Another icy blast coming?

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tich
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Another icy blast coming?

Unread post by tich »

The latest MetService long-range forecast has taken me by surprise. They obviously believe there's going to be a major injection of very cold air into the east of the South Island by Friday, and the east of the North Island during the weekend. The recent models I've seen show isobars coming from a high latitude around the high to the south, but with the 528 thickness line staying well to the southeast. Earlier there were predictions of snow to 800 metres in Canterbury late in the week - now they're going for falls to near sea-level! (though not heavy). Whether all this eventuates, we'll have to see, but the current snowfalls in Central Otago and Southland weren't anticipated until they were beginning to happen.

Ben
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Unread post by tich »

The latest long-range is still going for snow to very low levels in the east of the South Island on Saturday, but not tomorrow. (I wouldn't consider 600 metres a very low level) Raining steadily this afternoon in Chch - not heavily, but more than the drizzle that MetService is forecasting.
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Unread post by Dean. »

Drizzle is turning to rain in Ashburton,temp 5.9 degrees.
With the temperature dropping and the precipitation becoming widespread on the Rakaia radar there will be some snow falling further inland tonight.
Cheers.
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Unread post by tich »

I earlier saw the MetService forecast for drizzle as being for Central and South Canterbury, and rain for North Canterbury. I get confused to whether Christchurch is in North or Central Canterbury when forecasts are concerned. Anyway rain is now forecast for Central Canterbury.

I notice there are, and have been a number of icy southerly blasts in the southern hemisphere. I've hard there's recently been one in South Africa, bringing snow to Table Mountain, above Capetown, and snow has been forecast for higher hills southeast of Perth early tomorrow. And linked to cold southeasterlies over NZ, MetService suggests the possibility of snow flurries at the Chatham Islands this weekend. Winter's not over yet.
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Unread post by Michael »

On the various charts around the world there seems to be lots of extra"tropical" depressions in the Southern Hemisphere not associated with the westerly circumpolar belt.

As for winter not over The seasons are lagging way behind the sun -Like the leaves were still falling off in June and when its supposadly spring the southerlies keep returning then at Xmas when everyones on holiday the changeable spring westerly conditions prevail then in March and April it is dry and almost summerlike when its supposed to be Autumn. ;)
tich wrote: And linked to cold southeasterlies over NZ, MetService suggests the possibility of snow flurries at the Chatham Islands this weekend. Winter's not over yet.
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Unread post by Dean. »

I have just returned from a drive inland and the snow level is a lot lower than Metservice forecast,it has just started snowing at Methven at an altitude of only 320 metres.Cold steady rain in Ashburton temperature 4.8 degrees.
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Unread post by Thunder »

Snow! Cool Dean!

Ummm.....what else to say? Can anyone tell me when Thunderstorm season begins here in Cantab / South Island? (Ha! that just gave me a funny thought, imagine if humans had a mating season!) Enoughy silly nonsense! Does anyone know anything referring to the Ts question.

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Aaron Wilkinson
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Unread post by Dean. »

Methven only ended up with a skiff of snow overnight.
I have recorded 38 mm of rain since Thursday morning,with Mt Hutt receiving 45 cm of new snow :) .
The long range outlook looks very intersting from August 30 onwards with perhaps another polar outbreak on the cards.
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Unread post by tich »

Methven only ended up with a skiff of snow overnight.
I have recorded 38 mm of rain since Thursday morning,with Mt Hutt receiving 45 cm of new snow .
Well it seems we probably won't be getting snow to sea-level (though I still might have to eat my words tomorrow), but snow to 300 metres is still a sign that we're in a cold outbreak in Cantebrury, even if it's only a light skiff. Anyway, the models were never predicting particularly low thickness levels for this period, even though the isobars have been coming from a long way south aroung the high.

[/quote]
The long range outlook looks very intersting from August 30 onwards with perhaps another polar outbreak on the cards.
UNISYS is going for this polar blast scenario (at least for South island in a southwesterly) for September 1st. It's a long way off, but still an indication of what sort of pattern is likely to emerge. I notice on the weather forum of a ski-site (ski.com), someone has been mentioning ultra long-range AVN models, one recent one suggesting thicknesses as low as 520 over eastern North Island for September 3rd!

Wet this morning in Chch, but dry for most of the afternoon (I think - I was watching a movie between 2.30 and 4PM); the latest radar showing areas of drizzle or light rain around many parts of Cantebrury, but not here in the city.
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Unread post by Dean. »

Yeah this southeasterly system is a cold outbreak alright,especially with highs of only 4-5 degrees yesterday here.
Passing heavy showers this morning,looking nice and lumpy out to sea on the NOAA sat picture.
Mt Hutt have been saved for the season with 60 cm of snow accumulating since Thursday.
Cheers. :) .
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Unread post by Dean. »

Showers of sleet now falling,some nice towering clouds about.
Temperature now only 3.8.
Must be some colder air being dragged up from the south seas.
Great rugby weather.
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Unread post by Thunder »

Yes Dean, here in Chch today (23rd) I have seen a few good Cu clouds, some glaciating to Cb's (the tops are not that high me thinks). I took a photo but it's with a film camera so won't develop them until the film runs out. I have only noticed small bits of rain and nothing like sleet.

Surely there must of been some Cb's up north today looking at sat pics with them possibly even turning thundery, anyone get anything!

Cheers
Aaron Wilkinson
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Unread post by Michael »

When the forked lightning was going yesterday when I drove through it was quite spectacular but unfortunately I left my digital camera in Auckland ;)
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Unread post by NZ Thunderstorm Soc »

Hi Aaron,
A 'boringly" interesting day here in Chch.
Lots of wintry Cu development... but not doing much although driving up Manchester Street about noon, did encounter a wintry hail shower. There must of been others around the city judging by the cloud forms.
Not much wind but it is interesting in situations like this, there always seems to be a slight breeze from the W/WSW even though it is obvious a S or SE weather scenario ??

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Unread post by Dean. »

The icy showers petered out on Saturday afternoon,cleared to a heavy frost this morning.
Clouding over again now.
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Unread post by Thunder »

Yes John, this stuff is all wintery. So it's understandable why it is boringly interesting as the clouds look goodish but there not producing what we want which is a Thunderstorm! I didn't notice any small hail showers here, and didn't notice the wind situation you were talking about, probably because I'm right on the coast.

Cheers
Aaron Wilkinson

Also John or anyone, is this summer looking la nina or la neno (you get what I mean! I can't remember how there spelt let alone what there called, did I get it right?). And is the second one the one that's good for Thunderstorms here in Cantab?
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Unread post by NZstorm »

Best situation for thunder in Canterbury is low pressure/trough over the region in the months November to January. Lots of sunshine (the more the better) to give good thermal forcing, and sea breezes. Sea breezes encourage convergence(particularly ahead of a southerly change) and also provide more moist air. The higher the temperatures and humidity the better.

Both la Nina and El nino can provide such situations. Perhaps the Vintage year in Canterbury for thunder was way back in 1982/83 when there was
a very strong El nino.

As a quick check for the potential of thunder, check the sounding for the K index. You will find this on a skew-t diagram. Roughly, K index reading of 15 to 25 indicates a slight chance of thunder, 25 to 30 a moderate chance, above 30 Thunder likely. Above 35...severe Tstorms possible.
Ofcourse the K index can change quickly over a short period of time.
K indices for NZ at midday today, Auckland 13, Wellington -3, Invercargill -9. So the upper air quite stable today with NO chance of thunder. Yesterday and friday the K index in the north was around 25 hence a few cb's, ts/hail in Waikato.

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Unread post by NZ Thunderstorm Soc »

Can anyone tell me when Thunderstorm season begins here in Cantab / South Island?

Hi Aaron and Steven.
I normally regard the period from the 1st of October to 31st of March as being the thunderstorm season for Canterbury but over the past 10 to 15 years there have been thunderstorms here outside this period.
This year I think the thunderstorm potential for Canterbury will be basically NIL as we are moving into a weak La Nina period. This is a direct opposite to last years thunderstorm season where we had an added bonus of tornados on the Sunday of Labour WE. La Nina's can produce thunderstorms but it is mainly an El Nino period for good thunderstorm activity for Canterbury. The El Ninos of the 1960s brought a lot of good thunderstorm activity to Canterbury plus 1982/3. On the other hand the strong El Nino of 1996 period was absolutely useless as many of the southerlies were too dry to produce any significance.

Steven,
Good explanation of ts potential for Canterbury. Convection does play an important part.

Aaron, (and other) you may be interested in a video/DVD from ASWA coutesy of Jimmy Deguara of storm chases in the USA in 2003

http://www.thunderbolttours.com/shop.html

with a preview at

http://www.australiasevereweather.com/v ... ay2001.wmv



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Unread post by NZstorm »

While on the topic of thermal convective thunderstorms, I reckon the best spot to observe them in the SI is the Strath Taieri area (just inland from Dunedin). The silly season for them is from about the 20th November through to Xmas.
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Unread post by Thunder »

Thanks guy's!

I'll keep an eye on that K index when potential looks good Steven.

Chances look nil! Thats no good John, very many things I've got to do to keep me busy in the mean time though. Still, not good, I've found a great interest in Ts and this forum has been great in keeping me with it.

Cheers
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Unread post by NZ Thunderstorm Soc »

Sorry, the cat just walked over my keypad hense the strange message just then.
No it's no hidden worn/virus whatever !!

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Unread post by tich »

Showers of sleet now falling,some nice towering clouds about.
Temperature now only 3.8.
Must be some colder air being dragged up from the south seas.
I noticed a sleet shower as I was coming down the Akaroa side of Hilltop on Sunday morning. The sleet changed to rain at about 150-200 metres asl. There was a light dusting of snow above about 600 metres. No hail showers evident in the Akaroa area, just showery periods both Saturday and Sunday, though only drizzly showers on Sunday. (not particularly plesant though)

Ben
Christchurch (mild here today - the cold weekend is now just a memory)[/quote]
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