"Radar ornithology" is the practice of using Doppler radar to track migrating birds (and, in truth, other airborne objects like bats, insects, and even pollen). There is an excellent tutorial available at Clemson University Radar Ornithology Laboratory, but here's the bottom line: radar shows where birds are moving, in what direction, and estimates of how many are aloft. If you combine those features from the radar with the the weather forecast you can make reasonable predictions about what a morning of birding will produce: does it look like new birds will be arriving overnight? Will they fly right past your area, leaving a paucity of birds in your local habitats? Will a weather system drop the majority in your region (the fabled "fall out")?
Yes, with some meteorological acumen you can determine whether you should call in before the work day begins or if you should save your sick days for another time.
There are several blogs that use radar to comment on migration, some provide interpretation and predict what your morning should look like. I'm not skilled enough to predict fall-outs or where the best locations for your morning birding might be, but I enjoy commenting on what's going on at the moment.
And here's another excellent resource I hope to use more often: friend and science-blogger Paul Hurtado recently reminded our local listserve that he archives radar each night. I find the still images I've posted are an interesting snapshot of that moment in time, but Paul's dynamic loops make migration come alive. Instead of seeing birds aloft, you can watch them explode into the air at sunset, then descend in the morning hours.
Here's a 24-hour loop, starting at 3:00 PM, 23 April through 3:00 PM today (24 April 2009).
If the presentation looks goofy it's because I messed with the aspect ratio.
The blue, circular blobs that appear a few seconds into the loop are the beginning of nocturnal migration. If you look in the map's header there is a clock divided into "night" and "day" to orient you temporally. Because last night was so active it's easier to peg when evening begins by the explosion of blue on the map rather than looking at the clock.
There are a few storms in there, look at the greenish-yellow lines over Lake Michigan and another across Illinois-Kentucky-Tennessee. These dissipate over Pennsylvania and New York by the end of the loop, but as the evening progress you'll see some green mix in with those blue blobs of migration (look specifically across the gulf coast, northeastern Florida and coastal South Carolina, in eastern Kansas and western Missouri): those aren't rain, they represent a huge concentration of birds!
You can find these archives at Paul's radar site, an amazing resource to explore. Hopefully much of May will look like this, but selfishly with more activity over the northeast.