An atmospheric model in which the hydrostatic approximation is not made, so that the vertical momentum equation is solved. This allows nonhydrostatic models to be used successfully for horizontal scales of the order of 100 m, resolving small-scale mesoscale circulations such as cumulus convection and sea-breeze circulations. In recent years, computer power has made mesoscale weather prediction with nonhydrostatic models feasible, and several such models are in routine use by major meteorological modeling groups and operational centers. See hydrostatic model.