Mosjøen is located less than 100 km south of the polar circle and experiences maximum day temperatures above 30 °C. Weather station Laksfors measured a peak of 33.4 °C on July 14, 2025. For the coming six days temperatures around 30 °C are forecasted as well (link).
Although not the highest measured temperatures of all times for Norway (Nesbyen 35.6 °C on June 20, 1970) , travelers shall have in mind that also these Northern latitudes can experience such high temperatures. The weather situation which carries warm air from the South or East of Europe "through the backdoor" to Norway is not new but with climate change this situation can happen more often and / or hefty.
A few years ago it was hitting also Northern Norway so much that reindeer groups were searching for cooling in street tunnels.
So, no drama but a heads up that Norwegian weather has a significant range of temperatures which travelers shall know when preparing a travel into this beautiful country.