Where the Kp index and the aurora probability come from

1Independent and not a space weather agency

The site prepares freely published space weather data for travellers. It takes no measurements of its own, runs no model of its own and issues no alerts.

Official forecasts, watches, warnings and alerts come from NOAA SWPC, the Space Weather Prediction Center of the US National Oceanic and Atmospheric Administration. NOAA takes no part in this site and does not endorse it.

2The Kp index

Four NOAA SWPC products feed the Kp blocks. The observed planetary Kp index arrives as one value per 3-hour interval. The 3-day forecast gives a Kp value for every 3-hour slot, marked by NOAA as estimated or predicted, together with the G level of the NOAA scale where Kp reaches 5 or more. The 27-day outlook gives the largest Kp expected on each day. The alerts feed shows the NOAA watch, warning or alert in force, if any.

The NOAA scale maps Kp 5 to G1, Kp 6 to G2, Kp 7 to G3, Kp 8 to G4 and Kp 9 to G5. Values below Kp 5 are shown as below G1.

All four products are published openly by NOAA on services.swpc.noaa.gov. According to the National Weather Service they are in the public domain and may be used for any lawful purpose as long as they are not claimed as one's own. They are shown here unchanged, with the attribution Data: NOAA SWPC.

3The aurora probability per destination

The probability comes from NOAA's OVATION model, a 30 to 90 minute forecast of the location and intensity of the aurora. NOAA publishes it as a grid of one degree in longitude and latitude with a probability in percent for each point. For every destination the page reads the point closest to its coordinates, for example 70 degrees north and 19 degrees east for Tromsø.

The list covers 30 places on both hemispheres, from Longyearbyen on Svalbard at 78 degrees north to Ushuaia in Argentina at 55 degrees south. The table on the home page sorts them by the current probability.

4Refresh, caching and missing data

Each NOAA product is kept for at most 15 minutes and then fetched again. Pages with live data are rebuilt on the server at the same rhythm, and the page copy expires together with the oldest product in it, so a value is never older than 15 minutes plus NOAA's own publication delay. Each live block shows the time of its last fetch from NOAA.

When NOAA SWPC does not respond, the block says so and shows no value. The page never fills a gap with an old number or an estimate of its own. Beyond NOAA's horizon of 3 days in detail and 27 days as a daily maximum there is no forecast.

5How the site is funded

Where a page links to a northern lights tour, that link is an affiliate link. When a booking is made through it, the site receives a commission and the price for the traveller does not change. This has no influence on the data shown, which comes from NOAA in every case. How visits are counted is explained in the privacy policy.