The combustion of an idealized "pancake-shaped" natural gas and air fuel cloud mixture (height=30 m, diameter ∼800 m) with central ignition on the ground is described for a high burning velocity flame. The induced overpressures, velocities, and temperatures are predicted in a two-dimensional axisymmetric geometry using a n Eulerian code which solves the dynamic multiphase equations of motion with a n implicit finite difference technique. The maximum predicted name speed (85 m /s) and overpressure (100 mbar) occur at ∼I s after ignition which corresponds to the initiation of upper fuel boundary burnout when the ∼3 m thick flame has reached a height and radius of ∼60 m. Buoyancy forces and inward acceleration of combustion products cause the formation of a strong vortex flow field. Peak upward velocities of ∼185 m/s are predicted at ∼=9.5 s.