My suggestion is: just say it exactly as you have said it! Don't worry about polishing your English. They are your friends, and to them your accent is just part of your personality. Your meaning is completely clear. There is an expression used about giving gifts: "It's the thought that counts." Never worry about the exact form of words when the message is something like "Thinking of you," or "Sorry to hear about this," or "Congratulations." Politeness and courtesy are not in the form of words. It's the thought that counts. They will be pleased to know you heard about the snowstorm and that you are thinking of them.

"Stay safe" or "I'm sorry to hear about the snowstorm."

I would say: "I'm sorry to hear that you guys are facing such terrible storms. I hope that you and your family are safe."