Cooked boundaries: Preliminary results from numerical experiments

A type of preexisting airmass boundary exists where the cooler, relatively more dense side is more conditionally unstable than its warmer less dense side. This boundary is often referred to as a cooked boundary. These boundaries have influenced several significant severe weather events including the Dimmit and Friona, Texas tornadoes on 2 June 1995 and the record-breaking hailstone of the Aurora, Nebraska supercell on 22 June 2003. A boundary is considered cooked when the near-surface virtual potential temperature gradient is directed towards the warmer less dense air, and the near-surface equivalent potential temperature gradient is directed towards the cooler, denser air.

Preexisting thunderstorm outflow provides the starting point for the beginning of a cooked boundary. Research aims to test the following hypothesized mechanisms responsible for cooked boundary formation: (1) As insolation occurs throughout the day, water vapor on the cooler side will decrease at a slower rate due to smaller vertical mixing; (2) low-level moisture pooling along the boundary interface occurs due to confluent flow along the boundary interface; and (3) moisture flux from the surface can create a localized area of high moisture on the cool side because it is vertically mixed through a shallower layer than on the warm side.

Experiments will be conducted using the Weather Research and Forecasting (WRF) model. The overall objectives are to provide insight into the evolution difference between a regularly evolving preexisting boundary and a cooked boundary, and to determine the necessary environmental properties for development of a cooked boundary. Preliminary results will be presented at the conference.