Two fronts will slide through between Saturday evening and Monday morning and with more seaso nal frontal passages and cool weather, bird watchers will witness migrations. With duck season upon us, hunters will also have an eye to the sky. Bird watchers report that the ever popular Ruby Throated Hummingbird will leave our area this month with a few staying year-round. The website: hummingbirds.net reports that in addition to the Ruby Throated Hummingbird, twelve species of hummingbirds, from the Rufous and Black-chinned to the Broad-tailed, Broad-billed and Green-eared enjoy their stay in south Louisiana.  The Ruby-throated hummingbird is the only species that breeds east of the Rockies and will journey to their wintering grounds in Central America. Experts suggest keeping your feeders in place for some stragglers. Also, WBRZ, Channel 2 was the first television station in Baton Rouge to introduce Doppler Radar in 1989.  In 1842 the Austrian physicist, J.C. Doppler experimented with sound waves.  Doppler Radar detects the motion of precipitation inside thunderstorms.  We target storms and determine if there's rotation that warrants tornadic development.  On the radar screen the "returns" are painted in a bright red color and purple or magenta colors indicate strong winds and possible tornadoes. The forward average speed of a tornado is between 25 and 40 miles per hour. Some have traveled as slowly as 5 miles per hour and some have skipped across the land at nearly 70 miles per hour.