Imagine a baseball dropped from an airplane flying at 30,000 feet ... imagine that baseball reaching speeds of 120 MPH as it falls to the ground ... and imagine you're under it!
Imagine you're driving along at 70 MPH...or your crops are under the hail producing thunderstorm...or your home is under the thunderstorm...
Hail causes $1 billion dollars in damage to crops and property each year
How does hail form?
- Inside of a thunderstorm are strong updrafts of warm air and downdrafts of cold air.
- If a water droplet is picked up by the updrafts...it can be carried well above the freezing level. With temperatures below 32F...our water droplet freezes.
- As the frozen droplet begins to fall...carried by cold downdrafts...it may thaw as it moves into warmer air toward the bottom of the thunderstorm
- But...our little half-frozen droplet may also get picked up again by another updraft...carrying it back into very cold air and re-freezing it. With each trip above and below the freezing level our frozen droplet adds another layer of ice.
- Finally...our frozen water droplet...with many layers of ice - much like the rings in a tree...falls to the ground - as hail!
Estimating Hail Size
Pea = 1/4 inch diameter
Marble/mothball = 1/2 inch diameter
Dime/Penny = 3/4 inch diameter - hail penny size or larger is considered severe
Nickel = 7/8 inch
Quarter = 1 inch
Ping-Pong Ball = 1 1/2 inch
Golf Ball = 1 3/4 inches
Tennis Ball = 2 1/2 inches
Baseball = 2 3/4 inches
Tea cup = 3 inches
Grapefruit = 4 inches
Softball = 4 1/2 inches
Hail size distributions tend to be localized with some roofs damaged, while others are not. Wind direction plays an important role, as well as roof pitch. A direct impact of hail on a shingle is more damaging than that of a glancing blow. Figure below illustrates the dynamics of hail impact on two different roof pitches.
Many roofs carry this rating. For steep slope, these roofs include some metal roofs, some tile and some composition shingles. For flat roofs, these are some gravel-surfaced built-up, and some spray foam (with the right coating system), and just a few others.
Installing a Class IV hail resistant roof may qualify you for lower insurance premiums, depending on where you live. Call your agent for verification. Keep this in mind, too, not many agents and adjusters will know the specifics about hail resistant roofs. Consult either a good roofing contractor.
The home on the left would sustain more roof damage than that on the right, because of the more direct impact on the left as opposed to the less damaging, glancing, blow to the right. Wind conditions can distort damage to a home as illustrated in Figure below. The home on the left has more glancing blows to the roof from the wind, while the windward wall comes under attack from direct hail impact.
The right wall is protected and undamaged from the hail. The home on the right will more likely sustain roof damage on the windward side because of the more direct impact. Assessing hail damage is often accomplished by a roof inspection, which usually occurs several days to several months after the hail event. Determination of whether hail actually fell at a site can be made through statements and weather reports. Inspection of thin, aluminum fixtures helps verify hail impact.