The “White Plague” that people have been familiar with for centuries is actually a vernacular term for tuberculosis, but borrowing it to describe the unpleasant effects of a hail storm might be appropriate. Hail does not kill as many people as tuberculosis, but it does an incredible amount of damage every year: in the U.S. alone, average losses to property and crops are well over one billion dollars. The costliest hailstorm on record did two billion dollars’ worth of damage to the Kansas City area in a single day in April, 2001.
Hail forms when water droplets are carried up and down inside a thunderstorm. Warm updrafts carry water aloft to the upper part of the storm, where they freeze and are either pushed downward by cold downdrafts, or fall on their own due to gravity. Sometimes they are caught again by another updraft, and the process can repeat itself several times, each cycle building another layer of ice on the growing hailstone, like layers on an onion. Eventually, the hailstone will become too heavy to be lifted by the updrafts, and falls to the ground. Most hail is very small, and hail over two inches in diameter is rare. Only the largest and most powerful storms, like the supercells that can produce tornadoes, are capable of generating hail of awe-inspiring proportions, the kind described in reports as “baseball-sized” or even larger. Very large hail is almost always formed of several smaller hailstones that have frozen together, and has an irregular, lumpy appearance. According to the National Weather Service, hail over three-fourths of an inch in diameter, or “penny-sized,” is considered severe, and capable of causing significant damage.
The damage caused by hail is a matter of simple physics. Gravity and downdraft winds can propel a small hailstone at 90 miles per hour or more, sufficient force to break a window, shatter a roof tile, or dent sheet metal on a car. Heavier and faster hailstones carry even more momentum. Multiply the effects of one of these little icy bullets by hundreds of millions falling in a very short time over a relatively small area, and the results can be grim. The biggest losses due to hail every year are in crops. A hailstorm of even modest proportions can flatten entire fields, destroying a harvest. Hail might actually be good for business for people in the roofing and auto body repair businesses, but for farmers hail truly is a “white plague,” and one that they are completely powerless to prevent.
Learn more at:
National Weather Service; information about hail:
http://www.erh.noaa.gov/er/cae/svrwx/hail.htm
Federal Alliance for Safe Homes; description of hail damage hazards:
http://www.flash.org/activity.cfm?currentPeril=5&activityID=164
Sakatchewan Lung Association; all about tuberculosis:
http://www.lung.ca/tb/abouttb/what/
