Very cold southerly blast NZ wide Sept 7-9th

[spwill]

Models showing some cold air to cross NZ around Wednesday into Thursday next week, snow on the hills, will be brief.

[Bradley]

Both GFS and EC both going for a brief but intense cold blast on Thursday for the South Island with thickness levels at 520 for a time and 850hpa temps around -7C at its coldest, moisture levels aren't huge due to it being a SW airflow but still this is something to watch as both models have been showing it for a few days now

[NZ Thunderstorm Soc]

Yes. I'm working on a violent thunderstorm for Canterbury, in the afternoon or evening with the cold southerly change, if it doesn't happen which looks likely as we get closer to the event, the NZThS will be on hold until interesting weather picks up. I've forgotten what thunder sounds like, sadly.
Maybe in Geraldine, I could start up the NZ Inclement Weather society, which would include non-thunderstormic weather????

[Bradley]

Yes. I'm working on a violent thunderstorm for Canterbury, in the afternoon or evening with the cold southerly change, if it doesn't happen which looks likely as we get closer to the event, the NZThS will be on hold until interesting weather picks up. I've forgotten what thunder sounds like, sadly.
Maybe in Geraldine, I could start up the NZ Inclement Weather society, which would include non-thunderstormic weather????

It's been beyond pathetic hasn't it John, here's to another September 19th 2005 system, or similar

[NZ Thunderstorm Soc]

It's been beyond pathetic hasn't it John, here's to another September 19th 2005 system, or similar

Yes, that was a good one, sadly I don't think there will be a repeat

[mikestormchaser]

Yes. I'm working on a violent thunderstorm for Canterbury, in the afternoon or evening with the cold southerly change, if it doesn't happen which looks likely as we get closer to the event, the NZThS will be on hold until interesting weather picks up. I've forgotten what thunder sounds like, sadly.
Maybe in Geraldine, I could start up the NZ Inclement Weather society, which would include non-thunderstormic weather????

Wednesday afternoon looks like there could be low-mod risk for thunder/hail coastal Canterbury. Southerly buster type of storm if anything. Don't hold off the NZTHD John. We always go through these quiet times. And then get a huge storm come in or a couple in one season. It will come

[Bradley]

Looks to be around a 500m level for snow in Canterbury on Thursday with around 5-10mm, latest run of EC tonight has it a tad colder then this mornings run

[Bradley]

This cold front on Wednesday/Thursday is getting colder and colder with every model run, another 1C colder with 5-10mm more precipitation we will have an event very similar to the September 19th 2005 event. I see also the Metservice is calling this a significant event in their severe weather outlook

[mikestormchaser]

I'm still keeping eye on a risk of thunder/ hail wensday along the coast of Canterbury. The two things that don't make it a big risk is the fact it's a strong NW before b change and the timing looks abit off for storms but there will be a risk of lightning!

[NZ Thunderstorm Soc]

This cold front on Wednesday/Thursday is getting colder and colder with every model run, another 1C colder with 5-10mm more precipitation we will have an event very similar to the September 19th 2005 event. I see also the Metservice is calling this a significant event in their severe weather outlook

Good.
I've got a lot of firewood to burn that I don't want to take down to Geraldine, so I don't want too many warm spring days at the moment

[NZ Thunderstorm Soc]

I'm still keeping eye on a risk of thunder/ hail wensday along the coast of Canterbury. The two things that don't make it a big risk is the fact it's a strong NW before b change and the timing looks abit off for storms but there will be a risk of lightning!

It's a shame that we couldn't work yesterday's ENE in against the southerly change and drop the barometer pressure down

[Bradley]

I remember Tony saying in the 24-48 hours before the 2005 event that the cold front had thickness values around 523/524 and 850hpa temps of -7C which he believed would produce snow to sea-level, this event has thickness values even a little colder around 522 and the same 850hpa temps so I wonder why that event is being forecast for snow only to 300m yet the 2005 event had snow right down to sea level? (and a decent amount too)

[mikestormchaser]

I remember Tony saying in the 24-48 hours before the 2005 event that the cold front had thickness values around 523/524 and 850hpa temps of -7C which he believed would produce snow to sea-level, this event has thickness values even a little colder around 522 and the same 850hpa temps so I wonder why that event is being forecast for snow only to 300m yet the 2005 event had snow right down to sea level? (and a decent amount too)

I don't know or take as much interest in snow as I would trying to keep eye on thunderstorm activity however I'll take a guess and say there are layers in the atmosphere that are to warm at this stage for ground level snow ?

[03Stormchaser]

Massive swells along the Canterbury coast on thursday morning. Over 5m waves at magnet bay forecasted

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[spwill]

Looks like the best wintry trough of this cold season for the South Island on Wed/Thurs . I am in the South Island this week around Queenstown/Te Anau

[Tornado Tim]

Yes Wednesday Thursday looks best, a ripper of a cold southerly forecast!

[Bradley]

Saw something interesting on NIWA's forecasting page for Christchurch this morning, it says 4cm of snow for Christchurch on Thursday instead of mm, a computer error perhaps...

[NZstorm]

Looking like a cold outbreak for the country. Severe southerly gales in east. Snow showers to low levels. Isolated squally thunderstorms.

West of the North Island could catch an isolated thunderstorm/hail.

GFS 850mb temps Thursday 00Z

[Bradley]

Latest severe weather watch from Metservice mentions the possibility of snow down to 100m for mid and north Canterbury, EC is truly the odd model out here with all other models agreeing with this snow level yet EC only has snow to 500m for mid Canterbury overnight Wednesday and Thursday, maybe 400m at a push, interesting times ahead...

"Snow is expected to fall above 200 metres in the south and east of the South Island during Wednesday, and possibly as low as 100 metres in Mid and North Canterbury during Thursday morning. This Watch covers the possibility that snow accumulations between 300 and 500 metres could come close to reaching the warning criteria of 10cm in six hours in the following places"

[NZstorm]

I see my dates for the event were in error. Thanks for correcting and updating thread Nev.

[Richard]

Good to see what hopefully will be the first for the Canterbury thunderstorm season with the southerly blast due Wednesday

Valid to: Midnight Wednesday 7 Sep 2016

Issued at: 10:29am Tuesday 6 Sep 2016 by the MetService

Very cold and unstable air spreads across southern and central New Zealand,bringing squally showers to many places, and snow to low levels over the south and east of the South Island. There is a low risk of thunderstorms over Southland, Otago and the Canterbury High Country through the afternoon. There is a moderate risk of thunderstorms over Westland and Buller, easing from the south during the afternoon and evening. A gale force southerly change is forecast to move northwards across the Canterbury coast and Plains, Marlborough and the lower North Island during the afternoon and evening. There is a moderate risk of thunderstorms with this change, easing to a low risk from Kapiti to central Hawkes Bay at night. These thunderstorms may produce brief heavy rain,strong wind gusts of 90 to 110 km/h, and hail.

[mikestormchaser]

Yes as mentioned a couple days ago tomorrow did look like a risk for a storm up the Canterbury coast. Southerly buster/gust front if anything

[03Stormchaser]

Will be heading into work late on Thursday, hoping to get into one of the south bays on BP. Wed looks promising aswell

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[Bradley]

I see NIWA is going for sea-level snow as well in their forecast:

A major theme associated with this cold outbreak is the threat for near sea-level snowfall for several locations around New Zealand. With temperatures plummeting on Wednesday evening in the South Island, light accumulations will be possible by Thursday morning in the hills around Dunedin, with even the possibility of minor accumulation in the city itself. This could cause travel issues on Thursday morning. Farther north, a Thursday morning dusting will be possible in Christchurch and its northern suburbs. However, the snow may not be confined to the South Island on Thursday, as the Wellington area could see light accumulations also. Here, the best chance for snow will be in the morning in the higher elevation suburbs such as Brooklyn, Karori, and Johnsonville. It’s possible the city centre will see snowflakes flying as well, but accumulation is not expected at sea level in Wellington.

[Razor]

Christchurch and its northern suburbs ? Oh dear