So I thought I'd kick this topic off as a way for people to discuss the hows, whats, whys, whens etc. of recent events culminating in the tragedies that happened in Toowoomba as well as for communities along the Lockyer Creek on Monday the 10th of January. In addition to that event we saw further heavy rain received on the 11th in catchment areas that has Brisbane in it's most serious flood situation since 1974.

The idea behind kicking this thread off is to create a thread where we can (re)visit some of the facts surrounding the weather in the lead up to the event, the weather of the actual event, model accuracy as well as also looking at responses from the community, the authorities as well as the media.

I think it would be appropriate for members to feel free to list their thoughts and opinions so that we can revisit them at a future point in time when hindsight is a bit more 20/20. I would encourage people to be objective in their posts as much as they can, I know emotions are running raw at the moment and sometimes they'll be difficult to deal with but I'm optimistic that if we can make this a rational discussion that many positives will be gleaned from this event.

Cheers,

Andy

Good topic mate Ill post in here soon as my report is done!

The one thing that several people have mentioned both in the print and TV media is the lack of warnings that occured in Toowoomba. This was put to bed quite quickly by the BoM Spokesman who stated quite clearly that although Australia has world class forecasting systems in place the rain event happened so quickly that no warnings where able to be given. Brisbane/Ipswitch on the other hand had at least 2 days clear warning what was about to occur and acted accordingly.

I think the first thing needed is an accurate time line - exactly when did the rain hit Esk, the ranges in from of Toowoomba, Toowoomba itself, what time was the flash flood in Toowomba, what time did the flash floods hit the townships below Toowoomba.

The first real warning on the thread here on WZ seems to have been at 12.16pm by Anthony C, and the next serious comment by buster at 1.10pm and Adam Ant at 1.41pm. Having a time line would help put these posts in context.

126 Radar 10/01/11
256 Radar 10/01/11

Can someone archive these loops. Eventually they will disappear from this site. Also does anyone know if you can get the radar rainfall images somewhere?

Reading back into the thread, a couple of posts have given my shivers up my spine.


















I could go on and on with the quotes...

Couple more interesting posts


And finally here is the warning




and at 5.04pm

Adam Ant,

Funny, I was just going through the forum and picking out the same quotes as you did !

Permanent radar archives are available online - start here then change the dates/times to show what you want to illustrate:

http://www.theweatherchaser.com/radar-loop/IDR663-brisbane/

The 24 hour rainfall total maps from the radar are still available - is that what you meant?

http://www.bom.gov.au/products/IDR66D.loop.shtml

Pause the looping, click the print button and you can save them.

MB

Keep them coming guys, I'm assembling a timeline as quick as I can between work commitments I'll post it once I've got a few more events listed. I'll also try and figure out if I can make it user friendly by adding URLs to individual posts etc. I mucked around in Google Docs for a while to see if we could do a collaborative effort but the timeline gadget is a bit rudimentary and doesn't really allow us to 'zoom down' as posts / warnings were given out, hence I'm using good ole MS-Excel.

Someone has done up a radar image on you tube for this day

For some reason I can never get that weatherchaser site to work. Any chance someone else could get it for me? Im after the boms hourly rainfall rates since 9am for that particular storm that are produced by the radar.

Heres one for the whole week !

Radar for the 4 Jan to 12 Jan

It might take a while to load, but its well worth it. Put it on the fastest speed. Its just amazing

Thanks Adam Ant but my PC could not handle the week of scans it went crash lol.

I'm only posting this for illustration purposes showing how quickly a small stream can rise from saturated grounds that had a deluge re the radar image I posted before. It was a very sad day and lives were lost, but every disaster that happens we learn from this epecially if your in a area that you think it will not flood this is a great example, and also gives flash flooding a whole new name and could possibly happen again during this wet season so be aware.

Adam, here's those 24 hour doppler accumulated rainfalls:







In terms of the Toowoomba/Lockyer valley blob...I can recall the first two levels of the 100+ red colour from that cell itself. The 24 hour falls are affected by the beginnings of the intense rain/storm line for Tuesday, as it was building on the ranges between midnight and sunrise on Tuesday morning.

Just reading this thread, I had no idea some of these posts were so damning...I don't even remember making half of them! Been so crazy since early Tuesday afternoon when the first reports out of Toowoomba and the upper Lockyer appeared.

AC and I have mentioned to each other multiple times in the last few days that the damage in the upper Lockyer looks like tornado damage...some solid mid-range 'tornado damage' with houses completely swept off their foundations etc etc. Just maybe minus all the trees being uprooted and being stripped of all their branches!

I never quite understood why this event was so severe. 56mm in an hour, or 111m in 2 hours does not seem enough to produce the amount of flooding I witnessed. The radar signature to me seemed to be consistent with such falls. Note that on the next next day somewhere near Strathpine had 100mm in one hour, and also at Savages Crossing there were falls of >80mm in successive hours, and maybe half a dozen times I saw falls of about 50-60mm in an hour around Maleny or near Noosa. And rainfall rates of 60mm in an hour probably happen several times each year at least.

Is it just because of where the rain falls that we saw such an extreme flash flood? Were there other walls of water associated with some of these other falls that hit empty forest with no one in them? Were there perhaps much larger rainfall amounts that didn't fall in the official BOM gauges? Jeff Masters claimed that 150mm fell in half an hour, which feels more in accord with the severity of the event (link). Or was it just that the rain fell in the wrong area where the rain could be rapidly funnelled by steep hills into a populated area? Are there other such spots where what I would call typical heavy slow moving thunderstorm rainfall would produce the same result? Which would suggest knowing where these spots are so special warnings can be issued if a high precipitation storm is heading for such a spot.

Alrighty, I've whipped this together to get things started (clickable thumbnail):


So what I would like to do is start getting some of the BOM warnings together, some of the more standout observations as well as drilling down a few of the member's predictions/observations from the forum.

Mike, I've been surprised in the past week by creek level rises as the result of fairly minor rainfall. I think the saturated ground is the greatest factor in the creek level rises.

Ditto that...the Logan River's nearly hit moderate flooding at Waterford after barely a fraction of the rainfall in the catchment that the Brisbane/Bremer/Lockyer/Caboolture/everywhere else has had over the last few days... I have had puddles in lower lying areas of my yard (sandy loam and/or clay soil) for quite literally WEEKS...for the time being, every mm of rainfall across SE QLD (and many other parts of the state at the moment) becomes runoff, and hence the severity of an event like Toowoomba

Mike, If you look at my post above (with the accumulated precip images) you can see that yes it is very likely that there were falls approaching 100mm in an hour in the catchment above Grantham/Helidon. I remember watching the radar and there just wasn't a rain gauge underneath the blob...as the network is a little on the sparse side. Frustratingly, even though this cell was very large, it was *just* missing the gauges to its north and south! As the event was unfolding I was really looking for some confirmation of the heavy rainfall underneath this cell, but just couldn't quite confirm it until the Helidon flood gauge shot up!

However two key factors in my opinion are:

1) The incredible saturation of the entire escarpment region - Andy has a story on what the soil is like at his property at the foot of Cunningham's Gap - is hugely responsible. There are landslides everywhere along the escarpment in recent weeks as a result. Cunningham's Gap has probably spent more time closed than open since Xmas!!! There is no soaking into the soils at the moment, just pure runoff. This comparison is not entirely accurate, but if you get 100mm in quick time, you could consider it more like 200mm at the moment!

If there's ever a time for the incorrect use of the scientific term 'supersaturation' then now is the time. Supercells, super storms all these other super words!

This saturation would only have been made worse by the fact that the area received 100-150mm in the 24 hours leading up to the event (Upper Sandy Creek Alert recorded 131mm in that period).

2) Also the size of this rain blob was right up there in terms of the largest cells I've seen on radar over the years. Often in a lot of flash flooding/intense rainfall scenarios, you have a relatively small area that cops the rain, and you can see brief flash flooding down streets etc which quickly goes down. On this occasion we had a much wider area copping those (effective) 100-200mm/h rain rates...which adds up to an epic wall of water thundering down the hill in multiple creeks, and out onto the floodplain.

Also of note...Grantham had been flooded twice between Christmas and New Year, its really sad to reflect on a news story only a week ago on how things were a bit tough there...but they were soldiering on.



Looking at the radar loop I'm pretty confident that there would be in other catchments to the NE...which coincidentally enough is in empty forest with nobody in them just as you say.



I think there’s also a bit of this funnelling effect…around Helidon and Grantham it’s a flatter area where all the creeks in the hills merge, so certainly could’ve been a double whammy style effect there.

I am not here to scare people, but because of the extreme saturation, everyone should be aware that all of SEQ is vulnerable to these extreme flash flooding events at the moment. Not quite up there with what we've seen in the upper Lockyer, but certainly of the "water flowing where you've never seen it flow before" type scenario.

Here's a loop of the cell itself for anyone who wants to have a look for themself:

http://www.theweatherchaser.com/radar-loop/IDR663-brisbane/2011-01-10-01/2011-01-10-05

I did not see any rollback plan for this one but had given prior endorsement on Sunday. It was not until the Wife dropped me the Tuesday 10:30AM texter “Have you been evacuated yet?” that it all began for this little country town, BrisVenice.

Lately it's been worth a wx check before the week kicks off to find an exception to the norm. There's a backlog of outdoor activities building longer than a queue of cars chasing sandbags 24 hours out from ground zero. I do not even recall what activities I had planned to do this week, it may have been the hedging or the spiders – but web archive recalls the forecast that was presented while having a look on Sunday evening (and was continued to be published by the BOM during Monday I believe):

Monday - Rain, heavy at times
Tuesday - Rain periods, possible thunder
Wednesday - A few showers
Thursday - A shower or two
Friday - A shower or two

Normally posting about the weather isn't something I do on Facebook unless it's somewhat significant. This season we've become normalised to showers, mostly (and rain, somewhat). The monotony is really getting to us. So why do I drop this post on my Facebook account Sunday 9th Jan about the wx ? Significant one would assume

That’s a computer model and three days out they are fairly accurate. It forecasts 400mls in a few days for most of the South East Queensland corner. That’s 133mls per day for three days in the entire Brisbane River Catchment (SEQ). So let’s reflect the facts in a revised forecast and have another go retrospectively shall we? This would have come in handy for a few around town. I could have planned the week a bit better.

The rain gauge at Somerset Dam sits near the centre of the catchment and matches the centre of that red 400mls hotspot in the accumulated precipitation forecast, so here’ s the precipitation forecast based purely off the GFS:

Monday - January’s Average Monthly Rainfall
Tuesday - January’s Average Monthly Rainfall again: perhaps finish up work early
Wednesday - January’s Average Monthly Rainfall: but this might come earlier, either way it's incoming
Thursday - Not much: ^ is enough
Friday - Not much

It may have been this thread that encouraged me to run that GFS out to the social network on Sunday as it had reached that level-of-certainty threshold to publish.

The events Brisbane experienced this week were clearly not articulated in the 5-day forecast and I hear on the news they are already calls into an enquiry on it. I’m no meteorologist, but I do know how to read a few tools. If you want to see where it fell during Monday (over Toowoomba) and Tuesday (in the Brisbane Valley) check out Chops .

I look forward to the BOM 2011 Flood Report, which will be the best read since this one from 1974 .