Parts of Norway are now bracing for some very unusual weather. An atmospheric river is expected to dump extreme amounts of precipitation over 48 hours, up to 200 - 300 mm in some places, and rain is expected as high as 1200 masl. Such amounts of rain in a short time combined with snow melt will result in extreme flooding.
Sounds extremely similar to
what happened here back in November. A heavy atmospheric river with warm temperature and high snow levels in winter is a perfect recipe for flooding. For us it was roughly a one in 100 year flood event. Fingers crossed it won't be as bad in Norway.
I thought these atmospheric rivers mostly happened in the Pacific and needed a feed from the Tropics?
Atmospheric rivers are common over all mid-latitude oceans connected to the tropics. They tend to move eastward and poleward. A good way to visualize them is by total precipitable water, like the loop below from 2019 (or you can
go here for current data.) In this loop you can see several of them. They are normal, though global warming is expected to make them warmer and wetter, so areas that tend to get them (and especially when they normally fall as snow in the mountains) may expect more extreme flooding events in the future.