SR/SSD 99-11


Technical Attachment

Recent NCEP Model and Guidance Developments

Scientific Services Division

NWS Southern Region Headquarters

INCREASED NCEP SUPPORT FOR TERMINAL FORECASTS. NCEP is increasing their support for TAF forecasts by producing model forecast soundings, meteograms and time sections from all four runs of the Eta-32. Eta model soundings (in the BUFR format) for 655 sites have been available on the OSO server for over four years. These data have been downloaded and processed to produce NAWIPS graphical metafiles and input to the BUFKIT sounding analysis program. Until recently, meteograms for only 88 sites had been available via the Web (

NCEP recently added the display of low, middle and high clouds to the meteogram displays of surface variables and sensible weather, increased the number of viewable sites four-fold, and added sites in Alaska, Hawaii and Puerto Rico (selectable by name). To further improve the usefulness of the Eta Model BUFR data as TAF guidance, NCEP plans the following actions.

Expansion of the station list has necessitated going from a five-digit to a six-digit station ID which will require minor changes to BUFR tables and data access scripts. These changes will be coordinated with a soon-to-be-released Y2K patch for the BUFR decoder. A sample of a time-height display under consideration can be viewed at: research/meteo1.html. Thanks to the Herculean efforts of Keith Brill, you can find the expanded BUFR site list, cross-referenced with the current list and site maps at:

ETA FOUS BULLETIN MAKER. NCEP's Central Operations has upgraded their Eta FOUS bulletin maker. This code interpolates model output from a grid to selected sites and then formats that data into character bulletins for transmission. The current system uses the NGM-look-alike files from the Eta model which are on a fairly coarse (83 km) polar-stereographic grid covering North America (AWIPS Grid #104). The upgraded system will use AWIPS Grid #221 which is a Lambert conic- conformal grid with 32 km resolution covering the North American domain of the Eta model. The output bulletins will have the identical appearance and format, but they will have been generated with much less interpolation distortion. For example, Seattle's elevation as perceived by the new Eta FOUS will be 110.90 m as compared to 388.96 m in the old Eta FOUS. This code change will also affect the FRH - freezing level and RH FOUS40-- messages as well.

TEST OF CHANGES TO THE ETA-32 3DVAR. NCEP has initiated testing of a modified version of the 3DVAR data assimilation scheme. They are performing two tests at 80 km: retrospective runs moving forward from 0000 UTC December 3, 1998, and a real-time parallel run which started 1200 UTC March 3, 1999. Graphical displays of various grids of both control and experimental (new 3DVAR) can be found at: for 0000 UTC runs and for 1200 UTC runs.

As an example, there was nearly a 10 mb difference in the sea-level pressure in the 48-hr forecast of a low approaching the Northwest coast in the run from 1200 UTC March 15. NCEP hopes that forecasters will examine these runs from time-to-time to help assess whether the 3DVAR changes are in the right direction.

CHANGES TO NCEP GLOBAL DATA ASSIMILATION SYSTEM. On 1200 UTC March 8, changes were made to NCEP's global data assimilation system (no changes were made to the forecast model). Additional radiance data from the NOAA-15 High Resolution Infrared Sounder (HIRS-3) and the Advanced Microwave Sounding Unit, for temperature, (AMSU-A) are now included in the global analysis. The change was made based on the availability of the NOAA-15 data, the recent loss of NOAA-11 microwave sounding unit data, and the imminent loss of NOAA-11 HIRS data. Testing showed minor impact in the Northern Hemisphere and improvements to large scale weather features in the Southern Hemisphere. On-line documentation of the change is available at: