This morning he got replaced by a screen that you don't have to swipe up to view, and includes both hourly and 10 day forecasts.
I followed some instructions I found elsewhere to clear google search data (settings: apps: google app: storage & cache: Manage space) and that brought the frog back for about 10 minutes. Then the weather line disappeared entirely from At A Glance. I rebooted the phone and got the weather back in the widget, but the frog was gone again.
Would really like him back... is there something else I can try.
ETA 5 days later my froggy friend is back... I hadn't tried changing anything else, it seems just random