- Basic Equations:
**Option 1 -**- Non-hydrostatic time-split compressible (Tripoli and Cotton, 1980)
**Option 2 -**- Hydrostatic incompressible or compressible (Tremback
*et al.*, 1985)

- Dimensionality: 1, 2, or 3 spatial dimensions

- Vertical Coordinate:
**Option 1 -**- Standard cartesian
**Option 2 -**- Sigma-z

- Horizontal Coordinate:
**Option 1 -**- Standard cartesian
**Option 2 -**- Polar stereographic

- Grid Structure:
- Arakawa-C grid stagger
- Unlimited number of nested grids
- Unlimited number of levels of nesting

- Finite Differencing:
**Option 1 -**- Leapfrog on long timestep, forward-backward on small timestep, 2nd or 4th order flux conservative advection.
**Option 2 -**- Forward-backward time split, 6th order flux conservative (Tremback
*et al.*, 1987)

- Turbulence Closure:
**Option 1 -**- Smagorinsky-type eddy viscosity with dependence
**Option 2 -**- Level 2.5 type closure using eddy viscosity as a function of a prognostic turbulent kinetic energy
**Option 3 -**- O'Brien profile function in a convective boundary layer (Mahrer and Pielke, 1977); local exchange coefficient in a stable boundary layer (McNider, 1981).

- Condensation:
**Option 1 -**- Grid points fully saturated or unsaturated
**Option 2 -**- No condensation

- Cloud Microphysics:
**Option 1 -**- Warm rain conversion and accretion of cloud water to raindrops, evaporation and sedimentation (Tripoli and Cotton, 1980)
**Option 2 -**- Option 1 plus specified nucleation of ice crystals, conversion nucleation
and accretion of graupel, growth of ice crystals, evaporation, melting
and sedimentation (see Cotton
*et al.*, 1982) **Option 3 -**- Option 1 plus option 2 plus predicted nucleation and sink of crystal
concentration, conversion and growth of aggregates, melting, evaporation
and sedimentation The nucleation model includes: sorption/deposition,

**figure:**Flow diagram.

Contact nucleation by Brownian collision plus thermophoresis plus diffusiophoresis, secondary ice crystal production by rime-splinter mechanism. **Option 4 -**- No precipitation processes

- Radiation:
**Option 1 -**- Shortwave radiation model including molecular scattering, absorption of clear air (Yamamoto, 1962), ozone absorption (Lacis and Hansen, 1974) and reflectance, transmittance and absorptance of a cloud layer (Stephens, 1978), clear-cloudy mixed layer approach (Stephens, 1977)
**Option 2 -**- Shortwave radiation model described by Mahrer and Pielke (1977) which includes the effects of forward Rayleigh scattering (Atwater and Brown, 1974), absorption by water vapor (McDonald, 1960), and terrain slope (Kondrat'yev, 1969).
**Option 3 -**- Longwave radiation model including emissivity of a clear atmosphere (Rodgers, 1967), emissivity of cloud layer (Stephens, 1978), and emissivity of ``clear and cloudy'' mixed layer (Herman and Goody, 1976)
**Option 4 -**- Longwave radiation model described by Mahrer and Pielke (1977) including
emissivities of water vapor (Jacobs
*et al.,*1974) and carbon dioxide (Kondrat'yev, 1969) and the computationally efficient technique of Sasamori (1972). **Option 5 -**- No radiation

- Transport & Diffusion Modules:
**Option 1 -**- Advection-diffusion model (Segal
*et al.*, 1980) (To be implemented.) **Option 2 -**- Semi-stochastic particle model for point and line sources of pollution (McNider, 1981) (To be implemented.)

- Lower Boundary:
**Option 1 -**- Specified surface temperature and moisture function or specified surface fluxes coupled with constant flux layer condition based on similarity theory (Manton and Cotton, 1977)
**Option 2 -**- Surface layer temperature and moisture fluxes are diagnosed as a function of the ground surface temperature derived from a surface energy balance (Mahrer and Pielke, 1977). The energy balance includes longwave and shortwave radiative fluxes, latent and sensible heat fluxes, and conduction from below the surface. To include the latter effect, a multi-level prognostic soil temperature model is computed.
**Option 3 -**- Modified form of Option 2 with prognostic surface equations (Tremback and Kessler, 1985)
**Option 4 -**- Same as Option 2, except vegetation parameterizations are included (McCumber and Pielke, 1981; McCumber, 1980) (To be implemented)

- Upper Boundary Conditions:
**Option 1 -**- Rigid lid
**Option 2 -**- Rayleigh Friction layer plus Option 1-4
**Option 3 -**- Prognostic surface pressure (hydrostatic only)
**Option 4 -**- Material surface top. (Hydrostatic only) (Mahrer and Pielke, 1977)
**Option 5 -**- Gravity wave radiation condition (Klemp and Durran, 1983)

- Lateral Boundary Conditions:
**Option 1 -**- Klemp and Wilhelmson (1978) radiative boundary conditions
**Option 2 -**- Orlanski (1976) radiative boundary conditions
**Option 3 -**- Klemp and Lilly (1978) radiative boundary condition
**Option 4 -**- Option 1, 2 or 3 coupled with Mesoscale Compensation Region (MCR) described
by Tripoli and Cotton (1982) with fixed conditions at MCR boundary
**figure:**Mesoscale Compensation Region

**Option 5 -**- The sponge boundary condition of Perkey and Kreitzberg (1976) when large scale data is available from objectively analyzed data fields or a larger scale model run. This condition includes a viscous region and the introduction of the large scale fields into the model computations near the lateral boundaries.

- Initialization:
**Option 1 -**- Horizontally homogeneous.
**Option 2 -**- Option 1 plus variations to force cloud initiation.
**Option 3 -**- NMC data and/or soundings objectively analyzed on isentropic surface and interpolated to the model grid.
**Option 4 -**- NMC data interpolated to the model grid.

**1)**__By including a character in the first column of a line of code, that line can be ``activated" or ``eliminated" from the compile file. This allows for conditional compilation of single lines or entire sections of code.__**2)**__A pre-processor variable can be set to a value. This variable can then be used in other expressions including a pre-processor IF or block IF to conditionally set other pre-processor variables. These variables also can be converted to FORTRAN PARAMETER statements which can be inserted anywhere in the rest of the code.__**3)**__A group of statements can be delineated as a ``global" which then can be inserted anywhere in the code. This is very useful for groups of COMMON and PARAMETER statements.__**4)**__DO loops can be constructed in a DO/ENDDO syntax, eliminating the need for statement labels on the DO loops.__

**1)**- There is no imposed limit (only a practical one) to the number of nested grids which can be used.
**2)**- When two grids B and C are nested within grid A, they may be either independent (occupying different space) or C may be nested within B.
**3)**- The increase in spatial resolution of a nested grid may be any integer multiple of its parent grid resolution. Moreover, this multiple may be specified independently for the three coordinate directions.
**4)**- A nested grid may, but need not, start from the ground and extend to
the model domain top.