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Offline crikey  
#1 Posted : Monday, 23 September 2019 9:08:37 AM(UTC)
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I thought seeing there was already discussion on the possibility of this event and some model divergence.
Thought it would be good to give this its own thread.

After all rain has been sparse in this region.

Just the prospect should drum up some interest.

ACC g has are precipitation signal near troughing line in QLD and it seems to hang around, stall? for a few days.
Lets hope something comes of this for everyone who needs it.

A drop,of pressure over Darwin means a positive shift in the SOI

UserPostedImage

source
http://www.bom.gov.au/au...chartSubmit=Refresh+View

Edited by moderator Sunday, 29 September 2019 7:14:05 PM(UTC)  | Reason: Not specified

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Offline juztchillin  
#2 Posted : Monday, 23 September 2019 6:19:46 PM(UTC)
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Skyweather news seem to be on board with the above scenario

A video presentation of the build up

https://twitter.com/SkyW...atus/1175515736422244352

https://www.skyweather.com.au/video/6088252106001

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Offline CantSpellNarangba  
#3 Posted : Monday, 23 September 2019 7:30:00 PM(UTC)
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Haha... You beat me to it!
Mainly because I didn't know what to write about it.

Fingers crossed the planets (well wind really) align and we get something. I would be bloody impressed if it does, because the timing would be almost perfect to what Ken said over one week ago in the day to day thread. ThumpUp

Great links juztchillin Dancing

Edited by user Monday, 23 September 2019 7:32:02 PM(UTC)  | Reason: Not specified

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Offline crikey  
#4 Posted : Tuesday, 24 September 2019 8:30:53 AM(UTC)
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A small downgrade by ACC . However l think that most of that is due tothe start of the event appearing on ACC r which always shows a weaker rain signal than ACC g.

The weak precipitation signal on thursday afternoon is appearing mainly during diurnal max on the 4pm time slot.
This tends to indicate convective activity with embedded storms a possibility.?

The signal has a NW/SE orientation and runs roughly from Winton to the border at Tweed heads.

see map below

Friday afternoon the signal looks stronger.



26th sept 19 qld trough rain.jpg
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Offline CantSpellNarangba  
#5 Posted : Tuesday, 24 September 2019 7:52:27 PM(UTC)
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WATL (as it currently stands) has a small amount of colour for Friday and Saturdays but less than a couple of mm.

PME24_aus.png

PME24_aus (1).png
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Offline crikey  
#6 Posted : Wednesday, 25 September 2019 7:53:33 AM(UTC)
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Thanks for the rainfall forecast CSN.

The ACC r totals look generally small. The troughing lasts for 4 days . From thursday lunch on into next monday with pretty much

the same thing each day. Diurnal max precipitation signal in the afternoon.

A small amount of coral infeed perhaps. If there are storms then some would get more.

Of concern is the high pressure cell south of the rain band which if expands northward would push the rain band northward .


qld trough sept 25.jpg

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Offline juztchillin  
#7 Posted : Wednesday, 25 September 2019 9:11:23 AM(UTC)
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Quite a bit of cloud cover rolling in from the QLD interior. With some speckles of rain in the west of the state.

Some nice thick grey cloud about this morning

The BOM forecast giving the Gold coast very little currently.


Thursday 26 September

Summary
Min 12
Max 23
Shower or two.
Possible rainfall: 0 to 2 mm
Chance of any rain: 60%

Gold Coast area

Cloudy. Medium (60%) chance of showers, most likely from the late morning. Light winds becoming northeasterly 15 to 25 km/h in the middle of the day then tending northerly 15 to 20 km/h in the evening.



The synoptic has some rain pencilled in sparodically over the next few days , so l am up for any surprises

[img]http://www.bom.gov.au/australia/charts/4day_col.shtml[/img]

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Offline crikey  
#8 Posted : Wednesday, 25 September 2019 2:33:34 PM(UTC)
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Quite cloudy at the Tweed.Took a photo down near Pottsville today. Showing the thicker cloud is over the hinterland.
East is Sunny out at sea

The 10am synoptic shows at the border we are at the tail end of the trough here already.

BTW. The radio weather news said chance of storms on friday afternoon


UserPostedImage

DSCF0221.JPG

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Offline juztchillin  
#9 Posted : Wednesday, 25 September 2019 5:59:04 PM(UTC)
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Nice picture Crikey.Love the dogs. That is a nice place. Know it wellBigGrin

Ok .So now we have gone from a forecast of no storms , to storms Friday and now they appear on tomorrows forecast.

So this gets more interesting.

List of towns with storms possible on their forecast

Esk, Gatton,Laidley, Dalby,,Toowoomba , Warwick, Chinchilla, Miles, Oakey,Kingaroy,,Rolleston,Taroom, Tambo,,Roma,AugThella,Injune

The forecast all says late storms .A great start to this event

Edited by user Wednesday, 25 September 2019 6:01:14 PM(UTC)  | Reason: Not specified

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Offline i4hanish  
#10 Posted : Wednesday, 25 September 2019 6:15:14 PM(UTC)
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Practicing some storm analysis here .

Lifted index for tomorrow 4pm. So what does the minus 1 and 2 mean? Is that a significant number?


lifted index qld 26/9/19
http://stormcast.com.au/...00:2019092606:qld:li:#sc
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Offline Ken  
#11 Posted : Wednesday, 25 September 2019 6:43:29 PM(UTC)
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LI = the temp of the environmental air at the height of the 500hpa pressure level (about 18,500 feet up) - the temp of an air parcel if it was lifted to that height (nominally from the surface).

So for example, if the temp of an air parcel that rose to the 500hpa height was -10C and the surrounding air at that height was -15C, the LI would be -5.

In other words, negative LI values indicate that the air parcel is still staying warmer than the surrounding air at that height and therefore will want to keep rising (which are needed to form thunderstorms). The more negative an LI value, the more unstable the air (generally speaking).

BUT just like other indices that measure instability, it relies on various assumptions and has limitations. For example, if the forecast moisture or temp of the air parcel that rises from the surface doesn't reflect reality, the forecast LI value also won't be realistic. Furthermore, parcels of air often don't rise just from the surface on sunny warm days when the lower atmosphere is thoroughly mixed (instead, they rise from that mixed layer that can be thousands of feet deep) so the surface LI values you see on BSCH charts aren't always representative of true instability. And lastly, LI only uses a single fixed height (500hpa) so there can be situations where the temp difference between a rising air parcel and the surrounding environmental air is different at other heights which in turn affects the true instability. CAPE partly overcomes this limitation because it integrates the temp difference through all heights where the parcel stays warmer than the surrounding air but it too, relies on assumptions about the air parcel.

This is why it's a lot better to check forecast soundings (side-on profiles of the atmosphere at any given point) to get an idea of what the instability is like through the whole atmosphere but it can be daunting for people to try and interpret if they're not used to it so LI's still do give a rough idea of where there may be instability.

Any afternoon/evening thunderstorm activity that occurs tomorrow looks somewhat isolated in nature to me, and mainly over inland and southern parts of our region.
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Offline Colmait  
#12 Posted : Wednesday, 25 September 2019 7:16:44 PM(UTC)
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Originally Posted by: i4hanish Go to Quoted Post
Practicing some storm analysis here .

Lifted index for tomorrow 4pm. So what does the minus 1 and 2 mean? Is that a significant number?


lifted index qld 26/9/19
http://stormcast.com.au/...00:2019092606:qld:li:#sc


We are building a thread about thunderstorms and forecasting them. It was started by Squall19. I have been trying to make everything simple. The next part of the thread will be looking at Soundings and how to understand them. I need to really get that part posted ASAP. We are trying to get everyone involved, their input and also for people to ask lots of questions. It will be fun.

https://www.weatherforum...-formation-and-structure

Colin Maitland.
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Offline i4hanish  
#13 Posted : Wednesday, 25 September 2019 7:29:26 PM(UTC)
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Thank you so much for that detailed explanation of LI KEN BigGrin . It is worthwhile keeping so l will copy and paste it in the thunderstorm section where it will not be lost.

Thanks colmait for your tutorial on thunderstorms . I have been reading and will continue to follow.BigGrin

I look forward to checking the radar tomorrow to see how the forecast goes.

I have been looking at some sites on forecasting models.,Way too technical for me.Blushing


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Offline StKildaClare  
#14 Posted : Wednesday, 25 September 2019 7:48:49 PM(UTC)
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I normally click on other forums, but found my way here... Great explanation and nice and simple for me to learn. Thank you Ken!
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Offline i4hanish  
#15 Posted : Thursday, 26 September 2019 9:11:38 AM(UTC)
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The false color satellite is showing some convection and potential in the areas forecast. Also in the negative lifted Index area forecast.


Cool
UserPostedImage

Edited by user Thursday, 26 September 2019 9:12:55 AM(UTC)  | Reason: Not specified

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Offline Ken  
#16 Posted : Thursday, 26 September 2019 9:23:07 AM(UTC)
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UserPostedImage


Most of that's actually just fairly flat low cloud near the coast at the moment with some patchy midlevel cloud as well as you can see in the latest post-processed Himawari satellite imagery above (the colour legend is on the bottom).
There's some deeper cloud further inland although it's not producing much at the moment.
Ideally, you actually want less cloud cover at this time of day so the sun can heat the surface a lot more but there may still be some activity this afternoon and night, mainly favouring southern and possibly western parts.

Edited by user Thursday, 26 September 2019 9:24:08 AM(UTC)  | Reason: Not specified

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Offline SatMan  
#17 Posted : Thursday, 26 September 2019 10:08:05 AM(UTC)
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Wonderful information i4Hamish and Ken. Lots of great information and images to learn from. I live the post-processing image too. I wonder if that is done on cloud top temperature from IR images, or some funky measuring of altitude?

Just had a tiny shower of rain here. More drizzle, with a couple of larger drops. Nothing that can be measured though.


(What I love is there doesn't seem to be any egos here, like I have seen in other forums in the past. A group of people sharing ideas and knowledge to help everyone learn. ThumpUp)

Edited by user Thursday, 26 September 2019 10:12:04 AM(UTC)  | Reason: I had managed to type great 5 times in one message! My English teach would not have been happy.

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Offline whiskyzulu2  
#18 Posted : Thursday, 26 September 2019 12:49:16 PM(UTC)
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The technology we have these days is outstanding. We can really appreciate the science that is involved in weather watching.

I for one am absolutely captivated.!BigGrin
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Offline juztchillin  
#19 Posted : Thursday, 26 September 2019 2:15:59 PM(UTC)
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Lightning tracker showing a strike or 2 out west QLD way. The national loop showing increasing convection along the trough line as expected.
https://www.lightningmap...ceania/index.php?lang=en

I have to report . We have a troughy mess upstairs in the sky. On the ground a daily continues layer of greasy , dusty particles on everything. The car and entertaining area just covered. Again. Not sure if the car will get a free wash today

Headlines from the Gold Coast SUN newspaper. Honey production down by 20% due to bush fires and drought.
The suppliers warning of price increases. Canungra , Mt Tamborine and Mudgereba badly affected

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Offline i4hanish  
#20 Posted : Thursday, 26 September 2019 3:54:12 PM(UTC)
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I am quite impressed with the lifted index forecast by GFS (bsch stormcast)

The current activity is exactly where it was forecast to be .Charleville ,Roma way

Might have a look at tomorrows a bit later on.

26th sept central qld.jpg


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