Australian Severe Weather Forum

In relation to occlusion.  When a thunderstorm tower - either supercellular or 'standard' is described as having an occluded tower, what is meant by this?  Is there a pic that can be shown to display this if it is something not common per se?

Also in relation to supercells generally within the eastern states: what percentage of these are right movers and how many encountered were left movers?  A simply ratio or percentage figure will suffice thanks gentlemen !

Mike

Hi Mike,

Try compaing there two images of the same tornado:





You can see the top image is in its reasonably strong mature stage - well it took out a house causing F2 damage at the time and the second image shows the process of the occlusion. The process of occlusion sees the gradual separation from the supercell of an updraft as the fuel or inflow gradually gets cut off. This is when you normally see roping out of the tornado - sometimes in sunshine!

For cyclic supercells, this is not a problem as usually a second mesocyclone is in operation and ready to drop another tornado or one is on the ground. The supercell above produced 5 tornadoes during the afternoon and evening.

Regards,

Jimmy Deguara

Hi Jimmy, 

So as far as this scenario : observing a developing wall cloud with good lowering and rotation and subsequent funnel emerged, why would the tower be in the stages of occulsion at the same time?  If occlusion is the separation or lifting mechanism of different air temp masses/boundaries etc, would not the supercell be dissipating and tornadogensis weaken if this was happening?

So occlusion does not necesarily mean dissipation if the updraught is strong and there is a strong middle or high level jet to discard any precip that may impede inlfow and meso formation - hence the funnel formed even though the tower was occluding?  It's just that the storm was strong enough to keep the inflow warm by actually inhibiting the precip and cold pool from impeding its progress?

As your photos depicted and you mentioned that the same cell produced more tornadoes, if it's cyclic then my comment above is correct?

I think i'm on the right track - I'm picturing it in my head...and probably answered it myself but you can sympathize with me as I try to get the terminology right with what's in my head!

Mike

If you had easterly winds at 20kts from 750 to 500mb constant and above that they dropped off and below that they started at 10kts, that would not be classified as significant shear would it?  As it's not increasing or changing direction with height it would not be classed as 'shear' could it?  Or is shear in this sense a strong wind profile within a certain Mb that is unchanging with height?

Mike

I was watching some weak convection today over the Islands to our north - they tend to spark the onset of buildup convectioin this time of year - i was observing a line of clouds and it occurred to me that do these small scale CU clouds exhibit the same properties of maturing thunderstorms?

 I observed what looked like an inflow tail and a wall cloud underneath on one in particular - it certainly was a textbook shape and fanned out slightly at the lower edges and then lifted back up into the cloud.  There were strong winds in the uppers as the domes were being pushed out to the side in opposition to the direction the thick clouds were travelling.  Now is this possible to observe this or was i just seeing what i thought looked like a small wall cloud. It was not scud and definitely had the lowering shape and structure - if this Cu was an actual thunderstorm i'd almost be convinced.

Mike

Mike,

Without photographs it becomes rather difficult to visualise what you mean.

Are you referring to a base structure like this?



or



Regards,

Jimmy Deguara

Is difficult to visualise i know, but i was at work having a break outside.  The cloud formations weren't as the photos.  The best was to describe it would be fairly fat CU with flat blue/grey base, medium sized core with definite 'bubbling' or rising of the tower with what looked like an inflow finger on the left hand side of the base and below a wall cloud (or close to it!) - of a definiative shape, gradually lowered and the base of that fanned out slightly and then rose up into the base once the towers were bent to the left.  It was like a thunderstorm in its early stages before it anvils out and dissipates due to weakening...beats me - it just looked pretty neat considering....

MO

Hi guys,

Mike: Good to hear your seeing some nice storm structures up there! Do you have the means to keep a small digital camera with you at all (though these days some of the small cameras rival the lager non-SLR versions!) I'm in the same boat as you, as far as not having any means to catch anything interesting that may show up while I'm out at work? I have my Mob. phone camera but it just doesn't cut it lol.

Jimmy: Just a quick question for you- In that first (top) reference picture you've posted, is that lower base cloud structure still class-able as lenticular even though it is under the higher cloud features, anvil, towers and inflow bands and such? Ive seen similar structured cloud under storm bases before and I've always been curious about it?

Cheers and thanks for your time
Shauno

Hey Shauno.  Bit early for storms, but just a bit of convective stuff that puffed up as the transition period is taking its steps towards the buildup period and more instability later down the weeks ahead.  Signs are good for an early wet by what BoM says in their MJO and SOI reports - fingers crossed.

MO

Shaun,


I would say it is some sort of lenticular or capping type of cloud that has developed under the large cumulus feature.

Regards,

Jimmy Deguara

Hi guys,


Sounds good Mike! I hope you can get some great shots to share with us this year!


Thanks Jimmy, much appreciated! (It was just one of those weird little curious questions that pop up now and again?)

Cheers and take care.
Shauno

Now Thats funny!!! Then again we were all noobies once, Hell (compared to some of these guys (veterans)) i still am lol

QUOTE(2) Jimmy mentioned that LIs less than -6 or lower there would not be much storm potential, yet other forum members said they go by LI of -3 at times?  I don't get it.  Is it the higher the LI the better potential for storm activity, is that it?END QUOTE

If other Variables are in order you can have lighting (hence thunder) -1 or zero even, though unlikly especially in the current climate.

So what im getting at is: You can potentially get Thunderstorms with any negative Value. The more Negative the stronger the updraft. (Up draft is lotsa air going up lol) oh yeh LI is short for Lifted Index. But yeh most people will tell you if its not more negative than say -2 or -3 you prolly shouldnt bother, though -3 is certainly getting there. One day check out the Tornedo ally Lifted index in the US. They must have masive updrafts.

I think maybe it depends where in Aust your chasing too. When I lived in SE qld, during like 2002 to 2004, there were regularly storms that only had LI's of -1, or -2. on the GFS charts

I also find that the more CAPE the more lightning, but im sure I'll be told this is not necasarily the case. You can potentially have lightning with CAPE values of as little as 100. 9if all other variables are good) with 100 CAPE you may get 1 to 5 Strikes per minute. But for as decent lightshow you really need upwards of say 700. With values in the thousands mother nature really tendss to turn it on. The lightning that is.

***NOTE***You shouldnt take what I say too seriosuly as Im very lay indeed with Storm chasing. So just use what I said as a guide a bit.

One day I am going to write a book that shows primary school children how to forecast a thunderstorm. I may even contact the "for dummies" assoc and see if I cant write a "storm Chasing 'for dummies' book. Just ill need to get a little more educated on general meteorology so as not to lead these poor kids astray with crap. Im also a chronic procrastinator, so Unless someone beats me to it, it may never happen by me... hint hint nudge nudge anyone?!?!?  anyone wanna colaborate. Id be a good person to do it with. If I cant understand it no one can lol

Hi Supercellwish,

That quote of mine is now a double misquote or misinterpretation. I recall correcting the last person on that one.

In terms of LI or Surface lifted Index for those browsing this forum for the first time represents a measure of estimating the instability of the atmosphere. Thy are derived from soundings or models but are just a good measure of what potential exists. Obviously, there are other factors in play as well to consider which includes moisture depth that could contaminate some soundings if too shallow, the trigger to set things off in the first place, and heating. The more dynamic the atmosphere, the more potentially severe the storms can get.

I hope this summary places you on the direct path to understanding. Try reading other threads in this forum and you will find out more.

Regards,

Jimmy Deguara

  Hi there Supercellwish.  Long post but i feel some valuable info for you re your book.

Here's a table of what Lifted Index values are:

2 or greater (stable) (+ values)
1 to 0 (almost unstable)
-1 to -4 (troposphere marginally unstable)
-4 to -7 (large instability)
-8 or less (extreme instability)

As I have found out recently you can have massive CAPE and moderate LI numbers but no cloud whatsoever!  There's several elements Mother Nature needs to spark convection properly, without one or the other you'll get zip.

Re your book:

Mr recommendation would be that if your'e writing something for younger folk I would not bother with adding technical stuff  as in LI index numbers as it will only confuse them more - and if you want to keep it in layman's terms use the KISS method - Keep It Simple Stupid (of course not directed personally!).  You can probably use CAPE (Convective Available Potential Energy) as this is the basis for storm type and character.  If you're handy with computer software graphics use simple pics for how storms form - but make your own designs. 

Simple wording without too much technical stuff, but if your book is on storm chasing for dummies you will need to add the techno stuff - it's the fundamentals of storm structure and if you don't include it they'll be missing the point of it all. If your age bracket is aimed at older folk - say 14 upwards you could most likely add the technical stuff because if they're looking to have a career in Met then it would be beneficial. 

Remember to have your book set out in stages, a beginning, a middle and an end.  Keep specific topics within their chapters for ease of reference.  If you use any websites or books as reference make sure you acknowledge them between sentences or on the last credit pages of your book.  Email prospective authors of these resources if you want to use any of their text/graphics - very important you do that because of copyright laws.  I've found that most authors are quite happy to let you do it so long as you ask first.  Because you intend of selling your work for profit it makes it even more important to ask - the best thing is to use your own words and modify references to your own explanations.

The resources within this forum on cloud types, observation are vast so check them out.  You could also visit http://downunderchase.com/storminfo/ which has a comprehensive area on soundings and all the how to's - it's easily worded and is a valuable resource.

Once you get a handle on how things work re storms it will be easy.  Keep things easy for yourself, if you can't undertand it how will anyone else reading your book!  Take your time and make changes.  Read and re-read your work even when you think it's finished, you may have missed something or want to add things.

Printing your book will depend on your budget.  As I'm in the printing game of sorts workwise, go for an A4 sized booklet or smaller. Much like a coffee table type book.  Something that is easy to handle, durable.  The type of paper you decide on, whether you want shiny, matt, gloss.  How many pages?  All these factor in the cost.  Do you want it binded or stapled?  How many photos/graphics? 

First thing you need to do is this:  Make a mock copy of your book with cover, text, photos, graphics and a front/back cover.  Then once you have done take it to a printing business (there's hundreds) and show them what you've done.  They'll work with you re layout, paper, sizing, what they can and can't do and give you a price. What is your market?  Sale price of the book?  Where will you have the book for sale?  Commission prices to those establishments who sell your book - what percentage?  It's not so simple huh!!!!?

 I know I have been quoted to produce my own 30 page photographic storm book in Darwin in A4 size with satin pages for around $3-4,000 with a run of say 5000.  It's not that expensive and you can tailor your book to suit your budget.

Making the book is the easy bit but there's other things to take into account on getting your dream off the ground - but you've started so keep going. You sound like you have a passion so follow it, you won't be dissappointed if you follow through.

If you need a hand with setting the text out i'll give you some assistance with grammar, spelling and the like - as a court typist also it's all i do (boring!!)

Best of luck.

Mike

Thank you mike. Jimmy. I really do understand CAPE and LI. I have had it explained quite a few times, a few years back. Also jimmy, I didnt mean to make it look like I was quoating you. Actually I was trying to make it look like I recogocnised the fact that you said no such thing and that it was incorrect. I was actually trying to just add my thoughts and experinces (even if only few) to the topic. I thought maybe one noob would understand another nube beter than a nube would understand a veteran. It would see that not only do noobs not understand veterans, but vets seem to not understand noobs. LOL. So yeh in effect I belive I did not actually quote you, but quoted the person who quoted you. You actually said no such thing. It was a post right before or after yours. And the bloke who miss quoted/understood Just got the nic mixed up because somebody actually did state that you cant get storms unless you got -6 Li which even I know is inccorect to say the least. So I was actually trying to make a bit of a Joke out of it.

Moving along now to Mike, thanks heaps for you tips there. I have copy pasted that into my personal documeants folder on my file/webserver for later when I begin the book. I want to go through another season of chasing first I think before I set about writing the book. So come may 2008 when the weather (I like) has gone. Il begin writing, drawing etc, oh yes and researching. Not a single line will be printed or proposed for printing untill its beeen tripple checked for accuracy by some chasers and Met men respectively. Also it will be for teens upward. Im sure theres plenty of books with pictures and brief descriptions. I want write a handbook, or manual. So yes I would love for you (or anyone else) to help me with spelling and grammar as I am hopless with it. Sometimes though its just because i type faster than I should and end up hitting wrong keys, then out of pure laziness I fail to check or correct my spelling. Though this really is limited to forums and Instant messaging. no excuse I know lol. So thanks again friend

Oh one more thing, Did I get somthing wrong when I was explaining to what his name about CAPE and Li?

Happy Chasing Guys.

Hopefully I will be seing some lightning off of Cape Otway Vic tommorow afternoon/evening /Based on the 06Z GFS Run looking at the 03z image of Vic CAPE and Li. 03Z fri 1000mb CAPE and LiftX
Click on that to see the same image im looking at. That was the lates run at the time of typing this. Im not very good at looking at Skew-t's and understanding them, but from the guides of been reading around here over the years I cant tell they are imperative. So it looks like there is plenty of Windspeed var with heaight but not alot of change in dir. My main dilema is could there be lightning earlier than say 03z , I was thinking (hoping) that because the air is so cold, their might be significant temp variation between the ocean and the air. Am I on the right track? So I though maybe even though the sun has not yet cooked the clouds the o0cean may provide enough energy to throw some sparks my way. I have seen Lightning predominately over the ocean in the last 4 months. Some of which has not even begun firing untill the early hours of the morning. I guess what im really asking is: Is there any difference between the nocturnal cooling mechanisms on land or out to sea?

I dont supose any one knows somebody whos got a boat going 200k off the SW vic coast do they lol, could be real nice out there hehe. But Gee Wiz it wil be cold lol

Thanks heaps fellas, you are all my heroes Happy Chasing!!!