Andy,
The temperature was real nice during the day. I was comfortable in a polypro top, but then I was usually moving. If you want to know the temperatures I recommend you click on "weather" on the Whitney Portal Store page, then click on Whitney Portal Weather under NOAA. Now go to the little map and hit the "+" until it's big enough you can read "Mirror Lake" and "Big Horn Park". You may have to click and drag the picture around to get them centered. You will see a blue lake where Big Horn Park is. It's a mistake. Now double-click on Big Horn Park and you will reset the weather predictions for Big Horn Park. If you look in the upper left corner it should read something like "10 miles West of Lone Pine" and "Elevation 10266 ft". Now you can see what the Highs and Lows are for every day at Big Horn Park. Looks like currently the highs are in the high 40's and the lows are in the 20's.
There may still be a fair amount of snow at BHP on May 15. But if we don't get anymore storms there may be plenty of tracks for you to follow to the summit. All you can do is watch the weather and try it. If you sleep at BHP and get started up by 0600 you should have a good shot. Good climbing! - Walter