The National Weather Service held its annual advanced weather spotter training class on May 8 at the ANB Bank Center in the Pathfinder Building. This event was open to people of all ages and featured lead forecaster Jared Allen.
Tornadoes and severe weather in general were discussed at length; peak tornado season in southeast Wyoming occurs between mid May and mid June (even though tornadoes have been reported as late as August).
Allen mentioned that super cell thunderstorms (storms that rotate) need four key ingredients: Instability, Lifting mechanism (such as a front), moisture, and wind shear. Instability, otherwise known as Convective Available Potential Energy or CAPE, is a measurement of how stable or unstable the atmosphere is. The Higher the CAPE values are, the more unstable the atmosphere is. There are points where there can be high CAPE values, but nothing will happen due to the fact that there may be a strong inversion in the atmosphere.
The second key ingredient that a super cell storm needs is a lifting mechanism, Allen said. Imagine somebody wearing a baseball cap. If the cap stays on, hair stays in place and nothing happens, but if the cap is removed, hair goes crazy. Same thing happens with a thunderstorm. If the cap remains firmly in place nothing will happen, but if a front moves through, this allows storms to blossom.
The third key ingredient is moisture. Most of the moisture that generally fuels severe thunderstorms comes from the Gulf of Mexico.
The fourth and final key is wind shear. Wind shear, according to Allen, is turning of the winds with height. Let’s say somebody had a fan facing east and had it on high, and had another fan facing the north with a decrease in wind speed at the same point. Wherever those winds intersect, they start to roll in the horizontal. If a storm is strong enough and basically overtakes the wind shear, that horizontal tube will go into the vertical, which causes the storm to rotate. If the rotation elongates and tightens up, a mesocyclone and wall cloud will form. If it tightens up even further, there is the potential for a tornado to form.
This event concluded with attendees learning to forecast the storm that hit southeast Wyoming on Monday, May 6.