Cold/Wind Chill in Copper River Basin, Alaska

Wind chills below -40F were observed through passes around the periphery of the Copper River Basin, where cold, dense air from the Interior became channeled and increased winds. Within the basin itself, winds remained much calmer. An Alaska Department of Transportation observing station in Mentasta Pass reported persistent gusting above 15 mph with wind chills as low as -55F beginning late on December 22. By the afternoon of December 23, winds became sustained at 15 mph or greater, with wind chills remaining below -40F into the morning of December 24. Wind chills below -40F were also recorded at an observation site in Chickaloon. Wind chills below -40F were most widespread from the evening of December 23 into the morning hours of December 24. Winds diminished by midday on December 24, allowing the cold wind chills to end.

A strong upper-level trough originating in the Arctic dove southwestward across Southcentral Alaska on the evening of December 22 through December 23, bringing a reinforcing shot of cold, dense Arctic air into an already cold environment. This combined with a pre-existing strong pressure gradient between strong surface high pressure in Interior Alaska and low pressure over the Gulf of Alaska to produce strong winds through gaps and passes across southern mainland Alaska. Blizzard conditions were seen in the Matanuska Valley, where 65 to 83 mph winds lofted snow and reduced visibility. Winds knocked out power to 7000 residents in the Matanuska Valley and the Anchorage Bowl. Blowing and drifting snow, as well as wind chills as low as 55 degrees below zero were also observed in other portions of Southcentral Alaska.

The trough closed off into a low pressure system aloft late on December 23 as it began to track westward across Southwest Alaska and into the Eastern Bering Sea, allowing conditions to gradually improve over Southcentral Alaska. The upper level low began to interact with a weak surface low crossing the Alaska Peninsula into Bristol Bay on December 24, dropping snow in both regions. Combined with gusty winds, blowing snow affected portions of Bristol Bay and the Pribilof Islands on the evening of December 24 into the morning of December 25 as the system continued into the eastern Bering Sea. Active weather diminished as the low tracked further west into the Bering Sea over the following days.