How reliable is a 10-day forecast?

Forecasts get less certain the further ahead they go. How Fintväder shows how sure the forecast is – hour by hour and day by day.

Uncertainty grows with time

The weather in the next few hours can often be forecast well. Further ahead, small errors in the starting point grow, and after a few days forecasts can differ a lot. That is why weather services run many versions of the same forecast – an ensemble – and look at how much they differ.

The confidence meter

Fintväder compares the forecasts from SMHI and MET Norway and weighs in how widely their ensembles spread. When they agree we show high confidence; when they differ we show medium or low. This applies to every hour, every day and the current conditions at the top of the page.

In the 48-hour chart, the band around the temperature line shows how wide the range is. A wide band means the temperature may turn out different from the line.

How often has the forecast been right here?

Under Forecast accuracy on the place page we show how often SMHI and MET Norway were right for that very place in the last 30 days, compared with SMHI’s weather station nearby. That shows how far you can trust tomorrow’s forecast where you live.