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.
This is a streamline plot of 300 mb winds. The lines follow the direction of the wind. Small arrows denote actual direction. The streamlines are colored based on their speed.