I think tseeb has described accurately the range of conditions you might expect at Squaw/Alpine in April. My own spring experience at Squaw/Alpine is limited as Mammoth's advantage in conditions increases every week the farther you advance into spring. Comparing tseeb's and my reports this week shows that difference already vs. south Tahoe areas that are higher and usually retain winter snow longer than Squaw/Alpine do.
My one day at Squaw this season was on
February 10, and it was in full on spring mode that day, though much of that was due to wet fog the prior day. However, note that was overall a quite positive report. Squaw in particular is so vast that if only half the mountain has pleasant snow conditions you can still have a great day.
One issue with Squaw is that the volume lifts out of the base are the tram and Funitel enclosed lifts. In February I chose to leave the base via KT-22 and move up the mountain via chairs. I do not think Squaw is a good place to be on weekends with COVID capacity limits. And we have all heard that Fridays seem to be part of the weekend as far as ski area crowds are concerned this season. My son Andrew is a liftie at Mammoth this year and he says Fridays are busier than Sundays there.
The below average snowpack will be of concern as spring advances. As one might expect in La Nina, Squaw (82%) has done a little better than Mammoth (77%) on snow so far in 2020-21. However if April is warm and dry, Squaw will lose snow much faster than Mammoth will.
If I ski both Mammoth and Bachelor in April, I might take a day at Squaw in between.