When weather observers woke up at the highest point of the Greenland Ice Sheet last Saturday, they didn't expect to see rain.

Sitting at an elevation of just over 3,200 metres at a latitude of 72.58°N, rain had never been observed at the ice sheet's Summit Station since its establishment in 1989.

But on Saturday, August 14, it rained at the Summit Station for several hours.

Image: Temperature and air pressure observations from Greenland's Summit Station on Saturday, August 14. Source: NSIDC / NOAA / NASA

According to the National Snow and Ice Data Centre (NSIDC), "this was the third time in less than a decade, and the latest date in the year on record, that the National Science Foundation's Summit Station had above-freezing temperatures and wet snow."

"There is no previous report of rainfall at this location, which reaches 3,216 meters in elevation."

The other three melt events in instrumental records occurred in 1995, 2012 and 2019. Prior to these years, ice core data suggests that melting has been absent at the site since the late 1880s.

All up, the temperature remained above 0ºC for about nine hours and rain fell for several hours on Saturday. The highest temperature of the day was 0.48ºC shortly before 9am local time.

Image: Change in surface air temperature on August 14 relative to the previous week (averaged from August 5 to 11), showing rapid warming over the Greenland ice sheet. Source: NASA

Saturday's abnormal warmth was caused by a stream of warm and moist south-southwesterly winds sandwiched between a low pressure system above Canada and a high pressure system over the North Atlantic Ocean.

This type of weather pattern also caused extensive surface melt events in Greenland back in late July this year.

But just how much rain fell at the summit of Greenland on the weekend will remain a mystery. Given liquid precipitation is so rare at that altitude, there isn't a rain gauge onsite.