An assessment of the value of 7 different observation data types (aircraft, profiler, rawinsonde, VAD (velocity azimuth display), GPS precipitable water, METAR, and mesonet) on short-range numerical forecasts is presented for a 10-day period from November-December 2006. A series of experiments was conducted using the Rapid Update Cycle (RUC) model/assimilation system in which various data sources were denied to assess the relative importance of the different data types for short-range (3-12h) wind, temperature, and moisture forecasts at different vertical levels and at the surface.

This study is unique in considering the effects of most of the currently assimilated high-frequency observing systems in a 1-h assimilation cycle. The previous observation impact experiments reported in Benjamin et al. (2005) were for wind profiler and commercial aircraft reports only and was only for effects on wind forecasts. This new study is much broader than the previous studies.

Here, a set of observational sensitivity experiments were carried out for a recent winter period using updated versions of the Rapid Update Cycle assimilation system and forecast model. The seven observing systems considered in this study include probably the most dominant wind-temperature observation types over the United States: rawinsondes, aircraft, surface, wind profilers, and VAD (velocity azimuth display) wind profiles from WSR-88D radars. Four of these five (excepting rawinsondes) provide hourly data. We do not consider satellite radiances or retrieved soundings in this study, although GOES-based cloud-top temperature/pressure retrievals and cloud-drift winds are also assimilated in the RUC 1-h cycle. We also include relative effects of METAR and mesonet surface observations.

Results from the relative impact from these different observation types will be presented at the conference.