A discretely propagating nocturnal Oklahoma squall line: Observations and numerical simulations

Storms often generate new cells via lifting over a precipitation-induced cold pool spreading along the surface. This has been termed "continuous propagation", the continuity being provided by the cold pool's persistence. Often, however, new convection is seen firing up ahead of established convection, close enough to suspect a causal relationship but with separation distances too large to explain away as merely cold pool lifting. In this case, which we are terming "discrete propagation", some other mechanism(s) must be operating.

A squall line propagated through Oklahoma in the early morning hours of 21 June 2003. As the line progressed, new convective cells were systematically generated 10-50 km ahead of the system, with distances confirmed with observations from the local mesonet. Thus, this was a rather spectacular case of discrete propagation. The mechanisms of this propagation are examined and inferred from observations as well as simulations using regional-scale and cloud-scale models.