Mosquito season in Broomfield County, CO: when it starts and ends
Mosquito months in Broomfield County
In a normal year mosquito season in Broomfield County, CO starts around April 20 and ends around October 20, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Broomfield County, and when
- Start tipping out standing water weekly by April 6.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 20.
- 35 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check CO spray notices.
Broomfield County against the rest of CO
Broomfield County has the 5th longest season of 64 CO counties, at 183 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 52°F.
- Prowers County: April 18 to October 20 (185 days, 9 WNV)
- Kiowa County: April 19 to October 21 (185 days, 2 WNV)
- Pueblo County: April 19 to October 18 (182 days, 37 WNV)
- Logan County: April 19 to October 17 (181 days, 19 WNV)
West Nile in Broomfield County
From 1999 to 2025, CDC ArboNET counted 118 human West Nile cases in Broomfield County (37 neuroinvasive) across 17 years. The worst was 2003 with 55; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.