Mosquito season in Grafton County, NH: when it starts and ends
Mosquito months in Grafton County
In a normal year mosquito season in Grafton County, NH starts around May 8 and ends around October 4, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Grafton County, and when
- Start tipping out standing water weekly by April 24.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 4.
- No West Nile cases since 2016, so bites in Grafton County are a nuisance; check window screens.
Grafton County against the rest of NH
Grafton County has the 9th longest season of 10 NH counties, at 149 days against 170 in Strafford County and 141 in Coos County. Its mean temperature is 42.8°F.
- Sullivan County: May 5 to October 7 (156 days, 0 WNV)
- Carroll County: May 7 to October 3 (150 days, 0 WNV)
- Coos County: May 12 to September 30 (141 days, 0 WNV)
West Nile in Grafton County
CDC ArboNET lists no human West Nile cases for Grafton County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 3 of those years.
Background: when the season starts across the US; how the dates are worked out.