The lowest speeds are not shaded. Above a certain level, the winds are shaded in alternating dark blue stippled and solid blue on 20 knot levels. It is 50 knots at 18 and 24 thousand feet and 70 knots at 30 and 36 thousand feet. These two maps are composite 500 mb height and sea level pressure maps for the entire northern and southern hemisphere. The color contours are the 500 mb height field which shows middle level air flow around the mid-latitudes.
Air follows the contours and the tighter the packing, the faster the flow.
Where air is moving from north to south, temperatures are generally below normal. Where air is moving south to north, temperatures are generally above normal. The sea level pressure field is plotted in black lines. High and low pressure systems can be determined from the locations of Hs and Ls on the plot. Low pressure systems usually have some kind of precipitation associated with them whether it be rain or snow.