07/11/97 - 05:05 PM ET - Click reload often for latest version

Source: USA TODAY research by Chad Palmer

How a low-pressure system affects weather

Often, you hear weather forecasters refer to a storm or low-pressure area moving toward your region. As you can see in the graphic above, air rises near low-pressure areas. As air rises, it cools and often condenses into clouds and precipitation. Usually, when forecasters say a low-pressure area is moving toward your region, cloudy weather and precipitation often result as the low-pressure area approaches. A steady rain or snow can fall to the north of the warm front as warm moist air from the south rises up and over the cold air ahead of the warm front. Showers and thunderstorms often fire up ahead of the cold front in the warm, unstable air. Usually, showers and thunderstorms ahead of the cold front are much shorter in duration than the precipitation ahead of the warm front. Due to the counterclockwise circulation around low-pressure areas in the northern hemisphere, cold air will likely be found to the north and west of low-pressure areas while warm air is most often found to the south and east of low-pressure areas.