From Ohio birding e-mail listserv :

Migration note

Date: Mon, 21 Apr 2008 23:59:31 -0400

There has been a rather heavy movement of birds into Fla over the last
several days. The weather there hasn't been conducive to rapid movement
northward, but is improving. Notes from the south supported by the radar
indicate heavy transgulf movement into the La to Texas coasts. Remember,
that the birds, after their flight across the Gulf have to replenish
their sustenance and then it can take several days to cover the distance
north to us. Tonight's radar has the whole midwest flyway lit up.
Remember, hawks are migrating in large numbers also and reflect more
radar rays. However, I believe their main motion is during the day. The
radar for this can often be seen through the Great Plains.

If you are able to handle the radar map, check
http://www.rap.ucar.edu/weather/radar/

set the end time to 0400 or later (= 11:00 pm EDT). To see some motion,
set the loop duration for as long as you want and click "Contiguous US".
Set the speedbar as fast as you care. Ohio is barely on the age at the
present time.

A number of people have asked me about the radar and thanked me for it,
so I offer this simplistic view for those whom it will help.
A very elementary idea for those needing the image, is to think of the
radar as a searchlight which highlights the clouds as it swings around.
If the images were retained (as in radar), you get a donut effect. With
rain, the radar picks up the reflection from all altitude levels and thus
creates a more constant image with well detected movement. Birds occur
mostly near one level with scattering somewhat above and below (like
stratus clouds). In some cases, images of larger concentrations of birds
(or larger birds), can exhibit a similar motion. Remember, hawks are
migrating in large numbers also and reflect more radar rays.