It’s raining in Greenland

On August 14, 2021, the highest point of the Greenland Ice Sheet saw rain for several hours and temperatures remained above freezing for about nine hours.

This was the third time in less than a decade and the last date of the year that the National Science Foundation’s Summit Station experienced above-freezing temperatures and wet snow. No precipitation has previously been reported at this location (72.58°N, 38.46°W), which reaches 3,216 meters (10,551 feet).

Earlier melting events in the instrumental record occurred in 1995, 2012, and 2019; prior to these events, judging by ice cores, melting had been absent since an event in the late 1800s. The cause of the melting that occurred between August 14 and 16, 2021, was similar to the late July event, when a strong low pressure center over Baffin Island and high atmospheric pressure southeast of Greenland combined, pushing warm air and moisture rapidly from the south.

Widespread surface melting and heavy precipitation along the southeast coast as far southeast as Greenland’s Summit area was observed on 14 and 15 August, and the melting area returned to moderate levels on 16 August.

The melting area peaked on August 14 at 872,000 square kilometers (337,000 square miles), dropping to 754,000 square kilometers on August 15 and 512,000 square kilometers (198,000 square miles) on August 16. More than one 800,000 square kilometers (309,000 square miles) of melting was observed in 2012 and 2021 alone, and the Aug. 14 event was the latest date for this magnitude of melting in satellite records.

Temperatures exceeded the freezing point at Summit Station around 07:00 UTC (5:00 a.m. local time) on August 14, at which time it began raining. It rained for the next few hours, and water droplets were visible on surfaces near the camp, as reported by observers at the station. At about 1400 UTC, thin plates of ice crystals began to form on the surface of the snow as the rain froze into the snow.

Winds were 9.8 meters per second (22 miles per hour) from the southwest with a mixture of icy and unfrozen rain. Temperatures reached a high of 0.48 degrees Celsius (33 degrees Fahrenheit) around 10:40 UTC and dropped below zero around 16:20 UTC. The temperature dropped steadily throughout the evening. When the skies cleared late in the evening, a sharp cold snap brought temperatures down to -8.5 degrees Celsius (16.7 degrees Fahrenheit) early in the afternoon of August 15. Temperatures at Summit did not reach the melting point on either August 15 or 16.

The total surface melt area (total melt area for the day) for 2021 through August 16 is 21.3 million square kilometers (8.2 million square miles), the fourteenth highest to date and well above the 1981-2010 average of 18.6 million square kilometers (7.2 million square miles).

Temperatures above freezing and precipitation were widespread in southern and western Greenland during the three-day period, with exceptional readings from several remote weather stations in the area. A total of 7 billion tons of precipitation fell on the ice sheet.

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