The MesoWest Data Quality Graphs are designed to help a user identify what why a station may be listed with a Caution quality control status.
The graph displayed shows the same absolute average statistics for temperature, dew point, and pressure data that are used to designate a station with a Caution quality control status. These statistics are logged everytime the linear regression quality control check is done, and are shown on the graph.
A station will be designated as Caution when one of the following occurs...
Absolute average difference for temperature (red graph line) rises above a value of 15.Absolute average difference for dew point (green graph line) rises above a value of 20.Absolute average difference for pressure (blue graph line) rises above a value of 15.Station does not pass a secondary statistical wind check, which can often be diagnosed by looking at the data itself.If the station is listed as Caution while all 3 lines on the graph remain below their designated thresholds, then the station likely is not passing the statistical check being conducted on wind observations. This check essentially looks for stagnant wind observations over the past 3 days (e.g. a long period of observations with the exact same wind direction, speed, or gust) which likely indicate issues with the wind data.
Additional information on MesoWest Quality Control methods can be found here, and information on the linear regression analysis can be found here.