Severe Thunderstorm & Hail

Severe Thunderstorms and Hailstorms

A thunderstorm is formed by atmospheric imbalance and turbulence caused by: (1) the rapid rising of unstable warm air into the atmosphere, (2) a sufficient amount of moisture to form clouds and produce rain, and (3) the collision of separate weather fronts (warm and cold) creating an upward lift of air currents. These conditions may result in severe thunderstorms, heavy rains (which may cause flash flooding), and strong winds reaching or exceeding 58 mph, tornadoes, or hail of at least 0.75 inches in diameter. 

Thunderstorms are common in Iowa and can occur singly, in clusters, or in lines. Most thunderstorms produce only thunder, lightning, and rain. Severe storms however, can produce tornadoes, high straight-line winds above 58 mph, microburst, lightning, hailstorms, and flooding. High straight-line winds, which can often exceed 60 mph, are common occurrences and are often mistaken for tornadoes.  Lightning occurs with all thunderstorms even if the buildup of electricity isn’t strong enough to send a bolt to the ground.

Between 1950 and 2010 there have been 455 severe thunderstorm, high wind, lightning, and hailstorm events that have affected Linn County.  These severe weather events were responsible for 2 deaths, 18 injuries, and $26 million in damages.

Common Hailstone Size Comparisons

Common Coin Sizes
Dime = 0.70 in          /          Penny = 0.75 in

Nickel = 0.83 in        /          Quarter = 0.955 in

Dollar = 1.04in        /           Half Dollar = 1.02 in

Other Objects  
Object   Diameter  
Inches Meters
Pea 0.24 5-9
Small Marble   0.51 10-15
Walnut/Ping Pong Ball 1.5 16-20
Golfball 1.7 21-30
Lime/Hen Egg 2.0 31-40
Tennis Ball 2.5 41-50
Baseball 2.8 51-60
Apple/Tea Cup 3.0 61-75
Grapefruit 4.3 76-90
Softball  4.5 91-100
Computer CD 5.0 >100

Typical HailDiameter (mm)   Typical Damage Impacts
5 No damage
5-15 Slight general damage to plants, crops
10-20 Significant damage to fruit, crops, vegetation
20-30 Severe damage to fruit and crops, damage to glass and plastic structures, paint and wood scored
25-40 Widespread glass damage, vehicle bodywork damage
30-50 Wholesale destruction of glass, damage to tiled roofs, significant risk of injuries
40-60 Bodywork of grounded aircraft dented, brick walls pitted
50-75 Severe roof damage, risk of serious injuries
60-90 Severe damage to aircraft bodywork
75-100 Extensive structural damage. Risk of severe or even fatal injuries to persons caught in the open
>100 Extensive structural damage. Risk of severe or even fatal injuries to persons caught in the open



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