Butte, MT
The average comparability of the individual sensors for Butte was 96%. The comparability for wind direction was less than expected. This assessment was subject to multiple uncontrolled variables such as observer estimates and interpolations of visibility, sky cover, etc. IFR and MVFR conditions occurred at Butte during 19 hours out of a total of about 491 hours. Analysis shows that visibility comparability was less than expected during these conditions. For the range of zero to two miles, the ASOS agreed with the human observer within the specified limits, 64% of the time; in the range above two miles through four miles the agreement was 32%; while at five miles the ASOS agreed with the human observer 91% of the time.