Physical Processes Influencing Elevated Convection Initiation during 25–26 June PECAN: Observations and Numerical Simulations

In this two-part study (see also Sun and Trier), we examine physical processes leading to elevated CI in the late evening over northwest Kansas during PECAN IOP 16. The CI of interest occurred as linear bands ahead of a large southeastward moving MCS (which originated during the daytime) but rearward of two adjacent lines that formed in the early evening north of a surface quasi-stationary front. An interesting and somewhat unusual aspect this late evening and subsequent overnight CI is its successive development northwest of, and to the rear, of the most recent initiations.

In this talk (part I), we use surface observations, PECAN radiosonde data, and output from a 50-member low-resolution (∆ = 15 km horizontal grid spacing) WRF ensemble to characterize the mesoscale environment in which this late evening elevated CI occurs. Here, thermodynamic destabilization above the PBL in PECAN soundings is linked to persistent mesoscale ascent in the CI region.

A single high-resolution simulation with a fine-scale nest having horizontal grid spacing of ∆ = 1 km replicates aspects of the overall observed convective organization during this IOP. In particular, this simulation captures the successive development of late evening convective lines rearward of the most recent initiations. This simulation is compared with observations and then used to formulate hypotheses concerning if and how ongoing convection might influence subsequent initiation in the already favorable mesoscale environment. In part II (Sun and Trier), we use a radar data assimilation system to construct a convective-scale reanalysis from which we investigate, in greater detail, the most likely relevant physical processes governing the successive late evening CI events.