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#1444085 - 07/12/2017 08:26 SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017
Ken Kato Offline
Weatherzone Addict

Registered: 05/03/2012
Posts: 4741
As at time of writing this, both Friday & Saturday look reasonably good to me for showers & thunderstorms, some possibly severe, for SE QLD, especially slightly inland (as a midlevel shortwave trough & coastal change approaches).
Slightly lower chances for NE NSW but I still wouldn't rule it out especially for the northern tablelands.

On Friday, the low level coastal capping in the morning should temporarily erode by early afternoon before returning again later in the afternoon as the seabreeze comes in. So I think this, combined with less capping inland & moderate WSW steering winds aloft, will probably allow storms to get quite close to, or even reach the coast (storms can often ride over the top of any low level capping or erode the cap if they're strong enough). Also the chance of some of the storms forming close to the coast in some places.
Shear isn't a problem (strong enough to support some severe storms).
Hotter than normal away from the coast so that should help as well.

Friday overnight has the outside chance of more localised showers/storms continuing for some places due to lingering instability and the approaching shortwave.

On Saturday, even if the poorly-defined weakish change does arrive in the morning, there's still the chance of storms forming over higher ground inland of the coast before getting advected towards the coast over the top of the slightly cooler post-change air (if there's still a fair bit of daytime heating even just behind the change and/or it's poorly defined & steering winds aloft are strong enough, storms can often reach the coast behind the change).
There's also the possibility of storms forming near the coast in northern parts ahead of the change.
Even though the midlevel winds themselves don't look hugely strong, the low level SE'lies behind the change undercutting the W to NW'lies aloft enhances the shear in the 0-6km layer so it could be enough to support severe storms.

The negatively-tilted shortwave pivots up over us on Saturday so I hope it's not enough to sustain too much convective cloud debris into the morning but at the same time, still helps with the storms.
We

At this stage, EC and ACCESS-R don't have that much morning cloud cover on either day for SE QLD (ACCESS-R does have a lot of early morning cloud cover on Sat morning but it decreases temporarily later in the morning to allow heating).

1st image - example of the outflow boundaries from storms showing up on EC on Friday evening (I wouldn't take the position of it literally though).

2nd and 3rd images - In the EC soundings below (the low resolution version) for 4pm Fri and 4pm Sat respectively, it's easy to see the aspects I was talking about above:









Edited by Seabreeze (11/12/2017 22:57)
Edit Reason: removed the word "possibly" to reflect what happened

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#1444087 - 07/12/2017 08:38 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Flowin Offline
Weather Freak

Registered: 15/10/2017
Posts: 153
Loc: Pinjarra Hills, Qld
Thanks for the detailed explanation Ken. I think this forum benefits greatly from your input.
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#1444089 - 07/12/2017 08:47 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Flowin]
Nature's Fury Offline
Weatherzone Addict

Registered: 29/11/2009
Posts: 1917
Loc: Brisbane Western Suburbs
Good overview Ken. What are your thoughts on the possibility of supercells with large hail and damaging winds on Saturday? Its quite cold upstairs and shear may not be too bad as you mentioned? Cloud cover and an early start to storms (or late carry-over from the previous night) are probably the biggest issue I can foresee.

Just looking at this set-up I just think it wouldn't take much to see some very nasty storms, although I'm thinking inland in the Brisbane Valley, trending eastward, might be the sweet spot.

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#1444092 - 07/12/2017 09:28 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
gleno71 Offline
Weatherzone Addict

Registered: 09/11/2007
Posts: 1324
Loc: Australia
Thanks Ken, is this capping that we talk about only confined to SE QLD region or does this happen in other parts of Australia? Does capping occur inland ?

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#1444093 - 07/12/2017 09:37 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4741
gleno: It often happens anywhere where a cooler afternoon seabreeze invades the lower levels.

NF: Yep I think a supercell or two is a distinct possibility given the coastal change adds helicity/shear... inland & northern parts look to have the greater risk although possible elsewhere. The midlevel temps aren't a problem as far as hail goes. But that's only provided the current scenario holds. Can never tell for sure until the day.

And no worries Flowin.

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#1444096 - 07/12/2017 10:16 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
gleno71 Offline
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Registered: 09/11/2007
Posts: 1324
Loc: Australia
Thanks Ken

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#1444118 - 07/12/2017 14:04 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4741
Here's a forecast sounding for 1pm Sat for Brisbane, this time from GFS via the Sharppy program displayed on the COD weather site.

The SARS section which matches forecast soundings with how many past similar soundings resulted in large hail only uses cases from the US and not Australia.

I've crossed out some of the parameters because they use cyclonically rotating supercells so they're only valid for the northern hemisphere. Temps are in Fahrenheit.

As you can see, mixed layer CAPE (ML CAPE) which will be fairly representative of the well-mixed atmosphere is showing 1567j/kg which is pretty good, equilibrium level (where rising air parcels stop becoming buoyant and typically indicates the tops of non-overshooting thunderstorms) is a bit under 11km up or just over 35,000ft, MBurst (microburst parameter) is a 3 which implies the slight chance of microburst, DCAPE (Downdraft CAPE) is 1162k/kg which is reasonable for downdraft potential, and ConvT or convective temperature needed to develop convection is 31.7C (but this only applies to parcels only rising from the surface and not a mixed layer like Fri/Sat will be).

The hodograph in the upper right panel is reasonably straight due to not much turning of the winds with height except in the low levels:



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#1444127 - 07/12/2017 16:24 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
HaVoC Offline
Weather Freak

Registered: 19/02/2003
Posts: 248
Loc: SE qld Redlands
Hey ken. Is the sharp py public available? I want to see the charts for boonah / rathdowney.

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#1444134 - 07/12/2017 17:33 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Mad Elf #1.5 Offline
Weatherzone Addict

Registered: 05/03/2012
Posts: 2963
Loc: Mt Hallen QLD
HaVoc, mate, I want to see lots of things but only get to see what others WOULD LIKE me to see. Cheers ;~}
Just a gentle suggestion.


Edited by Mad Elf #1.5 (07/12/2017 17:42)

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#1444137 - 07/12/2017 17:57 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Mad Elf #1.5 Offline
Weatherzone Addict

Registered: 05/03/2012
Posts: 2963
Loc: Mt Hallen QLD
Thanks for your posts & graphs Ken, I'd just like to know our chances of severe thunderstorm potential on Sat night, hosting a 21st & got lots of people coming. Much to worry about? BBQ as usual. Cheers Ta.


Edited by Mad Elf #1.5 (07/12/2017 18:02)

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#1444141 - 07/12/2017 18:36 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Stormwalker Offline
Weather Freak

Registered: 13/11/2013
Posts: 63
Thanks Ken.

Any suggestions as to where the most photogenic storms would likely form?

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#1444145 - 07/12/2017 18:51 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Flowin Offline
Weather Freak

Registered: 15/10/2017
Posts: 153
Loc: Pinjarra Hills, Qld
Nothing to do with potential storms in this thread,... I read some time ago that Moogerah near Boonah has aboriginal meaning for home of the thunderstorm

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#1444160 - 07/12/2017 19:56 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Flowin]
Sandstorm Offline
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Registered: 01/02/2003
Posts: 293
Loc: Highvale
Originally Posted By: Flowin
Nothing to do with potential storms in this thread,... I read some time ago that Moogerah near Boonah has aboriginal meaning for home of the thunderstorm

Correct... Aboriginal word Moojirah, meaning "home of the thunderstorm."
Source = Wikipedia
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Some mornings I wake up grumpy but most mornings I let her sleep in.

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#1444174 - 07/12/2017 20:53 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Ken Kato Offline
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Registered: 05/03/2012
Posts: 4741
Mad Elf: Assuming you're having it at Mt Hallen and it's after sunset, I'd rate storm chances as borderline, decreasing as you go further into the night. If you were in Brisbane, I'd say your chances would be a lot lower since much of the activity probably would've eased here by then but since you're a bit inland and a bit to the north, might just be the slight chance of lingering activity (or some showers) early in the evening. The later on it gets, the less the chances.
I'd check closer to the day though in case that changes.

Stormwalker: That good old general region around places like Boonah, Rathdowney, etc are often fairly reliable as a base... then play it by ear.

Havoc: Yep they're at http://weather.cod.edu/forecast/

The video below is ACCESS-C's current suggestion (via Weatherzone Layers at https://www.weatherzone.com.au/layers/) for how things might evolve between 6am and midnight Friday at 60min intervals - again, I definitely wouldn't treat the timings and positions of that precip literally but it gives a general idea of how things might eventuate.
I'd recommend signing up to Layers if you're any kind of weather enthusiast.

Example of those Sharppy soundings for Boonah for Saturday afternoon below:






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#1444183 - 07/12/2017 21:30 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Mad Elf #1.5 Offline
Weatherzone Addict

Registered: 05/03/2012
Posts: 2963
Loc: Mt Hallen QLD
Thanks Ken, any rain is good rain, but NOT on Saturday, cheers.

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#1444187 - 07/12/2017 22:04 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
gleno71 Offline
Weatherzone Addict

Registered: 09/11/2007
Posts: 1324
Loc: Australia
Weatherzone layers is awesome. I have learnt a lot from it

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#1444189 - 07/12/2017 22:13 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Mad Elf #1.5]
Flowin Offline
Weather Freak

Registered: 15/10/2017
Posts: 153
Loc: Pinjarra Hills, Qld
Originally Posted By: Mad Elf #1.5
Thanks Ken, any rain is good rain, but NOT on Saturday, cheers.


I would say situation is still in early possibility phase. Timing and location still up for further changes. For now something appears imminent
Three things to think about
1) be prepared for range of possibles
2) check the latest here and other trusted warning sources
3) have a backup plan

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#1444196 - 08/12/2017 08:16 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Ken Kato Offline
Weatherzone Addict

Registered: 05/03/2012
Posts: 4741
I really can't see too many things wrong with today's setup (albeit without the coastal change).

1st image - ACCESS-C trying to form a supercell/meso behind the Sunshine Coast later today which shows up in the wind fields from near the surface up to 700hpa... the 700hpa wind field below (via Weatherzone Layers)... definitely NOT one to take too literally though.

2nd image - self-explanatory (but uses yesterday's 00z run of those models because the latest 12z run of one of them wasn't available so it's bit outdated now).

3rd image - thunderstorm script output for between 6am and midnight today:







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#1444198 - 08/12/2017 08:24 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
Mad Elf #1.5 Offline
Weatherzone Addict

Registered: 05/03/2012
Posts: 2963
Loc: Mt Hallen QLD
Thanks Flowin, we have plenty cover but not enough for the cars if there is hail. Should be interesting couple of days.

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#1444200 - 08/12/2017 08:31 Re: SEQLD/NENSW - Thunderstorms, some severe - 8th/9th Dec 2017 [Re: Ken Kato]
storms95 Offline
Weather Freak

Registered: 09/11/2011
Posts: 572
Loc: Northside of Brisbane
Well it's finally Friday, which means we will finally see a classic hot summers day with the risk of afternoon severe storms! After a very disappointing November hopefully today and tomorrow can start making up for it!

Most models are hinting that activity could become scattered/ possibly even widespread right across the southeast corner, with the Access C model suggesting areas from Brisbane to Noosa will be a focus, but hopefully the Brisbane region will be as I think the Sunshine Coast have had there fair share this season 😜

It's a shame Mt Stapylton is down at the moment, hopefully it's up and running before this afternoon.

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