Climate Watch
By Rick Thoman Alaska Climate Specialist Alaska Center for Climate Assessment and Policy International Arctic Research Center/University of Alaska Fairbanks
Thawing weather has arrived for most of the western Alaska and there is a lot of snow to melt.
In the absence of any snowpack measurements in the region, we rely on the climate analysis model to give us an estimate of the snowpack, but it’s just that: an estimate based on a lot of assumptions.
The graphic plots the April 15 snowpack snow water equivalent (the amount the water that snowpack would melt down to) the model had for the greater Nome area (roughly Safety Sound west to Woolley Lagoon and inland about 20 miles) for each year since 1979. The modeled water content of the snowpack this year was very similar to April 15, 2023, and overall, this year had the fifth highest snow water equivalent for April 15th in the past 46 years. The only years with significantly more than this year were 1989 and 2019.
You might be wondering how a climate analysis model can estimate the amount of water in the snowpack when there are no observations. In essence, the model uses sophisticated accounting that simultaneously keeps track of how much snow and rain falls, how much snow (or rain) runs out of the snowpack, how much sublimates directly into the air without melting and the effects of sun and temperatures on the melting process. As you might expect, we think model precipitation is reasonably accurate but has the most trouble correctly capturing the melting process, which is controlled by very smallscale factors as well as the larger atmospheric conditions. For the most part it does seem to correlate well with the National Weather Service’s snow observation up until 2019. For example, April 15 snow depth was quite low in 1984 and 1992, and was fairly high in 1989 and 2018 and 2019.
The climate analysis model is a useful tool, but actual observations would allow us to make better use of this tool by giving us a better sense of its strength and limitations.