By Kate Companion, The Daily

Annual snowfall in the Pacific Northwest appears to have decreased since the 20th century, part of a larger trend of declining snowfalls in the western United States partially driven by climate change.

While the snowfall records in Washington are incomplete due to gaps in the data, and the measurements began in a particularly cold decade, there does appear to be a decreasing trend, according to Karin Bumbaco, assistant climatologist for Washington state.

The Pacific Northwest has a strong statistical relationship with the El Niño and La Niña climate patterns, which contributes to the variability in snowfall, according to Bumbaco. In La Niña years when water in the Pacific Ocean is colder, there tends to be a better snowpack in the mountains and a better chance of lowland snow.

“With climate change we do expect to see less snow in the lower elevations just due to warmer winters, especially in western Washington where we don’t really get below freezing very often,” Bumbaco said. “So, as our climate warms and changes we’re just going to be over that [temperature] threshold for snow more often.”

Places with year-over-year temperatures that increase but remain below freezing might see a period with more snowfall before levels decrease and temperatures climb above freezing. At higher temperatures below freezing, snow tends to be wetter and falls more heavily due to its higher water content.

The most critical snowfall occurs in the mountains and is stored throughout the winter as snowpack. These snowpacks reach their peak around April 1, and provide crucial water reservoirs for the state, especially during the spring and summer months. While spring snowpack does fluctuate from year-to-year, there has been about a 30% decline on average since 1955 according to Matthew Rogers, a research scientist with UW Climate Impacts Group.