How does WA mountain snowpack water supply look this year?

Spring started off cool and wet, but finished the month of April with some long-awaited warmer weather with sunshine – a taste of what is to come.

The final weather statistics for April reflected the overall cool and wet we experienced. SeaTac Airport had an average temperature (all highs and lows) of 48.5 degrees, 2.8 degrees below average. During the month, 3.86 inches of rain fell, close to seven-tenths of an inch above average.

Below average mountain snowpack likely to stage a comeback

Olympia averaged 46.3 degrees during April, just under two degrees below average. Rainfall was 6.21 inches, just over two and a half inches above average. To the north, Everett – Paine Field had an average temperature of 47.7 degrees, 1.6 degrees below average. During the month, 2.67 inches of rain fell, amazingly just nine-hundredths of an inch (0.09) above average.

In the far north Sound, Bellingham’s average temperature for the month was 48.5, just two-tenths of a degree below average. Bellingham missed out on the wetness, receiving 1.64 inches of rain in April, just over an inch below average.

The cool, wet start to spring provided a bonus for the snowpack in the Cascades that fell behind thanks to a drier-than-average first three months of the year. The Northwest Avalanche Center’s final snow depth summary was released on May 1, reflecting a wide spread of snow totals. Moving from north to south, Mt. Baker was at 92% of the average for a May 1 snow depth, Stevens Pass 81%, Snoqualmie Pass 94%, Crystal Mountain 104%, and White Pass was at a whopping 135% of average snow depth.

What really counts for water supply heading into summer and fall before winter snows return to the mountains is how much water is in the snow – what is called Snow Water Equivalent (SWE). The numbers offered by the Natural Resources Conservation Service (NRCS) show a brighter water supply picture in their latest summary.

The North Puget Sound region of the Cascade west slopes had a 95% of average SWE. The Central Puget Sound region had 132% of the average, the South Puget Sound region at 115%, and the Lower Columbia region was at 133% of the average. The Olympics were at 116% of the average.

So as summer and fall approach, there is a nice supply of water in the snowpack to help with water supplies for agriculture, municipal water, fish, recreation, and more.

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The latest seasonal weather outlook for the rest of this spring and through summer from the National Weather Service’s Climate Prediction Center tips the odds toward overall warmer and drier-than-average conditions. The odds are quite small for another heat dome like the one in late June 2021, yet it is something to keep an eye on. Last summer did not exceed 100 degrees, but SeaTac Airport had 13 days in the 90s – the highest number of days of 90 degrees or better on record. This summer has the potential of offering more 90-degree days above the usual average of 4 days per year.

Last year, SeaTac Airport only had 0.54 inches of rain from the summer solstice on June 21 to Oct. 21 – the driest period on record. Repeating that limited amount of rain again is quite unlikely, yet summer is the driest time of the year. The average amount of rain for July through September is 3.18 inches.

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