The Air Around You-Part 3 Stormy Skies

What Causes Storms? Pressure differences in our atmosphere’s air masses cause them to shift and change, along with our weather. With these air masses moving in the atmosphere, they collide when they bump into each other. They rarely mix due to the differences in density. Instead, storms and other severe weather phenomena form along the boundaries of air masses.

Weather Fronts Area formed along the boundaries of air masses. Four possible types: warm, cold, occluded, stationary.

Warm Fronts The leading edge of a mass of moving warm air. Usually move slowly and are often marked by rain and cloudy skies.

Cold Fronts Form when quickly moving cold air masses collide with more slowly moving warm air masses. Since cold air is denser, it sinks beneath warm air. Since cold fronts move quickly, they are associated with quickly changing weather conditions, including thunderstorms and heavy rain. Usually associated with low air pressure

Occluded Fronts Occur when a cold air front takes over a warm air front. This can be like an air mass ‘sandwich’, in which the warm air mass becomes stuck between two cold air masses. The denser cold air masses lodge themselves around the warm air mass, pushing the warm air mass farther from Earth’s surfaces. The cold air masses are left to mix near the ground, cooling the temperatures we experiences. Usually these fronts are associated with the drying of air.

Stationary Front Refers to the meeting of two air masses that do not overtake each other. A cold air mass and a warm air mass may be next to each other, but they move along at the same pace, leading to extended rain, snow, fog, or clouds at the boundary.

Stationary Front

Fronts and Weather Maps Displayed on the surface weather by thick lines. Blue lines represent cold fronts. Purple lines represent occluded fronts. Red lines represent warm fronts. Red/Blue combined lines represent stationary fronts. High pressure is indicated with a letter ‘H’ Low pressure with a letter ‘L’

Fronts and Weather Maps

Fronts and Storms Storms are associated with the different weather fronts. Storms can include strong winds, thunder and lightning, and precipitation. Sometimes, strong winds move dust and snow through the air masses.

Thunderstorms Usually occur during the spring and/or summer, when the air is warm and unstable, rising to ‘float’ above colder air. Five steps precede the occurrence of a thunderstorm. Warm, wet air rises from the ground. Once the air rises high enough, it begins to cool and form clouds, which continue to rise. Once the clouds rise about 40,000 feet, depending on the temperature, large heavy ice crystals begin to form. These particles fall back through the clouds, creating powerful downdrafts On Earth, we would likely experience the storm as heavy rain, thunder, and lightning.

Thunderstorms Lightning occurs as a static charge within the clouds. When the strength of the charge is greater than the insulating qualities of the atmosphere, lightning is the result. Thunder occurs because heated air expands explosively, creating a ‘shockwave’ as the surrounding air is compressed. The air contracts rapidly as it cools.

Thunderstorms We experience lightning before thunder because the speed of light is faster than the speed of sound.

Tornadoes Form when the warm, wet updrafts of a thunderstorm come close to a strong, central downdraft. If the wind hitting the top of the storm cloud is blowing in a different direction from the wind below it, the storm system starts to rotate. As the warm and cold air currents interact, the storm begins to rotate faster and faster.

Tornadoes Winds can accelerate up to 300 miles per hour. The funnel of a tornado can be as small as 50 feet, or as large as one mile wide, allowing tornadoes to damage areas up to 100 miles long. Most tornadoes last for fewer than 15 minutes.

Hurricanes Storms that form over very warm, tropical waters when unstable air has a unique mix of both high and low pressures. Essentially a cluster of several thunderstorms that have formed together. Classified as a hurricane if the storm winds are 74 mph or higher. Can last from several hours to several weeks.