Severe Storms and Tornadoes

Without water from rain, humans would not be able to survive. The processes that create rain are as important to our lives as the blood that runs through our bodies. Unfortunately, when conditions in our atmosphere are just right, these precipitation processes bring as much harm as good.

Severe storms and tornadoes often bring violent weather conditions that can destroy entire towns within moments.

Severe Storms
A storm is considered severe when it contains one or more of the following:

• 58 mile per hour wind gusts or stronger
• ¾ inch diameter hail or larger
• tornado

Severe storms are most common during late spring across the Midwest. These storms occur as low pressure weather systems make their way across the country.

Warm moist air from the Gulf of Mexico pushes northward ahead of low pressure systems. This warm moist air is then pushed upward by the cooler, less humid air behind the cool front. The interaction between the contrasting air masses is typically a major factor in severe storm development.

Not every low pressure system will produce severe weather, but there are several surface weather characteristics that can make it more likely.

• Extremely low central pressure within the storm
• Decreasing pressure at the center of the low
       (often called a strengthening or deepening low)
• High dew points (lots of moisture) east of the cold front
• Extremely different dew points on opposite sides of the cool front

If the upward motion within the clouds becomes strong, rain can be produced more quickly and a downdraft will begin to form. As this downdraft air reaches the ground, it spreads out rapidly producing strong gusty winds. When these winds top 58 miles per hour, the storm will be considered “severe”. On a few occasions these “downburst” winds have reached 130 miles per hour.

Upward motion can be produced in several ways.
As the cold front moves into the warm moist air mass, the warm air is forced upward. Cool air rushes downward to take its place - this is a downdraft. If the updraft is strong enough, hail will form. Hail will grow within the storm until it becomes heavy enough to fall through the updraft or until the updraft weakens.

Hail can do a great deal of damage to anything on the ground. Imagine a storm of baseballs coming down from the sky at 100 miles per hour and you begin to get an idea of how dangerous hail can be.