Automated Surface Observing System Asos

The National Weather Service has been installing Automated Surface Observing Systems (ASOS) at all first-order weather stations since 1991 as a part of their modernization program. The introduction of this new, automated method of observing the atmosphere has brought with it inherent differences in measuring surface meteorological conditions. One such affected variable is surface air temperature. When ASOS temperature readings at various weather stations were compared to simultaneous temperature readings reported by the Model HO83 instrument, which is used in conventional, man-made observations at those stations, discrepancies were often noted. These discrepancies lead to inevitable inhomogeneity in the temperature time series at stations where ASOS is installed. This investigation examines the sources contributing to these temperature differences for each of the 76 stations in this study. Examination of temperature differences between conventional observations (using the Model HO83 and designated as CONV for this study) and pre-commissioned ASOS observations have shown conventional observations are warmer (for a large majority of stations) than the corresponding ASOS temperature measurements. Comparing all synoptic hours for all seasons, the average ASOS - CONV temperature differences ranged from -2.56 deg F (ATL) to +0.61 deg F (ORH), with a mean value of -0.79 deg F.

Determines what ASOS (Automated Surface Observing System) problems exist and how effectively the National Weather Service (NWS) is resolving them, the cost of resolving these problems, and whether NWS' plans for implementing ASOS make sense in light of these problems. 4 charts and tables