Climate varies considerably across the United States.
You will probably need an umbrella, even in Las Vegas or Los Angeles. In the northern cities, such as Boston, Chicago, Pittsburgh, New York, Seattle, Washington, Denver, and Minneapolis you will need cold weather and snow gear. In the southern states, such as California and Florida, summers may be very hot and the winters mild. Depending on the part of the country, temperatures during the summer will run from the 70s through the 90s. No matter where you are in the US, you will probably need a sweater or jacket for part of the year.