Tues 02 Aug 2011 — National Composite

First image is the winds aloft at 850 mb (approx 5000 ft). Second image is a snapshot of the base reflectivity from all the radar stations across the USA, providing a composite image at 10:00 pm pdst.

This is a very interesting set of images.  You can see quite clearly how the migrants are responding to wind and weather conditions.  In the plains there is significant bird movement that is terminated on the east by a low pressure weather system and associated strong  westerly winds starting around central Illinois (up to 40 knots in Indiana), and on the south by the high pressure system over Louisiana.