Thunderstorms can be disruptive to businesses, and business owners must prepare well in advance for the wide variety of dangerous conditions that thunderstorms can bring.
Thunderstorms can occur any time of day year round, but are most common in the summer afternoons and evenings. The National Weather Service considers a thunderstorm severe if it produces hail at least three-quarters of an inch in diameter, has winds of 58 miles per hour or higher or produces a tornado. All thunderstorms produce lightning, which can be deadly. Virginia averages 35 to 45 thunderstorm days per year.
The National Weather Service issues watches and warning for severe thunderstorms. A severe thunderstorm watch means that conditions are favorable for the formation of a severe thunderstorm. A severe thunderstorm warning means that a severe thunderstorm has been sighted or has been indicated on NWS Doppler radar.
Every year, portions of Virginia are impacted by severe thunderstorms producing large hail measuring 0.75-inch (penny size) or larger. Rarely, however, does the hail reach tennis ball size (2.5 inches) or larger. This large hail occurs once or twice per year on average. A particularly severe hailstorm on May 9, 2003 caused extensive damage to trees, crops, homes and some businesses and crops across portions of central and interior southeast Virginia. Areas from Amelia and Powhatan counties to Southampton County were most impacted by hailstones ranging from golfball size (1.75 inches) to softball size (4.5 inches).
Downburst winds annually affect many areas of the Commonwealth. In general, these sustained winds of 50 mph or greater are strong enough to blow large limbs out of trees or to down trees. Winds exceeding 60 mph can cause structural damage to homes and businesses and cause more extensive damage to trees and power lines, creating isolated and sporadic damage. Occasionally, a strong line of thunderstorms will produce winds exceeding 70 mph over a large area, causing extensive, occasionally severe, damage.
Lightning is random and unpredictable and second only to flash floods in causing deaths in the United States. Temperatures of lightning can reach 50,000°F with speeds approaching one third the speed of light.
All areas in Virginia are equally vulnerable to the impacts of thunderstorms. While severe thunderstorms are not as common in Virginia as they are in the Midwest, Plains and deep South, large hail and damaging downburst winds can damage businesses. Severe thunderstorms are most common between the months of April and August, although they have affected the Commonwealth in every month of the year.
Virginia has more than 300,000 lightning strikes per year, with the majority occurring during the summer months. Though southeastern Virginia tends to receive the most lightning strikes of any other region in Virginia, all areas of the Commonwealth have the potential for lightning strikes. See U.S. Lightning Map. [external link -- opens in new browser window]
During thunderstorms, lightning strikes can suddenly expose a business' electrical circuit to a large surge of energy, adversely affecting the equipment. Blackouts are also possible.
United States insurance company statistics show one homeowner's damage claim for every 57 lightning strikes. In the United States, lightning annually causes more than 26,000 fires, with damage to property in excess of $5 billion to $6 billion (source: NLSI).
Lightning can kill people who are inside a modern building and talking on the telephone, bathing or showering, washing at the kitchen sink, touching electrical appliances or touching or near a metal door or window.
Thunderstorms can develop in less than 30 minutes, allowing little time for warning. The National Weather Service does not issue warnings for ordinary thunderstorms or for lightning. The NWS does highlight the potential for thunderstorms in daily forecasts and statements. Be alert to the signs of changing weather, such as darkening skies, a sudden windshift and drop in temperature. Get a warning device such as a NOAA Weather Radio. Staying alert and listening to a NOAA Weather Radio could mean the difference between life and death when a thunderstorm hits.