Why stations differ

Two stations a few kilometres apart can differ noticeably on the same night. That is usually not a fault in either of them. Temperature near the ground depends strongly on the surroundings, and SMHI describes several reasons why.

Clear, calm nights

On a clear night without strong wind, the ground loses heat by radiation and cools the air closest to it. An inversion forms and the temperature near the ground keeps falling through the night. SMHI notes that the cooling can continue for a while after sunrise, which is why the temperature is often lowest at dawn. Low clouds dampen the cooling, and a strong wind stops the inversion from forming. On such nights, small differences in terrain make a large difference.

Valleys and heights

According to SMHI, the coldest air in winter often collects in valleys. In summer it is the other way round, and it is coolest on the mountain tops. On summer days valleys are warmer than the heights around them, because the temperature falls by about 0.7 °C per 100 metres of height.

Sea and coast

SMHI explains that the nearness of the North Atlantic and the prevailing winds give Sweden a very mild winter climate for its latitude. The differences within the country are still large: January means reach one or two degrees above zero in many places along the coasts of Götaland, while the coldest inland valleys of Lappland average about −15 °C in January.

Towns

Dense buildings and many sealed surfaces create a local heat island, an increase in air temperature in those areas, according to SMHI. A station in a town centre and one in open country outside it can therefore differ even when the weather is the same.

The station itself

A station's type of shield, its exact site and the period it has measured all affect its series. A station that has moved can show a jump that has nothing to do with the weather. When a station has moved 2 times or more, Temperaturkollen says that the series may contain level shifts.

Stations also measure at different rates. SMHI's own automatic stations report every minute and other automatic stations every hour, while manual stations are usually read two or three times a day. That matters little for a daily mean, but it does affect how quickly a station's latest value reflects a change in the weather.

How we choose a station for a place

• One series is one station. Measurements from different stations are never joined.
• Only stations that publish a daily mean are candidates. We rank them by distance plus a penalty in kilometres for a short series or a missing official normal, within 80 km. The station must be active and have reported within the last 21 days.
• The chosen station is always shown with its real distance.
• If another station within 30 km covers earlier years, a link to it is shown.

If you know a place well and the numbers look surprising, check which station they come from. The station page shows its position and the years it has measured.