From 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.
Sometimes during a geomagnetic storm, the sky appears to be blank–no auroras. The display may be too faint to see with the unaided eye. Try using your camera: a 15+ second exposure can reveal colorful auroras just below the threshold of naked-eye visibility. An example of “photographic auroras” over Colorado may be found in our most recent aurora gallery: