Minnehaha and Lincoln County Hazard Information Type of Hazard Summer Storms Definition: Severe summer storms are generated by temperature imbalances in the atmosphere, and as warm, moist air rises the thunderstorm develops. These conditions will produce updrafts and downdrafts. Both the updrafts and downdrafts can reach velocities of 170 MPH. Updrafts and downdrafts are the reason for gust fronts, heavy rain (flash flooding), lightning, hail, and high winds. Downburst or straight-line winds can be as deadly as tornadoes. If the thunderstorm continues to intensify, a tornado may develop. Listed below is an explanation of summer storm conditions.
Downbursts/ Straight Line Winds form along the leading edge of a thunderstorm. They are intense concentrations of sinking air which can fan out upon striking the earth’s surface producing damaging ‘straight’ winds. Frequently, damage attributed to tornadoes is caused by straight line winds from a downburst. Downbursts can produce a ‘roaring’ sound and damage similar to a tornado but are not tornadoes because the winds do not rotate. They don’t tend to last long but can approach 100 mph. Hail is precipitation in the form of a lump of ice that forms during some thunderstorms. A hailstone can range in size from a pea to a grapefruit. They are usually round but can be conical or irregular in shape. The major hazard is to crops, aircraft, automobiles, roofs and windows. Hail tends to fall in swaths ranging from 20 to 150 miles in length and 5 to 30 miles wide. The destructiveness of hailstorms is not just from the hail alone but it’s accompaniment of wind and rain. This makes it difficult to exact the damage caused by hail. Lightening is produced by the interaction of charged particles producing an intense electrical field witin a thunderstorm’s cloud. Lightening occurs in attempt to balance the positive and negagive electrical charges between the storm and the earth’s surface. Electrical potential in lightening storms can equal 100 million volts. Tornadoes are the most violent weather phenomenon known to man. Tornadoes are generally defined as violently rotating columns of air that are in contact with the ground. A tornado may last from a few seconds to more than an hour. A tornado can remain nearly stationary or move through the countryside at speeds up to 70 mph with wind forces ranging from 100 to 250 mph. Flash Floods are capable of developing from severe summer storms due to heavy rains. Flash floods are discussed in the section detailing Floods.