I just noticed today that Google Maps will now pop up weather warnings should you have the map showing an affected area. I'm not aware exactly when this change was made. These types of warnings have been shown as cards in Google Now, but having this information available to a broader user base (presumably you don't have to be logged in) is a welcome improvement. I saw it on the full web site, but I would think it would show up on the mobile app as well, especially if you're navigating through a warned area.
This has been going on for awhile now. Anywhere in Canada or the US (I haven't seen it anywhere else) that has a weather warning will pop up.