I use the following to help sort out if I need to stay home or go try it. Works well for Dove, Geese, Ducks, etc. It will give reads on crows and other migratory birds, but if it shows a good flight happening, I've had it hold true in the field as well.
birdcast.info
Just thought I would share.
Live bird migration maps - BirdCast
See real-time analysis maps of intensities of actual nocturnal bird migration, as detected by the US weather surveillance radar network between local sunset to sunrise. Cornell Lab of Ornithology currently produces these maps.
Just thought I would share.