LITTLE ROCK, Ark. – Thursday, March 3, 2022: The National Weather Service, in cooperation with the Arkansas Department of Emergency Management, has proclaimed the week of February 27th through March 5th as Severe Weather Awareness Week in Arkansas. A different topic is being discussed each day. Thursday’s topic is Severe Thunderstorms.
At any given moment around the world, approximately 1800 thunderstorms are occurring. Lightning, flash floods, hail, straight-line winds, and tornadoes all result from thunderstorms. Although thunderstorms are relatively small, when considered on a global scale of weather, all thunderstorms are dangerous, but all are not severe.
A thunderstorm is considered severe when it produces winds of at least 58 mph, hail of at least 1 inch in diameter (the size of a quarter), and/or a tornado. Hail forms in storm clouds where the air is subfreezing. Updrafts which feed storm clouds drive raindrops skyward, and liquid turns to ice. Quite often, hailstones will fall through the cloud, collect water, and updrafts will force them aloft. The stones refreeze and get larger.
The largest hailstone on record in the U.S. fell Vivian, SD, July 23, 2010. It is recorded to have a diameter of 8″ and a weight of nearly two pounds. However, before verified, it was reported to have a diameter of 11″. A basketball has a diameter of 9.5″. That hailstone is preserved at the National Center of Atmospheric Research.
The largest hail in Arkansas in 2021 happened on March 27th. Baseball size and slightly larger stones were reported at Gurdon (Clark County), South Bend (Lonoke County), and Whelen Springs (Clark County). Large hail, on average, causes over one billion dollars in damage (property and crops) in the United States each year. However, there are instances of hailstorms costing $2-3 Billion in damage when they have hit in metropolitan areas. While large hail causes some injuries, deaths from hail are relatively rare. Animals fare far worse than humans.
When updrafts are overcome by rain and hail in storms, air from aloft can descend in a hurry. When these downdrafts hit the ground and spread out in all directions, damaging straight-line wind gusts sometimes result. Some of the strongest gusts in 2021 in Arkansas occurred across northern sections of the state on May 4th. Gusts from 85 mph to more than 90 mph were noted at Hoxie (Lawrence County), Manson (Randolph County), and near Paragould (Greene County). From 2011 to 2021, damaging wind accounted for 21 deaths in Arkansas. Across the country, damaging wind accounts for 60 deaths per year on average.
Occasionally, thunderstorms spawn tornadoes. Most of these are produced in the spring and fall during the afternoon and evening. There are 37 tornadoes in a typical year. There were 35 tornadoes locally in 2021, and these resulted in two fatalities.
All thunderstorms have lightning, but no amount of lightning can make a storm severe. Whenever thunder is heard, there is lightning nearby. Lightning is deadly, especially in the summer when people are outdoors.
The occurrence of Flash floods is another thunderstorm hazard. Vehicles driven into flooded areas result in the greatest number of flash flood deaths. Across the country, the top three deadliest thunderstorm hazards in the last 30 years years were flash floods, tornadoes, and lightning (in that order).
…Some Severe Weather Safety Rules…
1: Know the difference between a watch and a warning. The National Weather Service issues watches when conditions are favorable for the development of severe weather. Warnings are reserved for cases where severe weather is imminent or occurring.
2: If a Severe Thunderstorm Warning or Tornado Warning is issued for your area, do not hesitate to find a place of safety. If a safe room is not available, the next best location is the lowest floor of a permanent structure in an interior room away from windows. Put as many walls between you and the outdoors as you can.
3: Have a source to receive the latest information, such as Arkansas Storm Team Coverage on KARK 4 and FOX 16, the Arkansas Storm Team App, NOAA Weather Radio All Hazards, commercial radio, or cable TV. Other sources of warning information can include telephone notification services, to which people subscribe, and cell phones.