How often does the aurora reach my town?

The tool counts days per year when Kp reached the level that puts the average oval edge overhead, from the GFZ record since 1932. Darkness and cloud then decide what you can see.

Why do some years have far more days?

Geomagnetic activity follows the roughly 11-year solar cycle. The strip shows the waves.

Where does the Kp data come from?

GFZ Potsdam, the producer of the definitive Kp index, under CC BY 4.0. Recent days are nowcasts that can still change.

How often does the aurora reach me? Kp since 1932

How often has activity been high enough for my location?

Answer

Karlskoga sits at 58.5 degrees geomagnetic, so the average oval edge is overhead at Kp 4. In the GFZ record the median year since 1932 has 125 such days; the last 10 complete years averaged 84. 1951 had the most, 233.

Kp 4

level that puts the oval edge over Karlskoga

IGRF-14 dipole, SWPC oval rule, GFZ Kp since 1932

Worked example

Anchorage sits at 61.9 degrees geomagnetic, so the average oval edge is overhead at Kp 3. In the GFZ record the median year since 1932 has 228 such days; the last 10 complete years averaged 175. 1951 had the most, 322.

The yearly counts rise and fall with the solar cycle, so a quiet year and a busy one can differ several times over. Plan on the median, and treat busy years as a bonus.

How the count works

Glow turns your coordinates into a centered dipole latitude with IGRF-14, then applies SWPC's rule of thumb: the average oval edge sits at 66 degrees at Kp 0 and moves 2 degrees toward the equator per Kp step. The smallest whole Kp whose edge reaches you is your level.

For every UTC day since 1932 the GFZ Potsdam file gives eight 3-hour Kp values. A day counts when its highest value is your level or more, in whole numbers, so 5- does not count as 5.

What the count leaves out

The edge rule describes the average oval; SWPC calls it approximate. Aurora is often visible hundreds of kilometers equatorward of the edge, so a day below your level can still show aurora low on the horizon.

A Kp day says nothing about local darkness or cloud. A storm at local noon or under overcast sky does not help. Pair this count with the dark season and cloud on your town page.

Questions

How often does the aurora reach my town?: The tool counts days per year when Kp reached the level that puts the average oval edge overhead, from the GFZ record since 1932. Darkness and cloud then decide what you can see.
Why do some years have far more days?: Geomagnetic activity follows the roughly 11-year solar cycle. The strip shows the waves.
Where does the Kp data come from?: GFZ Potsdam, the producer of the definitive Kp index, under CC BY 4.0. Recent days are nowcasts that can still change.