county holds 1.8% of the 1,956 flood events recorded in Colorado; its 5.0 per 100 square miles compares with 1.9 statewide.
NCEI attributes 4 deaths in the county to floods and flash floods.
Compared with Colorado
| Measure | Boulder County | Colorado | US |
|---|---|---|---|
| Flood events since 1950 | 36 | 1,956 | 183,559 |
| Per 100 square miles | 5.0 | 1.9 | 5.2 |
| Per 10,000 residents | 1.1 | 3.4 | 5.5 |
| Deaths recorded | 4 | 47 | 2,961 |
| Busiest month | September | July | June |
By year
Seasonality
0Feb
0Mar
0Apr
0May
2Jun
2Jul
14Aug
1Sep
17Oct
0Nov
0Dec
0
Recorded events
All 36 events, most recent first. Magnitude is hail size, tornado rating or wind speed as recorded.
| Date | Event type | Magnitude | Property damage | Crop damage | Deaths | Injuries | Geography |
|---|---|---|---|---|---|---|---|
| 31 Jul 2021 | Flash Flood | — | $10K | — | — | — | County |
| 30 Jul 2021 | Flash Flood | — | $20K | — | — | — | County |
| 27 Jun 2021 | Flash Flood | — | $10K | $10K | — | — | County |
| 4 Jun 2015 | Flash Flood | — | $15K | — | — | — | County |
| 8 May 2015 | Flood | — | $100K | $10K | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flood | — | $297M | $250K | — | 3 | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flood | — | — | — | — | — | County |
| 12 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 11 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 11 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 11 Sep 2013 | Flash Flood | — | — | — | — | — | County |
| 11 Sep 2013 | Flash Flood | — | — | — | 3 | 2 | County |
| 11 Sep 2013 | Flash Flood | — | — | — | 1 | — | County |
| 11 Sep 2013 | Flood | — | — | — | — | — | County |
| 30 Jul 2012 | Flash Flood | — | $15K | $10K | — | — | County |
| 7 Jul 2012 | Flash Flood | — | $25K | $15K | — | — | County |
| 7 Jul 2012 | Flash Flood | — | $5K | $10K | — | — | County |
| 5 Jul 2012 | Flash Flood | — | $10K | $15K | — | — | County |
| 17 Jul 2011 | Flash Flood | — | $300K | — | — | — | County |
| 13 Jul 2011 | Flash Flood | — | $300K | $20K | — | — | County |
| 7 Jul 2011 | Flash Flood | — | $5K | $5K | — | — | County |
| 28 Jul 2010 | Flash Flood | — | $20K | — | — | — | County |
| 20 Jul 2006 | Flash Flood | — | — | — | — | — | County |
| 25 Jul 2005 | Flash Flood | — | — | — | — | — | County |
| 23 Jul 2004 | Flash Flood | — | — | — | — | — | County |
| 15 May 2003 | Flash Flood | — | — | — | — | — | County |
| 4 Aug 1999 | Flood | — | — | — | — | — | County |
| 30 Jul 1997 | Flash Flood | — | $100K | — | — | — | County |
Questions and answers
How many flood events has Boulder County had?
36 events in the NCEI Storm Events record between 1950 and 2026. Reporting of floods and flash floods became far more complete after 1996, so early decades undercount.
When was the last recorded flood event in Boulder County?
31 Jul 2021 (Flash Flood). Records reach NCEI about 120 days after the month ends.
What was the most damaging flood event recorded in Boulder County?
The flood of 12 Sep 2013, with property damage estimated by NCEI at $297M and crop damage at $250K.
How does Boulder County compare with Colorado for flood?
5.0 events per 100 square miles against 1.9 statewide; the county holds 36 of the state's 1,956 recorded events.
Provenance
NOAA NCEI Storm Events Database, yearly details files through 30 Jun 2026, public domain. County-recorded events plus zone-recorded events whose forecast zone is named for the county (marked "Forecast zone"). Population and area from the US Census Bureau (2021). Built 1 Oct 2026. See the methodology, the Flood hub and the county page.