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3 Ways Thunderstorms Form

Here's what turns a simple unstable atmosphere into a severe weather event.

1) Airmass

Airmass thunderstorms are the most common type of thunderstorms. They're often found in tropical environments like Florida, and their development is not dependent on warm or cold fronts.

An unstable atmosphere is the first building block of any thunderstorm. This means that a cold airmass is overlying a warmer airmass. Warm air under a blanket of cold air is unstable, because the warm layer is less dense, and thus has buoyancy.

An excellent indicator of an unstable atmosphere is a lapse rate that is considerably higher than standard (2*C or 3.5*F per 1,000 ft). You can find the lapse rate on a winds and temp aloft product produced by the National Weather Service (Learn more here).

This instability creates a lifting action, allowing the warmer air to rise. The result of this motion is the building of towering cumulus clouds, which are easily identifiable. In the mature stage of an airmass thunderstorm, intense downdrafts cause heavy rain to be released as the air cools and loses its upward energy.

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2) Frontal

Frontal thunderstorms are associated with the collision of two air masses, which are referred to as a front. These fronts are depicted on NWS surface analysis plot.

Frontal thunderstorms form along cold fronts and can be either single-cell storms bound together or well-organized lines of cells referred to as squall lines.

Frontal thunderstorms form when a cold airmass forces a warm, moist airmass above it. This violent lifting motion can develop into significant vertical movement, resulting in a thunderstorm. Layers of precipitation and hail form high in the cloud, and eventually fall to the ground as they cool.

Wind shear is a common characteristic of a frontal storm forming, indicated either by gusting winds or winds from multiple directions. Winds during the mature stage of a frontal thunderstorm can easily reach speeds of 60-80 knots.

NOAA

3) Orographic

Orographic thunderstorms are caused by the atmosphere interacting with the terrain. These are most common in the late spring and early summer, along the windward side of the Rocky Mountains and Appalachian Mountain ranges. The lifting motion is provided by the upslope terrain of a mountain. This forces moist, hot air to rise.

When this warmer air interacts with the cold air above it, it condenses, causing heavy precipitation and powerful downdrafts. Oftentimes orographic thunderstorms can reach updraft and downdrafts speeds of 6,000 feet per minute.

Regardless of the origin of a thunderstorm, remember to keep your distance, and fly on the upwind side of a thunderstorm whenever possible.

Want to learn how read and understand aviation forecasts like a pro? Sign up for our Aviation Weather course here.

Nicolas Shelton

Nicolas is a private pilot from Southern California. He is currently studying at Purdue University, where he is working on advanced pilot ratings. You can reach him at nicolas@boldmethod.com.

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