Aurora Borealis Forecast

How our aurora forecast works

For any US location, the tonight tool answers Yes, Maybe or Unlikely for seeing the northern lights tonight. Every input is public government data. We don't run our own aurora model.

Data sources

DataSourceHow often we refresh it
3-day Kp forecast, current Kp, watches and warningsNOAA Space Weather Prediction CenterEvery 5 minutes
Short-range aurora probability (OVATION, about 30–90 minutes ahead)NOAA SWPC OVATION modelEvery 5 minutes
Hourly cloud coverNational Weather Service (US only)Cached up to 1 hour
Sun and moon positionCalculated from standard astronomical formulasEvery request
ZIP code locationsGeoNames (CC BY 4.0)Static

How the answer is decided

  1. Is it dark? We find tonight's dark window: when the sun is more than 12° below the horizon. If it never gets that dark, the answer is Unlikely.
  2. What Kp does your location need? We convert your location to geomagnetic latitude and use the NOAA Space Weather Scales: Kp 6 reaches about 55°, Kp 7 about 50°, Kp 8 about 45°, Kp 9 about 40°. NOAA gives no latitude north of 55°, so we extend the same line. That makes Alaska values an estimate.
  3. Kp forecast: if the highest forecast Kp during your dark window meets the Kp you need, the aurora signal is Yes. Within 1 Kp of it, Maybe.
  4. Short-range aurora map: when NOAA's OVATION forecast covers your dark window, an aurora probability of 10% or more overhead (within about 2° of latitude north of you) also gives Yes. A 3% chance overhead, or 10% or more low on the northern horizon (up to 8° north), give Maybe.
  5. Clouds: if average cloud cover during the best window (or the whole night, when there isn't one) is 70% or more, a Yes drops to Maybe. When cloud data is missing, we say so instead of assuming clear skies.
  6. Moon: when the moon is more than 60% lit and up for more than a quarter of the dark hours, we warn that faint aurora will be washed out. This doesn't change the answer.

Limits