Severe weather season is well underway in the Miami Valley and relatively speaking, we have seen a fairly active start with several storms producing multiple tornadoes in the area and significant straight line wind damage.
Each weather set-up is different and requires us to look at them differently. When forecasting for severe storms, there are several factors that we analyze for storm development including: shear, lift, instability and moisture or SLIM. It is how the ingredients come together that can determine how strong the storms will become and what kind of weather hazards will form.
Lift can come from any driving force that does exactly that, provide lift to a parcel of air. A warm or cold front, upper level energy or terrain, like mountains, can all provide the lift needed to begin the process.
Meteorologists often speak about instability, which is another very important and interesting factor that is vital for storm development. Think of instability as a hot air balloon. As it warms, it becomes less dense than the air around it and thus, begins to lift. If a parcel of air is warmed, it will become more buoyant and its ability to rise and produce thunderstorms increases.
The amount of moisture in the air is another very important ingredient we monitor. The Gulf of Mexico is typically our source of atmospheric moisture. The greater the moisture content, the higher the dew points and better potential for storms.
For a thunderstorm to become strong or severe, we also look for the presence of what’s called, shear. Generally speaking, this is the change of wind speed or direction with height. This weather phenomena can take a ‘garden variety storm’, and amplify it into one much larger and stronger than it originally was. Different combinations of speed and directional shear can lead to different types of severe weather. Speed sheer is often associated with storms that produce strong to damaging winds. That, combined with directional shear, can lead to rotation within a storm promoting tornado development.
No two weather scenarios are the same. For this reason, we monitor closely, not only the strength of each of the ingredients, but also the combination of them and how they are interacting with one another. The slightest change in the strength of lift and instability, the amount of moisture or fluctuation of sheer will greatly impact the outcome of a system; causing a storm to either rapidly diminish or intensify.
Kirstie Zontini, a WHIO StormCenter 7 meteorologist, is filling in today for Eric Elwell, WHIO StormCenter 7 Chief Meteorologist. Follow them both on Facebook and Twitter.