First, go to your device settings to applications, to 1Weather and toggle the storage permission off and back on. Does that help?
If not, we have had several customers with Nougat and Oreo who have reported this issue and it appears that adjusting the new Display Size setting added in Nougat has helped. There's some helpful info on that setting here:
After toggling the font and display size settings, then toggling them back, the radar should work properly.
We're looking for root cause and will get an update out to mitigate this ASAP.