Mosquito season in Alamosa County, CO: when it starts and ends
Mosquito months in Alamosa County
In a normal year mosquito season in Alamosa County, CO starts around May 16 and ends around September 27, about 19 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Alamosa County, and when
- Start tipping out standing water weekly by May 2.
- Book any yard treatment for mid May, ahead of the July peak.
- Repellent can go away after September 27.
- 2 West Nile cases since 2016 (last 2023): you should use repellent at dusk July, more so if over 60.
Alamosa County against the rest of CO
Alamosa County has the 39th longest season of 64 CO counties, at 134 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 42.6°F.
- Conejos County: May 13 to September 29 (139 days, 0 WNV)
- Saguache County: May 15 to September 28 (137 days, 1 WNV)
- Rio Grande County: May 19 to September 26 (130 days, 1 WNV)
- Archuleta County: May 23 to September 30 (130 days, 4 WNV)
West Nile in Alamosa County
From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in Alamosa County (1 neuroinvasive) across 4 years. The worst was 2003 with 3; the latest was 2023.
See how the dates are worked out, and when mosquitoes go away for the winter.