Analysis of Nocturnal Convection Initiation Using Convective-Scale Data Assimilation of Observations Collected during PECAN

Ongoing research by the coauthors and collaborators is exploring improvements in mesoscale details of the environments and triggering mechanisms associated with nocturnal convection initiation (CI) that occurred during the Plains Elevated Convection at Night (PECAN) experiment of Jun-Jul of 2015. In one event, CI was observed with mobile radars, sondes, profilers, aircraft, and mesonets on 24 June in eastern Nebraska, during which southerly Gulf of Mexico flow aided by a moderate low level jet, was lifted along a warm front located in northern Kansas. The goal of this project is to provide the most detailed set of four-dimensional gridded kinematic and thermodynamic analyses possible for examination of processes triggering nocturnal CI, including details of the stability and shear in the surrounding environment that dictate the specific location and timing of convection.

The mesoscale analyses shown will demonstrate the relative impacts of assimilating frequent PECAN soundings, vertical profilers (wind and thermodynamic retrievals), low-flying research aircraft in situ data, and mobile radar clear air radial velocities. Although analyses assimilating no observations for a 4-5 hour period prior to CI do reasonably well at producing the observed convection, and all analyses initiate convection 1-2 hours early, all assimilated research observation types at least subtly improve the ensemble representation of convection at its earliest stages. A possible exception includes the assimilation of large quantities of clear air radar radial velocities directly surrounding the location of CI. Surprisingly, assimilation such data appear to disrupt the observed organization of storms at their CI stage. This presentation will demonstrate what aspects of the environment (e.g., local areas of elevated mesoscale convergence, gravity waves, elevated moisture, etc.) are improved via the assimilation of non-conventional observation types that were collected in PECAN.