High Risk of Thunderstorms - SI, Sunday 10 January

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Manukau heads obs
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Manukau heads obs »

i think the point made that there was storms in inland south canterbury was the important point
that there was storms somewhere...and you just had to be in the right place at the right time
canterbury is fickle for storms....things have to be just right....not this time
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Weetbicks »

All that Melja's post needed was a winky emoticon and I think it would have completely changed the tone of it and stopped all the bickering. When I first read it I just thought he was being cheeky & sarcastic, maybe that didn't come across strong enuf.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by spwill »

A few isolated lightning strikes can qualify as a High risk day with the MetService convective outlooks so for storm chasing you need to also use your own knowledge/experience. As others have said the cloud cover yesterday was a very good sign that it was going to be a tough day for storm chasing especially given the dewpoints being on the dry side and upper level temps being not particularly cold as Aaron said.

The SouthCanterbury storms were in poor chase country,just the Waitaki valley Rd and Omarama to Fairlie Rd I believe.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Lacertae »

The t-storm risk has shifted significantly for the SI ... not going for a chase finally ... >_<
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Manukau heads obs »

not going for a chase finally ...
aw come on now, how far is to drive to nelson?
in the USA storm chasing we drove 6 hours every day to get to where the storms were


just stirring!!!!
LOL
:mrgreen: :mrgreen: :mrgreen:
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Weetbicks »

That's true, if this was america then "true" storm chasers would drive as far north as the Waikato to see storms of a given day, ferry crossing mandatory! ;) ;) ;)
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Lacertae »

I know you're just stirring, but for someone like me who earns only $13.5/h, going for a 300+ km chase represents a significant amount of money for the petrol ... and it only takes me (in a straight line) to Methven and back.
I would have the chance to work "as usual" (i.e. at least $19/h) and not in a supermarket that I wouldn't mind going for a chase in an other region as I could easily afford it.

Anyway ... :rolleyes:
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Manukau heads obs »

although its only the visiting (from other countries or eastern USA) storm chasers or the real dedicated local ones....local ones , where as some local ones more waited for the storms to come to them or only would drive if an hour away e.g....thats the impression I got....
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Manukau heads obs »

you guys should car pool (ie meet up first) maybe? (to share the petrol costs)
Last edited by Manukau heads obs on Mon 11/01/2010 10:37, edited 1 time in total.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Lacertae »

I thought about car pooling, as Andrew and Mike (and Aaron ?) did yesterday but I prefer to chase on my own. If I take a bad decision about where to go, I do not bring anyone else with me to the wrong place. Also if I take some risks on the road, I'm the only one in the car. And then if I need to go home because I have to be at work at 7pm, I turn back whenever I want.

Probably not as funny and exciting to chase on my own and it costs me more (in a sense), but I think it's the best solution for me.

Plus the more cars there are out chasing, the more chances there are that one of them will be at the right place at the right time (see the Waddington funnel cloud episode).

Anyway ...
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Manukau heads obs »

yup, all valid points too
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Paul Mallinson »

Pages 5 & 6 were an interesting read!

You have to remember that these threat forecasts are just that. They endeavour to delineate an area in which conditions come together (in varying degrees - hence the low, moderate and high risk ratings). Remember too that we are dealing with a very complex animal and that convective forecasting often hinges on rather subtle small scale effects.

For yesterday, you might remember the text part of the forecast mentioned thunderstorms triggering in the southern part of the area and then moving northeast over Canterbury in the afternoon with the southerly change (that was the reason for the relatively large area). Well, they did trigger in the south as has been discussed, but the whole lot died out further north due to the rain and cloud. One certainly has to consider the suppressive effect of cloud etc on temperatures, but you can't always rely on a sufficient amount of cloud being in place and effecting the heating over the majority of an area. It turns out the rain in Canterbury was much more extensive than expected (and forecast). It easy to pick up these things in hindsight and it is also a different matter to actually put pen to paper for all the see (and criticise). If we had totally gone along with the idea there would have been too much cloud for convection yesterday, then we would not have indicated the threat of the thunderstorms that did develop in the south. So its a tricky matter with many aspects to consider.

Paul

PS
A colleague has just remarked to me that many times when you look at the risk areas on threats maps for other countries (only a few countries do them to my knowledge - i.e. Europe and the US), their threat areas are often very large - in the order of the size of the whole of NZ or several states etc. (But sometimes in these continental areas, these larger areas are warranted.)
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by NZ Thunderstorm Soc »

...to add my 20 cents worth.
What does the word 'risk' mean?
It's only a possibility of something happen, not actually happening.
Met Service did right by posting a risk up but the possibilties of anything happening did not look like the case.
I was in Greymouth yesterday morning and no way it looked like that it was going to be lots of thunderstorms with say tornadoes forming as decribed on their thunderstorm forecast. I only heard one rogue clap of thunder and no lightning was seen as the sky was low overcast with a 8/8 cloud cover and steady rain falling straight down.
I wouldn't be surprised if there were anymore, well there in Grey anyway.
As I said there was steady rain all the way to Arthurs Pass and that was just that.
I could of hang around longer but I saw no need to and there were thunderstorms forecasted on the east coast as well, so we headed back.
As soon as we crossed Porters Pass, the NW was blowing quite strong and there was high cloud cover across the Canterbury plains so I knew then that thunderstorms forecasted for today would not eventuate as the scenario wasn't in place. When we got home the wind had turned to SW which usually cancels any likelihood of anything thundery to happen.We got a good rain though which we need here.

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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by MoorfNZ »

Good grief, people, it's all a bit of fun and excitement that each of us has within the boundaries of our means (both financial and time-wise) Half the fun is the chase or the sitting and waiting and wondering and drinking cold coffee... especially when there's only a risk and no reports of sightings to go on... whether you're doing it on the ground in your car or if you're sitting in front of the PC, like me. :mrgreen:

Sorry, had to chime in as this forum has always been so fab at accepting us amateurs and pro's alike and I felt comfortable - then some numpty has to chime in with a totally unnecessary comment about the quality of chasing. :rolleyes:
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by tunster »

Paul Mallinson wrote: A colleague has just remarked to me that many times when you look at the risk areas on threats maps for other countries (only a few countries do them to my knowledge - i.e. Europe and the US), their threat areas are often very large - in the order of the size of the whole of NZ or several states etc. (But sometimes in these continental areas, these larger areas are warranted.)
eg at http://www.estofex.org/
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by dogmelon »

I remember there was a thunderstorm here in Chc when a front came through with a warm gusty NWer ahead of it a year or two ago so its not entirely impossible for it to happen. I remember it was mentioned on here that pre frontal ridging occurred allowing a storm to boil up or something. I dunno much about anything, but it must be so bloody hard to pinpoint where a thunderstorm is going to happen in this fickle weather little country. Keep your chins up metservice people and keep up the good work! Thanks.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by optrex »

The good thing I used to like about ESTOFEX was that they would overlay the actual strikes over the warning map, so that you could verify their accuracy after the event. Unfortunately, they lost that feature following a recent server crash. However they do still overlay the severe events as can be seen by the cyan dots on this example, indicating heavy rain.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Chris Raine »

As I read the topic just now , a lightning strike has just set fire to gorse bushes in the Nelson area
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Paul Mallinson »

Chris Raine wrote:As I read the topic just now , a lightning strike has just set fire to gorse bushes in the Nelson area
Very interesting report. We have recorded 1 positive lightning strike in Nelson a little while ago.

Paul

(Its the +ve strikes that often start forest fires)
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by dogmelon »

Are you able to work out how far these +ve lightning strikes go from the cloud, as in a bolt from the blue type thing? I reckon that would be horribly undy soiling to have one of those meanies drop down near you when the storm you're watching isn't right near you.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Weetbicks »

While on topic of lightning, could someone please explain what +IC, -IC, +CG and -CG mean? I seem to recall CG means Cloud to Ground strike, but I have never known what the + and - refer to, and what IC stands for? Thanks.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Nev »

Yes, CG stands for 'Cloud-to-Ground' lightning, IC stands for 'Intra-Cloud' lighting and the + or - stands for the positive or negative charge of the lightning.

Cb's tend to have positively charged ice-crystals at top and negatively charged ones in the middle and bottom layers.

Intracloud lightning (also known as sheet-lightning) is the most common form of lightning and occurs completely inside the Cb, jumping between the different charged regions within the cloud.

Negatively charged CG's originate from the middle or bottom of the storm cloud and tend to strike the ground near the centre of a storm

Positively charged CG's are rarer than the other two forms of lightning, but are also the most powerful and dangerous. They originate from high in the anvil of the storm cloud and can travel a few kms ahead of the main storm before before turning vertically towards the ground.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Lawrence »

Weetbicks wrote:While on topic of lightning, could someone please explain what +IC, -IC, +CG and -CG mean? I seem to recall CG means Cloud to Ground strike, but I have never known what the + and - refer to, and what IC stands for? Thanks.
IC stands for Inter Cloud or cloud to cloud strikes or Sheet lightning, theses can be of a positive charge or Negative depending on the structure of the cloud itself, or when it occurs between areas of differing electric potential within a single cloud.Positive strikes are usually the most intense and dangerous charges.Cloud-to-ground lightning is a lightning discharge between a cloud and the ground. It is initiated by a leader stroke moving down from the cloud.

http://www.srh.noaa.gov/jetstream/light ... sitive.htm :wave:
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by Myself »

Positive lightning is more common in NZ than most other countries.
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Re: High Risk of Thunderstorms - SI, Sunday 10 January

Unread post by mikestormchaser »

Alot of people say the lightning moves from the ground up? each time iv brought a subject like that up infront of people they tend to correct me and say it starts from the ground up but im not so sure its tru iv always thought it goes from cloud to ground..

Anyways cool start today in chch wind has been S-SW all day i think, saw a nice bit on convective stuff towards BP way this afternoon around 3pm maybe abit of convergance going on there. Also looked bit unstable towards TC this afternoon John :lol:

cheers
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