Rain or sunshine?
It's not always the case that SMHI's weather forecasts are entirely accurate. But it's not the weather itself that's in focus when a yellow warning is issued.
It's actually the consequences we're warning about, says Therese Fougman, meteorologist at SMHI.
On Wednesday, SMHI issued a yellow warning for rain and thunderstorms over southern Sweden. Before a warning is issued, the authority looks at data models that calculate how much rain can be expected.
Then we weigh different factors that are conducive to it becoming like this, such as heavy thunderstorms and large amounts of rainfall, says Therese Fougman.
Together with the County Administrative Board and the Swedish Civil Contingencies Agency (MSB), there are threshold values for when consequences can be expected for critical societal functions.
In this case, we saw it already yesterday (Tuesday, ed. note) and we've seen it coming for several days.
Decision after warning
Västtrafik warned about cancelled departures already on Tuesday, and on Wednesday morning, several train journeys in western Sweden were cancelled. But how the warning affects companies is not something SMHI concerns itself with, says Fougman.
We can only talk about how the conditions look: This is what we think and here are the risks with the approaching weather. Then the recipient has to make a decision about whether to operate.
Warnings fail
In 2023, SMHI had an accuracy rate of 73 percent with its warnings, according to their annual report. This means that more than every fourth warning turned out to be incorrect. In 2022, the accuracy rate was higher, 81 percent, but then the authority also issued half as many warnings. The increase is due to 2023 being an intense weather year.
In almost all cases, it becomes what we thought. Sometimes we miss, it happens. It's still forecasts we're working with.
But even if the forecast doesn't always come true, it's not primarily the weather itself that SMHI warns about.
When we see that there's a risk of consequences for critical societal functions, we issue a warning, says Fougman.
Corrected: An earlier version contained incorrect information about when Västtrafik cancelled train departures.
SMHI (Swedish Meteorological and Hydrological Institute) issues weather warnings on three levels.
Yellow warning: Consequences for society, some risks for the general public.
Orange warning: Serious consequences for society, danger for the general public.
Red warning: Very serious consequences for society, great danger for the general public.
