Hail Definition, Causes, and Formation

Hail Definition, Causes, and Formation Hail is a form of precipitation that falls from the sky as pellets of ice. The pellets can range in size from small pea-sized pellets to hailstones as large as grapefruits (more on hail size below). The formation of hail means a severe thunderstorm is likely in your vicinity. You should monitor your weather situation closely for thunder, lightning, torrential rain, and possibly even tornadoes. Not a Winter Weather Event Because its made of ice, hail is often mistaken as a cold weather event, but in reality, it is associated with severe thunderstorms  - not winter weather.    While hailstorms technically can occur year-round, some of the most destructive hail events have occurred at  the height of summer. (This makes sense seeing as how  hail is associated with thunderstorms, and thunderstorms, in turn, are most common in the summertime when theres an abundance of heat in the atmosphere to help fuel their development.)   Hail Forms High Up, in Cold Clouds If hail is a summer rather than winter weather event, how do temperatures get cold enough to form ice? Hailstones  form inside of cumulonimbus clouds that can tower at heights of up to 50,000 feet. While the lower regions of these  storms contain warm air, the upper regions are below freezing. strong updrafts  Ã‚   Updrafts within the storm system can whisk raindrops up into this sub-zero region, causing them to freeze into ice crystals. These ice particles are then carried back down into the clouds lower levels by the downdraft where it thaws  and collects additional water droplets  and back up via the updraft where it re-freezes. This  cycle may continue  multiple times. With each trip above and below the freezing level, a new layer of ice is added to the frozen droplet until it  grows too heavy for the updraft to carry it. (If you cut a hailstone in half, you would see alternating concentric layers inside it, resembling tree rings.) It  then falls out of the cloud to the ground. The stronger the updraft, the heavier a hailstone it can carry, and the longer that hailstone cycles through the freezing process (that is, the larger it grows). Short-Lived Storms Hail usually forms over an area and leaves within a few minutes. However,  there have been instances when it stayed in the same area for several minutes, leaving several inches of ice covering the ground. Hailstone Size and Speed Hailstones are measured according to their diameter. But unless you have a knack for eyeballing measurements  or are  able to slice a  hailstone in half, its easier to estimate its size by comparing it  to everyday  items. Description Size (Diameter) Typical Fall Speed Pea 1/4 inch Marble 1/2 inch Dime/Penny 3/4 inch 43 mph Nickel 7/8 inch Quarter 1 inch 50 mph Golf Ball 1 3/4 inch 66 mph Baseball 2 3/4 inch 85 mph Grapefruit 4 inch 106 mph Softball 4 1/2 inch To date, the largest hailstone recorded in the U.S.  fell in Vivian, South Dakota  on July 23, 2010.  It measured 8 inches in diameter, 18.2 inches around, and weighed 1 pound 15 ounces. The velocity of hail varies by shape and size. The largest and heaviest can fall at speeds upwards of 100 mph! Hail Damage With their hard exteriors and relatively fast fall speeds, hailstones often cause extensive damage. On average, over $1  billion dollars in damage to crops and property is sustained each year in the U.S. The most susceptible objects to hail damage include  vehicles  and roofs.   One of the most costly hail events in  recent weather history occurred in  June 2012 when severe storms crossed over  the Rockies and Southwestern U.S. causing  over $1.0 billion dollars in damage  in the state of Colorado. The Top 10 Hail-Prone Cities in  the U.S. Amarillo, TexasWichita, KansasTulsa, OklahomaOklahoma City, OklahomaMidwest City OklahomaAurora, ColoradoColorado Springs, ColoradoKansas City, KansasFort Worth, TexasDenver, Colorado