A prolonged pattern of upper level troughing and repeated regional storm systems have added quite a bit of snow to mountains of the Pacific Northwest over the past week. As of the end of the day on March 4, the snow-water equivalent (SWE) value for the Northwest was 88% of the median for this time of year. Compare that to February 25 where the SWE value was 73% of median for that date.
Snow-water equivalent is a useful measure for predicting water availability and wildfire risk. It is a measure of how much water would be present if one melted down a column of snow at a specific location. Regional values are averaged from numerous SNOTEL sites located mainly in mountainous regions.
The Pacific Northwest region includes the entire Columbia River watershed as well as some other watersheds in the region. It captures all of Washington, Oregon, and Idaho, large portions of Montana and British Columbia, and small bits of Wyoming and Nevada.
Despite strong increases, snowpack in British Columbia and the northern half of Washington is still lacking. This is fairly typical of an El Niño year when the prevailing pattern has two primary storm tracks – one aimed at California and the other at Southeast Alaska.
Some precipitation, including mountain snow, is forecast in Southeast Oregon, Southern Idaho, and the Grand Teton region of Wyoming Tuesday and Wednesday. These are areas that are already doing well compared to seasonal averages. Elsewhere in the region expect dry weather and a lack of snow as a short-lived ridge of high pressure moves overhead.
The next storm train begins Saturday and will bring ample snow to Vancouver Island and the B.C. Coast Ranges which probably have the lowest SWE values compared to average in the greater Northwest. The following storm, Sunday into Monday, aims at Washington. It won’t be a long-lasting blizzard like California recently experienced but it should provide welcome increases.
The small amounts of snow shown on modeling for the Puget Sound Region and around both Vancouver and Victoria aren’t likely to be anything more than what has been seen this week – occasional snow showers with short-lived accumulations of up to half an inch (1 cm) or so.
One last storm moves in Wednesday for another round of mountain snow throughout the Northwest. Beyond that, weather models are favoring a long lasting ridge setup across the west coast of North America. Assuming the models are reasonably correct this will produce dry conditions and warmer temperatures for a while.
Winter snowpack has major implications on water availability over the summer growing season. How big of a deal it is depends a lot on what someone is growing and where they are growing it. Some tree fruit growers outside of Selah use a threshold of 10 feet (3 meters) of snow up at White Pass Ski Area as a good determinant behind whether or not they will have enough water. On the morning of March 5, the upper base of White Pass reported 114 inches (289 cm) of snow – just short but with plenty of time to go.
By contrast, wheat growers in the Horse Heaven Hills and on the Palouse rely far less on mountain snow because very few of them irrigate. On the Palouse, spring and early summer moisture usually comes in the form of thunderstorms.
Fire conditions take in a variety of measures. One is how much snow melted, providing trees with much needed moisture. This is not the only metric of consequence, however. When the snow melts and how much moisture is received in the spring and summer determine how much brush growth occurs. A wet start to the warm season can lead to large amounts of brush.
If the summer then becomes abnormally hot, that material will dry out and provide ample fuel for fires to start, spread, and potentially light trees regardless of how much moisture they got from snow in the winter. The Climate Prediction Center indicates that Spring 2024 may bring below average precipitation and above average temperatures to the Northwest. Not great for farmers who irrigate and a mixed bag for fire concerns.
Cities such as Seattle, Portland, Eugene, and Walla Walla draw their municipal water supply directly from mountain watersheds. Both Seattle and Portland experienced shortages from theses sources during the late summer and early fall of 2023 due to drought conditions. Areas of moderate drought continue on the east slopes of the Oregon Cascades, in the Olympics, and portions of Washington’s North Cascades but the situation is far improved from six months ago.
The featured image is a chart showing Pacific Northwest snowpack as of the end of day March 4 from USDA.
