How to use it
- Type your 5-digit ZIP, or your city and state (like Duluth, MN), and press Check tonight. Or press Use my location.
- Read the answer on the green highlight: good chance, possible, unlikely, very unlikely, or too bright. Under it you get the dark hours in your own time zone, the best hours, which way to face, and the moon.
- Optional: add the National Weather Service cloud forecast. Thick clouds lower the answer one step, because you can't see aurora through them.
- Check again after dark. NOAA's live model only looks 30–90 minutes ahead, so the picture changes during the night.
How we decide
We combine four things. Darkness: we work out when the sun is at least 12° below your horizon (dark enough) and 18° below (darkest), using Astronomy Engine and checked against the U.S. Naval Observatory. If it never gets 12° below, the answer is “too bright”, whatever NOAA says.
The Kp you need: NOAA's tips say the edge of the aurora sits near 66° geomagnetic latitude at Kp 0 and moves about 2° toward the equator for each step of Kp. We compute your geomagnetic latitude from the IGRF-14 magnetic field model and round the Kp you need up to the next third, the way NOAA publishes Kp (5-, 5, 5+).
NOAA's Kp forecast: the highest 3-hour Kp NOAA forecasts during your dark hours. If it meets the Kp you need, that's a good chance; within one point, possible; further below, unlikely. Very far south (below about 40° geomagnetic, past even NOAA's strongest storm level), it's very unlikely.
Clouds and moon: if you turn clouds on and they're forecast above 70% of the sky, the answer drops one step. A bright moon doesn't change the word, but we warn you that it washes out faint aurora.
Want the details, including the view-line formula? Read how it works.
Four example nights
- Seattle, Oct 9, 2026: dark enough 7:39 pm – 6:15 am PDT, new moon. You usually need about Kp 6⅔ there; NOAA's saved forecast said up to Kp 4, so: unlikely. With clouds on (about 81% cover) it drops to very unlikely.
- Minneapolis, Dec 21, 2026: a long night, dark enough 5:45 pm – 6:38 am CST, but a 95% moon is up all night. You need about Kp 6⅓.
- Fairbanks, June 21, 2027: the sun barely dips below the horizon, so the sky never gets dark enough. Too bright, even though Fairbanks sits almost under the aurora (Kp ⅓ would do).
- Boston, March 20, 2027: darkest 8:31 pm – 5:12 am EDT (daylight time began a week earlier), a 98% moon, and you need about Kp 7⅓.