Tonight

The auroral oval expands toward the equator as Kp rises, so reach compares the night's peak Kp against the Kp this location's geomagnetic latitude requires. It is a fifty-fifty line: at exactly that Kp the aurora sits low on the northern horizon rather than overhead.

The aurora is only visible against a dark sky. Twilight, and the midnight sun at high latitudes, can wash it out even under a strong oval.

A bright Moon adds skyglow that washes out faint aurora. A full Moon hurts most, a new or down Moon not at all.

Clouds block the view entirely regardless of how strong the aurora is, so clear skies are the final gate.