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Hazard 101
Dive deep into wind and hail. Explore the science, meteorology, and wind engineering behind the perils that damage roofs so frequently.
Wind
Wind in the Boundary Layer
Wind speeds over the earth’s surface are created by weather systems ranging in size from large low-pressure systems and tropical cyclones to smaller scale thunderstorms and tornadoes. As wind interacts with the roughness of Earth’s surface, eddies and vortices create turbulence in the wind that influence the very localized winds that can damage buildings.
Because of Earth’s rough surface trees, and structures, wind speeds are generally slower closer to the ground and faster higher up in the atmosphere. These same surface features create turbulence.
Turbulence produces wind gusts—intermittent peaks in wind speed. Wind gusts cause the highest pressures on buildings.
This change of wind speed and turbulence with height near the ground is known as the boundary layer profile.
Terrain & Topography
The surrounding terrain—whether that is an open ocean, open grassland, suburbia, or dense urban development—changes the shape of the boundary layer profile of the wind because of the change in friction at the surface.
For example, a building in suburban terrain will experience lower wind speeds but more turbulence compared to a building in open terrain such as grassland.
Topography further influences wind speeds. Mountains, hills, or escarpments can accelerate wind speeds because these features block the flow. As wind moves over a hill, it is forced up by the topography, and speeds up.
Generally speaking, the smoother the upwind conditions the building has, the more severe the wind speed will be.
Wind Climate
The geographic location of a building influences what types of storms cause the most severe winds.
- In coastal areas, the most severe winds are driven by hurricanes.
- Inland, the most severe winds are generally generated by thunderstorms—sometimes called severe convective storms.
The probability of these types of events occurring varies by location. Based on weather records and computer modeling, the probabilities of different severities of wind speeds can be estimated for different locations.
The wind climate of a particular building site can also have a pronounced directionality that engineers can consider when determining the probability of severe winds of different directions impacting a building.
Measuring Wind
The hardest question to answer is often “what was the wind speed?” A building experiences rapid peaks in wind speeds from turbulence, and these peaks inflict the highest pressures on a building and determine how the building and its materials will react to these winds. These wind speeds are reported in different ways including as a one-hour average, a 10-minute average, the peak gust within 10 minutes, or the peak gust within one hour, etc.
Wind gusts can be calculated in different ways based on the moving average used to process raw wind speed data, for example a 3-second moving average.
Additionally, because of the boundary layer profile, the reported wind speed also depends on the height of the measurement.
Typical wind speed reports include:
- 3-second wind gusts based on the highest 3-second moving average over a 10-minute period measured at a height of 10 meters.
- Sustained winds:
- Globally, sustained winds are averaged wind speeds over 10 minutes measured at a height of 10 meters.
- However, in the United States for hurricanes, a one-minute mean wind is considered a sustained wind.
- The ratio of the wind gust divided by its mean is called a gust factor.
Wind Loads
As wind flows over and around a building, it is forced to slow down in some places and speed up in others, applying different forces on the surfaces of the building. This results in the windward-facing wall experiencing a force, or wind load, pushing inward, while the other walls and roof experience a force pulling out and/or up. In fact, the uplift forces on the roof are immense and for a typical wood-framed house, these forces can be more than the weight of the house itself.
While some may see a building as a structure that supports the weight of the roof, during windstorms a structure must be able to hold the roof down.
If a window or door is broken, blown in, or left open, wind creates additional positive pressures inside the building that exacerbate the uplift forces on the roof. This can even double the uplift load the roof has to resist.
The magnitude of the uplift pressures depends on the square of the wind speed. Doubling the wind speed a building experiences will quadruple the pressure. This mathematical relationship underscores the importance of a building’s design wind speed to ensure it can withstand the forces exerted on it.
Just like wind flowing around an airplane wing, wind flowing over a building produces uplift pressures on the roof and suction pressures on exterior walls.
The terms 1 in 700-year event and 1 in 3,000-year event are often used to describe extreme events, but this often creates confusion as it gives the impression that the event occurs in cycles every 700 or 3,000 years. Instead, the event has a 1 in 700 chance or 1 in 3,000 chance of occurring every year. This is known as a return interval.
Designing for Wind
Designing a building for severe winds requires engineers to predict what severe wind speed could occur at the building’s location and what level of risk is considered acceptable for that structure and its occupancy. Wind climate, terrain, and topography influence design wind speeds.
The severity of the design wind speed is also based on the type of building. Buildings essential for public safety and basic needs, such as hospitals and power stations are designed to withstand higher wind speeds than commercial buildings and houses.
Typically, a house is designed for wind speeds that have a 1 in 700 (0.14%) chance of being exceeded in any given year, whereas a hospital is designed for wind speeds that have a 1 in 3,000 (0.03%) chance of being exceeded.
Examples:
- A house in Tampa, Florida should be designed for a 3-second gust wind speed of about 140 mph and a hospital should be designed for about 160 mph.
- A house in Chicago, Illinois should be designed for a 3-second gust wind speed of 107 mph and hospital should be designed for about 120 mph.
In the United States, the Standard known as ASCE-7, published by the American Society of Civil Engineers, provides the design wind speeds and wind loads across the country and for different building types.
Key Takeaways:
- Wind passing over and around a building can produce very large uplift forces, especially on the roof, and turbulence makes wind loading complex to determine.
- Wind speed can be defined many ways. Such as gust wind speeds and sustained winds. Care must be taken when comparing wind speeds from different sources.
- Wind climate, terrain, and topography influence the severity of the wind a building will experience. Design wind speeds used by engineers that take these factors into account are provided in wind loading standards.
- Engineers use wind load standards to provide basic regional wind speeds for building design based on the geographic location of the building. This wind speed can be modified by factors that account for the height of the building, the terrain, and the topography.
Wind in Tropical Cyclones
In coastal areas, the most extreme winds typically occur during tropical cyclones, or tropical storms and hurricanes as they are known in the Atlantic basin.
Tropical Cyclone Climatology
Tropical cyclones form in the Tropics, and this region largely extends from the Tropic of Cancer in the Northern Hemisphere to the Tropic of Capricorn in the Southern Hemisphere.
Due to the nature of earth’s rotation, tropical cyclones rarely form within +/- 5 degrees of the equator.
Tropical cyclone is the broad term for hurricanes, typhoons, and cyclones that form in the tropics. Different terminology is used in different geographies. Tropical cyclones with winds of at least 74 mph are called:
- hurricanes in the Caribbean, the Gulf, the North Atlantic Ocean, and the eastern and central North Pacific Ocean.
- typhoons in the western North Pacific.
- cyclones in the Bay of Bengal and the Arabian Sea.
- severe tropical cyclones in the western South Pacific and southeast Indian Ocean.
- tropical cyclones in the southeast Indian Ocean.
In the United States, the Gulf and Atlantic coastlines are impacted by storms that form in the Atlantic basin. Direct impacts to the Pacific coast and Hawaii are rare but occasionally occur from storms in the eastern North Pacific basin, like Hurricane Hilary (2023).
Hurricane season defines when most—but not all—storms occur.
- Eastern Pacific: May 15–November 30.
- Atlantic and Central Pacific: June 1–November 30.
The climatological peak of the Atlantic hurricane season early to mid-September.
Structure and Impacts
Hurricanes are low-pressure systems that form in warm ocean waters under low-wind shear conditions. A hurricane consists of an eye, an eyewall, outer rainbands, and an expansive wind field.
Eye: the roughly circular low-pressure center of a hurricane, typically devoid of both wind and rain.
Eyewall: the organized band of thunderstorms that surrounds the calm eye and contains the strongest winds.
Outer Rainbands: bands of heavy rain and thunderstorms that extend out from and spiral around the eyewall. These rainbands can also sometimes contain tornadoes.
Wind Field: the maximum extent of tropical storm force and hurricane force winds in any quadrant of a tropical cyclone.
In the northern hemisphere, the strongest winds within the eyewall are normally found within the right-front quadrant based on the direction of movement of a hurricane during landfall. However, hurricane dynamics—especially in rapidly intensifying storms—can alter this.
The Saffir-Simpson Hurricane Wind Scale classifies hurricanes on a 1 to 5 rating scale based on a storm’s maximum sustained wind speed. Hurricanes rated category 3 and higher are considered “major hurricanes” and cause the most catastrophic wind damage. This scale does not account for other hazards like storm surge, flooding, or tornadoes.
| Classification | Wind |
|---|---|
| Tropical Depression | <34 mph |
| Tropical Storm | 34–73 mph |
| Category One | 74–95 mph |
| Category Two | 96–110 mph |
| Category Three | 111–129 mph |
| Category Four | 130–156 mph |
| Category Five | 157+ mph |
Other Impacts:
- Heavy Rain: Widespread heavy rain can lead to flash flooding. Wind-driven rain can force water into homes through openings around windows and doors, as well as through small gaps or cracks in siding or roofs, leading to interior water damage.
- Storm Surge: In addition to flooding from heavy rain, hurricanes produce storm surge—the piling up of water along the coastline due to strong winds pushing water onto the shore. This is the deadliest hazard of a hurricane and is the dominant forcing factor in the issuance of evacuation orders.
- Tornadoes: Landfalling tropical systems often produce tornadoes within the storm’s rainbands. These tornadoes are generally less intense than those produced by severe convective storms, but stronger tornadoes can occur.
Duration & Fatigue
Impacts from a hurricane can be felt at a particular location for long periods of time, often for 12 hours or more as the storm approaches, makes landfall, and then moves away from the location. Winds normally decrease significantly within the first 12 hours after landfall, but stronger, faster storms can bring hurricane-force winds inland up to approximately 150 miles.
These long-duration wind events can tear buildings apart, causing roofs and walls to fail as nails and fasteners are pulled out and metal building components such as roof cladding become fatigued due to the long length of time that the buildings are subjected to the high winds. The winds experienced at a particular location may also change direction, depending on the position within the storm, adding another fatigue component to a structure. Additionally, flying debris can also impact openings such as windows and doors, causing additional damage to homes.
Wind in Severe Convective Storms
Away from the coastline, the most severe winds are often caused by small-scale thunderstorms, and the intensity and duration of those winds can vary by storm mode. The ingredients needed to form a thunderstorm can be distilled into one acronym, S.L.I.M. – Shear, Lift, Instability, and Moisture. The geography of the US is largely responsible for conditioning the atmosphere with S.L.I.M.
The weather at midlatitudes of planet Earth is heavily influenced by the polar and subtropical jet streams. It is the presence of these upper-level jet streams that result in atmospheric wind shear and surface pressure gradients. Pressure gradients control surface wind speed and direction and result in air-mass boundaries that provide lift.
Finally, vertical atmospheric temperature contrasts between the hot, dry air of the desert southwest at mid-levels and abundant, low-level moisture from the Gulf work in concert to produce instability needed to form thunderstorms.
Typical Thunderstorms
Thunderstorms form when moist, unstable air near the surface rises. This lift can come from thermals generated from the heat of Earth’s surface, a frontal boundary forcing air upward, a terrain feature, or upward motion from winds converging near the surface.
The small-scale current of warm, moist rising air in a thunderstorm that begins a thunderstorm’s life cycle is the updraft. As a storm matures, an accompanying downdraft sends cool air back to the Earth’s surface. When the downdraft becomes dominant and eventually cuts off the warm, moist air supplied by the updraft, the thunderstorm begins to collapse and dissipates.
The life cycle of a typical thunderstorm spans approximately 30 minutes. These storms are known as single-cell or pulse thunderstorms.
Severe Thunderstorms
The difference between a typical thunderstorm and a severe convective storm—or severe thunderstorm—is that updrafts in severe thunderstorms are tilted by strong vertical wind shear, or the change of wind speed and direction with height. The tilt allows heavy precipitation to fall out of the updraft and ahead of the downdraft without impeding the flow of warm, moist rising air and thus allowing the storm to maintain its mature state for longer periods of time.
In meteorology, convection refers to the vertical transport of heat and moisture in the atmosphere usually by updrafts and downdrafts. “Convection” and “thunderstorms” are often used interchangeably although there are other forms of convection.
The National Weather Service classifies a severe thunderstorm as having:
- Wind gusts of at least 58 mph,
- Hail at least 1-inch in diameter, and/or
- A tornado.
Severe thunderstorms can form year-round but are most common during the spring and summer months when there is an abundance of warm, moist, unstable air available. While severe thunderstorms can occur anywhere in the United States, most occur east of the Rocky Mountains.
Severe thunderstorms can generally be divided into three categories:
- Supercell: A highly organized, long-lived thunderstorm with a rotating updraft known as a mesocyclone, supercells are known for producing large hail, damaging wind gusts, and violent tornadoes. These individual storms can sustain themselves for hours. Discrete supercells one of the most potent thunderstorm modes and thrive in high-wind shear environments. Supercells produce most of the violent EF-3 and greater tornadoes as well as very large and giant hail.
- Multi-cell: A cluster of convective cells that can produce strong winds, hail, occasional tornadoes, and heavy rain. While individual cells have a lifespan of 30 to 60 minutes, the system can last for several hours as new cells form along the leading edge of the storm by the continued lifting of warm, moist air ahead of it.
- Squall Line: A line of usually quick-moving thunderstorms, squall lines can produce strong winds, hail, occasional tornadoes, and heavy rain. Squall lines can be hundreds of miles long but are usually only 10 to 20 miles wide, meaning the greatest impacts generally last less than an hour at any given location.
Within these severe storms are the mechanisms that produce damaging severe convective storm winds at different time scales and geographic scales.
Tornadoes
A tornado is the most destructive atmospheric phenomenon. The violently rotating column of air with circulation reaching the ground typically begins as a funnel cloud that extends below the mesocyclone of a supercell thunderstorm. While tornadoes can also form embedded in squall lines, supercells produce the stronger tornadoes.
Tornadoes form in areas of high-wind shear—where wind speed and direction vary with height in the atmosphere. This creates areas of horizontal rotation near the surface that can be pulled upward into a thunderstorm’s updraft, tilting the rotation vertically.
The El Reno, Oklahoma tornado that occurred on May 31, 2013, is recognized as the widest tornado on record, at 2.6 miles across.
Eventually, the cloud base of the storm may begin to lower forming a wall cloud, and then a condensation funnel that reaches to the ground, becoming a tornado. The width of a tornado can range from a few feet wide, to over a mile.
Tornadoes are the most violent windstorms on Earth. While Doppler radar can provide estimates of tornado wind speeds when a storm is in progress, tornadoes are assigned a rating using the Enhanced Fujita Scale based on damage corresponding estimated wind speeds.
The Enhanced Fujita Scale is a subjective set of wind estimates determined by the level of damage observed. It provides estimated three-second gusts at the point of damage for 28 damage indicators (DIs) found in communities including structures like homes and apartment buildings as well as vegetative damage indicators. For those 28 DIs, 8 degrees of damage (DoDs) describe the level of damage and correlate to wind speeds that likely caused the damage. National Weather Service meteorologists conduct damage surveys after events to assign EF ratings to tornadoes.
The original Fujita (F) Scale was developed in 1971 by Dr. T. Theodore Fujita to estimate tornado wind speeds based on damage. A forum of meteorologists and wind engineers developed the Enhanced Fujita (EF) Scale to improve on the original F-Scale and add additional variables. The National Weather Service adopted the EF Scale, and it became operational in 2007.
| Enhanced Fujita Scale | |
|---|---|
| EF Rating | Estimated 3-second gust (mph) |
| 0 | 65–85 |
| 1 | 86–110 |
| 2 | 111–135 |
| 3 | 136–165 |
| 4 | 166–200 |
| 5 | Over 200 |
Tornadoes occur in many parts of the world but are most prolific in the United States where, on average, 1,200 tornadoes occur each year.
While tornadoes have been reported in all 50 states, they are most common in the areas east of the Rocky Mountains and west of the Appalachian Mountains encompassing the Great Plains, Midwest, and Southeast. Over the last few decades, tornado activity in the Southeast has expanded further.
Tornadoes occur in any month of the year but are most common in the warmer spring and summer months. The “peak” tornado season varies by geographic location:
- May–June: Southern Plains
- March–May and November-December: Gulf Coast/Southeast
- June–July: Northern Plains/Upper Midwest
Tornadoes can occur both during the daytime and nighttime, but most commonly form during the late afternoon and early evening hours to coincide with peak daytime heating when most thunderstorms occur.
Straight-Line Winds
Damaging surface winds without significant curvature are commonly referred to as straight-line winds to differentiate them from tornadic winds. As cool, dense air descends rapidly in thunderstorm downdrafts, it can bring with it stronger winds aloft. When these stronger winds hit the ground, they spread out horizontally, creating a relatively straight swath of damage. These are generally referred to as thunderstorm outflow winds.
Downbursts
Downbursts occur at the scale of an individual thunderstorm when the updraft can no longer support the mass of rain-cooled air aloft, it falls rapidly toward the ground. As this happens, if the air below the storm is relatively drier, additional precipitation can evaporate, cooling the air further and making it denser.
Once the accelerating downdraft hits the ground, it spreads out in all directions, causing damaging straight-line winds called outflow. Downbursts have been known to produce winds of more than 150 mph but last only 2–5 minutes.
Downbursts occur over a horizontal area of up to 6 miles and can be further subdivided into macrobursts and microbursts. A microburst is a downburst with an outflow diameter up to 2.5 miles, while a macroburst is a downburst with an outflow diameter greater than 2.5 miles.
These winds can occur with or without precipitation at the ground. A wet microburst brings rain with it. A dry microburst occurs when the precipitation evaporates before reaching the ground.
Because downbursts occur within thunderstorms, they can happen any time of the year, particularly in warm climates. However, wet downbursts are most common across the southeastern United States during the warm, moist summer months while dry downbursts are most common in high plains and intermountain west during the summer months.
While a supercell may contain a tornado, a supercell’s rear-flank downdraft (RFD) can also produce damaging winds. The RFD is a downward rush of air on the backside of a storm that descends along with the tornado, located just to the rear or southwest of the wall cloud, and causes the hook echo feature to be visible on radar images as precipitation is wrapped around the updraft. The RFD can cause strong surface winds and occasional embedded downbursts that can lead to severe wind damage. Some wind gusts can reach 80-100 mph in the RFD, and the damage those winds cause can be mistaken for tornado damage until NWS surveys verify the cause. Damage from RFD winds are sometimes described by their scale as a microburst or macroburst.
Photos shared by the National Weather Service show examples of a wet microburst (top) and dry microburst (bottom).
Bow Echoes & Derechos
A squall line may begin to show a bowing curvature on radar when higher momentum, unidirectional winds in the upper atmosphere are transported down to the surface. Once the strong winds reach the surface, the wind accelerates outward as the cooler, denser air of the thunderstorm’s rain-cooled downdraft, known as the cold pool, hugs the surface and spreads forward. As the cold pool strengthens, a rear inflow develops on the back side of the line of storms and these processes can cause the radar depiction to take on a bowing shape.
The leading edge of the cold pool is called the gust front, and along this boundary, warm, moist, less-dense air is lifted, generating new thunderstorm cells. The regeneration of storms along the gust front and balanced outflow of the cold pool allows the bow echo to reach a semi-steady state.
A more significant type of bow echo, classified after the event, is a derecho. This is a long-lived damaging line of thunderstorms that produces numerous wind gusts of at least 58 mph for at least 240 miles. Derechos have been known to produce wind gusts of more than 100 mph, and these high winds typically last 10–20 minutes at any one location. As the bow echo persists, it is this gust front that helps derechos produce widespread and persistent damage over a long distance and duration.
Derechos in the United States occur most often between the months of May and August.
Hail
Journey of a Hailstone
Hail occurs with more frequency in the United States than anywhere else in the world. Hail climatology in the US is concentrated in the eastern two-thirds of the country while hail occurrence west of the Rocky Mountains is rare. The Great Plains and the front range of the Rocky Mountains boast the most frequent and severe hail occurrence whereas eastern portions of the US experience comparatively lower hail frequency and severity.
Over the lifecycle of a long-lived supercell thunderstorm, more hailstones are grown than there are trees on the planet. Because supercells are the most prolific hail producers, they will be the focus for understanding the journey of a hailstone.
Hail Embryos
All hailstones begin as hail embryos. Most hail embryos are graupel particles, but sleet pellets, small debris, and bugs can also serve as embryos. Graupel particles are small, spongy collections of frozen water droplets.
Hail Growth
Thunderstorm updrafts ingest these hail embryos and lift them up above the freezing level where they encounter supercooled liquid water droplets. These encounters allow the embryo to grow into a hailstone. The layer within a thunderstorm updraft where this happens is known as the Hail Growth Zone (HGZ) and is typically characterized with temperatures between –10° C and –30° C.
Hailstones grow in one pass through the HGZ, and it is rare for hailstones to be re-ingested into the updraft for a second round of growth. For this reason, a wider updraft is more favorable for hailstone growth – the longer a hailstone stays in the HGZ, the bigger it can become.
Supercooled water droplets in the HGZ remain as liquid water because the water molecules have difficulty arranging into the hexagonal structure of ice. When a supercooled water droplet touches a hail embryo, the droplet seemingly instantaneously turns to ice because the embryo provides a template for the droplet to build its ice structure. This process is known as accretion and is the primary way an embryo grows into a hailstone. Accretion happens at different rates within the HGZ.
There are two main types of hailstone growth: wet growth and dry growth. Factors that control the type of hailstone growth include:
- Varying rates of accretion,
- Size, temperature, and velocity of supercooled liquid water droplets.
- Temperature of the growing hailstone.
Wet growth occurs when supercooled liquid water droplets to freeze completely upon contact with the hail embryo, and the supercooled droplet has time to fill cavities within the hailstone before freezing. Wet growth is also known as high-density growth.
Conversely, dry growth occurs when growth factors allow the droplets to freeze in spherical shapes immediately upon contact with the hail embryo, leaving air pockets between each other. Dry growth is also known as low-density growth.
Wet growth appears clear, and dry growth appears as opaque, white ice. A cross-section of a hailstone tells the story of growth conditions that the hailstone went through, much like rings on a tree stump.
In a thunderstorm updraft, hail growth is diverse, meaning one storm produces hail of multiple sizes. However, how a hailstone grows controls its physical characteristics. How long a hailstone spends within the HGZ influences factors like size and compressive strength of the hailstone; growth regimes that the hailstone encounters control the density distribution of the stone.
Hailstone Shapes
Hailstones are not spherical and tend to move chaotically while falling. Chaotic motion results in the growth of lumps and bumps on a hailstone. Pronounced lumps and bumps can also act as rotors by inducing rapid rotation of the hailstone, generating lift, and slightly slowing the fall speed of the hailstone.
IBHS pioneered the 3D laser scanning of hailstones to capture and preserve their unique shapes in September 2015. Now, the IBHS database contains hundreds of digital hailstone models, including state record hailstones. 3D scanning has enabled new research avenues including modeling how radar detects hail, improving weather forecast models, developing laboratory hailstones in realistic shapes, and helping to develop deployable hail sondes to map trajectories.
Hail Fall Speeds
Hailstones of different sizes fall from a thunderstorm at different speeds, and this range of fall speeds results in size sorting of hailstones. The largest hailstones will fall closest to the updraft, while smaller hailstones will be lofted farther away.
Hail Reporting and Detection
Documenting the occurrence of hail generally falls to the National Weather Service (NWS) who relies heavily on public reporting. Hail can be reported to the NWS directly, through open-source platforms like mPING, and by networks of trained observers such as CoCoRaHS. Despite challenges with public reports, the database of local storm reports (LSRs) relies on public reporting. These challenges include population bias and measurement accuracy.
- Population bias results in plentiful hail reports in areas of dense population and along road networks but sparse hail reports in rural areas. This means that most hail falling from a storm goes unreported. Population bias is the largest roadblock in using LSRs as a tool for identifying the occurrence frequency of each hail size across the country.
- Scientific measurements of hail are captured using a caliper while public reports often rely on a comparison object for size or a ruler.
Since 2008, commercially- and publicly-available hail swath products designed to estimate from radar how big hail is and where it is falling have been available. Despite the major advances in weather radar science since 2008, the parameters used for hail detection in publicly-available swath products have changed little. As an example, the Hail Size Discrimination Algorithm (HSDA) is the only publicly available hail swath product that uses polarimetric radar products for hail detection. Other swath products such as MESH rely on radar reflectivity and information about the vertical temperature profile to determine size and spatial extent of hail at the ground. Basic radar products such as reflectivity have skill in identifying the presence of hail in a storm, but low skill in estimating hail size and its spatial distribution.
Dual polarimetric—colloquially referred to as dual-pol radar by meteorologists—is a more sophisticated type of radar sampling that provides greater detail of atmospheric particles like raindrops and hailstones. This technology transmits and receives pulses in the horizontal and the vertical.
Climate Signals
While there are clear signals that spatial climatology of tornado frequency and the environments that are favorable to them are expanding eastward from the Great Plains of the United States, there is little evidence of increasing hail severity and occurrence across the country. What little evidence there is of the climate’s effect on hail suggests that hail severity is increasing, and the consensus is that hail events in total will become less frequent but more severe. However, there are many environmental factors that control hail growth, many of which the meteorological community has yet to fully understand.
IBHS Hail Field Study team, with its impact disdrometers and hail crushers, joined with 14 other institutions and 4 international partners to capture the most holistic data on hail-producing thunderstorms during the first federally funded field campaign focused on hail in over 40 years.
