A powerful cold air mass of polar origin is over Brazil. This unusual sharp cooling has been producing freezing temperatures.

Look at some vocabulary to describe the weather here.

Now, the only thing I can think of, to tell people is:

“Make sure you keep warm!”

To keep/stay warm means to keep your body warm, meaning wear the right clothes or do the correct activity or thing to keep yourself warm (referring to body temperature).

It is a normal closing for good wishes. In the middle of winter, ‘stay warm’ would be taken as a wish that you keep warm now that the cold weather is upon us.

Next a few tips to deal with this cold weather: