The jet stream is made up of strong winds in the upper levels of earth's atmosphere. The winds flow from west to east, in general, but can vary greatly in their direction. At first glance, maps of the jet stream can be difficult to decipher. However, many maps from online weather sources can be interpreted with relative ease.
Open the physical or online map that details the jet stream.
Notice the many curved lines moving across the map from west to east. These are the directional flows of the jet stream. They are different from latitudinal lines, which are straight lines across the map.
Pay attention to the small numbers found on these wind-indicating lines. These will delineate the speed of the wind in a specific area. Some maps use colour-coded lines to indicate wind speed for even easier interpretation.
Identify the upper-case "H" and "L" indicators on the map, which indicate areas of high and low pressure. The jet stream often will be influenced by these fronts, which will shift the jet stream's direction, thereby affecting local weather.