HOT (91 degrees F/30 degrees C) with the odd afternoon thunderstorm. The best thing about Colorado is that there is no humidity, but with that comes intense sun! We are at 5430 feet above sea level here in Boulder (that's 1655 meters for the Brits), so make sure to always drink lots of water and pile on the sunscreen.
Summer Semi Formal.
Firstly, THANK YOU for coming all the way to Colorado! You're going to love it. Denver International Airport is our local here - all the major US carriers fly here (for those coming from different states). For those coming from the UK, British Airways, United Airlines and Norwegian Airways offer direct flights from Heathrow/Gatwick and other airlines (American, Lufthansa, Delta etc) fly here via a connection (usually Chicago, DC or Texas). We would highly suggest renting a car for your time here in CO so you can explore this great state on your own time!