From:
http://spaceweather.com/
An explosion on the sun yesterday (Aug. 16) hurled a coronal mass ejection (CME) toward Earth. The approaching cloud could spark a geomagnetic storm when it arrives, probably on August 18th. Sky watchers should be alert for auroras.
If a storm erupts, the best displays will be at higher latitudes: e.g., Alaska, Canada, and Scandinavia. However, auroras could descend to lower latitudes, too, spreading across northern-tier US states from Maine to Washington and elsewhere.