今天冷死啦！

It's freaking cold today!

另外，和天冷了有关的表达还有：

It's a bit nippy today , you might need a coat.
今天有点儿凉了，你可能要穿件大衣。
It was so cold that I was shivering.
太冷了，我直发抖。
You must be chilly without a coat on.
不穿大衣，你肯定会觉得凉。
We are having a cold snap.
我们遭遇了寒流。