The H's and L's represent high and low pressure centers, areas of swirling air.
- The air around a high pressure center circulates clockwise.
- The air around a low pressure system moves counter-clockwise.
The colored lines represent fronts: dividing lines between cold and warm air. Blue lines represent cold fronts, with warm air in front (to the right of) the line and cold air behind (to the left of) it.
The red lines represent warm fronts, with colder air in front of it and warm air behind.