For a reliable weather forecast, go to http://www.mountainweather.com/index.php?page=jackson_hole_forecast, where an expert local meteorologist provides a forecast on weekdays and the National Weather Service forecast is posted on weekends. There is also a climate tab if you want to know more about the general summer climate.
If you go to weather.com, you will see that the temperatures in Jackson Hole (the name for the entire valley which holds the town of Jackson, smaller areas like Wilson and Teton Village, and Grand Teton National Park) vary based on exact location and elevation. If you search "Jackson Hole", the forecast is for lower temps (not sure what exact point in the valley this forecast refers to) than if you search "Jackson, WY" and get the forecast for the town of Jackson.
For the wedding, we probably can expect temperatures in the low 80s, but with little humidity for a cooler feel than Boston's 80 degree days. As the sun goes down, the temp will likely drop to the 50s or 60s while we're still at the reception...and even lower after we all go to bed! So for the entire time you're in Jackson Hole, think in layers! Sweaters, jackets, maybe a light scarf...
