Unfortunately it filled the window well and started to overflow into the basement, so I bailed about a third of a yard of water(*) while standing in the window well and hoped the lightning wouldn't notice somebody mostly below ground. Deferred maintenance; don't ask. But at least the landscaping I improvised in the back seems to have worked this year, and the sump pump had nothing to do for a change.
But we got a good soaking so I can't complain too much.
(*) The window well was modified to serve as an emergency exit for the basement, so it is all nice and legal for somebody to live down there and there won't be problems if we have to sell and move. So it is a bit wide. The rain filled up 10" of pea gravel and went on to fill in another 7" to lap at the window.