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.

Great shots @ Aussie Girl,

You were right in line with the boundary flow at that point in time. Storm chasers would have loved to have been there.

Those photos, especially the last 2, capture the formation of a shelf cloud and the violent turbulence especially at the storms base. That turbulence and the updrafts contributed to the formation of large hail in some of those areas close to where you were.

It was probably a good idea not to stop as hail was present. But you captured some brilliant photos of those storms.

Thank you so much for sharing.

I held back from posting about the potentials for storms on Saturday for quite a bit. Models were chopping and changing. BoM originally thought Friday was a Storm day earlier on in the week, then they said Saturday for the last 4 days.
It is not a great looking setup, but when you break it all down, there is definitely potential for storms and possibly severe.
( PS, I went to post this last night, Thursday and just ran out of time.)

What I have done, is I took the Soundings from Brisbane, Dalby, Kingaroy, Warwick and Moree and broke them down to get a broad perspective of the atmosphere. Below is the values in each of the Soundings



The break down of all of this with a quick technical update for Saturday (18 Oct). GFS-based soundings for Brisbane / Dalby / Kingaroy / Warwick / Moree show a conditionally unstable environment: modest–moderate CAPE (≈200–400 J/kg in many locations), small-to-modest CIN, and modest deep-layer shear (~20–30 kt).

Precipitable water is only low–moderate (mid 20s mm), and several soundings have relatively dry mid-levels.
That combination favours strong updrafts with efficient hail growth and evaporative downdrafts — so the primary risks (if storms develop) are hail and damaging wind gusts rather than long-duration heavy rain.

The key uncertainty is low-level moisture and timing. Models generally keep dew points on the low side; if surface moisture is greater than models indicate (i.e., dew points climb toward the high teens) and a trigger (front, trough, or convergence) lines up at the right time, storms could intensify quickly and produce severe cells.

Once again it is not your textbook widespread severe outbreak, but a conditional, pulse/semi-organised severe threat — the main watch is lower level moisture dewpoints) increase and timing of trough. I’ll update either Friday or Saturday morning when the actual Soundings are released.

So basically with the forecast conditions, storms could pop up quickly and a few may produce large hail and strong gusts if the everything slides into place. All the models have the Trough moving over at different times in the afternoon so that creates some uncertainty.

So as per always, these are my thoughts and anything can change rapidly. So keep an eye to the sky and on the radar and listen for any warnings if storms develop and become severe. — timing and local moisture will decide how it plays out.

Edited by user Friday, 17 October 2025 8:17:18 AM(UTC)  | Reason: Not specified