The jet stream is fast flowing air that circulates around the globe. It separates warm air from cold air and causes storm systems to develop. The jet stream can flow from west to east, north to south or south to north and looks like a wave of troughs and ridges if you were to view it from space.
Computer models simulate troughs and ridges over time and typically you get stormy weather with troughs. On the eastern side of a trough, air diverges and rising motion is abundant and that's where you'll find most of your precipitation. So in the images below, notice the placement of the troughs and you'll see how it correlates to the precipitation forecast.
WEAK STORM SYSTEM #1: MONDAY-TUESDAY AM
Showers are possible across west Alabama on Monday afternoon. Best chance across central Alabama is during the evening and overnight hours. Overall, precipitation is expected to be light. 40% chance.
STRONGER SYSTEM ON FRIDAY INTO SATURDAY:
60% chance for showers and storms. A strong or severe threat is possible but too far out for many details regarding that seeing the models don't agree on the exact track of the surface low.
STRONG SYSTEM ON THE 22-23RD:
Jill Gilardi Fox 6 Meteorologist