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September 2015

August Review

Posted: September 4th, 2015


Through the first week-and-a-half of last month it was looking like we were going to endure our third warmest-ever month in a row. In fact, day 1 hit 92 degrees, which tied the daily record and extended 2015’s daily occurrence record to 12 days. By August’s ides, though, the pattern really changed, and for the first time since March or April, it rained substantially.


It’s true that we experienced an early bout of on-shore flow, strong enough to produce a Puget Sound Convergence Zone event on the 5th. Once-familiar bands of mostly light rain┬átemporarily lifted the spirits of water supply managers when it touched the edges of SPU’s Tolt River Watershed. But the persistent ridge of high pressure, the one that paired with “The Blob” to scorch Seattle since May, really fell apart when the first of three upper-level low pressure systems made their way through the region starting during August’s ides.


The first shot across Seattle’s parched bow came as surprise on the 12th. But the main event arrived two days later when a surface low pressure system passed directly over the city. Reminiscent of a monsoon, the storm provided nearly 2 inches of rain (normal rainfall for the entire month is 0.88 inches).


One thunderstorm embedded within the system provided Seattle with one of its most intense downpours on record. SPU’s U-District rain gage recorded 0.93″ in 30 minutes, which is likely well beyond a 99th percentile event for that duration, and another extreme to add to recent upward trends. Unfortunately, SPU’s watersheds received less than the customers they serve, but the confusingly realigned atmosphere was not finished.


On Saturday August 29, Western Washington experienced its strongest windstorm on record. Likely fueled by pieces of hurricanes that passed Hawaii, the storm with area gusts to 70mph left nearly a half a million people without power. Rainfall was not as dramatic, however SPU’s watersheds fared better this time, getting up to 3 inches followed by additional accumulation in a suddenly strong and persistent on-shore wake.


With an average temperature of 68.7 degrees, August 2015 landed at number 4 all-time, and with 3.28 inches of rain it was also the 4th wettest on record. Hot, smoky, wet, windy, cool, even snowy (above 5,500 feet) all fit. But how about we just stick with weird. August was weird.