In this Friday, March 13, 2015, Mitch Seavey's lead dogs with frosty whiskers at the Huslia, Alaska, checkpoint for the Iditarod Trail Sled Dog Race. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Nathan Schroeder mushes into Kaltag, Alaska, during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Wade Marrs' lead dog Pop, far left, curls up to keep warm at the Kaltag, Alaska, checkpoint during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Nathan Schroeder mushes on the Yukon River between Nulato and Kaltag, Alaska, during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Tok musher Hugh Neff arrives in Kaltag, Alaska, during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Nathan Schroeder mushes into Kaltag, Alaska, during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

DeeDee Jonrowe arrives at the Ruby, Alaska checkpoint under the Northern Lights during the Iditarod Trail Sled Dog Race on Wednesday, March 11, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

In this Friday, March 13, 2015, Jessie Royer and her team arrive at the Huslia, Alaska, checkpoint for the Iditarod Trail Sled Dog Race. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Joar Liefseth Ulsom leaves the Kaltag, Alaska, checkpoint during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

In this 30-minute exposure, the streak of four-time Iditarod champion Jeff King's headlight shows his path as he mushes from theYukon River to Kaltag, Alaska, in the Iditarod Trail Sled Dog Race, Saturday, March 14, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Dallas Seavey mushes into the Unalakleet checkpoint in the Iditarod on Sunday, March 15, 2015. Aaron Burmeister, 39, was the first musher to reach Unalakleet, the first checkpoint on the Bering Sea coast. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Norwegian rookie Thomas Waerner mushes on the Yukon River between Nulato and Kaltag, Alaska, during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)

Norwegian rookie Thomas Waerner mushes towards Kaltag, Alaska, during the Iditarod Trail Sled Dog Race, Sunday, March 15, 2015. (Photo by Loren Holmes/AP Photo/Alaska Dispatch News)