The Weather Notebook: Under Pressure

Under Pressure
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Dave Thurlow, Host

When something starts getting to you at work or at home or wherever, it's like being under high pressure. But when it's the atmosphere putting you under high pressure, it's not so bothersome. That's because high pressure tends to give us great weather: clear, dry, and sunny. Hi, I'm Dave Thurlow and this is The Weather Notebook.

Current US Weather - TWC
A high-pressure center is like a mound of air piled up seven or eight miles high, hundreds of miles across. The air flows outward from the edges of a high, but sinks gently in the middle, making fine weather, because sinking air is dry air. When you're under high pressure, your barometer will typically read around 30 inches.

Highs (as they're called) are made when upper-level winds converge and force air to sink toward the ground. This can happen where it's warm or cold, from the tropics to the poles. But it's especially true in the centers of huge highs that form over Canada and Siberia during the long polar nights of winter.

If these get big and cold enough, they can spread outward like molasses poured onto a table. Throw in a strong jet stream flowing across the top of the puddle of molasses, uh, I mean high pressure area, that blows it southward, and you've got the Siberian Express, which can drive a bitter-cold high from Canada to Florida in just a couple of days.

Now in that case, Floridians might complain about the pressure, but it's another 5 or 6 months before that kind of atmospheric pressure shows up.

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