Reading Tonight's Aurora Forecast
An aurora forecast answers one question: is the sky over your part of the world likely to light up tonight? The single most useful number is the Kp index — a 0-to-9 scale that summarises how disturbed Earth's magnetic field is right now. When a stream of charged particles from the Sun strikes the magnetosphere, it dumps energy into the upper atmosphere near the poles, and oxygen and nitrogen atoms glow green, red and violet. The stronger the disturbance, the higher the Kp, and the further that glowing ring — the auroral oval — slides away from the pole and toward where people actually live.
The panel at the top of this page reads the live Kp index and NOAA's three-day outlook directly from the Space Weather Prediction Center (SWPC). Two numbers matter most: the Kp right now, and the forecast peak over the next three days. A peak of Kp 5 or more (a G1 storm or stronger) is the point at which the aurora becomes a realistic target for mid-latitude observers rather than just the far north.
What Kp You Need for Your Latitude
The aurora is not visible from everywhere at the same Kp. What counts is your geomagnetic latitude, which can differ from your map latitude by several degrees because Earth's magnetic pole is offset from the geographic pole. The United Kingdom and much of Canada, for instance, sit at a higher geomagnetic latitude than their geographic position suggests, which is why Scotland sees the aurora more often than its latitude alone would imply.
As a practical rule of thumb:
| Kp | NOAA Scale | Aurora May Be Visible From |
|---|---|---|
| 3 | — | Iceland, northern Scandinavia, northern Canada, Alaska |
| 4 | — | Southern Scandinavia, Scotland, southern Canada, northern-tier US states |
| 5 | G1 — Minor | Northern England, northern Germany, New York, Chicago, Seattle |
| 6 | G2 — Moderate | Central England, the Netherlands, Oregon, Michigan |
| 7 | G3 — Strong | Southern England, northern France, Illinois, Pennsylvania |
| 8 | G4 — Severe | Southern France, northern Spain, Texas, Florida |
| 9 | G5 — Extreme | Southern Europe and the southern US; the tropics in historic events |
These are threshold latitudes — the southern edge of where the aurora may appear low on the poleward horizon. Directly beneath the oval the display is overhead and dramatic; at the threshold it is usually a coloured glow to the north (or south, below the equator). Use the interactive explorer above to see how each level shifts the boundary.
The Best Conditions for Aurora Watching
A strong forecast is necessary but not sufficient — the sky has to cooperate too. Four things make or break a sighting:
- Darkness. The aurora is faint compared with daylight or twilight. You need genuine astronomical darkness, which is why displays are easiest to catch in the long nights from roughly September to March, and almost impossible during the bright summer nights at high latitudes.
- Clear skies. Cloud is the single most common reason a forecast storm goes unseen. Check a local cloud-cover forecast for your exact spot, not just the regional picture.
- Low light pollution. Get away from town. Even a moderate display that would be obvious from a dark rural site can be washed out completely under urban sky-glow.
- A clear view toward the pole. For most observers the aurora sits low on the northern horizon (southern, in the southern hemisphere), so an unobstructed view in that direction — over the sea, a moor or open fields — matters more than altitude.
The Moon is a secondary factor: a bright full Moon can dim a weak aurora, while a new or low Moon gives the darkest possible backdrop.
When to Look — Timing the Aurora
Geomagnetic activity is not constant through the night. It tends to intensify around local magnetic midnight, broadly the window from about 10pm to 2am, when your location rotates under the most active part of the oval. That is the time to be outside and dark-adapted. Substorms — sudden brightenings that send curtains rippling across the sky — can erupt within minutes and fade just as fast, so patience pays: a quiet sky at 11pm can explode into activity by midnight.
Over longer timescales, the equinox months (around March and September) are statistically the most active for geomagnetic storms, and aurora frequency rises and falls with the roughly 11-year solar cycle. Near solar maximum, strong storms that reach mid-latitudes become far more common.
How Accurate Is an Aurora Forecast?
Forecast confidence depends entirely on the lead time:
- Minutes ahead (high confidence). Spacecraft at the L1 point — DSCOVR and ACE, about 1.5 million km sunward of Earth — measure the solar wind's speed and, crucially, the north–south Bz component of its magnetic field. When Bz turns strongly southward, energy couples efficiently into the magnetosphere and a surge is imminent. This gives roughly 15–60 minutes of genuine warning.
- Hours to a day ahead (moderate). When a coronal mass ejection (CME) is launched toward Earth, models such as NASA's WSA-Enlil estimate its arrival time to within several hours. You can know a storm is coming, but not its exact strength.
- Three days ahead (indicative). The planetary Kp outlook shown above flags whether storm conditions are likely, based on solar features rotating into an Earth-facing position. It is a planning tool, not a guarantee of timing or intensity.
In short: use the three-day outlook to decide which nights to keep free, and the live Kp and Bz data — updated continuously — as the real go/no-go signal on the night.
Photographing the Aurora
A camera is far more sensitive to faint aurora than the human eye, and will often record colour and structure you can barely make out. Even a faint grey arc to the naked eye can photograph as vivid green. A few starting settings for any camera with manual control (including most phones in "night" or "pro" mode):
- Use a tripod or solid support — exposures are seconds long.
- Wide aperture (f/2.8 or lower if your lens allows) to gather as much light as possible.
- ISO 800–3200, adjusted to the brightness of the display.
- Exposure of 3–15 seconds — shorter when the aurora is moving fast to keep the curtains sharp, longer for a faint glow.
- Manual focus set to infinity, checked on a bright star, since autofocus struggles in the dark.