The ingredients of a thunderstorm

 

After a warm and sunny morning, a few showers moved through Michiana Monday afternoon.

And while we've heard a few rumbles of thunder in 2021, Michiana is still waiting for our first widespread thunderstorm activity of the year.

It's worth reviewing the ingredients that make a thunderstorm as severe weather season approaches. 

Meteorologists (like myself) often focus on four main factors: humidity (or moisture), instability, lift and shear. 

Humidity

Thunderstorms are dependent on warm and humid air near the ground. Typically, thunderstorms do not form unless surface dew points are above 55 degrees. One reason for the lack of storm activity across Michiana Monday was the dry air in place. Even with rain showers, most dew points were at or below 50 degrees. 

Instability

Instability is a measure of how much fuel a potential storm has to use from the atmosphere around it. We usually look at storm energy values, or CAPE (Convective Available Potential Energy), to see how likely thunderstorm development is on a particular day. Generally speaking, the higher the energy values, the higher storm chances are. Additionally, it's more likely those storms could be strong or severe with high CAPE values.

The biggest driver of instability is sunshine! The sun warms the ground along with air near the ground. When combined with colder air aloft, this usually leads to fast-rising pockets of air, which enhances the environment for thunderstorm development. The batch of showers early Monday afternoon likely cut off some storm energy across Michiana (which was already pretty low to begin with).

(Sources of) Lift

You can have all of the humidity and energy you want, but until you have something to lift that energized air upward, you (typically) don't have a thunderstorm. There are MANY possible sources of lift, but one of the most common ones is a front. A warm/stationary front was the forcing for Monday's showers. Stationary fronts typically don't produce strong thunderstorms, especially so early in the season. Another common source of lift for Michiana is due to differential heating, which leads to low-level convergence. This is what's happening when we see storms fire up because of the lake breeze during the summer! 

Shear

Shear is often the biggest factor in a thunderstorm going from ordinary to severe (defined as a storm with wind gusts of 58+ mph/1" hail or larger). Shear is the change in wind speed and/or direction with height. If winds are in the same direction but increase in speed with height, straight-line wind damage is usually a concern for forecasters. If there is a big change in wind direction with height (especially in the lowest levels of the atmosphere), tornadoes are a possibility. While there was a decent amount of shear near the lake on Monday, the lack of other storm ingredients made the threat of severe weather quite low across Michiana. 

While Michiana has a few more opportunities for rain this week, widespread thunderstorm activity is not expected. Typically, our area's storm season is during the summer months (June, July and August). 

Be sure to stick with ABC57 News for the latest forecast updates.