SECTION 4: RISK ASSESSMENT
Average Diameter 1.75 inch 2.0 inch 2.5 inch 2.75 inch 3.00 inch 4.00 inch
Corresponding Household Object
Golf ball Hen egg
Tennis ball
Baseball Teacup
Grapefruit
4.5 inch
Softball
Source: National Weather Service
The Tornado and Storm Research Organization (TORRO) has further described hail sizes by their typical damage impacts. Table 4.99 describes typical intensity and damage impacts of the various sizes of hail. Table 4.99 – Tornado and Storm Research Organization Hailstorm Intensity Scale
Intensity Category Hard Hail Potentially Damaging Significant
Diameter (mm)
Diameter (inches)
Size Description
Typical Damage Impacts
5-9
0.2-0.4
Pea
No damage
10-15
0.4-0.6
Mothball
Slight general damage to plants, crops
16-20
0.6-0.8
Marble, grape Significant damage to fruit, crops, vegetation
Severe damage to fruit and crops, damage to glass and plastic structures, paint and wood scored Widespread glass damage, vehicle bodywork damage Wholesale destruction of glass, damage to tiled roofs, significant risk of injuries Bodywork of grounded aircraft dented, brick walls pitted
Severe
21-30
0.8-1.2
Walnut
Pigeon’s egg > squash ball Golf ball > Pullet’s egg
Severe
31-40
1.2-1.6
Destructive
41-50
1.6-2.0
Destructive
51-60
2.0-2.4
Hen’s egg
Tennis ball > cricket ball Large orange > softball
Destructive
61-75
2.4-3.0
Severe roof damage, risk of serious injuries
Destructive
76-90
3.0-3.5
Severe damage to aircraft bodywork
Extensive structural damage. Risk of severe or even fatal injuries to persons caught in the open Extensive structural damage. Risk of severe or even fatal injuries to persons caught in the open
Super Hailstorms
91-100
3.6-3.9
Grapefruit
Super Hailstorms
>100
4.0+
Melon
Source: Tornado and Storm Research Organization (TORRO), Department of Geography, Oxford Brookes University Notes: In addition to hail diameter, factors including number and density of hailstones, hail fall speed and surface wind speeds affect severity.
The average hailstone size recorded between 1998 and 2023 in Wake County was a little over 1” in diameter; t he second largest hailstone was 2.75”, recorded on September 1, 2017. This storm resulted in a recorded $10 million in property damage per NCEI. The largest hailstone ever recorded in the U.S. fell in Vivian, SD on June 23, 2010, with a diameter of 8 inches and a circumference of 18.62 inches.
Impact: 1 – Minor
Hailstorms frequently accompany thunderstorms, so their locations and spatial extents coincide. Wake
Wake County, NC Multi-Jurisdictional Hazard Mitigation Plan
WSP June 2024 Page 191
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