Mosquito season in Broadwater County, MT: when it starts and ends
Mosquito months in Broadwater County
In a normal year mosquito season in Broadwater County, MT starts around May 7 and ends around October 1, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Broadwater County, and when
- Start tipping out standing water weekly by April 23.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 1.
- 1 West Nile case since 2016 (last 2025): you should use repellent at dusk July, more so if over 60.
Broadwater County against the rest of MT
Broadwater County has the 18th longest season of 56 MT counties, at 147 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 44.9°F.
- McCone County: May 6 to October 1 (148 days, 7 WNV)
- Blaine County: May 6 to September 30 (147 days, 4 WNV)
- Musselshell County: May 7 to October 1 (147 days, 0 WNV)
- Petroleum County: May 7 to September 29 (145 days, 0 WNV)
West Nile in Broadwater County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Broadwater County (0 neuroinvasive) across 1 year. The worst was 2025 with 1; the latest was 2025.
More: how the dates are worked out · when mosquitoes go away for the winter.