October 11, 2018 Queensland Supercells – What Made Them So Severe?

On October 11, 2018 – multiple supercells tracked across the Darling Downs and Wide Bay Burnett district producing destructive winds, tennis ball sized hail and even reports of tornadoes with a very rare tornado warning issued for areas of the Wide Bay & Burnett district!  Many outlets suggested the previous day would be the worst day, and while some severe storms happened they were short lived and localised.  We suggested in our forecasts to clients and Facebook that it would be Thursday (October 11), that would see the worst of the conditions – but why the big difference?

October 11 was a very significant “Ridge Cradled Trough” setup – these are the most volatile storm setups in Queensland hands down.  Whenever these setups occur they nearly always produce destructive supercells.  There are two big factors these setups generate:

  • Increased instability from the introduction of low level moisture mixing in with the hotter air ahead of the change (note most storms develop BEHIND the southeast change in these setups which is different to most other storm setups).
  • Increased shear from the strong E to NE winds (the trough that is cradled by the ridge tilts the winds E to NE, even though the airmass is coming from the SE, this enhances low level shear).
  • The increased instability allows for large thunderstorms to develop.  The increased wind shear allows for thunderstorms to become organised and develop into supercells which are more likely to be destructive

Read below for a more technical overview of what made this setup so significant.