A 23 year comparison of the MMTS (maximum/minimum temperature system) and LIG (liquid in glass) temperatures in a Hazen shelter from Fort Collins, CO

Over time, changes have been made not only to the Cooperative (COOP) Observer Network, but also to other instrumentation used at the historic Fort Collins Weather Station. This paper will provide a comparison of daily maximum and minimum temperatures from two temperature measurement systems in place since 1988.

In the mid – 1980's the National Weather Service transitioned many COOP sites from the traditional liquid in glass thermometers to the maximum/minimum temperatures system (MMTS). Many studies have compared these two measurements and found biases to exist, particularly in daily maximum temperatures with fresh snow cover and low wind speeds. However, most studies used LIG temperatures from a Cotton Region Shelter (CRS), not the more elaborate Hazen Shelter which has been used at the Fort Collins site since 1889. This study will update previous evaluations of the two systems to verify if the relationships found earlier still hold true or if they have changed over the past 23 years. This study update will also attempt to correlate meteorological conditions, which are co-located with the temperature systems, such as wind speed and direction, solar radiation and snow cover to the observed temperature biases. General conclusions on operation and reliability of the two systems will also be discussed.