Wind Types and the Damage Patterns they Create
by Steve Roberts, CCM, President & Forensic Weather Expert
Wind can be a destructive force and contributes to a significant amount of insurance claims each year. Some of those claims can end in litigated matters. When it comes to insurance claims, the type of wind responsible for damage can be critical for how a claim is evaluated and processed. Many people do not fully understand the different types of wind and unique damage patterns they create. Let’s explore the main types of wind.
Straight-line winds are simply winds that move horizontally along the ground that are not associated with a tornado. These winds can be generated by a variety of weather phenomenon ranging from large scale storm systems spanning several hundred miles down to individual thunderstorms. The straight-line winds produced by large scale storm systems are caused by differences in air pressure over large distances and are known more specifically as gradient wind events. Although some gradient wind events can be strong enough to produce damage, most do not.
Another type of straight-line wind comes from a thunderstorm downdraft. Downdrafts originate overhead in a thunderstorm and descend toward the ground. Once they make contact with the ground, the air is forced to spread out horizontally along the ground as straight-line wind. Thunderstorm downdrafts can cause damage and when those wind gusts reach 58 mph or greater, the thunderstorm is classified as “severe”. In some instances, thunderstorm downdrafts can be organized and strong enough to be classified as a microburst or microburst. Those are very intense, short-lived downbursts that can produce winds exceeding 100 mph.
Microbursts and macrobursts have a defined center point where the thunderstorm downdraft initially reaches the ground. Once reaching the ground, the strong winds spread out in all directions. This results in damage patterns that lay down debris in straight lines radially outward from the center. Microbursts and macrobursts have the same origins, but are classified by the size of the damage footprint they leave behind. A microburst has a damage area of up to 2.5 miles in diameter. A macroburst has a larger damage area of greater than 2.5 miles.
Whether damaging straight-line winds are created by a large-scale storm system or from a thunderstorm downdraft, they create damage patterns where the debris is blown in the direction the wind is travelling.
A tornado is a violent rotating column of air that makes contact with the ground. Tornadoes form when rotation within a thunderstorm updraft creates a spinning vortex or “funnel cloud”. This funnel cloud is not classified as a tornado until the funnel makes contact with the ground. Tornadoes are typically small with damage paths less than 1/2 mile wide. However, some of the largest tornadoes have reached over 2 miles in width.
Tornadoes are one of the most destructive forces on the planet. They can generate wind speeds in excess of 300 mph, wiping homes off their foundations and turning cars into flying missiles. The damage from a tornado can be easily distinguished from straight-line winds due to the twisted and scattered nature of the damage left behind. Trees will often look shredded where they are sheared off, with the bark and tree fragments twisted. Although the damage itself shows evidence of twisting, tornadoes travel in a fairly straight line. Tornadoes can create sporadic damage patterns along their paths by transitioning back and forth between funnel clouds and tornadoes along their paths.
Hurricanes are large symmetrical storms with intense winds that wrap around the entire storm. These winds are often accompanied by heavy rain. Hurricanes form in tropical regions and get their fuel from warm ocean water. A mature hurricane will contain surface winds of at least 74 mph. It will often form a cloud-free center known as the “eye” where weather conditions can be relatively tranquil. In sharp contrast, the strongest winds of a hurricane circulate around the outer edge of the eye in the “eyewall”. In general, the wind speeds in a hurricane diminish as you move further away from the eyewall.
The strong winds produced by a hurricane are considered straight-line winds. However, a hurricane can occasionally spawn tornadoes in its rain bands. Hurricane winds can change direction several times as the storm completes its trek through a location. The damage patterns left in their wake can be fairly chaotic with debris laying in all directions. Therefore, it is often difficult to distinguish if wind damage in a hurricane was caused by straight-line hurricane winds, or an isolated tornado within the hurricane.
In conclusion, there are two basic types of wind that cause damage: straight-line wind and tornadic wind. Straight-line wind causes damage with debris falling in the direction the wind is travelling. Conversely, tornadoes throw debris in all directions and show signs of twisting and rotation within the debris field. When verifying insurance claims, it can be important to understand which type of wind caused damage. Only a qualified forensic meteorologist can comb through the data and determine which type of wind caused the damage.
Give CompuWeather a call at (845) 227-8500. Speak with our Certified Consulting Meteorologists and see how their expertise can add value to your legal case or claim.