Damaging Winds

5/11/2018 (Permalink)

• Straight-line wind is a term used to define any thunderstorm wind that is not associated with rotation, and is used mainly to differentiate from tornado winds.
•  Downdraft is a small-scale column of air that rapidly sinks toward the ground.
•  Down burst is a result of a strong downdraft. A down burst is a strong downdraft with horizontal dimensions larger than 4 km (2.5 mi) resulting in an outward burst of damaging winds on or near the ground. (Imagine the way water comes out of a faucet and hits the bottom of the sink.) Down burst winds may begin as a micro burst and spread out over a wider area, sometimes producing damage similar to a strong tornado. Although usually associated with thunderstorms, down bursts can occur with showers too weak to produce thunder. 
•  Microburst is a small concentrated down burst that produces an outward burst of damaging winds at the surface. Micro bursts are generally small (less than 4 km across) and short-lived, lasting only 5-10 minutes, with maximum wind speeds up to 168 mph. There are two kinds of micro bursts: wet and dry. A wet micro burst is accompanied by heavy precipitation at the surface. Dry micro bursts, common in places like the high plains and the inter-mountain west, occur with little or no precipitation reaching the ground. 
• Gust front is the leading edge of rain-cooled air that clashes with warmer thunderstorm inflow. Gust fronts are characterized by a wind shift, temperature drop, and gusty winds out ahead of a thunderstorm. Sometimes the winds push up air above them, forming a shelf cloud or detached roll cloud.
• Derecho is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. A typical derecho consists of numerous micro bursts, down bursts, and down burst clusters. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.