How hot, dry will it get? A preview of the Seattle summer weather

The National Weather Service’s Climate Prediction Center recently released the latest seasonal weather outlook for Seattle. So what does this summer and beyond have in store?

The odds are stacked in favor of warmer-than-average temperatures and below-average precipitation for the entire period of June through September.

Flash floods, thunderstorms join PNW’s erratic streak of weather

In comparison with last summer, this summer may be quite similar, yet likely neither as dry nor have as many 90-degree or greater days.

Last summer at Sea-Tac Airport, only 0.54 inches of rain fell from June 21 until October 21 – the driest period ever on record. Last summer also had a record number of 90-degree-plus days, the most ever. To have such record warm and dry conditions two years in a row would be quite rare.

Yet, prepare for another overall warm and dry summer in western Washington. Seattle gets an average of about four days per year reaching 90 degrees or higher. In the last 15 years, though, the average has risen to just over six days per year, including in 2011, which never reached 90, and 2007 which had just one day of temperatures in the 90s.

The ‘heat dome’ was in late June 2021, and that year had eight days of 90 degrees or higher, including the three record hot days of 100-degree weather topping off at the new all-time record high of 108 degrees at Sea-Tac Airport.

Could another ‘heat dome’ like that occur?

Referencing a presentation on that event at the recent Pacific Northwest Weather Workshop, that dome of hot air was quite a rare anomaly. Yet in this era of a warming planet, it cannot be ruled out in future decades.

Sea-Tac Airport averages 3.18 inches of rain in all from July through September. Last year’s record lack of summer rainfall led to extremely dry conditions with elevated wildfire conditions. Western Washington once again suffered wildfire smoke last year, with the primary source coming from the Bolt Creek Wildfire along US 2 leading up to Stevens Pass.

Wildfire smoke has blanketed the region five out of the last six years, beginning with smoke originating from the interior of British Columbia wildfires in 2017. Other wildfire sources in recent years have come from eastern Washington, Oregon, and even California.

Fortunately, last week’s high-altitude Alberta wildfire smoke did not spoil air quality at the surface in western Washington. Yet, that event served as another reminder of the rising number of wildfires in western North America each summer, elevating the threat of more wildfire smoke finding its way into western Washington.

Wildfire smoke from Canada impacting Seattle skies

There has been a lot of talk about the return of El Niño this winter. El Niño is when sea surface temperatures in the Eastern Pacific tropical waters – the waters west of Peru – are warmer than average, as opposed to the recent and rare three years in a row of La Niña when those waters were cooler than average. El Niño adjusts winter season weather patterns around the globe, including impacts along the West Coast.

The latest seasonal weather outlook for this fall and summer reflects a typical El Niño weather pattern for the Pacific Northwest with above-average temperatures and below-normal precipitation. With those average winter weather conditions, it may be an uphill struggle to have even an average mountain snowpack, meaning the water supply for 2024 could be challenging.

It is early, and the trend toward El Niño this winter could evolve through this summer as it continues to be monitored.

In the meantime, enjoy the summer weather. Be sure to wear a life jacket when visiting area waterways as those waters will remain quite cold through the season, wear sunscreen, particularly during the middle of the day when UV rays are highest, and ‘check the back seat’ to avoid leaving young children and pets in hot cars.

Follow Ted Buehner, the KIRO FM news meteorologist on Twitter