Ideal thunderstorm conditions?

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Vertigo
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Ideal thunderstorm conditions?

Unread post by Vertigo »

Hi,
In my efforts to understand and predict thunderstorm activity, could you guys explain to me what conditions must be met, and why?
For example, Ive noticed a lot of you talking about dewpoints and instability in the atmosphere, mind elaborating why these are important?
Much apprecaited.
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C-Nimbus
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Re: Ideal thunderstorm conditions?

Unread post by C-Nimbus »

Basically you need some moist warm air at low levels and cold air at high levels. When T/S development happens that warm moist air will be forced up (bouyancy) and as it hits the cooler air above the two airmasses have difficulty in mixing - hence those lovely cauliflower tops you often see.

If the atmosphere allows for vertical development (this can happen if the atmosphere profile is relatively clear of temperature inversions up to the tropopause) then thunder can be on the cards - you need height for any thunder to happen.

But in a nutshell you need instability, moisture and convective potential to spawn a thunderstorm.

Probably the most knowledgeable person on here re: this topic is NZstorm and he has a website http://www.thunderstorm.co.nz and i think he talks about thunderstorm development on there, so check his site out.

My understanding of dewpoints is this - the closer the dp is to the ambient temp then the higher the risk of rain.

I think for T/s development around auckland dp's of around 13 - 17 deg c with and ambient temp of 20 - 25 should be good but i'm not to sure of this.

One thing i do know tho is that the height of a cloud base is an indication of dp's. If the cloud base is close to the ground then the dp's will be close to the ambient temps and vice versa. Often you'll see a grunty looking T/Cu but the cloud base is very high which to me indicates a big difference between the dp and the air temp.

Thats my thoughts anyway, to be honest i dont know the technical side that well so I may be wrong with some of the comments above. Most of my weather watching is based around what I see up above :mrgreen:
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NZstorm
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Re: Ideal thunderstorm conditions?

Unread post by NZstorm »

A good summary there C-Nimbus.

Dewpoints are important as moisture holds latent heat. So the higher the surface dewpoints the warmer the surface air is for convective purposes. Very humid air is often highly convective. We see that in the tropics.

For meteorology/forecasting education I think Haby Hints is worth a look at. From memory he goes into convective forecasting in detail.

http://www.theweatherprediction.com/habyhints/

start with hint 141
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Vertigo
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Re: Ideal thunderstorm conditions?

Unread post by Vertigo »

Hi again,

Learnt a lot about CAPE and lifted index recently, as well as dew point. More questions tho!

What are the general characteristics of New Zealand thunderstorms? Do they have anything in common to US-style mesocyclones? What do we have in NZ that prevents their formation?

Thanks. Always learning.
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Re: Ideal thunderstorm conditions?

Unread post by mikestormchaser »

vertigo-- i am a thunderstorm enthusiast like most people on this forum :)
from my understanding our storms are abit different to the states, especially the mid west, and anyone please correct me on this but i think we don't get supercells here in new Zealand due to our land not being wide/ big enough? thats one guess although here in canterbury we are known for large storm occasionally.

cheers
Mike
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Re: Ideal thunderstorm conditions?

Unread post by NZstorm »

What are the general characteristics of New Zealand thunderstorms?
Compared with other parts of the world NZ has a low CAPE thunderstorm environment. The type of wind shear we get in NZ promotes the multicell mode of storm. Severe thunderstorms in NZ would be organised multicells rather than supercells. I wouldn't like to say its not possible to get a supercell in NZ.
Do they have anything in common to US-style mesocyclones?
No. USA has a unique geographic set up that allows high CAPE to combine with strong directional wind shear. Ideal conditions for rotating severe thunderstorms. There is no where else on the planet that has comparable severe thunderstorm climatology to the USA.
What do we have in NZ that prevents their formation?
A mesocyclone is produced by strong directional wind shear within a certain amount of instability. That combination seems to be very rare in NZ. Blame it on our geography.
Last edited by NZstorm on Sat 29/12/2007 21:53, edited 1 time in total.
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Re: Ideal thunderstorm conditions?

Unread post by Storm Struck »

We certainly dont get any storms as bad or as big as the ones in the US, but when they happen we remember them well.
Conditions that are ideal for thunderstorms vary depending on where you live in NZ, as often the topography of your surrounding land can create fohn winds or evern coastal.
For example one key component apart from cold upper air etc, is a good onshore moist NE here when there is a colder S or SW windflow coming up the island and we get a majority of our storms through these two converging winds.
Other places such as in the far north get thunderstorms from the westerly and northerly quarters, like Auckland exposed to the westerly fronts like the west coast of the south island gets thunderstorms.
So in other words there are winds across NZ which can help development of thunderstorms depending on where you live.
Obviously our NW here in Cantebury is a real killer when it comes to cold snaps going up against it, well it has been in the last century or so.
I would like to know myself why about 15 years ago we could get beaut thunderstorms roll up after it had just been NW :-k .
Other contributing factors are daytime heating, moisture which has already fallen on ground surfaces in warm temps.
This is without models and other weather data which is what I believe you were asking about Vertigo?.
I am sure there are other things I have missed anyone? :-k
Cheers
Jason.
Canterbury, home of good rugby and severe storms
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