Are we in for a Repeat of Yesterday’s Severe Storms?

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Yesterday saw a huge amount of rainfall in a short period of time that paralysed Brisbane’s rail network and brought winds that knocked down trees. Are we in for a repeat of yesterday’s severe storms today?

BSCH Stormcast Storm Probabilities for Thursday 20/11/2014

BSCH Stormcast Storm Probabilities for Thursday 20/11/2014

Forecasts for today indicate it’s much less likely for Brisbane to have storms today. Storms are more likely to the west and northwest of Brisbane. Areas such as Toowoomba, the Lockyer Valley and Ipswich could get storms. Storms are also likely in the Wide Bay & Burnett regions. Both Weatherzone and the Bureau of Meteorology both go for just showers in Brisbane and a chance of a storm.

Why is there less chance of a storm in Brisbane today?

Forecast Sounding for Brisbane 4pm Thursday 20/11/2014

Forecast Sounding for Brisbane 4pm Thursday 20/11/2014

The chart above today shows a forecast sounding for Brisbane at 4pm today. The red line on the right indicates the temperature at different altitudes through the atmosphere. The grey line shows the temperature a standard parcel of air would be expect to decrease to if it was raised to that altitude from the ground. When the red temperature line is to the right of the grey standard parcel line the atmosphere is considered to be stable. This means that air at ground level is less able to rise.

Let’s compare that to the forecast sounding at the BSCH Storm Probability bullseye south west of Gympie:

BSCH Stormcast Forecast sounding for SW of Gympie at 4pm 20/11/2014

BSCH Stormcast Forecast sounding for SW of Gympie at 4pm 20/11/2014

This sounding is much more favourable for storms. The temperature line(the right red line) is to the left of the standard parcel grey line. This means that the atmosphere is unstable, meaning air can rise from the ground to high altitudes. More information about soundings is available in this article.

Another noteworthy thing today is the forecast soundings indicate much less moisture in the atmosphere than yesterday. Yesterday the temperature(right red line) and dew point(left red line) lines were close together most of the way up the atmosphere. Today they are well separated, even in the location most likely to get storms.

Obviously these are forecast soundings, generated by computer models. They can be inaccurate, but they do provide a good indication of what is likely to occur today.

So in summary, there is still a chance of storms today but much less likely in Brisbane than yesterday. Storms are also likely to deliver less rainfall.