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2002/06/11 DM06-02.02 - CHANGE TO THE NCEP RUC SURFACE ASSIMILATION SYSTEM /RSAS/ NOXX10 KWBC 032026 DATA MGT MESSAGE 06-02.02 ATTN USERS OF PRODUCTS AND SERVICES FROM RTH WASHINGTON DATA MANAGEMENT NOTICE OF INTENT TO CHANGE THE NCEP RUC SURFACE ASSIMILATION SYSTEM /RSAS/ EFFECTIVE DATE JUNE 11... 2002 Brief description of change(s): RSAS will increase its horizontal resolution and extend its domain boundaries. The horizontal resolution will change from 60 km to 15 km, and the domain, formerly covering the 48 contiguous states, will now stretch from Alaska in the north to Central America in the south, and also cover significantly more oceanic areas. Treatment of the model backgrounds will also be improved. To better fit the observations, for example, the RSAS altimeter analysis will use an Eta altimeter grid (derived from Eta surface pressure and elevation grids) as its model background, rather than the Eta sea-level pressure grid that was used by the previous version. RSAS will continue to provide hourly surface analyses, updated twice per hour (currently at 5 and 21 minutes past the hour), for RSAS sea-level pressure, NWS sea-level pressure, altimeter, potential temperature, dew point temperature, dew point depression, 3h pressure change, and surface winds. In addition, temperature, specific humidity, and equivalent potential temperature will be provided as derived grids. The temperature derivation requires the use of a topography grid that defines the elevation of each RSAS grid point. In the new RSAS, this grid will be improved to better match the actual observation elevations, with the result that RSAS temperature grids will provide a better fit to temperature observations, particularly in mountainous terrain. "Look-alike" 60 km grids (grid number 87) will be produced from the 15 km RSAS, and AWIPS grids 211 and 212 will continue to be produced. Grid number 88 will contain the new 15 km, North-American grid. RSAS will also continue to produce hourly, daily, weekly, and monthly Quality Control (QC) bulletins for ASOS observations. The bulletins contain QC statistics which are based on the results of RSAS quality control checks (which include validity, internal consistency, temporal and spatial consistency), and include frequency of failure for each station, as well as the RMS and mean errors of those failures. The bulletins will also now contain statistics for Alaskan ASOS stations. More information is available from the RSAS Technical Procedures Bulletin (TPB) available at http://www-sdd.fsl.noaa.gov/MSAS/rsas_tpb.html Reason for Change(s): To produce more accurate quality control statistics and surface analyses that are closer to the observations, and that also cover more geographic areas, e.g. Alaska. Surface analyses are important to weather forecasting because they provide direct measurements of surface conditions, permit inference of conditions aloft, and often give crucial indicators of the potential for severe weather. They are particularly valuable at the mesoscale where the frequency, completeness, and density of the surface data are unmatched among in situ observations. QC statistics are useful for identifying surface stations with hardware or software failures. Schedule for change: Final testing: real-time parallel testing conducted by the NCO, expected completion by June 2002. Expected implementation: 11 June 2002 Description of testing: The 15 km RSAS has been in real-time testing at NCEP, and at FSL, since December of 2000. Both subjective evaluation and statistical verification show considerable improvement over the 60 km version. Statistical summaries: Statistics on the 15 km RSAS analysis fit to observations are given in the RSAS TPB for eight different geographic regions and ten variables (RSAS sea-level pressure, NWS sea-level pressure, altimeter, 3h pressure change, u-component of the surface wind, v-component of the surface wind, potential temperature, temperature, dewpoint temperature, and dewpoint depression) for the period from December 2000 to Jan 2002. The statistics indicate that RSAS analyses closely fit the available surface observations. There are several reasons for this. First, the RSAS correlation functions take into account elevation and surface potential temperature differences and, therefore, preserve surface gradients better. Also, because RSAS does not initialize a forecast model, the analysis is performed on the actual terrain and not along a model topography. Hence, no model surface-to-station elevation extrapolations are required, and all surface observations may be used. The new, 15 km RSAS improves upon the 60 km fit to the observations, in many cases significantly, and also provides surface analyses in Alaska, Canada, Mexico, and Central America. Specific example of note: In October of 2001, Fred Mosher and Larry Hinson of NCEP's Aviation Weather Center performed a subjective evaluation of the new 15 km RSAS. They reported that they had analyzed the surface temperature fields in the mountains using METAR observations and satellite IR sampled temperatures as the ground truth. The new RSAS was able to correctly identify mountains and the corresponding cooler temperatures. In West Virginia, there was an observation of snow with an air temperature of 37 degrees F. The 60 km RSAS had temperatures in the low 40 range, while the 15 km RSAS correctly had a temperature of 37 at the surface observing site with slightly cooler temperatures in the higher elevations. In the clear air in western North Carolina, the 15 km RSAS had the colder temperatures observed on the satellite IR temperatures in the mountains around Asheville, while the 60 km version did not have any indication of colder temperatures in that area. Looking at the near offshore waters and using ship reports and satellite sea surface temperatures as ground truth, again the 15 km RSAS seemed to correctly capture the surface temperature conditions off shore much better than the 60 km. Anticipated impact on analyses: Improved fit to surface observations, and greater geographic coverage. Changes to product suite or their delivery times: "Look-alike" 60 km grids (grid number 87) will be produced from the 15 km RSAS, and AWIPS grids 211 and 212 will continue to be produced. Grid number 88 will contain the new 15 km, North-American grid. RSAS grids are available in grib format via anonymous ftp at the OOS server tgsv1.nws.noaa.gov in directory /ncep/RUCS." THE RSAS GRIDS ARE ALSO AVAILABLE ON THE NWS FTP SERVERS AT THE FOLLOWING LOCATION /SL.us008001/ST.opnl/MT.rsas_CY.hh/RD.yyyymmdd/PT.grid_DF.gr1/ ON THE ABOVE EFFECTIVE DATE... TWO NEW GRIDS WILL BE ADDED TO THE NWS FTP SERVERS: fh.anal_tl.press_gr.awip212 fh.anal_tl.press_gr.na15km ALSO... EFFECTIVE JUNE 18... 2002... THE RSAS FILES THAT ARE CURRENTLY ON THE TGSV1 SERVER WILL BE REMOVED. WITH RSAS UPGRADE TO 15 KM RESOLUTION AND THE ADDITION OF THE TWO NEW GRIDS... THE TOTAL VOLUME PER DAY IS 120 MB PER DAY. Human point of contact for further information: Patty Miller 303-497-6365 Patricia.A.Miller@xxxxxxxx Field Evaluation: Subjective evaluations have been performed at the Reno, NV forecast office, and at the Aviation Weather Center. Both organizations reported significant improvements over the 60 km version. Approvals: NCEP Director: Louis Uccellini Date: 29 May 2002 Future Changes: In the near future, we plan to upgrade RSAS to allow for the ingest, QC, and analysis of surface "mesonet" observations from over 4000 surface stations run by research organizations, private firms, and local, state, and federal agencies. The NCEP database is currently being upgraded to include these observations. FOR FOS/NOAAPORT AND NON-AWIPS CUSTOMERS - IF YOU HAVE ANY QUESTIONS REGARDING THIS NOTICE... PLEASE CONTACT DATA MANAGEMENT LOWER CASE EMAIL NWS.DM/AT SYMBOL/NOAA.GOV DATA MANAGEMENT TELECOMMUNICATION OPERATIONS CENTER RTH WASHINGTON SENDS
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