Tornado or not? Experts probe trail of destruction
A trio of severe weather experts will determine how a powerful storm destroyed a swath of Waurn Ponds homes and whether residents were given enough warning.
A downburst occurs when a rapidly descending column of air hits the ground and spreads with straight-line winds, compared to the spinning vortex that characteristics a tornado.
The ferocious storm cell was in a squall line moving at approximately 100km/h when it ploughed into the neighbourhood and undoubtedly produced winds greater than that on the ground, according to Bureau of Meteorology Victoria State Manager Andrew Tupper.
Mr Tupper said the state's lead forecaster and two experts in severe and extreme weather had been on site to assess the damage, with the help of the SES and firefighters, to piece together the event.
Initial reports estimate wind speeds reached 150km/h, putting it close to the highest speed officially observed in the region of 164km/h at Point Henry in September 1962.
Mr Tupper said the investigating team hopes to establish "as quickly as possible … how the wind came down in that spot".
"At the moment we're in the early stages of finding out what has happened in terms of the severe storm itself, so I've sent three severe weather specialists to have a look at the damage together with SES and firefighters, who have been doing the survey work, and we don't know until they report back whether it was a tornado or downburst," he said.
"They'll assess that based on the damage patterns and what the Doppler radar said and then we'll ask if we could have put the warning out earlier."
Geelong's forecast for Tuesday warned of the potential for thunderstorms late in the evening, as did the Wednesday forecast for the early morning.
But a specific Severe Thunderstorm Warning was not issued for the affected area until 1.15am, when the storm was already raging.
A warning was also issued at 11.19pm Tuesday, but only extended as far east as Winchelsea and as far south as Meredith.
Asked whether he felt the bureau provided adequate warning, Mr Tupper said:
"The line of storms intensified as they got to Geelong. So we had signalled severe storms with an earlier warning that didn't include that area, and the updated warning went out pretty much as the storms reached the impacted area.
"Particularly for overnight storms it's quite difficult. While it's nice to get a warning out half an hour in advance, the reality is you really want to have a very good sense, like three hours before the time everyone's thinking about going to bed when there's a chance the warning has been received, so with this severe storm it's really very difficult."
"The challenge you have in forecasting is always catching the little parts of the line (of storms) as they evolve, as the line is a very dynamic kind of creature."
Geelong Weather Services' Lindsay Smail said the city averaged three severe storms each year, but this was one of the more powerful for strong winds in recent times.
Five tornadoes have been recorded in the wider Geelong region this century, including two in urban Geelong.
• A line of severe thunderstorms moved through Geelong, likely producing 100km/h+ wind gusts in the Waurn Ponds and Mt Duneed
• Geelong's main weather recording station observed a maximum wind gust of only 61km/h and 9.6mm of rain. Ballarat was the nearest weather station to have a 'damaging' wind gust (98km/h)
• Vic SES had 147 requests for assistance, with 61 in Waurn Ponds and 57 in Mount Duneed
• It is likely a downburst or tornado caused the damage on Ironbark St
According to BoM Vic State Manager Andrew Tupper:
• A downburst is "a swath of straight line winds the descends from the storm and pushes damage out ahead of the storm front"
• A tornado is a "twisting vortex that can cause a winding line of damage not necessarily in the same direction of the storm"
Originally published as Tornado or not? Experts probe trail of destruction