Classic severe weather setup brings strong storms to Missouri
Thursday featured a typical severe weather setup for any season, especially in winter when less energy is needed for storms.
The ingredients for severe weather were all provided by an approaching front and a trough of low pressure ahead of it. These key factors are sometimes called the "SLIM" ingredients.
Though it sounds like a diet trend, "SLIM" stands for shear, lift, instability, and moisture. These elements often work together in severe weather forecasting.
Shear refers to winds that change direction and speed with altitude, which can cause storms to rotate if enough shear is present. On Thursday, surface winds were from the southwest, while higher winds were more westerly, and this difference can cause storms to turn.
Lift is necessary to raise moist air from the ground into the air for clouds. Lift was supplied by the approaching cold front.
Instability was less certain in this forecast, but even in winter, a little can go a long way. Temperatures were over 20 degrees above average, providing sufficient energy for storms.
Moisture is closely related to instability and temperature—warmer air holds more moisture and is more energetic. Water can store heat, allowing moist air to stay buoyant longer.
South of us, there was much heavier moisture and instability, resulting in damaging winds, large hail, and tornadoes in Oklahoma and parts of Kansas.
Low-level winds carried some of that moisture and energy into our area, resulting in heavy rain and loud thunder early in the day.
A short-lived tornado warning was issued in St. Clair County, southwest of the Lake of the Ozarks, based on radar-indicated rotation, though no official tornado reports have been received.
