Around 7 a.m. this morning, under clear skies, the temperature stood at 41 degrees at Sea-Tac Airport. A mere nine miles to the north at Boeing Field, however, the mercury only read 34 degrees—a difference of seven degrees. With such a short distance between the airports, how can the temperature range possibly be this high?
The answer: easterly winds, or lack thereof.
Higher pressure east of the Cascades has drawn in some wind to Western Washington, especially near the foothills, where wind gusts have topped 35 mph in recent days. For most of the Seattle metro area, wind speeds have been noticeably lighter—and at times completely non-existent, depending on location.
Such is the case for Boeing Field. Easterly winds there gusted above 20 mph for a few hours yesterday afternoon, causing the temperature to jump to 60 degrees. Why? In Seattle, an easterly wind means a wind blowing off the Cascades. As air moves down a mountain range, it warms up significantly, meaning that adjacent cities can get quite toasty (relatively speaking, Phoenix). How far west the winds spread depends on their strength as they accelerate down the Cascades. Yesterday, the easterly winds were strong enough to spread across the entire Seattle area, but by nightfall, they had diminished enough to affect only “select” locations.
Those choice places? Areas near the foothills (closer to the source of the wind), or—drumroll please—areas located on hilltops, like Sea-Tac Airport. While you might not think of SeaTac as being a particularly hilly locale, it actually sits on a bluff 427 feet above sea level. Most of the time, this elevation is irrelevant (unless you want to win big at trivia night), but this morning, it meant not wearing that heavy coat.
For all other areas, including Boeing Field, the easterly winds were virtually non-existent early this morning. To wit, the winds at Boeing Field—which lies in a valley only 16 feet above sea level—sharply diminished as nightfall set in. Once the clock struck midnight, the winds went dead calm—and the temperature fell rapidly.
Moral of the story? If you want to skip that extra layer of clothing tomorrow morning (yes, the easterly winds will be back again tonight for a select few), considering renting a hotel near Sea-Tac. After all, who wouldn’t want to spend a night perched atop a 400-foot-plus bluff?
