Tuesdays breakdown using multi models and soundings. You can observe as each run was observed the chances for storms have continued to build in confidence but not guaranteed.
The synoptic pattern and model guidance still favour a potentially significant severe-storm episode across SEQ / NE-NSW on Saturday. The latest GFS/derived charts show very high surface-based CAPE in the warm sector, a stout mid-level cap that delays initiation, improving low-level moisture through the day, and sufficient deep-layer shear to support organised multiple cell clusters and isolated supercells. BOM’s TT’s are highlighting a convective risk for damaging winds, large hail and heavy rainfall.
Instability
Surface-based CAPE (SBCAPE): very high — model guidance indicates SBCAPE likely in the ~1500–3500 J/kg range across parts of SEQ in the late-afternoon (peak heating). (User note: you reported “very high CAPE” and TT ≈ 56; latest maps are consistent with that magnitude).
TT-Index / Torro/Tornado potential: TT near ~56, that’s a notable severe parameter when combined with adequate shear and low LCLs.
Capping (CIN)
Strong cap present in many model soundings — a cap (CIN) likely large enough to suppress early-day convection and allow surface heating to steepen lapse rates. That cap is the “hold-it-in” mechanism; if and when it breaks in the late afternoon/early evening, development can be explosive. Expect CIN values variable but potentially several tens to a few hundred J/kg depending on exact location and timing.
Moisture & low-levels
Low-level moisture: marginal to improving — dew points are modelled to lift through the morning/afternoon. Expect surface dew points from the mid-teens into the high teens (°C) across inland areas and better onshore return near the coast — enough to support strong updrafts if the cap erodes. Observations show increasing low-level moisture into the afternoon.
LCL / LFC: LCLs likely moderate to low in the areas with higher dew points (favouring stronger low-level buoyancy and potential for hail/strong downdrafts). LFC should be reachable once the cap breaks.
Shear & storm probability
Deep-layer shear (0–6 km): model analyses indicate moderate–strong shear (roughly 20–40 kt / 10–20 m/s in many solutions) — enough for organized multicells and isolated supercells, especially where low-level shear (0–1 km) strengthens.
Low-level shear / helicity: pockets of enhanced low-level directional shear are possible near any boundary/trough — this raises the chance of rotating updrafts (tornadic risk remains conditional/low but non-zero if storms acquire strong low-level SRH).
Expected storm mode: start as small cells where the cap breaks; rapid upscale growth into multi cell clusters and bowing segments with a risk of damaging straight-line winds and microbursts. Isolated supercells are possible in the stronger shear/instability overlap.
Thermodynamic lapse rates
Steep mid-level lapse rates in model soundings — supports strong, buoyant updrafts and large hail potential if storms remain discrete for long enough. Elevated lapse rates aloft increase hail potential.
Timing & storm development
Cap holds through much of the day; initiation window is likely late afternoon → early evening (peak heating + approaching trough/front). If the cap delays initiation too long, activity may be more discrete but explosive; an earlier weaker break could spread storms out and reduce extreme hits in any single location.
Uncertainty: exact timing/placement of boundaries (e.g., coastal convergence, local sea breeze, inland trough) is the controlling factor — small shifts in the boundary can make a big difference to which towns get the worst of it. BOM watches/warnings should be monitored closely.
Immediate practical assessment for severe storms shows the ingredients for severe weather are present: very high instability, sufficient shear, steep lapse rates, and improving low-level moisture. The main limiting factor is the cap — but if it breaks over populated areas (Brisbane, Ipswich, Gold Coast, Lockyer Valley, Darling Downs, Moreton Bay coast), expect a rapid escalation to severe thunderstorms with large hail, damaging gusts / microbursts, intense rainfall and localized flash flooding. Recent regional reporting and BOM messaging already reflect this threat.
