The warning was issued on Thursday and is valid until Midsummer's Eve at 23.00.
It applies to large parts of Götaland, Svealand and southern Norrland.
On Saturday, the risk of spreading forest fires in Örebro County culminates, and then decreases again on Sunday.
- The temperature has no effect, but it is sun and lack of rain that is the big factor.
If it starts to burn, heat is a negative thing especially for extinguishing work as it is hot enough anyway.
A local shower is not enough more than to dampen it temporarily, says Per Stenborg, SVT's meteorologist.
Those who are going to fire outdoors should be very careful, writes SMHI on its website.