28 How a Sea Breeze Front can Generate Supercells in Marginal Environments

Monday, 22 October 2018
Stowe & Atrium rooms (Stoweflake Mountain Resort )
Harald Richter, BoM, Melbourne, Australia; and L. Bosart and J. S. Soderholm

On 13 November 2016 a series of nonsevere thunderstorms moved across a sea breeze front

that was propagating inland (south-westward) over Brisbane, Australia. To varying degrees, each of the storms developed at least some supercell characteristics after crossing into the sea breeze air. The last of the storms to cross the sea breeze boundary briefly assumed classic supercell characteristics over Brisbane airport and was responsible for significant wind damage with measured 10 m wind gusts of ~43 m s-1.

This study documents the synoptic and mesoscale environmental ingredients conducive to supercell formation within the sea breeze boundary layer and it examines the roles of the sea breeze front in the intensification of those storms that interacted with this boundary. Of particular interest is that the storms only remained severe across a narrow zone behind the sea breeze front, beyond which they quickly weakened as they crossed deeper into the maritime air.

A notable aspect in this event was the minimal modification of the sea breeze surface parcels by the downdrafts of the various storms. Surface temperatures and dew point temperatures only dipped by 2-3oC before quickly recovering to their pre-storm values in northerly to north-easterly surface flow off the warm Coral Sea. With downdraft cooling hard to achieve in such a moist boundary layer, we hypothesize that dynamically forced low-level parcel acceleration was a particularly important forcing mechanism for the observed destructive winds associated with these storms.

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