An analysis has been conducted of a suspected daily maximum temperature (DMT) bias introduced by the replacement of the National Weather Service (NWS) HO-63 hygrothermograph with a modernized HO-83 instrument at Albany, New York, on 6 February 1985. The analysis involves an assessment of the bias before and after the changeover and has four components: 1) a bias comparison with seven surrounding NWS Cooperative Observer Network (COOP) stations; 2) a comparison of the DMT with the highest reported hourly temperature during the summer; 3) a comparison of 1800 and 2100 UTC model output statistics (MOS) operational temperature forecasts from the 0000 UTC forecast cycle during the summer with the observed temperatures; and 4) a comparison of the reported maximum surface temperature with the observed 850-mb temperature at the time of the surface maximum temperature in July for days with at least 75% of possible sunshine.
The results show that the reported DMT at Albany has increased by ~0.5°C relative to the surrounding COOP locations since the introduction of the HO-83 sensor. The warm bias is largest on sunny, light wind days. Roughly two-thirds (one-third) of the warm bias can be attributed to stratification of the data by wind speed (percent of possible sunshine), suggestive of an aspiration problem in the sensor housing. Subsequent to the installation of the HO-83 sensor, 1) the percentage of observed DMTs that exceeded the highest reported hourly value increased from 39.8% to 64.1% (8.7% and 16.1%) across the 0.56°C (1.12°C) threshold, amounting to an overall 0.18°C warm bias, 2) the MOS temperature analysis revealed the existence of a net warming of 0.56°C (0.35°C) at 1800 UTC (2100 UTC), and 3) the observed maximum surface temperature warmed 1.17°C relative to the given 850-mb temperature on sunny July days.
*Present affiliation: General Sciences Corporation, Laurel, Maryland.