Although we are in April, the weather has suddenly gotten cold. It's like we are back in the winter season.
ご質問ありがとうございます。
"Although we are in April, the weather has suddenly gotten cold."=「4月なのに、気候が突然寒くなりました。」
(又は、"the temperature has suddenly dropped."=「気温が突然下がりました」とも言えます。)
"It's like we are back in the winter season."=「まるで冬の季節に戻ってしまったようです。」
ご参考に。