Seeing:

In the summer time astronomical seeing is typically between 1 and 2 arcseconds. The seeing is sub-arcsecond about 20% of the time. This is significantly below the historical performance of the observatory.
 

Surface Brightness of the Sky:

Measurement made in the summer's of 1998 and 1999 have shown the sky brightness, in magnitudes per square arcsecond to be:
 

The near infrared sky brightness compares favorably to that found at other optically dark sites. Measurements of the sky brightness in J, H, K' are planned in the near future to determine whether the near infrared skybrightness in these bands is as good as at other sites.