Just looking at the data that was available, and it is limited to the Brisbane Soundings, and then triangulating those two with the Himawari- 9 Satellite to see why, even though it was not a text book picture perfect setup, we still managed to see some big storms late yesterday afternoon and into the early hours of this morning. Unfortunately the Brisbane Airport was the only place I could retrieve the Morning and Afternoon Soundings, then you have to look at realtime obs.
So to summarise the data, Brisbane’s environment yesterday evolved subtly but decisively between morning and afternoon.
Instability: Morning conditions were already primed (LI ≈ −6, CAPE ≈ 1.3 kJ/kg).
Daytime heating lifted surface temps from ~33 °C to ~34 °C, slightly deepening the convective layer and raising CAPE to around 1.8 kJ/kg.
Moisture: Surface dewpoints near 19 °C persisted through the day, maintaining a deep moist boundary layer — much higher than the GFS initially forecast.
Capping: CIN weakened by afternoon, allowing parcels to reach the LFC more easily. This transition was key; once the cap was gone, convection initiated explosively.
Shear and structure: Moderate 0–6 km shear (~30–40 kt) supported sustained multicells and storm mergers rather than isolated supercells.
Storm dynamics: Satellite imagery and Zehr overlays showed tops cooling to −50 °C, confirming extremely strong updrafts (overshooting tops) north and northwest of Brisbane.
So the outcome of all of this was, Storm mergers enhanced local inflow and rotation, producing hail cores with jagged, multi-layered hailstones (evidence of violent cycling through the growth zone).
Summary: Even with no textbook setup, the combination of sustained low-level moisture, strong heating, weakening CIN, and interacting outflows yielded severe hail in the 4–6 cm range.
Comparing the 2 soundings
Morning Brisbane Sounding
Afternoon Brisbane Sounding.
Infrared +Zehr
So to put it simply, the atmosphere over Brisbane on Sunday showed that even without a classic storm setup, the ingredients were still there for development.
Morning conditions were already quite unstable and, as the day warmed, the cap weakened just enough for storms to form.
Moist air near the surface and good heating through the afternoon helped storms become stronger once they developed.
Satellite images showed very cold cloud tops (around –50 °C) with some cells north and northwest of Brisbane, indicating strong updrafts.
These updrafts were enough to support moderate to large hail, with reports of 4–6 cm stones from the more intense cells.
It was a good reminder that, even when models show only modest potential, local heating and storm interaction can still tip the balance toward severe weather.
