Damaging Winds: What and Where?
Wind is defined as “the movement of air caused by the uneven heating of the Earth by the Sun and the Earth’s own rotation." Let’s examine this further.
The uneven heating of the Earth imparts differences in air pressure across the globe. Warm air heated at the equator rises and migrates towards the north and south poles, while cooler air (which is denser than warm air, and sinks) moves towards the Equator to replace it. This simplified process of global air movement was originally described by George Hadley in 1735, which is known as the Hadley cell in meteorology. While Hadley’s original theory has since been modified, the premise of air moving from areas of high pressure to areas of low pressure still holds true, and brings about the wind we experience on any given day.
There are many different types of winds. Some of the common wind types that affect the United States are coastal, frontal, mountain and valley winds, straight-line winds (including downbursts and derechos), and dust storms and haboobs.
Frontal winds can occur anywhere in the United States. As the name implies, these are winds associated with a frontal system. As the pressure gradient gets stronger, so do the winds. In these winds, sustained speeds can easily reach 40 miles per hour, with wind gusts significantly higher. In the mountains and the Great Plains, frontal winds have been known to knock over semi-trucks and buses, and are very dangerous when combined with a wildfire as it allows a fire to grow rapidly.
Coastal winds are also aptly named. When a large storm system moves onshore and inland, the winds associated with these storms can knock over power lines, leaving affected residents in the dark for days. These storms also can cause coastal erosion and damage coastline properties. As with frontal winds, the stronger the pressure gradient (i.e., the deeper the low pressure), the stronger the winds. Hurricanes and typhoons are excellent examples of how damaging a coastal wind event can be, but it doesn’t have to be a named storm to wreak havoc.
Mountain and valley winds in the U.S. that typically cause the most damage are downslope winds and Santa Ana winds. Downslope winds occur when warm and dry air rapidly descends down a mountain, bringing sustained wind speeds over 40 miles per hour and even stronger gusts. These winds are common on the eastern side of the Rockies, and are called Chinook winds in the region.
Santa Ana winds occur when high pressure sets up over the southwestern desert regions of the U.S., with low pressure off the California coast. The ensuing westward transport of air (remember: air flows from high to low pressure) creates dry winds that flow through the valleys of Southern California. These strong winds cause property damage, and are particularly concerning in conjunction with wildfires because the dry nature of the air combined with the high speed can quickly spread flames across the often dry region.
Severe thunderstorms bring damaging winds as well. Damaging winds associated with severe thunderstorms are typically called straight-line winds, as they result from winds that occur with no rotation, unlike tornadoes. Damaging winds in severe thunderstorms are officially classified as such when wind gusts reach over 57 miles per hour. With severe thunderstorms, hail and tornadoes are also threats to look out for.
Within the category of straight-line winds, downbursts and derechos are two further classifications of extremely damaging wind events. Downbursts can have wind speeds in excess of 100 miles per hour, and are caused by air being quite literally dragged down by heavy precipitation. When the air reaches the ground, it spreads outwards across the surface in a straight line. Meanwhile, a derecho is a long-lived, damaging thunderstorm event. To be classified as a derecho, the swath of wind damage must extend more than 240 miles with wind gusts at or above 57 miles per hour along most of the storm’s path.
Dust storms and haboobs can happen anywhere in the United States, but are of course most common in the Desert Southwest. These walls of dust and debris can be miles long and reach several thousand feet in the air, striking with little to no warning and making conditions hazardous. Dust storms may only last a few minutes, but those few minutes on a crowded roadway can cause massive pileups. If you encounter dense dust blowing across or approaching the roadway, pull your vehicle off the road as far as possible, stop, turn off lights, set the emergency brake and take your foot off the pedal so your taillights are not illuminated. The reason to do so is because motorists from behind may use your taillights as a guide for where the road is, taking them off the roadway and even colliding with your parked car. Never stop your car on the traveling portion of the road.
Damaging winds can clearly cause damage in many different places and in many different ways. Be sure to heed any and all official warnings about possible wind dangers, and keep track of noteworthy and imminent weather using the WeatherBug app.
Sources: National Geographic, weather.gov
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Story Image via Pixabay
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