Forecasters and meteorologists look at the upper atmosphere to determine a forecast. At 700 mb, omega is graphed or the vertical motion.
A 500 mb pressure map is what meteorologists look at to predict a forecast. This is the middle of the atmosphere and height levels are plotted and vorticity is determined.
Weather forecasters look at 300 mb, or the jet stream, to look at wind speeds in the upper atmosphere. This also can help determine the flow of the atmosphere.