...
But pretty much any time in April should give you a good consolidated snow base to climb on.
That's true barring recent snow fall.
The Eastern Sierra Avalanche Center provides daily reports on an area centered around Mammoth up to March 31. It's not ideal, but it might be worth looking at their summary of snowpack conditions as the time of your your visit approaches.
esavalanche.org
Dale B. Dalrymple
