NORTH CAROLINA -- Just like grandma's apple pie, a severe weather outbreak needs the proper ingredients. Ideally, four are needed. These include instability, wind shear, lifting, and moisture. And, the better the "quality" the more likely a severe weather event unfolds. So, let's quickly break each one down.

1. Instability: This refers to the condition when air will rise freely in the vertical due to positive buoyancy. The more instability, the higher the threat of severe weather. For example, warm is less dense than cold air. So, when you have warm air being created near the ground due to solar heating, and cold air high up in the atmosphere this will lead to instability.

2. Wind Shear: There are two types. Speed and directional. Speed shear is a significant increase of wind speed with height. This will tilt the storms updraft allowing the storm to sustain itself. Directional shear is the change of wind direction with height. This will allow storms to rotate.

3. Lifting: This refers to different mechanisms such as cold and warm fronts, outflow boundaries, and others. These mechanisms will aid vertical motion and instability.

4. Moisture: Bottom line, the more low level moisture the better. Moisture will aid in the atmosphere's instability.

So, ultimately the more "unstable" the earth's atmosphere, the more we can expect severe storms to fire. Now, not all of the ingredients are need for severe weather (excpect instability), or some might be weak. But, what would happen if grandma used store bought apples for her apple pie instead of home grown ones? Yes, you'd still get a pie, just not her blue ribbon one!