A busy tornado season is expected to kick off in South Dakota this month. According to AccuWeather, there's a good chance that between 200 and 275 tornadoes will develop in April -- well above the average of 155.
Last night's derecho in eastern South Dakota and parts of western Minnesota left a trail of severe weather damage, including at least one confirmed tornado. Governor Kristi Noem visited Castlewood Thursday to see the damage.
Weather patterns for tornadoes in South Dakota vary by county. Historically, eastern South Dakota is much more susceptible to tornadoes, according to Greg Harmon, a meteorologist with the National Weather Service’s Sioux Falls office.
While no single factor is responsible for this inconsistency, Harmon notes that the same climate factors that generally limit row crops to the east of the state also drive tornado activity in the west.
The Black Hills, which are sometimes referred to as an island rising out of a sea of grass, have a pleasantly semi-arid climate with mild winters and warm summers. Although summer temperatures are mild, the region does experience some dramatic thunderstorms.
In the winter, Rapid City typically sees snow accumulation of a few inches. Storms from the northwest can deliver heavy wet snow early in the season, while those that travel from the north tend to bring drier snow later on.
In 1971, University of Chicago meteorologist Ted Fujita created the F Scale to separate tornadoes into categories based on wind speed and damage. The scale was later adopted by the National Weather Service and now is known as the Enhanced Fujita Scale.
In South Dakota, the most common type of tornado is an EF2 tornado, which has sustained 85-110 mph winds. It has occurred 306 times in the state, and is responsible for 16 deaths and 396 injuries.
Another common type is an EF3 tornado, which has 110-140 mph winds. It has impacted the Prairie Coteau area in Deuel County and caused major damage in that region.
Tornadoes are one of nature’s most destructive events and can destroy entire towns in a matter of minutes. They are formed by a combination of heat, moisture and dry air from the south, northwest and southwest that clash in central North America.
The resulting super-cell thunderstorms spawn tornadoes that can be anywhere in the country, but tend to occur in a region called Tornado Alley. They travel at fast speeds and carry heavy loads of debris.
Taking shelter when a tornado is approaching can save lives and prevent serious injury or property damage. When possible, go to an interior room or hallway on the lowest level of your home or office. Stay clear of windows, doors and outside walls as debris will fly into these areas.
When a tornado warning is issued, citizens should seek shelter immediately. The best places to take shelter are in a basement or a storm cellar or the lowest floor of a sturdy nearby building.
If there is no basement, seek shelter in a central part of your home in a small room on the lowest level, like a closet or interior hallway. Be sure to cover yourself with pillows and blankets.
Tornadoes move rapidly and can rip through homes, vehicles or other structures at any time, making it difficult to escape. If a vehicle is in the path of a tornado, abandon it and go to a low place away from buildings such as a ditch or ravine.
A tornado also can destroy livestock, such as cows and goats. For this reason, it's important to keep cattle and other animals well-fed, watered and protected from severe weather, according to the Nebraska State Patrol.