The objective of the NCEP’s Regional Reanalysis (RR) is to create a long-term set of consistent climate data on a regional scale, for the North American domain. The RR, on its domain, will 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 arrived at within the NCEP’s GCIP-funded land-surface effort.

One of the expectations is that the RR will help answering questions of the variability of water in weather and climate, in particular as it concerns U.S. precipitation patterns. To that end, a special effort will be made to output all native grid time-integrated quantities of water and energy budgets. The RR should have a good handle on extreme events, such as floods and droughts, and should interface with 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 quite similar to the analyzed precipitation, in particular during the warmer seasons. 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 temperatures 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, tentative production at this resolution has started, even though some of the finishing touches are still in progress so that the 32-km reanalysis so far done, the second half of 1987 and early 1988, will be rerun once the system is frozen. It is planned to complete most of the 25 years of RR, 1979-2003, before the end of 2003. Once the 25 years are completed, the RR will continue to be run in real-time, like the “Climate Data Assimilation System” is being run as a real-time continuation of the GR.