High Pressure

High Pressure and The Coriolis Effect

High pressure weather systems typically have the following characteristics:
 1. Barometric pressure readings are higher
 2. Sinking air
 3. "fair" weather (lots of sun)
 4. can be warm or cold
 5. wind flows clockwise (in the northern hemisphere) around the central high pressure

Let's check all five of these characteristics individually to gain an understanding of high-pressure weather systems.

Barometric pressure readings are higher
"High" pressure means exactly what it implies. Barometric pressure readings will be higher closer to the center of a high pressure area. The following image contains an area of high pressure. Notice that close to the large "H" near St. Louis, Missouri the barometric pressure readings are highest.

Sinking air
In lesson 6 we created wind by making a circulation. On the cool side of our experiment the cooler, blue water was sinking. This side would represent higher pressure. Sinking air creates a higher pressure because not only does the weight of the atmosphere push down but the downward motion of the air is also pushing down as well.

"fair" weather
In lesson 9 & 10 we examined cloud formation, as well as precipitation formation processes. In both cases it was necessary to have rising air to force condensation.

Downward motion will have the opposite effect and will not only prevent condensation, but it can evaporate clouds and precipitation.

Click here to see the full map

High Pressure can be warm or cold
During the winter, high pressure areas can be extremely cold in middle Missouri. High pressure dominated the Midwest on January 5, 1999. The temperature in Jefferson City dropped to 10 degrees below zero that morning. Here is the surface weather map for the afternoon of January 5, 1999, note the strong areas of high pressure and the bitter cold temperatures.

Click here to see the full map

On the warm side, mostly sunny skies during the summer months will allow the strong summer sun to warm the afternoon very quickly. The following surface map shows very hot temperatures across the Midwest during the summer of 1999. On July 29, 1999 the temperature reached 104 degrees in Columbia. This surface map does not show a high-pressure symbol, however notice that the blue contours have a "ridged" shape through the Midwest.