Northern Lights Forecast — How to Know When to Go Outside?

KP Index — The Most Important Number

The KP index is a scale from 0–9 that measures geomagnetic activity — how strongly the solar wind disturbs Earth's magnetic field. The higher the KP, the stronger the aurora.

In Levi (67.8° N), the location beneath the aurora oval means northern lights can be seen even at low KP values:

• KP 2 = possible to see faint aurora on the northern horizon
• KP 3 = good probability — clear green arcs
• KP 5+ = strong aurora across the entire sky, colours (green, purple, red)
• KP 7+ = geomagnetic storm — rare but spectacular, the sky is on fire

For comparison: in Helsinki (60° N), KP 5+ is needed for aurora to be visible at all. Levi's northern location is a huge advantage.

Solar Wind

The sun constantly sends a stream of particles into space — this is called the solar wind. Normally it's steady and doesn't cause significant aurora. But when a massive particle cloud erupts from the sun's surface (CME = Coronal Mass Ejection), the situation changes dramatically.

CME particles travel through space in 1–3 days and hit Earth's magnetic field. This causes a geomagnetic storm — and aurora. Forecast services like NOAA and the Finnish Meteorological Institute monitor solar eruptions in real-time and predict when they'll hit Earth.

In practice: when a CME is observed on the sun, the aurora forecast 1–3 days ahead turns positive. This gives time to plan evening activities.

Cloud Cover — The Other Half of the Equation

KP could be 7 and a solar storm raging — but if the sky is cloudy, you won't see anything. Cloud cover is equally important as aurora activity, and often more decisive.

Northern lights occur at 100–300 km altitude. Clouds sit at 1–10 km. If there's a cloud layer between, the view is completely blocked.

Recommended cloud forecast services:
• Finnish Meteorological Institute (ilmatieteenlaitos.fi) — Finland's best, hourly forecast
• yr.no — Norwegian, very accurate for Lapland area
• Clear Outside — Designed for astronomers, shows cloud heights

Practical tip: check both — aurora forecast AND cloud forecast. Only when both are favourable is it worth going outside.

Best Apps and Websites

My Aurora Forecast (mobile app, iOS & Android) — Push notifications when KP rises to your chosen level. Simple and effective. Set the alert to e.g. KP 3+ to receive notifications.

NOAA Space Weather (spaceweather.gov) — Official US Space Weather Center KP forecast 3 days ahead. Most reliable long-term forecast.

Finnish Meteorological Institute (ilmatieteenlaitos.fi) — Finland's own space weather and cloud service. Accurate for Levi area.

leville.net/revontulet — Our own page with live forecast and aurora alert subscription.

Tip: Set My Aurora Forecast to alert at KP 3+ so you get a notification on your phone in the middle of the night. Many of our guests have seen their best aurora this way — woken by the app alert and stepping onto the balcony in pyjamas.

Practical Evening Guide

Simple 3-step strategy:

1. Check KP forecast in the afternoon — Is KP 3+? If yes, chances are good.

2. Check cloud forecast — Is the sky clear or partly cloudy? If cloud percentage is over 80%, seeing aurora is unlikely.

3. If both look good → go outside between 9 PM and 1 AM, to a dark place, and wait 15–30 minutes for your eyes to adjust to darkness. Don't look at your phone with a bright screen — it ruins your night vision.

Remember: aurora can appear and disappear quickly. Sometimes the display lasts 5 minutes, sometimes 2 hours. Patience pays off.

Don't Rely Solely on the Forecast

Northern lights can surprise in both directions. Sometimes KP is 1 but faint aurora appears on the northern sky — especially at Levi's northern latitude. Sometimes KP is 5 but clouds cover everything.

The best strategy is to go outside every evening for at least a moment and look at the sky — it's free and can surprise you. Many of the most unforgettable aurora experiences have happened by chance: stepping outside for an evening walk or coming out of the sauna.

A three-night holiday gives statistically good odds. On a week-long holiday, you'll almost certainly see aurora at least once, provided you visit during the right season (September–February).

Frequently Asked Questions

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