AuroraMethod
How we know
Every number on this site comes from measurements: all-sky cameras for aurora, airport weather reports for clouds, and astronomy for darkness and the moon. Each page says which winters and how many nights.
Aurora seen (camera)
The UEC Tromsø AI dataset classifies every image from all-sky cameras in Tromsø, Skibotn, Abisko and Kiruna (Nanjo et al. 2022, Scientific Reports 12:8038). A night counts when clearly visible aurora shows in at least one 15-minute slot. Under a bright moon the classifier files some aurora as "bright sky"; we count those detections at weight 0.548, from a blind eye check of camera frames. A night only counts when the camera could see: clouds are part of the result, as they would be for you.
Clear sky (airport)
Hourly METAR reports from the nearest airport, September 2016 to March 2026, from the Iowa Environmental Mesonet archive. A dark hour counts as clear when most reports in it have no broken or overcast layer and no fog. A CAVOK report means no cloud below 1,500 m and counts as clear, so this measure is about low cloud: mid and high cloud that dims the aurora can still be there, and many airports' automatic sensors can't see it. A night counts when it had at least two such dark hours.
Darkness and the moon
Dark hours have the sun 12° or more below the horizon. A dark hour is moon-free when the moon is below the horizon or less than 25% lit. Computed with PyEphem for each destination and night.
Tonight's forecast
Issued once a day, the afternoon before the night, by the same engine as the Aurora app: a model trained on three winters of camera data that combines solar wind, the Kp index and its forecast, cloud layers from MET Norway, darkness and moon brightness. It was tested on nights it never saw: in northern Norway and Sweden, nights rated Excellent had clearly visible aurora 79% of the time. Outside that area it runs at medium confidence and we make no accuracy claim.
Limits
- Aurora history exists only near the four cameras. Elsewhere we show low-cloud history from airport reports, which is about clouds, not aurora.
- Aurora activity follows the 11-year solar cycle. The 2023–26 winters were near solar maximum; activity declines from about 2027.
- An airport can be cloudier or clearer than the place you stand.
Sources
- MET Norway Locationforecast (CC BY 4.0)
- NOAA Space Weather Prediction Center
- GFZ Potsdam Kp index (CC BY 4.0)
- UEC Tromsø AI all-sky classification dataset
- Iowa Environmental Mesonet METAR archive
- PyEphem
Reuse
The figures, tables and data files on this site are published under Creative Commons Attribution 4.0 (CC BY 4.0). Use them freely, including commercially; credit "Aurora by Sterk Vekst" with a link to the page you used. Camera figures also rest on the UEC Tromsø AI dataset: credit Nanjo et al. 2022 too.
