For several days this summer, the temperatures climbed into the high nineties during the day and stayed in the high seventies at night. Days like that are the worst of the summer days. The humidity is so high that when I walk out of my air conditioning into the heat, the air feels alive as it clings to my skin, encasing me instantly in a wet blanket. The air is still and heavy, a palpable presence weighing me down. The weather people inform me that what I am experiencing is a heat dome. It’s not just a heat wave they assure me. Heat waves come and go with a few hot days, but the air moves and storms are bound to break it sooner or later. A heat dome is something special.
To get a heat dome, you need several ingredients. You need the Pacific Ocean, the trade winds, the prevailing westerlies, the jet stream, the sun, and heat.
We’ll start with the Pacific Ocean. First, to clarify my own confusion, the eastern Pacific is the part along the west coast of the Americas. The western Pacific is the water around Japan and southeast Asia. Remember, the earth is round, which makes east and west completely relative to where you are standing.
The trade winds are winds that blow from east to west in a band around the equator. They affect what happens to the water in the ocean. The trade winds move the warmer upper layers of water in the ocean from South America to Asia across the Pacific. This causes colder water from deeper in the ocean to rise to the surface along the west coast of the Americas. The ocean around Asia becomes warmer than the surface water around South America.
The prevailing westerlies are winds that blow from west to east in a band north of the trade winds.
The jet stream is a specific high—pressure current of air in the upper atmosphere that travels from west to east.
The sun—well you know what that is. And heat from the sun and the atmosphere is absorbed by the ocean waters which in turn heat the air above the surface.
Sometimes, like now, the trade winds blow harder than usual, causing more warm water to move westward towards Asia. All this warm water warms the air above it. And all this warm air over Asia rises up to where the prevailing westerlies push it back to the east. Meanwhile more cold water rises to the surface along the Americas. The cold water in the Pacific affects the jet stream, causing the current to bend northward. The hot air from Asia gets trapped under the jet stream. The jet stream, which is colder and higher pressure, pushes the hot air down, compressing it. This compression makes the hot air even hotter, which could explain why each day of our heat dome, the temps were higher than the day before.
Nothing stays static in the weather, and after a while, the high pressure holding the hot air down weakens, storms form, and blessed rain washes the air.
I know—it’s complicated. The takeaway though is that the weather that happens on Owl Acres is shaped by things that happen half a world away. We don’t have any oceans or glaciers anywhere near Owl Acres, and we live miles below the upper atmosphere. But as the glaciers melt and the oceans warm, the impact is already being felt on Owl Acres.
Photo by Author Alt text: Hard to take a picture of something made out of air (like a heat dome), so here’s one of an airborne activity happening at Owl Acres on a hot summer morning. A large quad drone is being used for aerial chemical application to the adjacent cornfield. The aircraft flies a pattern over the field, controlled by a computer and guided by GPS. It’s applying a broadleaf herbicide that kills every plant in the field that’s not corn, and a broad-spectrum (pyrethrin) insecticide that kills every insect it touches.