Unstable in Christchurch

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Unstable in Christchurch

Unread post by NZ Thunderstorm Soc »

An unstable sky developed here this afternoon with a brief thunderstorm passing over the city between 3pm and 4pm. This storm seemed to heading towards you Aaron.
I hope you are out and photographing.
I got on or 2 shots of lightning but as there is lots of blue sky around the lightning was hard to see against the cloud.


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Unread post by Dean. »

Some good looking clouds about,mostly out to the east,looking good for Christchurch John and Aaron.
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Unread post by Dean. »

Driving into a hailstorm 10km east of Ashburton.
About 3.50pm.
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Unread post by NZstorm »

Looks like a cb over coastal North Otago as well.
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Unread post by NZstorm »

Nice photo of the hail Deano.

Hopefully Aaron got some pics the the Christchurch storm.
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Unread post by tich »

I've just got back from Banks Peninula this evening. It got quite warm (high teens) this afternoon after the rain cleared late morning. Then areas of high cloud increased about midafternoon, with some showers from about 3.30 PM. I heard a few rumbles of thunder to the north about 5.30, and cloud was dark in that direction. This darkness was prominent to the northeast (offshore I presume) as I crossed over Hilltop about 6PM. Couldn't see any lightning though. Seems to have all cleared now as I write.
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Unread post by Weather Watcher »

Deano - nice picture. Do you or anyone else know how large the hail was in this storm, or any others in Canterbury today (Sunday)?
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Unread post by Dean. »

The hail seemed to pass over in a band,followed by heavy rain.
Approx 5mm in size.The storm then seemed to move in a southwesterly direction out towards the Rakaia river mouth and then onto Banks Peninsula.
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Unread post by Weather Watcher »

Thanks for that Deano...just your standard Kiwi hail by the sound!
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Unread post by NZ Thunderstorm Soc »

I'm surprised that Aaron hasn't come on line yet ???
The thunderstorm and unstable skies were caused by a westerly flow and an off shore southerly in behind a little low of about 988hpa just NE of BP at noon today. I saw no hail and encountered no heavy rain showers except for a few heavy drops. There must of been hail/heavy showers around according to the Rakaia radar and quite isloated. I see the airport recorded - 11 PM (3) Sep 13 60 (16) 51 (11) 29.23 (0990) ENE 6 heavy rain showers, with thunder - at 4pm today.
I was pleased with my 2 lightning shots today recorded on video.

:) JohnGaul
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Unread post by tich »

Driving into a hailstorm 10km east of Ashburton.
About 3.50pm.
The storm then seemed to move in a southwesterly direction out towards the Rakaia river mouth and then onto Banks Peninsula.
During the initial shower out on BP at about 3.30-3.50 PM, I didn't notice any thunder or lightning. The cloud was dark to the west for a while though, but from where I was (western side of Akaroa harbour), I couldn't see too far to the west because of 700 metre high hills. Like I said earlier, I heard some thunder to the north about 5.30 PM - Aaron , you probably would've noticed that thunderstorm from Southshore.
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Unread post by Thunder »

Hi John and Steven, yep, I've been out taking photos you bet! Due to my Dads business being computers (programing etc) he's on here all the time so it's hard to get on the PC. Then I got watching a movie so am up late doing this (1:50am in the morning!), it was "Last Action Hero" if anyones ever heard of it, anyway..moving on!

Cool pics Dean, and yes to all I pretty much got a front row seat where I was to watch the action (all be it limited, good cloud structure though). I long for a new video camera as I saw quite a few good flashes with the very first lightning flash being a big CG that went strait down into the ground somewhere in Chch city, I only had a photo camera so couldn't get lightning flashes, can't wait to see yours John at a later date. The thing about the Cb's about today were they were relatively LP (low percipatation) so you could see under the base of them really well, as they moved out to sea that's when they began to dump their rain, water, load, etc.

I just had a look outside and thought to myself "hmmm, those clouds look interesting", so I put my cameras in my bag and scootered (electric might I add) off to the esturary to see the developing clouds, it payed off as I got some allright shots I thought considering I only had my little dinky 2 megapixel camera. I did however take photos with my bigger manual film type camera but we'll have to see at a later date how they came out, Enough! to the pictuers! All pics taken from Southshore, 14/09/03 between about 2:30pm and 6:00pm

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First Cb which did produce lightning/thunder.

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This was probably the most rain I saw over the land. Rain falling on Chch city, First CG happened just before this, dam I wish I had a video camera!

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Cu clouds possibly glaciating to Cb, I think this cloud might of been part of the second Cb that moved through on this day

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Another picture of the base of the first Cb, lightning has gone off a few times by now with the thunder coming across very clearly from my location, good rumbles!

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Here's a pic of a Cu congestus type cloud from the days events. Thats actually blue sky it just looks black against the white cloud.

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Darky cloud...

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Lumpy base of cloud, could be a Cb above this or Cu congestus. Looking at Banks Peninsula

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Interesting horse shoe type gap in cloud (Cb is surrounding it), looking east I think.

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Lightning went off 5 or 6 times in this cloud, this is part of the second system that went through, must buy video camera. Looking towards BP (Sumner).

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Darky looking cloud winding its way towards me, part of second Cb. Note LP base.

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Second Cb, low percipitation base and the front of the Cb looks to be going up to form its anvil.

These next few shots I think are pretty cool:

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Quite a cool shot of the second Cb, LP base, front of Cb towering up towards its anvil, nice and darkish looking!

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Another nice looking shot just a few moments later.

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If a funnel cloud were ever to form yeaterday this would of been the spot I reckon, but of course nothing happened!

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A rainbow to finish off the day with perhaps a pot of gold at the end?

Considering these were all taken from my little tiny 2 M camera I think they are reasonably ok.

Cheers
Aaron Wilkinson
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Unread post by tich »

Great photos Aaron - you certainly got a better view of the last thunderstorm than I did. (I couldn't see the cb tops from the south) Were you actually under the thunderstorm? - I noticed the 6PM radar showing a bright patch right over New Brighton/Southshore.
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Unread post by Thunder »

Hi Ben

Was I under the Ts? Sort of. The first system passed right overhead with a few lightning flashes/rumbles and the second one seem to split into two and go just either side of me with part of the cloud going right overhead but with no lightning in it. I was though In a good place to view it. A few of the photos I took from my roof so that's why I look up high, I started getting freaked at some points and got down as not to be struck by anything but in the end no lightning occured right overhead of me during the second Cb/system.

Hey look, metservices forecast for tomorrow (16th):

Canterbury, Otago and Southland
Rain and thunderstorms developing tomorrow morning about the western ranges. Some showers and thunderstorms spreading farther east.

Cheers
Aaron Wilinson
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Unread post by NZstorm »

Aaron, I like the photos. The second one shows two precipitation cores so clearly a multicell there. I look forward to seeing more. Next storm day won't be far away. ;)

As for thunder tomorrow. The front will need to go through Canterbury early, the sun come and start heating the ground, and an easterly breeze kick in. If that happens the Tstorms may develop. But they won't spread off the alps as Met Service suggest. That does not happen. The Christchurch thunderstorm is very much a local thing and the dynamics are quite different to the West Coast /Alps Ts.
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Unread post by TonyT »

While I agree Steven that TS dont usually (in fact hardly ever) detach from the Alps and move across the Plains, they often develop over the western hill country which separates the Plains from the Alps, and a strong w flow, with plenty of shear will push them over the Plains towards the city. To people living in the city, they look for all the world as if they *have* come off the Alps themselves, because, often, storms can still be seen over the Alps.

Thats unstable westerly flow situation storms I am talking about, like what we saw on Sunday. Southwest flow storms are different.
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Unread post by NZstorm »

Tony, that is an interesting storm type. I suppose as it drifted toward the coast it would start feeding on moist coastal air and become more active.
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Unread post by tich »

Thunder and hail reaching Chch in a northwesterly would be unlikely, but not unknown. I think it would take a massive thunderstorm and heavy rain event in Buller/Westland for it to be able to push over the mountains. But I recall early January 2002, when Chch was hit by a night-time thunderstorm in a northerly/northwesterly flow, while heavy thunderstorms and rain were lashing the West Coast and the Alps. Plus I've read (from a Met Society newsletter) about a freak (albeit not very large) thunderstorm in the city back in January 1991. It occurred in an anticyclonic northwesterly flow and developed on its own!
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Unread post by TonyT »

You can often see the Cu developing quite rapidly over the western hills, being blown slantwise by the shear in the W flow, which helps form the anvil shape, then reaching full CB size with precip as rising air from the sun heated Plains reaches them on the eastern side of the Plains. In the Sunday storms there was no onshore flow, just westerly (at least where I was) which I think is why the precip was rather modest, of the order of a few drops, rather than significant rain. It may have been different for the storm Deano found in South Canty which had hail with it, there may have been some onshore flow there.

The cold westerly flow in the rear of a depression often brings this scenario, but when its just behind a cold front, there seems to be less instability lower down in the atmosphere, and the clouds rarely get past the towering CU stage. Northwest flow is different again, as it is usually stable over the Plains, which is why the NW storms Ben refers to are so rare.
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Unread post by NZstorm »

The storms that developed North Otago to Christchurch on Sunday where confined to near the coast. There would likely to have been some onshore breeze which provided moisture and perhaps some convergence. But I think the mild temperatures of the day/thermal lift played a significant role in destabilising the conditionaly unstable air.
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Unread post by TonyT »

The storms were confined to the coastal area, but the TCu clouds which grew into the storms began over the hills on the west of the Plains and blew east - I know, I watched them :) At least the ones over Chch did, I cant speak for the ones further south. Its fascinating to see the TCus suddenly put on a few km in height as they float over the warmer plains. And you are right about the onshore breeze, the METAR John posted for 4pm showed ENE 6 knots at the airport, which is probably why those clouds turned into CBs whereas the ones which floated past Amberley didnt (there being a moderate westerly here). Isnt mesoscale meteorology fun :)
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Unread post by Thunder »

Hi Steven

A multicell storm, awsome! I didn't know how people told if it was one of those or not, now I know. Are there any other factors that one can identify a multicellular storm?

I'm getting sferics as I type, most likely coming from alps, here's a shot outside looking at alps with Cb running up and down it.
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Unread post by NZstorm »

Multicell Ts have more than one main updruaght Aaron.

Fine here in Auckland too with distant spherics(from that front out east).
Max temp 20.7C in Grey Lynn.

Re your comments on video camera. Many digital cameras have a movie function built into them. I havn't tried the movie function yet so don't know if its any good. Next storm with CG's I will try it out. ;)
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Unread post by NZstorm »

Rain on a howling N'wester at Christchurch this evening is a turn up for the books.
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Unread post by Dean. »

Gusty northwester here tonight,a mild 10.4 degrees,some brief rain.
My photos were taken on a Sony digital camcorder with a memory stick for digital still pictures,I find a video camera excellent for recording thunder/snow storms etc,but might have to invest in a digital camera for higher quality photos.
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