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#1438688 - 24/10/2017 08:42 SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4683
Still a couple of days to go til Thursday, so I hope this setup doesn't change TOO much before then (especially the mainly sunny morning).

Here's some of my observations and thoughts about this setup:

* Thunderstorm outbreak (majority high-based)...possibly severe (damaging winds) in some places...afternoon & early evening....more likely in south & west of SE QLD (but could spread everywhere due to the strong steering winds).
* Mainly sunny morning skies according to current modelling... and hotter than normal.
* Storms initiating inland at first... then rapidly sweeping towards the coast due the impressively strong W'ly steering (if storms remain discrete).
* Although a squall line is possible due to the unidirectional strong W'ly flow through a deep slab of the atmosphere, if things stay too dry storms could remain discrete & not form a squall line. If a squall line does manage to form, it'll probably appear to move slower on radar.
* Main threat looks like damaging winds due to the drier low levels & momentum transfer of strong winds aloft. Large hail looks a lesser threat although maybe not impossible if any storms manage to ingest high dewpoint air from the low levels.
* Heavy rain also looks a lesser threat due to the drier low levels (rainfall should be short & sharp due to the fast-moving nature).
* Shear (and instability) looks great with bulk wind difference in the 0-6km layer up to 45-55kt in some places.

The only two things I don't like about this setup which I would've liked to have seen to make it better:
* Lack of a southerly coastal change.
* Relatively dry low levels due to the mainly NNW flow (I would've preferred a stronger seabreeze front to penetrate a bit further inland with more moisture). If a reasonable seabreeze front does manage to form late Thursday though, storms might strengthen as they get closer to the coast.

I don't know how accurate the thunderstorm outlook in Weatherzone Layers is, nor what algorithm it uses but it has a big belt of red all over us.

Here's an OCF map showing the percentages of the models currently going for any rainfall between 9am Thursday and 9am Friday:



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#1438700 - 24/10/2017 09:40 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Colin Maitland Offline
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Registered: 01/09/2009
Posts: 2383
Loc: North Brisbane ( Bracken Ridge...
Thanks Ken for the info and as always I like the summary.

I am waiting for this afternoons run to check the latest data. This morning TTs were up to 56 so a bit stronger than yesterday and cape was down slightly. I don't like the current seabreeze running parallel with the coast were yesterday there was a bit of a feeder. Looks like the moisture will need to feed of the inland trough going by EC.

I was thinking much along the same as squall lines being a possibility, and if we had a bit more energy/cape we could have seen a bit of a bow echo or derecho storm system but a few things missing at this point.
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#1438701 - 24/10/2017 09:40 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4683
No worries Colin.
The marginal moisture is the biggest turn-off in this setup for me.

I'm hoping it doesn't get too much drier because I've seen some cases where even slightly drier profiles have led to very little activity (or very isolated) even in those southern and western parts. And excessively dry profiles decrease the chances of a squall line even with a favourable vertical wind structure.


Edited by Ken Kato (24/10/2017 09:43)
Edit Reason: added stuff

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#1438707 - 24/10/2017 10:20 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
TWEEDSTORM Offline
Weather Freak

Registered: 08/01/2012
Posts: 616
Loc: Tweed Heads NSW
Where would we be without you guys! Might get an LP supercell with the low moisture profile or something vicious hopefully.

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#1438710 - 24/10/2017 10:25 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4683
I'm still nervous about the extent of the activity... it really wouldn't take much for things to be far more isolated than expected and to be confined much further to the south/southwest (I hope not though).

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#1438712 - 24/10/2017 10:35 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Mega Offline
Meteorological Motor Mouth

Registered: 03/02/2003
Posts: 6623
Loc: Maryborough, Wide Bay, QLD
Nobody answered my question in the other thread;

Is the shear profile linear or not? And I was under the impression that squall lines are less likely in a setup where shear is more linear?

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#1438718 - 24/10/2017 10:58 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Mega]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4683
Originally Posted By: Mega
Nobody answered my question in the other thread;

Is the shear profile linear or not? And I was under the impression that squall lines are less likely in a setup where shear is more linear?


Actually answered in one of the dot points I made...

" Although a squall line is possible due to the unidirectional strong W'ly flow through a deep slab of the atmosphere, if things stay too dry storms could remain discrete & not form a squall line. "

Squall lines tend to be more likely when there's a deep slab of reasonably strong westerlies aloft i.e. linear (unidirectional) flow combined with adequate moisture and instability. In Thursday's case, the deep linear westerly flow is there but the moisture is borderline.

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#1438719 - 24/10/2017 10:59 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Mega Offline
Meteorological Motor Mouth

Registered: 03/02/2003
Posts: 6623
Loc: Maryborough, Wide Bay, QLD
Okay, it looks as though I may have it the wrong way round. Linear / straight line winds = good for squall line development.

And I can't believe we're talking borderline moisture after such wet conditions for the last month or so.

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#1438729 - 24/10/2017 13:22 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Steve O Offline
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Registered: 02/03/2011
Posts: 2931
Loc: Beenleigh, QLD
Last I looked dewpoint was in the high teens on the surface but above the LCL there looked to be a lot of moisture with the big chunk of those W'lys aloft. I've seen this kind of profile before and it looks like a squall line setup even last nights ACC R had a long line of precip. As we know the conditions can change quite quickly with a different wind direction in the lower levels though this time not so favourable for a classic supercell when the winds are backing with height, this is much more straight line as noted above.

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#1438739 - 24/10/2017 14:54 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Steve O]
Nature's Fury Offline
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Registered: 29/11/2009
Posts: 1878
Loc: Brisbane Western Suburbs
I'd settle for a great squall line, but at this point I'm not convinced we'll see anything much at all.

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#1438750 - 24/10/2017 16:10 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
buster Offline
Weather Freak

Registered: 25/09/2006
Posts: 437
Loc: Kalbar (near Boonah) SEQ
Originally Posted By: Ken Kato
If a squall line does manage to form, it'll probably appear to move slower on radar.


Hey Ken, do you mean that a squall line would actually move slower than discrete cells in this situation or are you talking about it being an optical illusion? Whatever forms it will be nearly impossible to keep ahead of if you're chasing. You're right. Those 500 and 700 mb are rocking along, the speediest we've seen in a setup for some time. Might be just as well that hail's unlikely.

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#1438759 - 24/10/2017 17:08 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Steve O Offline
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Registered: 02/03/2011
Posts: 2931
Loc: Beenleigh, QLD
I think that because the radar is 6mins behind realtime obs, so if say a storm front was travelling at 100km/h that's 10ks ahead of the radar that we see. Considering if it was steering in a straight line.

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#1438764 - 24/10/2017 17:33 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4683
Nah it's nothing to do with the radar update rate (in fact, the radar imagery isn't always going to be 6mins behind the current time... 6 mins is the current interval between scans of the doppler radar... it depends on how long ago the last scan was made and when you're watching the radar image).

You can have both slow and fast moving squall lines but generally speaking, they appear to move more slowly on radar because of their size compared to small discrete cells, similar to how a 747 appears to fly more slowly when you see them taking off or descending compared to a smaller aircraft like a 737 even though they're usually going at a similar speed.


Edited by Ken Kato (24/10/2017 17:35)
Edit Reason: added stuff

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#1438785 - 24/10/2017 19:18 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Nature's Fury Offline
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Registered: 29/11/2009
Posts: 1878
Loc: Brisbane Western Suburbs
Last Friday afternoon, the BOM rep on 612 ABC said that the following Friday (Thursday) could see big storms. Even this afternoon there's confidence that it's 'the best setup we've seen in a while'. Great to hear that but looking at the forecast it's only 60% chance of storms in Brisbane. Just shows how this event has both high potential and is fairly marginal.

All 3 major models focus any activity on the Gold Coast with only GFS suggesting equal activity northward. Brisbane seems in the donut hole on all 3.


Edited by Nature's Fury (24/10/2017 19:20)

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#1438793 - 24/10/2017 19:34 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Nature's Fury]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4683
Originally Posted By: Nature's Fury
Last Friday afternoon, the BOM rep on 612 ABC said that the following Friday (Thursday) could see big storms. Even this afternoon there's confidence that it's 'the best setup we've seen in a while'. Great to hear that but looking at the forecast it's only 60% chance of storms in Brisbane. Just shows how this event has both high potential and is fairly marginal.

All 3 major models focus any activity on the Gold Coast with only GFS suggesting equal activity northward. Brisbane seems in the donut hole on all 3.


It's often a bad idea to treat model precip areas as areas where all storms will be confined to.
We've seen time and time again that when steering winds aloft are strong, some longer lived storms can get advected well outside those precip areas. It doesn't happen all the time but it happens often enough to warrant caution with treating those areas too literally. I usually treat those precip areas as the more likely areas where storms will form... then mentally extend them downstream a bit when steering winds are strong.
Not saying that'll definitely happen with Thursday but it's good to keep that in the back of the mind anyway.

Incidentally, early next week looks interesting for instability too.

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#1438806 - 24/10/2017 21:32 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Nature's Fury Offline
Weatherzone Addict

Registered: 29/11/2009
Posts: 1878
Loc: Brisbane Western Suburbs
Originally Posted By: Ken Kato
Originally Posted By: Nature's Fury
Last Friday afternoon, the BOM rep on 612 ABC said that the following Friday (Thursday) could see big storms. Even this afternoon there's confidence that it's 'the best setup we've seen in a while'. Great to hear that but looking at the forecast it's only 60% chance of storms in Brisbane. Just shows how this event has both high potential and is fairly marginal.

All 3 major models focus any activity on the Gold Coast with only GFS suggesting equal activity northward. Brisbane seems in the donut hole on all 3.


It's often a bad idea to treat model precip areas as areas where all storms will be confined to.
We've seen time and time again that when steering winds aloft are strong, some longer lived storms can get advected well outside those precip areas. It doesn't happen all the time but it happens often enough to warrant caution with treating those areas too literally. I usually treat those precip areas as the more likely areas where storms will form... then mentally extend them downstream a bit when steering winds are strong.
Not saying that'll definitely happen with Thursday but it's good to keep that in the back of the mind anyway.

Incidentally, early next week looks interesting for instability too.


Good points, although the NW'ly steering won't help our case. For anything to reach Brisbane it will have to form north-west of us unless it's a left-mover (don't think supercells are a high risk factor in this set-up though). I'd rather be south of Brisbane, particularly GC/border ranges.


Edited by Nature's Fury (24/10/2017 21:32)

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#1438807 - 24/10/2017 21:34 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4683
It's still a westerly steering flow according to most models.

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#1438809 - 24/10/2017 22:03 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
Colin Maitland Offline
Weatherzone Addict

Registered: 01/09/2009
Posts: 2383
Loc: North Brisbane ( Bracken Ridge...
Over the last 50 years I have been in some massive storms and supercells coming from the NorthWest , usually I associate these storms with strong winds and rain as the main destructive component.

Ec and GFS ( GFS being a little more generous although it would be great if this one came to fruition), has moisture and light rain moving in with this system but I donít think rain will be a problem at this stage.

Also I agree with Ken that it is is a Westerly steering. Ec and GFS are pretty close on this one.

Just on another note the ABC and WZ News has article calling Bunderberg the Tornado Alley of QLD. The BoM stated that there are more tornadoes than most people realise due to the vast open unpopulated areas, but as these are developing more tornadoes are spotted.I will try and post the article tomorrow in the day thread.
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#1438812 - 24/10/2017 23:49 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
ColdFront Offline
Meteorological Motor Mouth

Registered: 29/06/2008
Posts: 17921
Loc: Wide Bay..Near the beach
Bundaberg Colin wink

I have spoken to someone whose house was destroyed by that f4 in the 90's at Bucca near Bundaberg (he was at work like most thankfully) and another whose verandah was torn off by a tornado near Gin Gin in February last year. I've also seen a few very suspect looking cells on radar since moving down here and all were moving sth east down the front of an approaching trough from the sth west.

The one that took off the lady's verandah moved south east. Interestingly the Bucca f4 came up from the south west.
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#1438813 - 25/10/2017 00:20 Re: SEQLD/NENSW - Thunderstorms, some possibly severe - Thu 26th Oct 2017 [Re: Ken Kato]
bundybear Offline
Weatherzone Addict

Registered: 28/12/2010
Posts: 2130
Loc: Between Bundy and Gladstone
This is a bit of video from what we believe was a torando through our place years ago. You could see the track it took through our property. Neighbours either side had very little damage. We had trees twisted out of the ground. It went from a normal storm to instant Armageddon in a minute. Sounded like a freight train. It was so loud that we did not hear any of these trees drop.

https://www.youtube.com/watch?v=DIWfRNtn0q8

Excuse the poor quality video as it was recorded of an old vhs video on the tele.

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