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Fall snow levels can help predict a year’s total snowpack

Spring break often signals an ideal period for skiing, with extended daylight and milder temperatures. However, if one is planning their skiing adventures during the preceding fall, anticipating the best snow conditions for spring becomes challenging. 

Water resource scientists, too, are keen on determining seasonal snow volumes. Insights into total snowpack levels enables them to assess the subsequent water availability for hydropower, agricultural irrigation, and consumption later in the year.

Predicting snow accumulation 

Now, a team of researchers from the University of Washington (UW) has found that, for certain western states, the snow accumulated by the end of December can be an accurate indicator of the entire season’s snowpack. 

This predictive model is quite precise for northern states such as Alaska, Oregon, Washington, as well as some areas of Utah, Wyoming, and Colorado. However, states such as California, Nevada, New Mexico, and Arizona were found to offer less predictability, either due to their erratic weather fluctuations or the fact that significant precipitation occurs post-December.

Focus of the study

“The main thing water managers are asking for – aside from making it snow more, which is usually everyone’s first request – is longer lead-time forecasts,” said Jessica Lundquist, a professor of Civil and Environmental Engineering at UW. 

“These are hard predictions to make. We’re fairly good at long-term average forecasts: what will happen 50 years from now. And we can do short-term forecasts: what will happen less than a week from now. But as for what’s going to happen in the next three to four months, that’s been kind of a no-go zone. It was really interesting to find that the amount of snow on the ground by the end of December ended up being a good predictor of peak spring snow.”

How the research was conducted 

The researchers collected data from an extensive snow sensor grid spanning the western U.S., including Alaska. 

After examining air temperature and precipitation metrics from 2001-2022 for 873 sites, they compared snow accumulation by the end of December (fall snow) with the entire winter-spring snow accumulation (peak season snow).

What the researchers learned

Several factors drove the correlation between early and peak snow. For instance, in regions like Alaska, a majority of the snow falls before January, making the early snow almost identical with peak season snow. 

In other places, such as Interior Alaska, northeast Utah, and southwestern Wyoming, meteorological trends indicate that an above-average early snowfall reliably predicts an above-average late-season snowfall.

Air temperatures 

Moreover, cooler air temperatures can also be a reliable predictor of snow levels. For instance, in northern states such as Alaska, Washington, and Oregon, or in places at higher elevation, snow on the ground in the fall was less likely to melt between storms due to the fact that the air remained cool, meaning that this snow usually sticks around, adding to the total snowpack.

“Another really interesting pattern happens in Oregon and Washington. We get mixed rain and snow all along the west slope of the Cascades. This ‘wintry mix’ is so close to freezing that it could freeze or melt when it hits the ground. If you have above-average snowpack early in the year, then the wintry mix will stick to that snowpack and add to it. But if you have a below-average snowpack, that wintry mix is more likely to melt that snowpack and actually decrease it,” Lundquist explained.

Climate change 

Discussing the potential impact of climate change on snow predictability, Lundquist argued that it may have mixed results. 

While northern or higher-altitude regions might remain relatively unchanged, shifting weather patterns could render areas like northern Oregon as unpredictable as California.

Evolving patterns 

Lundquist concluded by emphasizing the importance of monitoring these evolving patterns. “These snow sensors are in long-term stations, so it’s easy to get the most recent data every year,” she said. 

“And then it’s just a simple analysis to predict which areas will likely have the largest snowpack. Though, as my family reminds me, it unfortunately does not let me predict powder days.”

The study is published in the journal Geophysical Research Letters.

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