Gridded fields of surface variables are an effective and fundamental tool for meteorological analysis and prediction within the NWS operational community. They provide direct measurements of surface conditions, permit inference of conditions aloft, and often give crucial indicators of the potential for severe weather. Surface analyses are particularly valuable at the mesoscale where the frequency, completeness, and density of the surface data are unmatched among in situ observations.

The Mesoscale Analysis and Prediction System (MAPS) Surface Assimilation System (MSAS) was implemented on AWIPS in 1998 for the purpose of providing timely and detailed surface analyses. Although the domain and resolution parameters of the system are flexible, the current configuration provides hourly analyses on a 60-km grid covering the 48 contiguous states and neighboring areas of Canada and Mexico. The analysis variables were chosen, whenever possible, to minimize the effects of varying terrain. Potential temperature, for instance, is analyzed instead of surface temperature because it varies more smoothly over mountainous terrain when the boundary layer is relatively deep and well mixed. MSAS also incorporates elevation and potential temperature differences in its correlation functions to help account for physical blocking by mountainous terrain, and improve the representation of surface gradients.

All of the surface observations on AWIPS are ingested by MSAS. This includes standard METARs, Coastal Marine Automated Network (C-MAN) observations, surface reports from fixed and drifting buoys, ships, and the NOAA Profiler Network, as well as surface observations from any local mesonets ingested through the AWIPS LDAD system. Sophisticated quality control (QC) checks are employed to help screen the surface observations. The results of the MSAS QC checks are passed to the AWIPS Quality Control and Monitoring System (QCMS) for display and QC database production. In addition, the MSAS analyses respect the QCMS subjective intervention lists maintained at each Forecast Office. Observations listed in the QCMS subjective reject list are not analyzed by MSAS, while observations listed in the QCMS subjective accept list are always analyzed, regardless of the outcome of the automated QC checks.

This paper will detail the analysis and QC techniques utilized by MSAS, and will also describe in detail AWIPS Build 5.2.2 plans to extend MSAS off CONUS, and to allow each NWS Forecast Office to specify the location, size, and resolution of their local MSAS domain.