Mosquito season in Okanogan County, WA: when it starts and ends

Mosquito months in Okanogan County

In a normal year mosquito season in Okanogan County, WA starts around April 24 and ends around October 8, about 24 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Okanogan County, and when

• Start tipping out standing water weekly by April 10.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 8.
• 1 West Nile case since 2016 (last 2017): you should use repellent at dusk July to July, more so if over 60.

Okanogan County against the rest of WA

Okanogan County has the 24th longest season of 39 WA counties, at 167 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 47.1°F.

• Garfield County: April 25 to October 12 (169 days, 0 WNV)
• Whitman County: April 26 to October 11 (168 days, 1 WNV)
• Kittitas County: April 25 to October 9 (167 days, 0 WNV)
• Spokane County: April 26 to October 10 (167 days, 12 WNV)

West Nile in Okanogan County

From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Okanogan County (1 neuroinvasive) across 1 year. The worst was 2017 with 1; the latest was 2017.

See how the dates are worked out, and when mosquitoes go away for the winter.