Wind Damage

High winds 

High winds can occur during a severe thunderstorm, with a strong weather system, or can flow down a mountain. When winds are sustained at 40-50 mph, isolated wind damage is possible. Widespread significant wind damage can occur with higher wind speeds. During strong thunderstorms, straight line wind speeds can exceed 100 mph. High winds can blow objects around and pose a significant threat to your safety. Understanding the risks can help you prepare for these events.  

Wind Advisory means that sustained winds of 30 mph for one hour and/or frequent gusts of at least 45 mph are occurring or expected within the next 36 hours. These winds will make it difficult to drive high profile vehicles. Small, unsecured objects may be blown around by these winds.  

High Wind Watch means that sustained winds of 40 mph for one hour and/or frequent gusts of at least 58 mph are expected within the next 12 to 48 hours. Check to make sure all loose objects outside are secured. Plan to postpone any unnecessary driving during this time since these winds will make driving difficult, especially for high profile vehicles. These winds may damage trees, power lines and small structures.  

High Wind Warning means that sustained winds of 40 mph for one hour and/or frequent gusts of at least 58 mph are occurring or expected within the next 36 hours. Ensure that all objects outside are secured. Refrain from any unnecessary driving during this time since these winds will make driving very difficult, especially for high profile vehicles. Winds this strong may damage trees, power lines and small structures.  

Staying Safe 

Below is a listing of ways you can reduce the inconvenience or damage done by strong winds: 

  • If strong winds are forecast, ensure that all lightweight or loose objects on your property (grills, patio furniture, trash cans, small toys, etc.) are secured or brought indoors. 
  • Strong winds make driving high profile vehicles very difficult and sudden wind gusts can cause one to lose control of these vehicles. Pay extra attention to the road if you must drive a high profile vehicle and be prepared for sudden changes in the wind. Try not to drive on roads that are perpendicular to the wind direction (ex. N-S roads with a W-E wind). 
  • Remove dead or rotting trees on your property long before a high wind event. Weak trees can fall over in even a moderately strong wind and possibly damage structures and take out power lines. 

What are damaging winds?  

Damaging winds are often called “straight-line” winds to differentiate the damage they cause from tornado damage. Strong thunderstorm winds can come from a number of different processes. Most thunderstorm winds that cause damage at the ground are a result of outflow generated by a thunderstorm downdraft. Damaging winds are classified as those exceeding 50-60 mph.  

Are damaging winds really a big deal?  

Damage from severe thunderstorm winds account for half of all severe reports in the lower 48 states and is more common than damage from tornadoes. Wind speeds can reach up to 100 mph and can produce a damage path extending for hundreds of miles.  

Who is at risk from damaging winds?  

Since most thunderstorms produce some straight-line winds as a result of outflow generated by the thunderstorm downdraft, anyone living in thunderstorm-prone areas of the world is at risk for experiencing this hazard.  
People living in mobile homes are especially at risk for injury and death. Even anchored mobile homes can be seriously damaged when winds gust over 80 mph. 

Thunderstorm Winds and Derechos 

When most people think about winds associated with a thunderstorm, they think tornadoes; however, most years there are far more damage reports from thunderstorm straight line winds than from tornadoes. Straight line winds are thunderstorm winds that have no rotation, i.e. not a tornado. 

Downbursts are a common cause of wind damage from a thunderstorm. They can reach over 100 mph and are caused by air being dragged down by precipitation. When the air reaches the ground, it spreads outward across the surface of the land it encounters in a straight line.  
A Derecho is a very long lived and damaging thunderstorm. A storm is classified as a derecho if wind damage swath extends more than 240 miles and has wind gusts of at least 58 mph or greater along most of the length of the storm’s path.  

Coastal and Frontal Winds 

Frontal Winds can impact anywhere in the United States. The stronger the pressure gradient, the stronger the wind! Because air flows counterclockwise around a low, often the temperature of the air blowing with frontal winds is quite chilly. Sustained wind speeds can reach over 40 mph with wind gusts much faster. These systems can cause problems in the mountains and Great Plains where it is common for high-profile vehicles, such as semi-trucks or buses, to be blown off the road and flipped over. They’re especially dangerous in areas where there are wildfires burning or dry brush that could easily catch fire when there is a spark. 

Coastal Winds stem from large storm systems moving onshore that can pack quite a punch. Often these storms move inland, knocking over power lines and leaving residents in the dark for days. Homes and businesses may be damaged when a strong storm moves onshore. In addition to damaging property, these winds can cause damage to the natural environment, knocking down trees and causing coastal erosion along the beaches. Along the immediate coast, items that are not properly secured may end up being washed out to sea. 

Mountain and Valley Winds 

Downslope Winds occur when warm/dry air descends rapidly down a mountain side. These are common on the east side of the Rocky Mountains, called Chinook Winds. These winds can blow over 40 mph, and can occur in sudden gusts that are even stronger, which can make driving hazardous. In addition, their dry conditions increase the risk of wildfires in the area. 

Santa Ana Winds occur when air from a region of high pressure over the dry, desert region of the southwestern U.S. flows westward towards low pressure located off the California coast. This creates dry winds that flow east to west through the mountain passages in Southern California. These winds are most common during the cooler months of the year, occurring from September through May. Santa Ana winds typically feel warm (or even hot) because as the cool desert air moves down the side of the mountain, it is compressed, which causes the temperature of the air to rise. These strong winds can cause major property damage. They also increase wildfire risk because of the dryness of the winds and the speed at which they can spread a flame across the landscape. 

What Are Straight Line Winds? 

Straight line winds are damaging winds that blow during severe thunderstorms. Occurring in a number of different ways, they are straight blowing winds of 58 MPH or greater that do not rotate like hurricane and tornadic winds. 

There are a number of types of straight line winds that can cause serious damage to homes and require owners to file claims to their homeowners insurance agencies. Such winds include downdrafts, downbursts and microbursts packing tornado-like force, gust fronts, and huge, merged storm systems called derechos. 

Insurance agencies advise that at higher wind speeds, these different storm winds can cause varying degrees of damage to homes and buildings in their path. 

Straight Line Wind Damage 

Although occurring under various weather conditions, homeowners insurance companies know that straight line winds can cause a significant amount of structural and environmental damage as speeds climb. 

  • Lighter damage caused by 60 to 70 MPH winds may include siding and shingles blown off a house and smaller, unsecured buildings like outbuildings and mobile homes may be blown over. 
  • Winds in the 70 to 80 MPH range can cause serious structural roof damage on houses and secured outbuildings and mobile homes. 
  • Winds of 90 MPH or greater can totally destroy even secured mobile homes and buildings. 

In all cases, structures may also be damaged by a variety of debris that can be lifted and blown. In addition, damage caused by downed trees and power lines is common. 

Protecting Homes from Wind Damage 

To prevent or reduce wind damage, homeowners must be aware of storm situations and know when wind damage is possible so preparations can be made. Unsecured items outside the house like furniture, lawn equipment, and toys should be brought inside. Anything that can be blown about should anchored to the ground. 

In locations known to experience severe winds, homeowners insurance companies suggest installing reinforced garage doors and shutters to protect windows as well as reinforced shingles and roofing material designed to withstand high storm winds. Metal roofing and siding may require additional fasteners to prevent it from blowing off. It is also recommended to remove trees close to the home that could fall on the house if uprooted. 

While it may not be possible to prevent all wind damage, homeowners insurance companies recommend that owners take precautions to keep their houses as wind-resistant as possible. Beyond preparing the structure to weather the storm, residents should also take care of themselves by seeking secure shelter on the lower level of their home. Home owners in wind-prone areas should review their homeowners insurance policy to ensure they have the coverage needed in the event their house sustains wind damage! 

What is a tornado? 

A tornado is a narrow, violently rotating column of air that extends from a thunderstorm to the ground. Because wind is invisible, it is hard to see a tornado unless it forms a condensation funnel made up of water droplets, dust and debris. Tornadoes can be among the most violent phenomena of all atmospheric storms we experience. 

What we do: Read more about NSSL’s tornado research here

Where do tornadoes occur? 

Tornadoes occur in many parts of the world, including Australia, Europe, Africa, Asia, and South America. Even New Zealand reports about 20 tornadoes each year. Two of the highest concentrations of tornadoes outside the U.S. are Argentina and Bangladesh.  

How many tornadoes occur in the U.S. each year? 

About 1,200 tornadoes hit the U.S. yearly. Since official tornado records only date back to 1950, we do not know the actual average number of tornadoes that occur each year. Plus, tornado spotting and reporting methods have changed a lot over the last several decades, which means that we are observing more tornadoes that actually happen. 

Where is Tornado Alley? 

Tornado Alley is a nickname invented by the media to refer to a broad area of relatively high tornado occurrence in the central United States. Various “Tornado Alley” maps look different because tornado occurrence can be measured many ways: by all tornadoes, tornado county-segments, strong and violent tornadoes only, and databases with different time periods.  
However, the idea of a “tornado alley” can be misleading. The U.S. tornado threat shifts from the Southeast in the cooler months of the year, toward the southern and central Plains in May and June, and the northern Plains and Midwest during early summer. Tornadoes can occur and have been reported in all fifty states! 
Please remember, violent tornadoes do happen outside “Tornado Alley” every year.  

When are tornadoes most likely? 

Tornado season usually refers to the time of year the U.S. sees the most tornadoes. The peak “tornado season” for the southern Plains (e.g., Texas, Oklahoma, and Kansas) is from May into early June. On the Gulf coast, it is earlier in the spring. In the northern Plains and upper Midwest (North and South Dakota, Nebraska, Iowa, Minnesota), tornado season is in June or July. But, remember, tornadoes can happen at any time of year. Tornadoes can also happen at any time of day or night, but most tornadoes occur between 4–9 p.m. 

What is the difference between a Tornado WATCH and a Tornado WARNING? 

A Tornado WATCH is issued by the NOAA Storm Prediction Center meteorologists who watch the weather 24/7 across the entire U.S. for weather conditions that are favorable for tornadoes and severe weather. A watch can cover parts of a state or several states. Watch and prepare for severe weather and stay tuned to NOAA Weather Radio to know when warnings are issued. 
A Tornado WARNING is issued by your local NOAA National Weather Service Forecast Office meteorologists who watch the weather 24/7 over a designated area. This means a tornado has been reported by spotters or indicated by radar and there is a serious threat to life and property to those in the path of the tornado. A tornado warning indicates that you should ACT NOW to find safe shelter! A warning can cover parts of counties or several counties in the path of danger. 

How is tornado strength rated? 

To determine the strength of a tornado, experts examine the damage it caused. From this information, we can estimate the wind speeds. An “Enhanced Fujita Scale” was implemented by the National Weather Service in 2007 to rate tornadoes in a more consistent and accurate manner. The EF-Scale takes into account more variables than the original Fujita Scale (F-Scale) when assigning a wind speed rating to a tornado, incorporating 28 damage indicators such as building type, structures and trees. For each damage indicator, there are 8 degrees of damage ranging from the beginning of visible damage to complete destruction of the damage indicator. The original F-scale did not take these details into account. The original F-Scale historical data base will not change. An F5 tornado rated years ago is still an F5, but the wind speed associated with the tornado may have been somewhat less than previously estimated. A correlation between the original F-Scale and the EF-Scale has been developed. This makes it possible to express ratings in terms of one scale to the other, preserving the historical database. 

How do tornadoes form?  

The truth is that we don’t fully understand. The most destructive tornadoes occur from supercells, which are rotating thunderstorms with a well-defined radar circulation called a mesocyclone. (Supercells can also produce damaging hail, severe non-tornadic winds, frequent lightning, and flash floods.) Tornado formation is believed to be dictated mainly by things which happen on the storm scale, in and around the mesocyclone. Recent theories and results from the VORTEX2 program suggest that once a mesocyclone is underway, tornado development is related to the temperature differences across the edge of downdraft air wrapping around the mesocyclone. Mathematical modeling studies of tornado formation also indicate that it can happen without such temperature patterns; and in fact, very little temperature variation was observed near some of the most destructive tornadoes in history on 3 May 1999. We still have lots of work to do. 

What do storm spotters look for when trying to identify a tornado or a dangerous storm? 

Inflow bands are ragged bands of low cumulus clouds extending from the main storm tower usually to the southeast or south. The presence of inflow bands suggests that the storm is gathering low-level air from several miles away. If the inflow bands have a spiraling nature to them, it suggests the presence of rotation. 
The beaver’s tail is a smooth, flat cloud band extending from the eastern edge of the rain-free base to the east or northeast. It usually skirts around the southern edge of the precipitation area. It also suggests the presence of rotation. 
wall cloud is an isolated cloud lowering attached to the rain-free base of the thunderstorm. The wall cloud is usually to the rear of the visible precipitation area. 
A wall cloud that may produce a tornado can exist for 10–20 minutes before a tornado appears, but not always. A wall cloud may also persistently rotate (often visibly), have strong surface winds flowing into it, and may have rapid vertical motion indicated by small cloud elements quickly rising into the rain-free base. 
As the storm intensifies, the updraft draws in low-level air from several miles around. Some low-level air is pulled into the updraft from the rain area. This rain-cooled air is very humid; the moisture in the rain-cooled air quickly condenses below the rain-free base to form the wall cloud.  

The rear flank downdraft (RFD) is a downward rush of air on the back side of the storm that descends along with the tornado. The RFD looks like a “clear slot” or “bright slot” just to the rear (southwest) of the wall cloud. It can also look like curtains of rain wrapping around the cloud base circulation. The RFD causes gusty surface winds that occasionally have embedded downbursts. The rear flank downdraft is the motion in the storm that causes the hook echo feature on radar. 
condensation funnel is made up of water droplets and extends downward from the base of the thunderstorm. If it is in contact with the ground it is a tornado; otherwise it is a funnel cloud. Dust and debris beneath the condensation funnel confirm a tornado’s presence. 
Be careful! Tornadoes can form and be in contact with the ground without a fully condensed funnel!