Information about ENSEMBLE Graphics:
At present, two sets of plots are generated from the ensemble data that are retrieved from NCEP (National Centers for Environmental Prediction):
1 - 5520 meter height contour of the 500 millibar pressure surface
2 - 5460 meter thickness (difference in heights) between the 1000 millibar and 500 millibar pressure surfaces

About the contour lines:
Solid black line - This is essentially the MRF (Medium-Range Forecast) Model run at 00Z or the AVN Model run at 12Z. For the 00Z run, it has a horizontal resolution of T162 (~100km) and changes to T62 (~200km) at 7 days out. For the 12Z run, it changes from T162 to T62 at 3 days out.
Dashed black line - This is a totally T62 "control" run made only at 00Z.
Other solid contours - In addition to the above mentioned runs, 14 additional runs are made starting from slightly perturbed initial analyses. 10 of these are run at 00Z and the other 4 are run at 12Z. Thus, between the 00Z and 12Z ensemble products, there are a total of 17 ensemble members - 12 at 00Z and 5 at 12Z. All of the forecasts are run out to 16 days.
So, the green to blue contours represent the negatively perturbed runs and the red contours represent the positively perturbed runs.

The graphics that are currently generated at the U of U are called "Spaghetti" diagrams. They are meant to show the similarities and differences that may develop from one initial time. More graphics will be developed and created in the futrue.

For more (and better explained) information, please link to the following site:
NCEP Ensemble Products and go to the Reference Page for the good stuff!