If you stepped outside in Seattle on Wednesday after seven-straight cooler than normal days, the change was apparent: the morning clouds burned away, the sun took over, and the official high at Sea-Tac Airport climbed to a comfortable 68°. That’s one degree above average!
But take a stroll out to the tip of Magnolia’s Discovery Park to visit the West Point Lighthouse, you will experience a completely different weather reality.
The National Weather Service’s weather station at West Point Light topped out at just 58°. In fact, a nearby weather station in Fremont was at 68°. That’s just three miles away!
This dramatic contrast is a classic spring and summer phenomenon, and it all comes down to the chilly temperature of the water of Puget Sound.
Right now, the water temperature in the main basin of the Sound is hovering in the low 50s. Water changes temperature much slower than land. So while the afternoon sun aggressively warms land areas, the water acts a bit like a massive ice bath.
West Point is uniquely vulnerable to this because of its geography. As a low spit of land jutting far out into the main channel of the Sound, it is surrounded by that cold water on three sides.
But it’s also about the wind. On sunny, warm days, land heats up and the air above it rises. To replace that rising air, cooler, dense air from over the water rushes inland. This creates a localized sea breeze, or “Sound breeze.”
That’s not all! The tip of Discovery Park often is right in the line for any other wind flowing down the Sound. Even before the afternoon sea breeze, the temperature sensor that sits next to the lighthouse is just getting hit non-stop with refrigerated air.
As we head into summer, the temperature differences from right on the waters of the coast or the Sound can be even greater then 10 degrees when the air temperature is warmer.
So if you’re in need of relief from the heat, run toward the water, but sure don’t jump in! The temperature of the ocean and the Sound don’t warm up much at all, even at the peak of summer.on
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