Upper air data is taken from balloons which measure upper air conditions over a particular location. This includes plots of data on the standard mandatory and height levels, contours of various upper air parameters and a set of sounding plots for most US sites. These data update once every 12 hours at around 9:45 EST.
Constant Height - FL180
This is a set of upper air charts for various flight levels primarily for aviation concerns. The plots include plotted data, temperatures are contoured in yellow, and wind speeds are contoured in blue. Increasing speeds are highlighted in varying shades of blue. 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. The lowest level of shading is 30 knots for 3, 6, 9 and 12 thousand feet. It is 50 knots at 18 and 24 thousand feet and 70 knots at 30 and 36 thousand feet.