Weather 101: High Pressure

Weather 101

If you love sunny weather, than you will love high pressure.

High pressure, the blue H you see on the weather map, is a region where the amount of air within a vertical column stretching from the surface to the top of our atmosphere is higher than the surrounding area. The air inside this column sinks to the surface and spreads outward (known as divergence). You can actually see this happening on weather maps!

To see high pressure in action, look for areas with clockwise rotation (northern hemisphere). If you are in the southern hemisphere, then counter-clockwise rotation = high pressure.

Surface map from Sunday, November 29 2020

The sinking air, or subsidence, associated with high pressure is also important for cloud formation!

Let’s start by looking at how a clouds forms. Besides needing enough moisture, you’ll need rising air to form a cloud. Air near the surface is warmer and therefore can hold more water vapor (gas form of water). As air rises, it cools at higher altitudes and becomes more saturated. This is because colder air can not hold as much water vapor as warmer air. Eventually, the air becomes fully saturated and a cloud will form.

When you have sinking air due to high pressure, the air above moves down to the surface and the opposite effect happens. As this air gets closure to the ground, it warms up and becomes less saturated. Eventually, this causes the cloud to “disappear” and we get a bright sunny sky!

Have something about the weather you are curious about? Send us an email weather to have it featured in a future edition of Weather 101!

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