Explainer
What is MET Norway?
The Norwegian Meteorological Institute is the national weather service of Norway, and it publishes its forecasts as open data. Its cloud forecast is half of every verdict on this site.
The institute
MET Norway (Meteorologisk institutt) was founded in 1866 and is the Norwegian state’s meteorological service, headquartered in Oslo with offices elsewhere in the country, including Tromsø. It issues weather warnings, runs numerical weather models, and monitors climate and sea ice in Norway and its Arctic waters.
Many people know its public face, Yr (yr.no), the weather site and app it runs together with the broadcaster NRK. Yr is one of the most widely used forecast services in Norway, and its data comes from the same models.
Open data
MET Norway makes its forecast data freely available through api.met.no, under open licences (Creative Commons 4.0 BY and the Norwegian Licence for Open Government Data). In return, it asks users to identify themselves with a proper User-Agent, cache responses and not hammer the service. We do all three, and we credit MET Norway in every page footer.
At a glance
- Founded
- 1866
- Type
- National weather service
- Based
- Oslo, Norway
- Public site
- yr.no
- We use
- Locationforecast 2.0
- Licence
- CC BY 4.0
From cloud to verdict
- We ask for the forecast at a pointFor each location we request MET Norway’s Locationforecast for its coordinates, rounded to four decimals as the service asks.
- We read cloud area fractionThe forecast includes the fraction of the sky covered by cloud, hour by hour, as a percentage.
- We keep only the dark hoursUsing the sun’s position at that spot, we keep hours when the sun is more than 6° below the horizon, within an evening window from 17:00 to 03:00 local time.
- We average and scoreMean cloud in those hours becomes the clear-sky score (100 − cloud), 65% of the verdict. The other 35% is the Kp score from NOAA.
- We find your best windowThe longest run of dark hours under 50% cloud is shown as the best window.
Why cloud matters most
Aurora happens 100 km or more above the ground, far above the weather. So cloud doesn’t reduce the aurora; it just hides it. That’s why in northern Norway the cloud forecast is usually a better predictor of a good night than Kp.
The coast and the inland behave differently. Tromsø and Lofoten sit on the Norwegian Sea and see changeable weather; inland Finnmark (Alta, Karasjok) and Swedish Lapland tend to be drier. A good aurora plan watches the cloud map for the next hour or two, not just the headline.
Aurora doesn’t care about the weather. You do.
How accurate is it?
Cloud is one of the harder things to forecast. For the next 24 hours it’s usually a useful guide; beyond three days treat it as a general trend. Near mountains and fjords, a point forecast can miss local effects, so if you can move, do: a one-hour drive can change your night.
MET Norway’s Nordic forecasts are most detailed over Norway, Sweden, Finland and Denmark, and use a coarser global model elsewhere. For Reykjavík, Fairbanks and Yellowknife our cloud data is therefore less fine-grained, and we say so on those pages.
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