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 winter and summer 10-day periods. A series of observation sensitivity experiments (OSEs) 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 (1-12h) 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 over the United States. The previous observation impact experiments reported in Benjamin et al. (2004) were for wind profiler and commercial aircraft reports only and were only for effects on wind forecasts. This new study is much broader than the previous studies, and now includes 2 seasons as well. It complements a recent impact study on TAMDAR regional aircraft data by Moninger et al. (2009), also using the RUC assimilation/model system.

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 these experiments include the following:

• Aircraft, profiler, and VAD wind observations all contribute to improved short-range tropospheric wind forecasts, in that order from largest to smallest impact.

• Rawinsonde observations provide the greatest impact on RH forecasts, but GPS precipitable water observations also make a significant contribution.

• Surface observations improve lower tropospheric forecasts of temperature and humidity, but mesonet observations make a smaller impact than do METAR observations.

• The overall improvement shown in RUC 1-12h forecasts from more recent forecasts is due to the heterogeneous mix of high-frequency observations available over the US.

References:

Benjamin, S.G., B.E. Schwartz, E.J. Szoke, and S.E. Koch, 2004: The value of wind profiler data in U.S. Weather Forecasting. Bull. Amer. Meteor. Soc.

Moninger, W. R., S. G. Benjamin, B. D. Jamison, T. W. Schlatter, T. L. Smith, and E. J. Szoke (2009): TAMDAR jet fleets and their impact on Rapid Update Cycle (RUC) forecasts. (This conference)