It’s going to be 10 degrees Celsius on Friday morning and 10 degrees again on Sunday morning, so how radically different could things possible be in the interim?
About as radical as it can get, it turns out, as the Norwegian Meteorological Institute is predicting Longyearbyen will set a new all-time record high temperature of 22 degrees Celsius, exceeding the current record of 21.3 degrees set in 1979.

Warm air from the east and cold air on the mainland forcing heat northward means temperatures will build up throughout Friday morning to about 18 degrees as of midnight Saturday, then keep increasing at a somewhat slower rate until peaking much of Saturday evening. Some early morning drizzle is possible, but skies will otherwise be partly to mostly clear, and there will be at best some mild breezes to take the edge of the heat off.
“The reason for these warm air masses is a low pressure over northern Scandinavia which is placed ideally for warm air advection towards Svalbard,” wrote Line Båserud, a researcher for the institute’s Division for Climate Services, in an e-mail. “The winds are flowing anti-clockwise around a low pressure so when it is positioned in Northern Scandinavia, you get cold northern winds over Norway and on the other side you get southern winds which brings warm air from Russia towards Svalbard.”

She noted area temperatures are expected to continue increasing over the long term, so “we expect to see more records for warmer temperatures than for cold.”
At the moment, however, “this is a rare occurrence as the normal average temperature for July is 5.9 degrees,” the weather service wrote on its official Twitter feed.
Torsten Hanssen, a journalist for Adresseavisen, noted in a response unusually warm days are an increasing norm for Longyearbyen.
“This year it is 60 years since it was first measured above 15 degrees in Longyearbyen,” he wrote. “On July 31 (that year), it was measured exactly 15.0 degrees. Since then, the 15-degree mark has been passed another 60 times, the last time on July 6 and 7 of last year (16.1 and 15.4 degrees, respectively).”

The weather service’s website description of its forecast on Saturday for Spitsbergen, by the way, is a rather vague and unintentionally humous “slightly scattered rain early in the day, otherwise mostly stay-at-home weather.”
Temperatures will drop rapidly after midnight Sunday, and the long-term forecast is for a consistent temperature of about 10 degrees, overcast skies and little wind until next weekend.
The weather service’s description of its forecast on Saturday for Spitsbergen, by the way, is a rather vague and unintentionally humous “slightly scattered rain early in the day, otherwise mostly stay-at-home weather.”
The forecast high, if reached, is the highest for all major municipalities in Norway. In fact, the lows for the day in many of them are expected to reach unusual below-freezing temperatures.
Freakishly high temperatures have become something of the “new normal” in Longyearbyen for years, including a streak of 111 months of above-average temperatures that ended earlier this year. The town’s accelerated rate of climate change, with temperatures rising twice as fast as the Arctic average and up to six times fast than Earth’s, has also attracted global headlines.