CFHT Cloud Sensor
  This page provides a graphical interface to realtime and historical data (beginning May 01, 2007) provided by the cloud sensor and skyprobe operated at the CFHT Observatory atop Mauna Kea. You can choose to graph one or two dates by (un)checking the Two dates? field and selecting your date criteria. If either of your selected dates do not have data, no charts will be displayed. Press the chart button to view the charts based on your criteria. The Default button is the default chart provided by partners of the cloud sensor device manufacturer. It charts data throughout the day and night in realtime. There is no auto-refresh of the charts. Hit the chart button to get updates once you have your criteria selected.

If the dewpoint depression (found in the (TSky-TAmb) vs Time chart) is less than 15C, the assumptions for Clear, Cirrus, Cloudy, and Very Cloudy seem to be lower than the actual sky's visual representation.

Two dates?
Skyprobe charts:  and (TSky-TAmb) vs Time  vs (TSky-TAmb) 
Sky Temperature charts:  (TSky-TAmb) vs Time  Histogram and CDF 
Archived Data Charts     All Cloud Sensor Data Charts