Basic equation:           Primitive equations with hydrostatic
                          approximation

Independent variables:    Latitude, longitude, sigma levels

Dependent variables:      Wind velocity components, potential temperature,
                          specific humidity and surface pressure.

Numerical techniques:     Arakawa-D system staggered grid.

Integration domain:       Hemispheric outmost grid, with nested interior
                          grid, surface to 50 mb.

Horizontal resolution:    84 km at 45oN and 91 km at 60oN.

Vertical levels:          16 sigma levels with approximately 
                          5 sigma levels below 850 mb,
                          depending on terrain elevation.

Forecast time:            48 h from the 00Z and 12Z runs.
  
Initial fields:           Regional Optimum Interpolation Analysis with 
                          +/- 3 hr cutoff.  Nonlinear, normal mode
                          (Temperton) initialization.

First-guess fields:       6-h forecast from Global Data Assimilation System.

Orography:                Spectrally filtered (T72) heights derived
                          from the GFDL 0.25o North American
                          terrain field and the U. S. Navy 1o
                          Northern Hemisphere field used on inner grid
                          and a smoother (R30) representation on the
                          outer grid.
         
Horizontal diffusion:     

Moisture physics:         Modified Kuo moist convective scheme and
                          Phillips grid-scale precipitation scheme.
                           
Radiation:                Long-wave and short-wave radiation. 

Gravity wave drag:        

Planetary boundary layer: 

Land surface:             

Ocean surface:            Sea surface temperature from NMC daily analysis;
                          snow and ice cover from weekly NESDIS analysis.

Additional reading:

"The Regional Analysis and Forecast System of the National Meteorological Center", Hoke, James E. et al., Weather and Forecasting, Vol. 4, No. 3, September, 1989.

"Performance of NMC's Regional Models", Junker, Norman W. et al., Weather and Forecasting, Vol. 4, No. 3, September 1989.

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