The MSO airport is a 15 minute drive from downtown Missoula. Ubers are available but are relatively expensive, they range from $25-$40 per trip. Carpooling strongly encouraged! You can also schedule a ride with the MSO shuttle service: https://www.msoshuttle.com Both the AC Hotel and the Residence Inn offer an airport shuttle service for their patrons, just call ahead to reserve.
Missoula in August is typically hot and dry during the day (with occasional Thunderstorms) and cool at night. You can anticipate daytime temperatures of around 85 and nighttime temperatures down in the 50s.