Yosemite in the first week of April?

Yosemite is a big place so it depends what you mean.

I have been to Yosemite Valley in early April a few times and the weather was Great, not too warm not too cold. Beautiful spring conditions.

The high country is a bit different.
Tuolumne will generally still be closed.
high country trails will most likely have snow, although this is a low snow year so far.

There are a ton of great trails to take even if the weather is cold. If there is a lot of snow (and this year, that seems like an insane fantasy right now) you can still hike the Wawona Grove of Giant Sequoias, the trail to Dewey with its stunning views of the valley, or most of the trails around Happy Isles/Nevada Falls, Glacier Point. And if the weather cooperates, you might also look at the hike to Hite Cove with its amazing wildflowers.

So those are all day hikes that keep you below the snow. You could also certainly tackle the backpacking trip from Hetch-hetchy to Rancheria Falls ( use them as a base camp to LeConte Point for a day hike) or hike around Lake Eleanor towards Laurel Lake and beyond. Depending on the snow level, you might easily get to Lake Vernon…

And if this weather continues, there won't be much snow at all, and you can go just about where you want. Sadly.

Impossible to know what the weather will be like first week of April in Yosemite.
Could be cold with rain/snow; could be warm and sunny.
That can be said for much of Northern CA and the Sierra.

If you want to be sure it's warm maybe look to Death Valley or Anza-Borrego… great spring flowers in the desert.

Billy