Mosquito season in Napa County, CA: when it starts and ends
Mosquito months in Napa County
In a normal year mosquito season in Napa County, CA starts around February 24 and ends around November 27, about 39 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Napa County, and when
- Start tipping out standing water weekly by February 10.
- Book any yard treatment for late February, ahead of the July peak.
- Repellent can go away after November 27.
- 1 West Nile case since 2016 (last 2018): you should use repellent at dusk July to August, more so if over 60.
Napa County against the rest of CA
Napa County has the 30th longest season of 58 CA counties, at 276 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 58.7°F.
- Shasta County: February 20 to November 28 (280 days, 16 WNV)
- Tulare County: February 23 to November 28 (278 days, 125 WNV)
- Yuba County: February 27 to November 28 (274 days, 24 WNV)
- Santa Barbara County: February 27 to November 27 (273 days, 2 WNV)
West Nile in Napa County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Napa County (2 neuroinvasive) across 4 years. The worst was 2018 with 1; the latest was 2018.
See how the dates are worked out, and when mosquitoes go away for the winter.