On April 21, 2017, there will be a total solar eclipse that crosses through the US. While there have been several annular eclipses in recent years, where a ring of Sun is visible around the Moon, a total eclipse, where the Moon totally covers the Sun, is less frequent. The difference is caused by the distance from the Earth to the Moon when the new Moon occurs; the new Moon this August is close enough so the apparent size is the same as the apparent size of the Sun. The last total solar eclipse visible in US was in 1979, and next one is not until April 2024. This five minute video explains how the Earth, Sun, and Moon line up during an eclipse.
In Tallahassee, the Moon will block about 85 percent of the Sun, and it will completely block the Sun a few hundred miles to the North. Here the eclipse will last from about 1:00 pm EDT until 4:00 pm EDT, with a maximum around 2:40 pm EDT. Here are tips from NASA for safe viewing. Eye protection is necessary to view the eclipse.
The shadow of the moon starts in Oregon and travels to South Carolina in about 1 hour 25 min, covering a path is about 65 miles wide. In Eastern US the eclipse is about 2:30 pm and lasts about 2.5 min. 15 miles from the center line, the eclipse will last 2.2 min.
The nearby big cities where the eclipse are visible are are Kansas City Kansas, Nashville Tennessee and Charleston South Carolina. Average cloud cover at eclipse time over the past 10 years is 50% in Kansas, 60% in Nashville and 70% in Charleston. Only West Coast mountains have low fraction of cloud cover. If you are in an eclipse area, be ready to move to an area where the weather is clear. No better forecast will exist until about a week before the eclipse.