Check out Bird Cast from Cornell

As spring migration heats up, you may be wondering when the best times to head out birding are. Bird migration can be a fickle thing, with many birds arriving on one day interspersed among quieter stretches without new arrivals. Birds often rely on favorable weather and wind conditions to make large movements.

The folks at Cornell University's Lab of Ornithology have put together a website devoted to forecasting the major migration movements across North America. Using radar observations and weather forecast, they produce maps showing intensity of projected movement for each night during spring migration season. The service is free and can help you decide when to go out birding if you're hoping to see high numbers of migrating birds.

The website is:  http://birdcast.info/