A storm swept through parts of Southcentral Alaska triggering an avalanche that shut down access in and out of the town of Valdez and broke the current Alaska snowfall record. Alaska’s Thompson Pass, a 2,678-foot pass where the Richardson Highway crosses over the Chugach Alaska mountain range just outside of the town of Valdez, was surprised with an incredible 10 inches of snow that piled up in a single hour.
Considering that’s about 1.7 inches every 10 minutes, this staggering snowfall rate has shocked residents as well as meteorologists. National Weather Service meteorologists reported 76 inches of snow over 5 days. Considering the town is one of the snowiest places in the US, Valdez’s average annual snowfall is still only about 300 inches. Thompson Pass, the only road in and out of the town, was closed between Miles 12-55 by an avalanche triggered by the snowfall, cutting off Valdez from the rest of the state.
But it’s the rate of the snowfall that shocked Alaskan residents. After the first 10 inches of snowfall in the first hour, the furious storm dropped another 5 inches in 30 minutes, for a remarkable 15 inches in a 90-minute period. This beats any previous Alaska snowfall record and marks one of the most intense snowfall rates ever recorded on the planet.
Weather Underground’s weather historian, Christopher Burt, told The Washington Post that previous snowfalls, such as the 12 inches that fell in 60 minutes in Copenhagen, N.Y. back in 1966, and 17.5 inches in a two hour period in Oswego, N.Y in 1972 were results of snow blowing off of Lake Ontario.
What is hitting the North Gulf Coast is what we like to call a “snow AR” or an atmospheric river that is producing snow instead of rain. Over the last 3 days, nearly 6 feet of snow has been recorded at Thompson Pass near Valdez, Alaska. pic.twitter.com/Hoa8XUAMGQ
— NWS APRFC (@NWSAPRFC) 6 December 2017
Burt says that although the record snowfall in Alaska wasn’t a lake-effect, there was still a similar amount of moisture involved. Very wet air transported warm, Pacific Ocean moisture all the way up into the high latitudes and into the mountainous coast of Alaska.
Although they’re no stranger to large snowfalls, the 4,000 residents of Valdez were still surprised to have been cut off from the rest of the state when the only road out of the town was buried in snow. It took several days before crews could clear the road.
This isn’t the first time that Thompson Pass was shut down due to avalanches. Two giant avalanches closed the road, one of which created a snow dam and backed up the Lowe River, in 2014.
Five days, 76 inches of snow and 24 inches more in the forecast. Here’s a view from the Richardson Highway, where ADOT&PF crews are working to reopen the highway. Closure updates at https://t.co/TYO2X8gsTC. pic.twitter.com/g5fC6CK9TR
— Alaska DOT&PF (@AlaskaDOTPF) 7 December 2017