3D Radar Loop of Brisbane Storm Intensifying as it Crosses Moisture Boundary - 30/10/2021

Modified southeast changes can generate high-end severe thunderstorms in Southeast Queensland. However not all southeast changes produce significant storms and they can generate "all or nothing" setups. On this day, a weak thunderstorm approached the boundary and intensified once it crossed the boundary into Brisbane. Fortunately the main intensification did not take place until the storm nearly moved out to sea but still managed to generate wind gusts of 100km/h at the Brisbane Airport and 107km/h at Inner Beacon offshore as the RFD (Rear Flank Downdraft) swept through. 

Modified southeast changes can become volatile as storms can cross areas from weak instability and wind shear to very strong instability and wind shear. However the offset is the airmass they move into is cooler so it's harder for the storm to "lift" new surface parcels of air through the stable layer (cap) in the lower atmosphere. If a storm can manage to do this, then they can become very intense.

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An example of the storms transitioning into the different environment can be seen looking at the soundings for this day below. In the western areas (where storms initiate), there is weak instability and no cap, while on the other side of the boundary both instability and the cap is much stronger.

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