が、今日は

but today

→ が
phrase Rare #39,895
but today Introduces a contrast between what is usually true or happened before and what is true today.
JA: いつもは電車で行きますが、今日は歩きます。
EN: I usually go by train, but today I’m walking.

今月は暑かったが、今日は例外だ。

This month has been hot, but today is an exception.

最近雨がひっきりなしに降っていたが、今日は天気がいいです。

It’s been raining nonstop lately, but the weather is nice today.

昨日は寒かったが、今日は更にいっそう寒い。

It was cold yesterday, but it's even colder today.

私は普段テニスをした後シャワーを浴びるが、今日はできなかった。

I usually take a shower after playing tennis, but I couldn’t today.