When forecasting for severe weather season, there are different ingredients that determine if thunderstorms will develop and if they could become severe, said Storm Center 7 Meteorologist Kirstie Zontini.
For typical thunderstorm development you need:
- Lift (a cold front or disturbance)
- Instability (density differences allows for parcels of air to rise freely and quickly)
- Moisture (especially the low levels, how high are dew points)
For storms to become severe, something called shear is needed. There are two types — speed and directional.
- Speed shear is the change of wind speed with height
- Directional shear is the change in direction of the wind with height
>>Tornado Sirens: Where are they, how they work
The combination of speed and directional shear or the presence of just one or the other can help determine the type of severe storms (organized lines, tornadoes, etc.)
If all four ingredients (S.L.I.M) are present, then there’s a threat for severe storms.
>> Tornado vs. Straight Line Winds: Why both are dangerous