Cloud-Scale Model Forecasts: Extreme Sensitivity to Environmental Conditions

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The COMMAS Cloud Model

• Modified Klemp and Wilhelmson (1978) model
• Split mode (vertically propagating sound waves solved implicitly)
• Improved numerics for momentum equations
• Second-order, upwind scalar advection
  • Monotonic for water variables
  • Monotonic potential temperature advection
  • Small numerical diffusion and phase errors compared to original KW '78
• Open boundaries
• Horizontally homogenous initialization, 1 km horizontal grid spacing, 70x70 km domain.
• Stretched vertical grid - 43 grid levels
• Kessler bulk water scheme
• Convection initialized with +3.5 K warm bubble
• Input soundings adjusted to remove superadiabatic layers

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