The objective of NCEP's Regional Reanalysis (RR) is to create a long-term set of consistent climate data on a regional scale. The RR, on the North American domain, should be superior to the completed NCEP/NCAR Global Reanalysis (GR), in both resolution and accuracy. This will be achieved using the GR to drive the RR system, and taking advantage of the regional Eta model, and of the various advances that have been made in regional modeling and data assimilation since the GR system starting time of 1995. These advances include assimilation of precipitation, direct assimilation of radiances, the use of additional data as well as improved data processing efforts, and several Eta model developments, in particular those within NCEP's GCIP-funded land-surface effort. A separate paper is submitted on the precipitation assimilation, a very effective component of the RR additional to the GR, ensuring that a much more realistic hydrologic cycle will be produced.

One of the expectations is that the RR will help answer questions of the GCIP/GAPP programs regarding water and energy budgets and U.S. precipitation patterns. The RR should have a good handle on extreme events, such as floods and droughts. It should interface with models focused on the Mississippi River Basin and other hydrological models as well.

Results of preliminary pilots, produced at 80-km horizontal resolution and 38 layers in the vertical, have been inspected in a variety of ways. The assimilation of precipitation during the reanalysis is very successful, obtaining model precipitation very similar to the analyzed precipitation, in particular during the warmer seasons, and with no degradation and some improvement in the other variables. In the 1998 pilot, temperature and vector wind RMS fits to raobs were considerably improved over those of the GR throughout the troposphere, both in January and in July, and both in the analyses and in the first guess fields. Improvements in the 2-m temperature and 10-m winds were seen as well.

It is expected that still better results will be obtained when the system is run at the 32-km/45-layer resolution for production. At the time of this writing, the pilot phase is nearly complete, and production is about to begin. It is expected to take 2-3 years to complete the 20+ or 25 years of RR, after which the RR will continue to be run in real-time, similar to the "Climate Data Assimilation System" being run as a real-time continuation of the GR.