It's so changeable at this time of year.
2.四月裏變化無常的天氣:
April weather.
3.這星期他脾氣變化無常，所以不要惹他生氣。:
His temper's is changeable this week, so do not annoy him.
變化無常: constantly changing
Examples:
1. 我希望妳不要再這樣變化無常了，快拿定主意吧！
I wish you wouldn't keep chopping and changing like this, make up your mind!
2. 那個女孩變化無常的性格讓我們很生氣。
The wantonness of the girl's character annoyed us.