Forecast › Data & method
Data & method
The forecast uses NOAA SWPC’s OVATION aurora model and three-day Kp forecast, MET Norway’s cloud forecast and a sun-position calculation for darkness. We combine them with a simple, published rule. If NOAA data cannot be loaded, we show no forecast instead of a guess. Every data time is shown.
Data sources
- OVATION aurora forecast (NOAA SWPC,
ovation_aurora_latest.json): a 30 to 90 minute forecast of the probability of seeing aurora, on a 1° grid. It is based on the OVATION model from Johns Hopkins University APL, driven by solar wind measured at the L1 point about 1.6 million km from Earth (NOAA). Fetched at most every 5 minutes. - Kp forecast (NOAA SWPC,
noaa-planetary-k-index-forecast.json): observed, estimated and predicted Kp in three-hour blocks. Fetched at most every 30 minutes. - Solar wind (NOAA SWPC real-time summary): speed and the Bz component of the magnetic field. Fetched at most every 5 minutes.
- Cloud cover (MET Norway Locationforecast, CC BY 4.0): hourly cloud fraction. Your coordinates are rounded to 0.1° (about 11 km) before our server asks MET Norway, and the answer is cached as long as MET Norway’s Expires header allows.
- Darkness: calculated in your browser from the sun’s position. “Dark” means the sun is more than 12° below the horizon.
- Place names: towns with 15,000 or more inhabitants from GeoNames (CC BY 4.0), filtered to the latitudes where aurora is relevant. The list is loaded only when you use the search box.
How we turn it into a chance
- Your geomagnetic latitude is calculated from the 2025 geomagnetic pole (80.85°N, 72.76°W, NOAA NCEI).
- The Kp needed for aurora overhead is (66 − geomagnetic latitude) ÷ 2, from NOAA’s rule that the oval edge is near 66° at Kp 0 and moves about 2° per Kp step (NOAA).
- “Kp tonight” is the highest predicted Kp in the blocks that overlap your dark hours.
- The verdict: Good chance if Kp tonight reaches the Kp needed, or if OVATION shows 30% or more within 1,000 km right now; Possible if Kp is within 2 of the needed value, or OVATION shows 10% or more within 1,000 km; Low chance if within 4; otherwise Unlikely. If average cloud cover while dark is 80% or more, we add “but cloudy”. If it never gets dark, the answer is “Too light tonight”.
- “Look towards” is the compass direction to the strongest OVATION value within 1,000 km, since NOAA says bright aurora can be seen from that far away.
This rule is our own simplification, not a NOAA product. The aurora is hard to forecast more than an hour ahead, so treat the result as a guide.
When data is missing
Our server keeps the last good NOAA data for a limited time (90 minutes for OVATION, 6 hours for the Kp forecast) and labels it when it is old. If there is no usable data, the page says so and shows no forecast.
Terms of use
NOAA/NWS information is in the public domain and may be used for any lawful purpose, as long as it is not presented as official government information or as endorsed by NOAA/NWS (NWS disclaimer). MET Norway data is CC BY 4.0 and requires identification and caching (MET Norway terms). GeoNames data is CC BY 4.0. Checked October 20, 2026.