“It definitely added a substantial amount of snow to southeastern Greenland,” Lauren Andrews, a NASA glaciologist, wrote in an email. “I don’t think we can be sure as to whether it cancels out all or part of the summer melt yet.”
The satellite images above show the change in snow cover near the Timmiarmiut Fjord between Sept. 5 and 14, primarily because of Larry.
Larry first developed on Aug. 31 from a tropical wave that had exited the coast of Africa near Senegal. It trekked west across the Atlantic’s “main development region,” commonly referred to as “Hurricane Alley,” before strengthening into a hurricane early on Sept. 2. It rapidly intensified and became a major hurricane with Category 3 winds by that evening. The Bermuda Weather Service issued a tropical storm warning on Sept. 8, and Larry fringed the island with gusty winds and choppy seas shortly thereafter — but its rain shield stayed entirely offshore.
From there, Larry barreled north, sweeping through the Avalon Peninsula of Newfoundland and lashing St. John’s with several inches of rain Friday night. It unleashed wind gusts of 113 mph at Cape St. Mary’s and 92 mph at Cape Pine. It was an enormous tempest with tropical-storm-force winds extending up to 240 miles from its center.
After blasting Newfoundland, Larry began to transition into an “extratropical,” or mid-latitude, storm while making a beeline for Greenland.
“Tropical cyclones cannot propel themselves, they need to be steered by larger-scale pressure patterns in the atmosphere. These steering currents were oriented more north-south than usual,” Gary Partyka, a senior scientist at NASA, wrote in an email. “While not very rare, if a tropical cyclone finds itself established in a steering pattern such as this, it will be moved to these high latitudes (such as where southern Greenland is).”
Partyka said the steering pattern, along with the higher-than-usual sea surface temperatures in the Atlantic, allowed Larry to last a bit longer as a purely tropical cyclone than would otherwise happen.
Larry retained tropical moisture as it moved into the icy Danish territory home to about 55,000 people. It was still classified as a hurricane until close to its arrival in Greenland. A frontal boundary near southern Greenland interacted with Larry as it morphed into an extratropical storm, which enhanced precipitation.
Most of Larry’s moisture fell as snow over Greenland, and probably by the foot. High-resolution satellite imagery depicted freshly fallen snow on the eastern half of the sprawling island.
“Generally, much of the snowfall in Greenland does happen in distinct events like this, and the role of atmospheric rivers in delivering moisture to the ice sheet is a pretty live area of research,” Ruth Mottram, a climate scientist at the Danish Meteorological Institute, wrote in an email.
Mottram added that “even though this event was quite big, the snowfall was concentrated on eastern Greenland and therefore won’t have much effect outside that area.”
The airport on Kulusuk Island, midway along Greenland’s east coast, clocked wind gusts to 101 mph Sunday as the transitioning remnants of Larry blew through and tapped into jet stream energy. Some mild air dragged north by the system converted snow to rain along the coastline.
Computer models estimated that parts of Greenland’s east coast saw the equivalent of two inches of liquid precipitation, which equates to approximately two to three feet of snow. NASA called the snowfall “abundant” and unusual for this time of the year.
“The snowfall that we modeled over the ice sheet was fairly high but not at record levels, ” wrote Mottram. “Perhaps the biggest surprise was just how spot-on the forecasts were. I have been working in Greenland for more than 12 years and this may have been one of the best [forecasts] I have ever seen.”
While snow events from former tropical systems are “not very common,” according to Partyka, they can happen perhaps a few times per decade. The leftovers of Hurricane Igor brought a similarly impressive dose of precipitation to Greenland in 2010.
The September snowfall comes after Greenland experienced a handful of major melting events this warm season. One in mid-August occurred as temperatures spiked to more than 15 degrees above normal and brought rain to Greenland’s summit for the first time on record.
During the height of the melting, Greenland was losing up to 4 to 8 gigatons of water per day. Estimates from Danish research institutions suggest that Larry may have dropped 10 gigatons of snow mass on Greenland on Sunday.
Larry later brought strong winds and a brief shot of mild air to Iceland, the storm’s swirl captured on satellite imagery as it churned into the Arctic North Atlantic.
Despite any slight improvement in Greenland’s mass balance this season, the trend is still sharply negative over time as Greenland continues to lose volume because of melting from rising temperatures. Warm seas continue to “undercut” glaciers and erode them from below, causing fragmentation that further amplifies and speeds up additional ice loss. In some places, the Greenland ice sheet is more than two miles thick, but melting has been outpacing ice accretion for the past quarter-century.