Save this
link to your Favorites and check it as often as needed as you get closer to your desired time in April. It is a Natl Weather Svc forecast and current conditions link that is pinpointed pretty close to the summit of Mt. Whitney. Actually, the current condition readings (temp, wind, etc.) will be from Bishop (not terribly relevant); but the 7-day forecast conditions will be for the location on the accompanying map that is pinpointed (summit of Whitney), and will be of much greater value to you in your planning.
CaT