# Check Northern Lights

> Live aurora borealis forecast for 20 destinations worldwide. Combines cloud cover (ECMWF & GFS models), Kp geomagnetic index, and real-time space weather to give a clear go/no-go verdict for northern lights viewing — updated every 30 minutes.

## What this site does

Check Northern Lights helps travellers and aurora chasers decide whether tonight (or the next 3 nights) is worth going out to see the northern lights. It answers the two questions that matter: **is the sky clear enough?** and **is the aurora active enough?**

The verdict system uses three levels:
- **Book it** (green) — good conditions, worth going out
- **Maybe** (orange) — uncertain, monitor closer to the time
- **Skip it** (red) — not worth it tonight

## Data sources

- **Cloud cover**: ECMWF IFS 0.25° and GFS 0.25° models via Open-Meteo, updated hourly
- **Kp index**: NOAA Space Weather Prediction Center 3-day forecast
- **Solar wind / Bz**: NOAA DSCOVR real-time data (1-minute cadence)
- **Aurora oval**: NOAA OVATION Prime real-time aurora oval (30-min forecast)
- **Viewing spots**: Wikipedia / Wikimedia Commons photos

## Destinations

20 curated aurora destinations across the Northern Hemisphere:

| City | Country | Min Kp needed |
|---|---|---|
| Tromsø | Norway | Kp 1 |
| Alta | Norway | Kp 1 |
| Longyearbyen | Norway | Kp 1 |
| Abisko | Sweden | Kp 1 |
| Kiruna | Sweden | Kp 1 |
| Rovaniemi | Finland | Kp 2 |
| Levi | Finland | Kp 1 |
| Saariselkä | Finland | Kp 1 |
| Inari | Finland | Kp 1 |
| Reykjavík | Iceland | Kp 1 |
| Akureyri | Iceland | Kp 1 |
| Tórshavn | Faroe Islands | Kp 2 |
| Inverness | Scotland | Kp 3 |
| Murmansk | Russia | Kp 2 |
| Kangerlussuaq | Greenland | Kp 1 |
| Ilulissat | Greenland | Kp 1 |
| Yellowknife | Canada | Kp 1 |
| Whitehorse | Canada | Kp 2 |
| Churchill | Canada | Kp 1 |
| Fairbanks | USA | Kp 1 |

Users can also enter any custom latitude/longitude for a personalised forecast.

## Pages

- `https://checknorthernlights.com/en` — Home, destination list
- `https://checknorthernlights.com/en/{city}` — City forecast page (e.g. `/en/tromso`, `/en/rovaniemi`)
- `https://checknorthernlights.com/en/custom?lat=…&lon=…&name=…` — Custom location forecast

All pages are available in 13 languages: English (en), French (fr), German (de), Norwegian (no), Finnish (fi), Swedish (sv), Italian (it), Spanish (es), Dutch (nl), Chinese Simplified (zh), Cantonese/Traditional Chinese (yue), Japanese (ja), Korean (ko).

## How the verdict works

1. **Cloud cover**: averaged over the dark viewing window (nautical or astronomical twilight). Below 30% = good, 30–60% = marginal, above 60% = poor.
2. **Kp index**: compared against the city's geomagnetic latitude threshold. Each city has a minimum Kp for overhead aurora and a minimum Kp for a likely sighting.
3. **Model agreement**: if ECMWF and GFS disagree significantly on cloud cover, the verdict flags uncertainty and shows an escape route.
4. **Escape route**: if the local forecast is poor, the nearest city within 160 km (2h drive) with better conditions is shown.
5. **Best window**: the clearest 2-hour block within the dark hours, identified hour by hour.

## Key concepts explained

**Bz (IMF south component)**: the north–south orientation of the interplanetary magnetic field. When Bz is negative (southward), it couples with Earth's magnetic field and allows solar particles in. Bz below −5 nT is favourable; below −15 nT is exceptional. This is the most important real-time indicator of aurora activity.

**Solar wind speed**: typical range 300–800 km/s. Higher speed means more energy input. Above 500 km/s combined with negative Bz is a strong aurora signal.

**OVATION**: NOAA's empirical model that predicts the aurora oval position and intensity 30–40 minutes ahead based on current solar wind conditions.

**Polar night / Midnight sun**: at very high latitudes, some dates have 24h darkness (polar night, great for aurora) or 24h daylight (midnight sun, aurora invisible). The site flags both.

## Owner

Built by Pascal R. — offshore sailor, developer, and Lapland tourist.