NZ Weather Forum

Looking like potential for quite a significant cold blast in the first week? GFS showing 10C here through the afternoon next Thursday dropping to 3C overnight. Those numbers for here would rival anything we had in actual winter this year

Ummmm.....

Yeah I've been watching next Wednesday into Thursday in the models for a few days now, it's looking ridiculously cold and throwing out numbers simular to the August 2011 snowfall.
-20c on the 750mb alongside -8c on the 850mb and -36c on the 500mb, plenty of moisture too so that would be a decent coating of snow to sea level from Dunedin up to Kaikoura.
Maybe even one of those polar events we see flurries in Wellington city.
I can't recall a snowfall in October in Christchurch before, but I do remember having snow falling in November briefly.

Only 6 out 50 members with EC are saying snow in Christchurch but certainly accumulations down to 200m looks likely…

That's quite a cold outbreak in the model outlooks for next week.

Looking at the thickness values in this run, that would translate to sea level snow over the lower NI (moisture permitting) and to about 400 m as far north as Auckland, would that sound about right?

Having said that, this latest GFS run has started to jog the coldest air off to the east just a bit, so maybe that's what will ultimately happen to the worst of it. Watching with interest...

Its a goodie, for sure! [500hpa forecast height and wind speed (colours) for 12Z Wednesday]

Storm Struck wrote: ↑Fri 30/09/2022 07:15 I can't recall a snowfall in October in Christchurch before, but I do remember having snow falling in November briefly.

Would've been this occasion:
https://paperspast.natlib.govt.nz/newsp ... 61111.2.45

Going through my weather diaries, I can't recall a snow event in October.
Before then, I can remember in my school day of a snow event in November 1967 where the Fairlie flyer train was recorded shunting wagons in the yard at Fairlie with snow on the cowcatcher of the Ab loco.

GFS surface temps on Thursday afternoon. Much colder than normal nationwide

Someone noted today at work that we had snow in Christchurch around show weekend one year.
It's a pity the change on Wednesday starts at 7am as it would have been a potential thunder producer, the models continue to show the polar outbreak with not too much change.
However for the first time I've never seen the 850mb temp at -10C over the south island before, almost too cold .

Snow on ground in Ashburton one Labour Weekend around 1985-1987, regret can't pinpoint the year.

Snowfall November 1967:

"Geraldine recorded snow fall to a depth of 11.5cm."

https://hwe.niwa.co.nz/event/November_1 ... o_Snowfall

and, yes, the snowfall just before Show Day November 1976.

And a frost to start October, 0.4°C at the moment and some thin high overcast.

28 of 50 EC members now suggesting snow in Christchurch on Wednesday

Bradley wrote:28 of 50 EC members now suggesting snow in Christchurch on Wednesday

What's Ashburton in comparison?

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Dean. wrote: ↑Sat 01/10/2022 08:32

Bradley wrote:28 of 50 EC members now suggesting snow in Christchurch on Wednesday

What's Ashburton in comparison?

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Unfortunately EC only does the major centres for member comparisons, it’s easily cold enough to snow though and certainly for 100m asl anything that falls on Wednesday night/Thursday morning should be snow…

Bradley wrote:

Dean. wrote: ↑Sat 01/10/2022 08:32 What's Ashburton in comparison?

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Unfortunately EC only does the major centres for member comparisons, it’s easily cold enough to snow though and certainly for 100m asl anything that falls on Wednesday night/Thursday morning should be snow…

Cheers...the flow may be too southwest for us by then

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Model consistency is key and that's something the mid week polar blast continues to show.
We have much colder numbers showing than we did for the early September dusting in the city, which brought brief snow and sleet showers.
I suspect going on current outputs that we could have abit more than just a light dusting, enough to disrupt roads by Thursday morning.
It was looking a bit SW for Thursday which it continues to show, except now on Thursday morning it's S-SW.
The second shortwave cold front due through Wednesday night is the one to watch, before that the freezing level will be around 200-300m.

Mod Note: Thought this potential 'Polar Blast' on Wed-Thu could do with its own thread.

Typed in some numbers in the GFS meteorgram and going by this graph.you would say a few cm looks on the cards for chch city for overnight Wednesday into Thursday morning.
Haven't seen temps like this since the 2011 snow.

mikestormchaser wrote: ↑Sun 02/10/2022 09:35 Typed in some numbers in the GFS meteorgram and going by this graph.you would say a few cm looks on the cards for chch city for overnight Wednesday into Thursday morning.
Haven't seen temps like this since the 2011 snow.

As cold as the August 2011 event but with 1/10th the moisture, I just can’t see ChCh getting 20mm out of this system like GFS is currently saying.

See below GFS data for August 2011

NIWA are forecasting a maximum of just 5°C at Invercargill on Wednesday (5th Oct) which is low (in my opinion) for Spring. This is equivalent to early April in the UK and I would not welcome that figure here in Devon at that time of the year.

https://twitter.com/NiwaWeather/status/ ... 3148157952

The numbers have come up a bit here, now showing 12/13 for Thursday instead of 10/11

Bradley wrote: ↑Sun 02/10/2022 09:54
As cold as the August 2011 event but with 1/10th the moisture, I just can’t see ChCh getting 20mm out of this system like GFS is currently saying.

See below GFS data for August 2011

No not expecting it Like the Aug 2011 event.just the temperatures look simula. It could well warm up abit as we get closer to the time. Important to note aswel even if the GFS was right with 20mm not all of that would be falling as snow anyway and if it was to snow to sea level it might only settle for few hours before being washed away or melt.
Ground temperatures will be warmer now.

Showers with the initial front then a coastal set up with a frosty Wednesday night....a non event for the bulk of Canterbury

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Dean. wrote: ↑Sun 02/10/2022 13:21 Showers with the initial front then a coastal set up with a frosty Wednesday night....a non event for the bulk of Canterbury

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I wouldn't be saying that with any certainty yet, personally