How to read an aurora forecast

Last reviewed 24 October 2026. Based on guidance from NOAA’s Space Weather Prediction Center.

Aurora forecasts are built around one number, the Kp index. It tells you how disturbed the Earth’s magnetic field is, and so how far from the pole the northern lights are likely to reach. It does not tell you whether it will be cloudy.

A bright green spiral of northern lights above bare birch trees and snow — The northern lights on Ringvassøya, near Tromsø, Norway. Photo: Svein-Magne Tunli - tunliweb.no, CC BY-SA 4.0, via Wikimedia Commons.

What the Kp number means

Kp runs from 0 to 9. The higher it is, the brighter the aurora and the further it spreads towards the equator.

Kp 0–2
Quiet
The aurora stays far north and is faint. You need to be at high latitude, such as northern Norway, Iceland or Alaska.
Kp 3–5
Active
Brighter and moving. From a good spot in the auroral zone this can be a very pleasing show.
Kp 6–7
Strong storm
Can be seen from the northern edge of the United States and similar latitudes elsewhere.
Kp 8–9
Severe storm
Can be seen overhead from the northern states of the United States, and low on the horizon much further south.

As a rough rule from NOAA, the southern edge of the aurora sits at about 66° magnetic latitude when Kp is 0 and moves about 2° towards the equator for each step, to around 48° at Kp 9. Magnetic latitude is not the same as the latitude on a map: in North America it is higher than map latitude, in Europe lower. Forecast maps take care of this for you.

Those maps show the furthest point from which the aurora may be seen, low on the horizon, not where it is overhead. The aurora itself can be hundreds of kilometres further north.

When to look

Time of night: the best displays usually come within an hour or two of local midnight, roughly 10 pm to 2 am. In a strong storm the window widens.
Season: NOAA says the best seasons are around the spring and autumn equinoxes, in March and September. Far north in summer the sky never gets dark, and the aurora is only visible when it is dark.
The Moon: a full Moon makes the aurora look fainter, though it is not. A dark, moonless night shows more.

Where to stand

Get away from town lights and find a clear view to the north (to the south in the southern hemisphere).
Height helps. A hill can let you see aurora much further north, over the horizon.
From a good spot inside the auroral zone, even Kp 3 or 4 can give a fine display. You do not need a big storm if you go to the right place.

Where to find the forecast

NOAA’s Space Weather Prediction Center publishes the official Kp forecast and a 30-minute aurora forecast, free. Check it on the day, then check the cloud forecast for where you are: a strong aurora behind clouds is invisible.

NOAA 30-minute aurora forecast

More guides

Sources

NOAA Space Weather Prediction Center, Tips on viewing the aurora: the Kp levels, the 66° to 48° rule, best hours, seasons, the Moon, location and maps.