March08
03 Dec 2008 04:27 UTC 2008338+0427 UTC

Greetings!

The planned upgrade to the NCEP North American Mesoscale (NAM) model will be implemented at 1200 UTC on Tuesday, 25 March to introduce the 2008 Spring Package advertised in TIN 07-96 (http://www.nws.noaa.gov/om/notification/tin07-96aab_nam_changes.txt). In this package, several changes will be made to the Weather Research & Forecast Non-hydrostatic Mesoscale Model (WRF NMM) running as the NAM, the NAM Data Assimilation System (NDAS), the Downscaled Global Forecast System with Eta Extension (DGEX), and the Gridpoint Statistical Interpolation Analysis which provides initial conditions to the NDAS and NAM forecasts.

The Model changes include:

1. NAM computational domain increased by 18% (map is attached to this message).
2. Two minor changes to the WRF-NMM model radiation parameterization,
3. Changes to the WRF-NMM orography and land-sea mask to use "3x3" (smoothed-desmoothed) terrain, a smaller, more realistic Great Salt Lake, and a better depiction of the Channel Islands off the California coast,
4. 12-36hr forecast precipitation from the 0000 UTC NAM run will supplement the CONUS-based Stage II/IV analysis outside of the CONUS for use as the driver for NDAS soil moisture during the NDAS forecast,
5. New, unified (with NCAR) land-surface physics module,
6. Modified horizontal advection algorithm for cloud water, specific humidity, and turbulent kinetic energy, and
7. Modified WRF-NMM model dynamics to include the effects of gravity-wave drag and mountain blocking.

The Analysis changes include:

1. Upgrade to the latest version of the Gridpoint Statistical Interpolation code,
2. Assimilation of new observation types including Atmospheric Infrared Sounder and GOES 1x1 pixel radiance data, MODIS and European Organisation for the Exploitation of Meteorological Satellites wind data, and surface MESONET wind data, and
3. Revised background error covariances to improve the analysis to fit the observations.

All WRF-NMM model changes will be simultaneously implemented into the DGEX.

The combined impact of these changes has led to:

1. Improved NAM forecast performance as measured by quantitative skill cores for heights and temperature, RMS error and bias, over both the CONUS and Alaska, specifically in reducing lower tropospheric/850/700mb cold bias and improved 10m wind forecasts.
2. Improved NDAS/NAM soil moisture states in regions outside of the CONUS.

More details about these changes are available at: http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/paralog/paralog.namexp.html

Page last modified on March 30, 2008, at 08:27 PM