If you’ve been around Western Washington in summertime, you’ve certainly seen big, billowing clouds bubbling up over the mountains while the skies above the lowlands are perfectly clear.
Around Puget Sound, you might see it in both directions, with showers and thunderstorms over both the Cascades and the Olympics.
It’s the mountains themselves that create that kind of stormy weather!
First, to get a thunderstorm, you need a trigger to force air upward. And our mountains do all the heavy lifting.
As winds blow inland (or from any other direction, for that matter), that air eventually slams into the steep slopes of the Olympics and Cascades. It has nowhere to go but up. As the air is forced up the mountain, it cools rapidly and condenses into towering storm clouds. This is called orographic lift. As mountains act as a natural “ramp” to launch these clouds upward, the flat lowlands simply don’t have that physical trigger to get the air rising.
Next, on a clear summer day, the often-rocky slopes of the mountains bake in the direct sunlight. They can heat up faster than lowland locations covered in grass and trees.
The hot air resting against the mountain slopes becomes buoyant and rapidly rises toward the peaks. When rising warm air from both sides of a mountain meets at the top, it keeps on accelerating upward. That creates clouds over the peaks, and sometimes even thunderstorms.
As upper-level winds then push the thunderstorms off the peaks, they can begin to diminish as they move away from the source of rising air currents. This can cause the air to start sinking, which naturally discourages clouds. This is also a reason lowland locations can stay relatively clear.
Lastly, thunderstorms need instability -- hot air at the surface but very cold air high in the atmosphere.
Our mountains, soaking up the sun’s rays, are simply closer to that very cold air aloft. This can create a highly unstable environment in which storms can easily erupt.
Down in the lowlands, we have the opposite setup. We benefit from what I often call “nature’s air conditioning”: the cool, marine breezes blowing in off the Pacific Ocean and Puget Sound. That cool marine air settles over the lowlands and doesn’t really want to rise easily, keeping the atmosphere stable and preventing storms from ever getting off the ground.
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