- We have looked at the circulation in the troposphere (the lowest of the earth's atmospheres, note below) and the water temperature west of Hawaii in the Pacific, says Torben König at the Rossby Center at SMHI.

Weather patterns

The flow goes north towards the Arctic and then south into the Atlantic and gives some weather patterns that the researchers have studied for about a year.

- We have seen a connection between what happens there and what later happens here. You can compare it to the fact that if you increase the water flow at one end of a bathtub, things happen at the other end a little later.

summer Subdivision

The discovery means that several months in advance SMHI can make a correct estimate of how much it will rain here in the summer.

- We have divided the summers into three types: normal rainfall, less than normal rainfall and more than normal rainfall.

The researchers have been around for about a year, but they have also looked at observations in the Pacific backwards over time and compared with forecasts in Scandinavia. With this new knowledge, they can explain about 40 percent of the total variation of rainfall during the summer.

- We see that we have a pretty good forecast quality and assume that this summer it will rain a little less than normal.