How is Hail Classified by Size?
Hail is one of the most unpredictable and damaging weather phenomena. Its destructive capacity depends directly on its size, fall speed, and ice density. To better understand the risks, meteorologists have developed scales that classify hail from small peas to grapefruit-sized balls.
The most widely used classification in South America and around the world is the TORRO Scale (Tornado and Storm Research Organisation), which ranges from H0 (small hail) to H10 (giant hail). Comparisons with everyday objects are also used to facilitate communication with the public.
Comparison with Everyday Objects
- Pea (0.5 cm): Very small hail, barely noticeable. No significant damage.
- Pea or lentil (0.6-1 cm): Common in summer storms. Can damage sensitive crops.
- Marble or dime (1.5-2 cm): Already poses a risk to vehicles and roofs.
- Golf ball (4-5 cm): Causes severe damage to roofs, cars, and crops.
- Tennis ball (6-7 cm): Very dangerous. Can break windows and cause serious injuries.
- Grapefruit (8-10 cm): Extremely destructive. Penetrates roofs and causes total crop losses.
- Softball (11-13 cm): Rare but devastating. Capable of destroying structures and causing fatalities.
How Does Hail Form and What Determines Its Size?
Hail forms inside storm clouds (cumulonimbus) when updrafts of warm, moist air lift water droplets to areas where the temperature is below freezing. There, the droplets freeze and begin to grow as they collide with other ice particles.
The final size of the hail depends on:
- Updraft strength: The higher the vertical wind speed (up to 160 km/h in severe storms), the longer the hail remains in the cloud and the larger it grows.
- Available moisture: The more water vapor there is, the more ice layers accumulate.
- Cloud temperature: Very cold temperatures (below -20°C) favor rapid growth.
The largest hail recorded in South America fell in Villa Carlos Paz, Argentina, in 2018, with a diameter of 14 cm, similar to a soccer ball. Fortunately, such events are extremely rare.
Destructive Power by Size
The impact of hail depends not only on its diameter but also on its terminal velocity. A 2 cm hailstone falls at about 70 km/h, while a 10 cm one can exceed 150 km/h. Kinetic energy increases with the square of the velocity, so damage grows exponentially.
Damage to Agricultural Crops
In countries like Argentina, Brazil, Chile, and Uruguay, hail is a constant threat to agriculture. The most vulnerable crops are:
- Soybeans and corn: Hail of 1 cm can already damage leaves and reduce yield.
- Vineyards and fruit trees: Hail of 2-3 cm breaks branches and fruits, causing millions in losses.
- Vegetables and flowers: Any hail larger than 0.5 cm can destroy entire plantations.
In the Cuyo region of Argentina, a single hailstorm in 2023 affected 15,000 hectares of vineyards, with losses estimated at 50 million dollars.
Damage to Infrastructure and Vehicles
- House roofs: Hail of 2-3 cm can puncture fiber cement or plastic tiles. From 5 cm onward, metal roofs dent and may collapse.
- Cars: With hail of 1.5 cm, dents appear. From 4 cm onward, windshields break and the body suffers severe damage.
- Solar panels: These are especially sensitive. Hail of 2 cm can crack photovoltaic cells.
Practical Tips for Protecting Yourself from Hail
When facing the threat of hail, preparation is key. Here are some tips based on the experience of farmers and insurers:
- Monitor weather alerts: Use apps like Contingencias to receive real-time notifications about storms with hail.
- Protect your crops: Install anti-hail nets on vineyards and fruit trees. For extensive crops, take out agricultural insurance.
- Secure your home and vehicle: Check that your insurance covers hail damage. Park your car under cover if there is a warning.
- During the storm: Stay indoors, away from windows. Do not go out to protect objects; your safety comes first.
Conclusion
The size of hail is the most determining factor of its destructive power, but not the only one. Fall speed, ice density, and the vulnerability of what it hits also matter. Knowing the classification of hail and its associated risks allows for informed decisions to protect lives, crops, and property.
In South America, where severe storms are becoming more frequent due to climate change, being prepared and having early warning tools makes the difference between a minor loss and a catastrophe.