Key Takeaways
- On Sunday, Sea‑Tac International Airport recorded a high of 81 °F, shattering its previous May record of 77 °F set in 1992.
- Several western Washington locations also broke or tied record highs, including Olympia (85 °F, beating a 1944 mark) and Bellingham (76 °F, surpassing a 1992 record).
- The heat wave was driven by a strengthening ridge of high pressure over western Washington and British Columbia, coupled with a developing thermal low west of the Cascades, pushing temperatures into the mid‑70s to mid‑80s—well above the seasonal low‑60s average.
- Coastal areas benefited from an afternoon sea breeze, keeping Puget Sound‑adjacent spots a few degrees cooler, while inland valleys, the South Sound, Southwest Interior, and Cascade foothills experienced the full brunt of the warmth.
- Temperatures are expected to ease beginning Monday, with interior highs staying in the 70s‑low 80s, but Sea‑Tac’s Monday forecast (79 °F) will not topple its May 4 record of 85 °F.
- A return of onshore flow will gradually cool the region through the week, bringing highs down to the mid‑60s‑low 70s by Thursday and Friday.
- May in Seattle typically gains about 20 minutes of sunset every two weeks (≈60‑70 minutes total added daylight) and averages just under 2 inches of rainfall, making it a relatively dry month despite the early‑season heat.
Summary
Unseasonably warm weather swept across western Washington on Sunday, delivering the first 80‑degree‑plus reading of the year at Seattle‑Tacoma International Airport. The airport’s official observation hit 81 °F, eclipsing the long‑standing May record of 77 °F that had stood since 1992. The heat was not isolated to the airport; a swath of cities and towns throughout the region posted new or tied high‑temperature marks. Olympia soared to 85 °F, surpassing its 1944 record of 82 °F, while Bellingham reached 76 °F, topping a 1992 benchmark of 74 °F. Hoquiam logged 74 °F (beating a 1956 record of 73 °F), and Quillayute matched its 1992 record at 83 °F.
Meteorologists attributed the surge to a strengthening ridge of high pressure anchored over western Washington and British Columbia, which acted as a lid that trapped warm air aloft. Simultaneously, a thermal low pressure system developed west of the Cascade Mountains, enhancing southerly flow and drawing heated air inland. The combined effect pushed daytime temperatures into the mid‑70s to mid‑80s across much of the region—substantially above the typical early‑May averages that linger in the low 60s.
Geography moderated the extremes somewhat. Areas immediately adjacent to Puget Sound enjoyed a brief respite from an afternoon sea breeze, which kept temperatures a few degrees lower than inland locations. In contrast, the South Sound, Southwest Interior, and the valleys and foothills of the Cascades bore the full force of the ridge‑driven heat, experiencing the highest readings.
The heat wave is already beginning to relax. Forecasts indicate that while interior zones will remain warm—highs expected in the 70s to low 80s on Monday—the airport’s projected high of 79 °F will fall short of challenging the May 4 record of 85 °F. As the week progresses, a return of onshore flow from the Pacific will usher in cooler marine air, gradually lowering temperatures. By Thursday and Friday, highs are anticipated to settle into the mid‑60s to low 70s range, more in line with climatological norms for the month.
Beyond the immediate temperature swing, the article notes the typical seasonal progression of daylight in May. The Seattle area gains roughly 20 minutes of sunset every two weeks, amounting to an additional 60‑70 minutes of daylight over the month. This increase in sunshine accompanies May’s characteristic dryness; historically, Seattle receives just under 2 inches of rain during the month, making it one of the drier periods of the year despite occasional warm spikes like the one observed on Sunday.
Overall, the early‑May heat event underscores how transient atmospheric patterns—specifically a strong ridge and a coastal thermal low—can produce notable temperature extremes even in a region known for its mild, maritime climate. While the record‑breaking warmth is expected to be short‑lived, it serves as a reminder of the variability inherent in Pacific Northwest spring weather and the importance of monitoring evolving pressure systems for both short‑term forecasts and longer‑term climate trends.