Storm Australian Severe Weather Forum
Severe Weather Discussion => General Weather - all topics not current severe weather. => Topic started by: orage on 31 December 2006, 09:24:14 AM
-
On this site, and in other places, I have seen terms such as CAPE, lifted index and wind shear etc.
Firstly, could anyone tell me whether there are any other measures of conditions which may effect the potential for a severe storm, and what do they mean.
Secondly, does anyone know how I might be able to find current figures, what charts I could use to use to work it out (and possibly how they should be read), or how I can observe it myself?
-
Nice post thanks John.
I've got a GFS forecast table on our weather site that attempts to show the convection around my home town, eg 'isolated showers' 'severe thunderstorms' etc, but at the moment it only looks at CAPE, so it is obviously somewhat deficient.
Does anyone have suggestions on combining some of these other parameters, such as shear and maybe LI, CIN, cloud cover, to come up with a useful forecast of the storm activity?
Best wishes,
Dave
-
Hi David,
Hopefully there is something you are able to find.
I guess though that is the fun of forecasting - to combine your own experiences as well as current conditions and compare with forecast models. Even if there was something that combined all parameters, how accurate are they?
This year, more than any other recent years at least, the models have on the whole been disappointing in pinpointing where the best area of convection will occur. Success at forecasting and storm chasing has been attributed to past experiences in my case at least.
Regards,
Jimmy Deguara
-
Cheers Jimmy. I guess my question was more on the best way to interpret the models rather than the usefulness of the models themselves.
I was thinking of something grossly along the lines of:
potential=CAPE/500
if ( shear(850,600) > 20 ) potential=potential + 1
if ( CIN > 200 ) potential=potential - 1
etc.
While no algorithm will encapsulate what's really happen, at the moment I rely on CAPE alone and there has to be something better than that. Maybe I should just use SWEAT instead?
Cheers,
Dave
-
Hi David,
I appreciate what you are saying and had thought about this concept about 2 years ago. If only I was a good programmer, I would have come up with a solution years back.
When I came across the GFS (I guess then the AVN models) back in 1998, it was a gold mine. With these models alone we were able to confidently expand our storm chasing beyond the horizon.
CAPE is a pretty useful variable as well as is surface lifted index. The sensitivity of CAPE though with only slight changes in temperature and moisture should not be underestimated. But using it as a guide is still helpful.
So any programmers?
Regards,
Jimmy Deguara
-
Hi John,
If you are searching for surface lifted index values off the models of the order of -6 and lower, you won't be doing much chasing in Australia! Particularly this year.
I tend to look for values of less than -2 depending of course on available moisture and sunshine. This will often determine whether the models have underestimated or overestimated the specific variables. And of course, it depends on the distance travelled and the risk for failure.
One has to be extremely careful though. On the days leading up to the Muswellbrook hailstorm, LI values of -10C were forecast for the north east NSW region. The Bureau even had hail and squally winds in the forecast up there. In the region from Mudgee to Muswellbrook, Taree to just south of Sydney, conditions indicated less forecast CAPE and lower LI values. We opted for the region near Mudgee and Gulgong. The result was a long lived supercell that tracked for nine hours. The north coast struggled to break the cap with only late night lightning in the distance as a storm(s) tracked up the coast.
Regards,
Jimmy Deguara
-
I'm a programmer and I'm very keen to code up something like this.
I've already got some python code that rips down bits and pieces of the NOMADS GFS data, the formatted output for my site is here:
http://narrabriweather.net/forecast.shtml (http://narrabriweather.net/forecast.shtml)
It's just that I'm new to the storm game and need some advice about the right way to put the different parameters together. Some of the suggestions already made by John are useful.
Cheers for the encouragement,
Dave
-
John,
No apologies required. Perhaps there could be a an indication for supercells as well givent eh complex nature of the program.
This is an important topic.
Regards,
Jimmy Deguara
-
5) Ill look at 500mb wind charts to see what the propagation of storm direction is going to be like over the target area.(steering flow is usually near the top of the troposphere)
I would say you need to look lower than that for steering. I tend to use the average from about 850 to 500 depending of how strong the winds are at various levels in that range. No set rules of course.
regards, Michael
-
John why do find LI and DP more useful than CAPE? I see the input parameters are different but isn't CAPE already an attempt to combine the convective potential of a parcel and the DP? Do you see much difference between the two approaches?
I could use a combination of exisiting indicies, such as LI or CAPE, as a general convective indicator like I currently am, but then also look at the ratio of that and something that incorporates shear, such SWEAT, as the trigger for warning of severe storms. Is it also worth looking at CIN?
Although if I go back and look at the input parameters that make these different quotients there's probably an even simpler implementation of what I'm seeking. If anyone wants to suggest an interesting combination of the GFS forecast parameters (http://nomad3.ncep.noaa.gov:9090/dods/gfs_master/gfs20070107/gfs_master_18z_anl.info) I'll code it up and put it on my site with a few of our locations so we can assess it. My current code can't generate maps, just forecasts for specific locations.
Even though they're for specific locations, I do need to change my algorithm to look at the surrounding 0.5 degree forecast points as well. There's been a few times where the reported convection was fairly low, because a front has gone through faster than the 3 hour forecast interval of the GFS, such that you don't see the storms if you just look at a single forecast point.
Regards,
Dave
-
This page describes how the existing stability indicies are calculated:
http://weather.cod.edu/sirvatka/si.html (http://weather.cod.edu/sirvatka/si.html)
-
I'm with you RE atmospheric soundings happening at the 'wrong' time of day. My site's 'thunderstorm potential' was initially based on the sounding data from Moree (100km North), but I found it essentially useless since it runs at 00z, so switched to using the GFS forecast data instead.
I may have this wrong, but isn't LI calculated by calculating the temperature of a parcel of air from the bottom 1km of the atmosphere, lifted to 500mb, and subtracting this from the actual temperature at 500mb? In which case you still need soundings (or forecasts of soundings) in order to know the actual temperature at that altitude?
Thanks,
Dave
-
Orage, myself being a novice also, the best advice I can give you from what I've learnt over the past months is two things: Ask questions and research. Even if your question is answered and you still don't understand the terminology - ask again for more clarification in layman's terms. One can't learn if one can't understand the terminology used and then apply it. Never think your questions may be irrelevant because they're not - because what you ask may be something that someone else is thinking.
Research as much as you can and take notes, copy pages and make up booklets on different subjects on storms/chasing/structure etc. It's what I've done and you can go back and reread as much as you want!
For the best info on Skew-T charts and explanations go to http://www.downunderchase.com - you'll find modules on every part of interpreting the sounding charts and also Jimmy's observation technique articles (http://www.australiasevereweather.com/techniques/) on observing clouds on this very site.
Get yourself a storm term glossary list also, this will enable you to know straight away when forum members are talking about CAPE, CIN, LI etc and will lessen the headache i assure you.
Hope this helps. Even a dummy like me has worked out the Skew-T soundings enough for me to know if there's potential for instability!
Mike
-
Hey there. Okay, i've got some figures for you mathematicians and experienced sounding observers. I've been reading the posts on this topic and getting some education on the sounding chart through the answers given. There's a host of questions so bear with me:
(1) At which level do winds steer storms so i can get an idea of where they're heading? At each level (as far as mb level on the sounding diagram) what wind speed am i looking for on the sounding that would help the generation/maturity of a/or storm(s)?
(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?
(3) As far as the wind barbs - for good storm potential is it better to have fewer barbs in all the levels? For example fewer barbs in the lower up to 900mb, fewer but stronger wind speed barbs in the middle to say 500mb and then how many aloft and at what knots? What wind speeds in knots should i be looking for on the sounding charts in these levels mentioned?
I have some figures for you from our sounding here - perhaps you can interpret. This would be of great help to me so that i can get an understanding of what ingredients i should be looking for when viewing the sounding. I've got the CAPE and some other aspects understood, there's just a bit more i need.
DP 27.68 (dew point?)
LI -6.28c (that must be average, no?)
CAP 0.17c
CIN 17j/kg
PS 1005 (what's that and is it important?)
CAPE 4791j/kg ( i know that's good)
SWEAT - what is that??
winds on the sounding were: surface to 900mb 7-11knots from SW, up to 500mb 16kt from SE, from there aloft they went NE at 9-16kt then E 14-30kt. The air was moist in below 600mb then nice and dry right up through the middle range and then moist again in the upper - that's a good sign no?
Sorry to be long-winded but this is quite important and i really do appreciate you guys helping me out.
Mike
-
Mike,
Can you tell me where I mentioned the following:
(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?
Regards,
Jimmy Deguara
-
Here it is - i was paraphrasing your sentence and put the word 'storm' in because that's what I believed you were referring to - but you did mention lifted index - apologies if misquoted, not being picky, just inquiring! Were you referring to something else again? :)
You said: If you are searching for surface lifted index values off the models of the order of -6 and lower, you won't be doing much chasing in Australia! Particularly this year.
I tend to look for values of less than -2 depending of course on available moisture and sunshine. This will often determine whether the models have underestimated or overestimated the specific variables. And of course, it depends on the distance travelled and the risk for failure.
All good :)
-
Mike,
That's better. Now that makes a fair bit of difference from what was paraphrased as I think my friends even will be confused if I did not chase -6LI:) My reference was to John's message if I recall referring to -6LI as a base point. He has corrected it in a subsequent message.
Regards,
Jimmy Deguara
-
Certainly - sometimes I have a bad habit of paraphrasing! comes with the employment i do! But all good, pretty sure your friends will be relieved!
Mike :)
-
I finally got around to coding up something that is (somewhat) superior to just relying on the GFS forecast for CAPE. It's very piece-wise, but if anyone can follow it I'd appreciate any suggestions or comments on the 'magic numbers'. Obviously it will never be perfect but I'd like something that 'kinda works' to use on my weather site.
shear=wind speed at 2700m (~720mb) in km/h
if cape<=120: No Storms
elif cape<=400: Cumulus Cloud
else (cape is >400):
if cin>-100:
if cape<600: Isolated Storms/Showers
elif cape<1200: Storms Possible
elif cape<1900: Storms
else (cape is >1900):
if shear>80: Severe Storms
elif shear>60: Severe Storms Possible
else (shear is <60): Storms
elif cin>-220:
if cape<900: No Storms
elif cape<1600: Cap but Storms Possible
elif cape<2000 or shear<70: Cap but Storms Likely
else (cape is >2000 and shear is >70): Cap but Severe Storms Possible
else (cin is <-220): Strong Cap - Storms Unlikely
Thanks!
Dave
-
Hi David,
Are you able to include shear at more than the one level ? It may be more useful in helping to identify areas where severe storms are possible, and also where turning is sufficient or not for supercells.
regards, Michael
-
The models produce velocity and direction numbers for the winds at 4572m, 3658m, 2743m, 1829m, 914m, 610m, 457m, 305m and 10m. I just picked the 2743m shear to start off as it's middle of the range. We could use more than two of the levels. But I'm not sure of the best way to incorporate multiple shear measurements into the forecast.
Perhaps we just add them, eg:
shear1 = vector_shear(ground, 914m)
shear2 = vector_shear(914m, 2743m)
total_shear = magnitude(shear1) + magnitude(shear2)
and then use total_shear in a similar way to the shear index in my previous post? Or is there a better way to integrate the different levels into the forecast rather than simply add their magnitudes together? Any suggestions which levels would be most useful to incorporate?
Many thanks,
Dave
-
Yes - it is going to be difficult and I'm not sure which levels amongst those would be most suitable for your program. It really depends if the shear is fairly linear or turning. If mainly linear you would need to average the speeds. Others on this forum may be able to explain all this : )
One thing though - I am of the understanding that so long as you have 40 knots of shear in total between the surface and 500hPa, it is sufficient for supercells given instability, humidity and temperature profile support storms. Eg. 15 knots NE at the surface and 25 kts SW at 500 is sufficient.
-
I like our sounding indices for today. Have not seen the skew-t but the numbers aren't too bad! CAPE 2902, CAPE with virtual temps 3161. TTs at 41 - but you'd never know looking out the window now at 4pm NT time. Don't know what the winds are doing as i can't bring up the sounding chart to view them so can't determine what type they'll be....;(
Mike.
(not relying on radar today - i'm just getting out there....!)
-
In relation to supercells/severe weather that NSW get; I'd like to know what specific conditions result in those storms. The storms that i have noticed have a lot of shear properties influencing them probably because of the number of spouts etc, but I'm not familiar with the 'conditions' that form the storms in that part of the woods. Could the members enlighten me with some info - please if you could include some indices for me. I've been focussing so much on tropical conditions that I wanted to expand the horizons.
Mike
-
At the end of most Storm News reports up until the end of the 2005/06 season I have included soundings and GFS run output. Might be a good idea to go through some of those and have a look at values and compare them to tropical setups. Last season many of the chases were discussed on this forum so there might be soundings and GFS output there as well.
http://australiasevereweather.com/storm_news/news2005.htm
etc
Certainly the temperature, humidity and wind shear profile can be quite different. Notice the cooler upper temps, drier upper levels, and the windshear contrast on the big days.
17 December 2005
http://australiasevereweather.com/storm_news/2005/docs/200512-04.htm
26 - 27 November 2005
http://australiasevereweather.com/storm_news/2005/docs/200511-06.htm
-
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:
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd25.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd26.jpg)
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?
(http://australiansevereweather.com.au/photography/photos/1993/1017jd01.jpg)
or
(http://australiansevereweather.com.au/photography/photos/1997/1115jd10.jpg)
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,
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?
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,
Signs are good for an early wet by what BoM says in their MJO and SOI reports - fingers crossed.
Sounds good Mike! I hope you can get some great shots to share with us this year! :)
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
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 (http://forecasts.bsch.au.com/gfs_plot.html?ctlfile=2007092706&ptype=map&variable=LFTXsfc&variable2=CAPEsfc&level=&level2=&date=2007092721&proj=vic&slon=138&flon=153&slat=-42&flat=-31&type=shaded&type2=bcontour&cint=cint&cint2=&white=&grid=on&plotsize=x800%20y600&mode=plot&timelinks=yes&simple=)
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!!!
-
Going back to the occluded supercells do they also get known as cumulonimbus that develop an anvil and the anvil separates from the main storm and repeats a few times?
storm boy
-
The occlusion process refers to the gradual separation of an updraft no anvil. As a tornado or mesocyclone wraps rain, it gradually cuts off the warm moist air supply and gradually the updraft shrivels from the mature storm. With cyclic supercells, this process can occur several times as new updrafts dominate and other updrafts separate from the main storm. (I guess this makes supercells a family of the multicell family in some respects although the dynamics and process taking place are different).
Perhaps search the occlusion process.
Regards,
Jimmy Deguara
-
Ok thank you for the information Jimmy. By the way what does it mean when you do look at a developing cell and the cumulonimbus or anvil decides to disconnect from the main cell?"
-
Stormboy,
Storms in their natural process go through stages - the developing stage, the mature stage and the dying stage. A supercell's dynamics is fairly complicated to explain in detail with the lack of time I have because a lot of favourable conditions must come together. I would suggest do a lot of reading on supercells right around the internet and brush up before even attempting to fully comprehend what what processes lead to cut off updrafts and tornadogenesis as well as cyclic mesocyclonic behaviour.
Generally though, it is believed all storms have more than one updraft and they are in different stages of development. In supercells, the most mature stage will have the strong tornadoes and these go through the rope out stage when the updraft occludes or goes through the stage of being cut off from the rest of the storm and eventually shrivels up.
As a case study, take for instance the event on May 12 2004. David Croan and I were top the east of the supercell that exploded and began to produce tornado after tornado - we captured 5 tornadoes including spinups. Three of those tornadoes were quite strong and you can see the sequence in these set of photographs:
http://www.australiasevereweather.com/photography/photos/2004/jd20040512.html (http://www.australiasevereweather.com/photography/photos/2004/jd20040512.html)
Just for an illustration of what an occlusion looks like, check out tornado 1. You can see the base is ragged and the inflow cut is beginning to separate the tornado and its attached base from the rest of the storm above us.
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd13.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd14.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd15.jpg)
Also check out the longer lasting tornado 2:
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd20.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd21.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd22.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd23.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd24.jpg)
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd25.jpg)
Even though the occlusion process is well under way by this last photgraph of this tornado, this is a better example where you can see the tornado is losing vertical tilt and becoming narrow. It roped out not long after this photograph. Also again you see a higher base and the cut off occurring.
(http://www.australiasevereweather.com/photography/thumbs/2004/0512jd26.jpg)
Regards,
Jimmy Deguara
-
Those are some nice shot of a tornado above Jimmy. Are they recent? And also are you still chasing in America? Also thank you for the brief description above. I will browse the web and look further into the definitions of the super cells as well as development stages.
Storm boy.
-
Thanks for taking the time to explain occlusion, JD. It's something I've neglected in my own chasing experiences - when it occurs for my purposes - and really no-one has explained it to me in other avenues as well as you have. One always hears of storms occluding or an occluding front so it gives a better insight into how the dynamics work. Kudos to you.
-
Hi, John. I'm def interested in the tree as per thunderstorm development....what can you offer by way of info?
-
John,
Is this the thunderstorm forecasting decision tree by John Colquhoun?
Regards,
Jimmy Deguara