Aurora Forecast Tonight

WatchSat shows the live planetary Kp index, NOAA’s G-scale geomagnetic storm level, and a 3-day geomagnetic outlook, then combines the current Kp with your latitude to give an honest visibility verdict — whether the aurora oval reaches overhead, might be visible low on the horizon, or is unlikely from where you are tonight.

What Kp and the G-scale mean

The planetary K index (Kp) is a 0–9 measure of global geomagnetic disturbance over a three-hour interval, derived from a worldwide network of magnetometers. NOAA maps it onto the G-scale of geomagnetic storms: Kp 5 is G1 (minor), 6 is G2 (moderate), 7 is G3 (strong), 8 is G4 (severe) and 9 is G5 (extreme); anything below Kp 5 is unsettled-to-active conditions rather than a storm. Kp is reported in thirds, and a “minus” third counts as the whole number it leads up to — the way NOAA’s own forecast labels it — so Kp 5.33 (5+) is G1, Kp 5.67 (6−) is already G2, and Kp 8.67 (9−) is still G4 because G5 needs a full 9.

Why your latitude decides the answer

Aurora rides the auroral oval, which is centred on the geomagnetic pole, not the geographic one — which is why Scotland sees more aurora than Moscow at the same latitude. WatchSat converts your position to corrected geomagnetic latitude through the centred-dipole approximation (IGRF-13 dipole axis, good to a degree or two) and compares it with the equatorward edge of the oval for the current Kp, a linear fit of 66.5° − 2.04 × Kp to the standard per-Kp oval table: about 66.5° at Kp 0, down to roughly 48° at Kp 9. Reach that line and the aurora is plausibly overhead. Within about six degrees equatorward of it, a bright display can still be glimpsed low on the poleward horizon, because the emission sits 100–300 km up and is visible from beyond the point where it is overhead.

Where the numbers come from

Space weather data comes from the NOAA Space Weather Prediction Center (public domain, US Government): the estimated planetary K index product for the current value and SWPC’s 3-day geomagnetic forecast for the outlook, both fetched through WatchSat’s /api/space-weather edge proxy and reduced to a daily maximum Kp per forecast day.

Darkness, the Moon and cloud

Once you share a location, WatchSat adds the other things that decide whether you could see the aurora tonight. The dark window is when the Sun is more than 18° below your horizon (the end of astronomical twilight), with sunset and civil and nautical dusk beside it; the Moon’s lit fraction and its rise or set across those hours; and the average cloud cover over them. The first two are computed on your device with Astronomy Engine; the cloud forecast comes from Open-Meteo, which is asked only for a location you set yourself, and only when the aurora could reach your latitude. If NOAA’s feed stops answering, the page keeps showing the last reading with its time and age instead of an error.

What a forecast cannot tell you

A high Kp reading is necessary but not sufficient. Seeing the aurora also needs darkness, a clear sky, a horizon that is not washed out by city light or moonlight, and patience — displays surge and fade over minutes. Kp is also a three-hour planetary average, so a short, sharp substorm can put aurora overhead while the index still looks quiet. Treat the verdict here as “is it worth going outside tonight”, not as a guarantee. While you are out there, the same dark sky is the best time to catch a satellite: try tonight’s ISS passes, a Starlink train, or the live tracker.

Explainers

Home · Live satellite map · Satellite directory · Starlink · OneWeb · Navigation satellites · Space stations · Other active satellites · Track the ISS · ISS visible passes · Starlink train · Rocket launches · Aurora forecast · Humans in space · Solar System · Deep Space · Embed widgets · Blog · Guide: spot the ISS · Guide: what is a TLE? · Guide: how many satellites? · Guide: satellite trackers compared · Discovery: Elias 2-24 b · About · FAQ · Data & methodology · Credits · Editorial policy · Accessibility · Contact · Privacy · Terms