Spring Weather Bomb - Gales and Snow - 26th - 29th September

[Cyclone Tracy]

Just 2 cents worth from a technical point of view. The developing symmetrical cold core cyclone that is deepening in the Tasman, will not be the same circulation that bombs south of NZ tomorrow morning. The new cyclone will spawn from the upper low that is currently moving up from Antarctic continent. Main global models have the first cyclone dropping 17 hPa before it is overcome by a 2nd rapidly deepening circulation near Stuart Island. The Stuart Island circulation takes off from early tomorrow morning at around 974 hPa and officially bombs into the 930's within that 24 cycle. UKMet thermal wind plot for the 2nd low.

[Bradley]

That’s 2 GFS runs now that have 850hpa temps of -10C right up to North Canterbury and -11C 850hpa temps around Southland, that’s 2 runs now showing these temps - there might actually be something to this upgrade now, especially with how all the major models have been getting colder the last few days, not warmer...

[Awhituobs]

sure looks impressive on the sat image currently!

[snowchaser01]

Latest GFS also brings significant moisture onto the Canterbury Plains and into Christchurch on Tuesday night.....

[Cyclone Tracy]

Plenty of gravity wave clouds now appearing over large areas of the SI and lower NI. It's getting turbulent up there.

[hozza95]

Calm before the storm down here, not even a breath of wind, good chance to do some outdoor work before it turns to custard

[Bradley]

Latest GFS also brings significant moisture onto the Canterbury Plains and into Christchurch on Tuesday night.....

Yep latest run has winds shifting southerly for a time bringing around 10cm of snow for places like Akaroa, 2-3cm for Christchurch and 1-2cm for places further inland on the central plains - better then nothing if it eventuates!!

[mikestormchaser]

Latest GFS also brings significant moisture onto the Canterbury Plains and into Christchurch on Tuesday night.....

Yup current upgraded models suggest snow to sea level now on the plains

[snow101]

GFS really bringing the upgrades with its 12z and 18z runs this morning. -11 850s Southland, Clutha, Otago is quite extreme cold for this area at this time of year. Snow risks for Christchurch increasing. Maybe we will see EC lean more with GFS tonight.

[hozza95]

Gore’s all time lowest September max of 3.0 °C that was set in the big snowfall event of 2010, could be under threat on Tuesday with MS forecasting a high of 3. Plenty of places forecast to reach as low as -6 overnight next week. Crazy cold for late September!

[Bradley]

Gore’s all time lowest September max of 3.0 °C that was set in the big snowfall event of 2010, could be under threat on Tuesday with MS forecasting a high of 3. Plenty of places forecast to reach as low as -6 overnight next week. Crazy cold for late September!

If it was few days later there would have been all-time October records being shattered by up to 5C from this event IMO!!

[Chris W]

Yes and the 700mb wind barbs were looking strong when I last looked yesterday. The wind has assistance from all levels of the troposphere and lower stratosphere/southerly polar jetstream. The subtropical jet isn't exactly hanging about either.

Nice warm morning in Chch, ran in temperatures about 5-10C higher than I've lately been training in so felt it, dry too with the NW! NW really dumps down in Lyttelton at times, so we'll see how it goes tonight.

Oops, hadn't spotted page 3 when I wrote this, so maybe a bit out of place! So yes, bloody cold.

[Chris W]

Latest water vapour image showing a dual polar injected streamer now coming together over the Southern Ocean, heading for the Tasman disturbance which is starting to aggressively spark on the occluded frontal boundary.

That's a beauty, perfect winter storm territory...in mid-spring!

[Nev]

Gore’s all time lowest September max of 3.0 °C that was set in the big snowfall event of 2010, could be under threat on Tuesday with MS forecasting a high of 3. Plenty of places forecast to reach as low as -6 overnight next week. Crazy cold for late September!

NIWA has MS's Gore AWS with a Tmax of only 2.5C for the 24 hrs from 9am on 18 Sep 2010 (although it did manage 3.3C in the hr just before 9am that calendar day). NIWA also has a much older Gore site with a Tmax of just 2.2C on 01 Sep 1919. Third place would be 3.3C on 28 Sep 1949.

[mikestormchaser]

The NOAA comes up with impressive cold numbers of the layers of atmosphere come Tuesday for chch/ Canterbury. Note: iv added in the 3D temperature 700mb aswel for reference. Havent seen it below -20 for ages. -18 is a good number for snow to sea level at 700

[Andy]

Anybody have any data for coldest Tmax temps for Sept for Alex, Queestown and Arrowtown?

[Chris W]

GFS 18Z continues its journey to the depths of cold as mentioned by Bradley and others, Wellington could see snow on Tuesday with -9C 850mb/-19C 700mb temperatures and moisture , though to what levels I don’t know. That is 2013 territory! Yes, I said it and no I haven’t been drinking . Maybe GFS is getting excited, but the numbers are there.

Sorry Andy I don’t know where the data is held, but someone else will.

NW suddenly picking up a bit in Lyttelton now, might close some of the windows/doors soonish.

[Storm Struck]

I have to admit that's the first time I've seen a 500mb temp of - 40C over Canterbury since the 2011 events, as others have said the 700mb is also very cold at - 20C which is more than cold enough.
The 850mb temps of - 8c don't even need to be any colder given these other variables.
Then you throw in some convection in the form of thunderstorm hail potential it brings heavier precipitation and cloud density, along with a now SSW flow and moisture.
What a sting this will be for the books if it pulls through

[Orion]

Northerly wind has started getting rackety here over the past half-hour or so, that hissing sound in the trees and shrubs.

16.8°C at present, falling.

[Nev]

Anybody have any data for coldest Tmax temps for Sept for Alex, Queestown and Arrowtown?

Alexandra's lowest Sep Tmax is 5.0C set in 1970 and 1931 since records began in 1930.

And Queenstown Aero's lowest Sep Tmax is 2.9C set in 1995 since records began in 1972, compared to the town's lowest of 3.8C set in 2012 since records began in 1930.

No records for Arrowtown, sorry.

[Chris Raine]

Nothing much in coastal Southland.Sun setting with blue sky appearing again from the overcast.Wind northerly 12 knots

[NZ Thunderstorm Soc]

Wind has died down here. Been windy since 2pm with gusts from the north.

[Razor]

Got the BBQ on in Halswell. Gentle breeze, nothing out of the ordinary so far

[Bradley]

Big downgrade in latest run of EC tonight for Canterbury with maximum 850’s of -7C for Canterbury and no moisture at all on the plains, will be interesting to see tomorrow mornings run but -10C for Canterbury always seemed pretty optimistic from GFS...

[Cantab03]

Big downgrade in latest run of EC tonight for Canterbury with maximum 850’s of -7C for Canterbury and no moisture at all on the plains, will be interesting to see tomorrow mornings run but -10C for Canterbury always seemed pretty optimistic from GFS...

Latest GFS has pulled back moisture on Tuesday for Canterbury too. Not really feeling this system in Canterbury still. Great totals further south though on the way.