Quite a big asteroid going past in our neighbourhood tomorrow, near-Earth asteroid 2005 YU55. About 400 meters or 1,300 feet in diameter, or about the size of a medium sized stadium, and will be passing about 202,000 miles away. 0.85 lunar distances. Quite close.
You won't see it though. It's going to be raining in Rome, so, as Vicky pointed out, even if it were a giant flaming ball, we'd miss it. But it is a type-c asteroid, the c is for "carbonaceous" which means it's quite dark and you will need special long-exposure equipment to see it if the sky is clear where you are.
As for it's potential, err...impact:
"Astronomers estimate objects in the 50 meters range impact on the Earth about once every thousand years and produce explosions equal to 10 megatons of TNT (several times the Hiroshima bomb). We know one such impact occurred in Siberia on June 30, 1908, and flattened more than a thousand square kilometers of forest."