Skew-t

Skew-T Log-P diagrams are commonly used for weather analysis and forecasting. They graph weather balloon data to show the vertical profile of the temperature and dew point through the atmosphere.

See the following Finger Lakes Soaring Club web link for a great article describing how glider pilots use skew-t graphs to predict weather for a days flight.
http://www.flsc.org/portals/12/PDF/Read_Skew_T.pdf

Features:
Uses data from http://rucsoundings.noaa.gov/
Automatically download the day's weather data
Use the slider to quickly view all hour-by-hour graphs.
Zoom to inspect the graph details
Configurable units and graph lines
Use different weather models
Show forecast graphs for the next few days
Saved favorites to quickly view different locations and/or weather models.
Here mode uses GPS to easily get graphs for your current location.
Load waypoints from files.