The Lowdown on High Pressure |
 Dave Thurlow, Host |
The kind of day I love here in the mountains is when it's bright and sunny, cold and windy. Crisp, might be a good word. What we call a high-pressure day. And even though the weather map says high pressure, which means fair weather, as the day moves on, the clouds and snow move in. Hi, I'm Dave Thurlow for the Mount Washington Observatory and this is The Weather Notebook.
High pressure is supposed to bring fair weather. But it doesn't all the time. High pressure is the result of air over a large area, geez sometimes as big as the whole country, being pushed down to the ground either by its own weight or by other air up above. It's called high because it makes a barometer indicator rise, higher.
But small pockets of air in a high-pressure area can go up even though most of the air is heading down. Picture one of those lava lamps - you know where little blobs bubble up through the...whatever that stuff is. Blobs of air too can bubble up in the atmosphere even when the air overall is laying flat on the land when the pressure is high. Here are some reasons why.
Blobs of air heat up and rise because of the sun, or the wind blows air into a mountain and up it goes, or air is heated and moistened by water like the Great Lakes and bubble up. In any case, the local result is clouds and precipitation, even if, in general, the pressure is high. The air rises, cools down as it does, moisture condenses, makes clouds, rain or snow falls. A beautiful mix of all kinds of weather on a high-pressure day.
The Weather Notebook is funded by Subaru and the National Science Foundation.
How a High Affects the Weather
Related Links
High-pressure systems tend to bring bright, sunny days with calm weather. - USA Today