I'm from Colorado, and I'm planning a road trip to Smith Rocks for a week in either April, May, or June. When do you think the conditions will be best for climbing/camping?

April will go to below freezing at night and a 50/50 chance of rain or snow(at least it always seems that way from my own experience). You will want to wait until 10 am or only grab first sun areas. But shady rock will always be cold. I'm not sure the showers at the bivy site are open in April. I assume you are camping. Crowded on good weather weekends.
May is better, still cold enough that you will wait for the sun to warm the rock(8-9am), but less chance of precip. Crowded on the weekends.
June is also a great month, though end of June the days can reach 80s already, but still be cool(40) at night. Crowded on the weekends. If you are planning something months in advance, I would say anytime in June.

Go in April. March & April are the best Spring months. If you go in May or later, you will be hiding from the sun all day, every day, and most of the classic lines are in the sun most of the day.

Agreed on April. It is HOT in May and June. April can have stormy weather, but Smith Rocks is its own microclimate, and is considerably dryer than Bend etc. I've climbed in the gorge (all shaded) in April - and it was cold, but very climable.

As your trip draws closer, you might want to check out the 6-day forecast on ClimbingWeather.com .

http://www.climbingweather.com/Oregon/Smith-Rock/

The site uses data from the National Weather Service digital forecast database. Unlike other weather websites, ClimbingWeather.com gets the weather for the specific latitude and longitude of a climbing area, not just the nearest town.

Hope you find it useful!

I have a house in Bend and was just climbing at Smith last weekend (3/29/08.) It snowed in the morning in Bend and the afternoon weather at Smith was wonderful--sunny and warm in the sun. If you are camping, the night time temperature is a little chilly in March--about 17F for a night time low. Mid-April should be really nice but bring some warm clothes for the evenings.