LOW PRESSURE AND FRONTS

What does falling air pressure tell you about the weather? Much of the time, it is telling you that stormy or wet weather is on the way. At our latitudes, a drop in barometric pressure means an area of low pressure is approaching. "Lows" are broad-scale storm systems which can bring with them differing types of changing weather, ranging from rain to snow, strong winds, and thunderstorms.

Lows are born on boundaries between two differing air masses which begin to mix. A circulation develops in a counter-clockwise direction around a center of lowering surface pressure. On a weather map, the center is denoted by an "L."

In the typical 3-D model of a low pressure system, cold air pushes southward and sinks to the west of the low; while to the east, warmer air pushes northward and rises. The boundaries of the cold and warm air are known as the cold front and the warm front, respectively. The fronts and area of low pressure begin to stir up clouds and precipitation. As the low pressure area grows stronger, the pressure decreases. And in turn, increases wind speeds and spreads the clouds and precipitation. In time, the cold and warm air finally wrap around the area of low pressure and mix. The low then begins to fill; pressure increases and winds subside, while clouds and precipitation dissipate. The lifetime of an area of low pressure usually lasts several days. But in that time, it has created a wide variety of weather across a good portion of the nation.

Forecasting the development and path of low pressure systems is a big part of a meteorologist's job. Not all low pressure systems behave in the same way. Differences in the upper atmosphere, surface conditions, and other factors can lead to varying outcomes. It's no wonder that Lows give us so many kinds of weather.

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