Polar Outbreak starting 07/06/2008

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Janos
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Re: Polar Outbreak starting 07/06/2008

Unread post by Janos »

Manukau heads observer wrote:anyone would think reading all these posts that you guys have never seen snow before,harden up fellas, LOL!
but I guess everyone got caught up in the excitment of it all
the fac the barometer did not rise after the front went through suggests to me that a low developed over the canterbury area, in behind the front, in the lee of the mountains, and so you ended up with the dropping barometer cooling the airmass
You are so right ...I have a friend in Maine near the Canadian boarder who would laugh his head off if he read this thread.
They only got 20 foot of snow this year...I could post some photos of him digging his garage out standing on the roof..but we would cry .
Berkshire North of Te Anau west of Hokitika.
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Re: Polar Outbreak starting 07/06/2008

Unread post by NZ Thunderstorm Soc »

Some pictures from West Melton from today's snowfall.

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Re: Polar Outbreak starting 07/06/2008

Unread post by Willoughby »

Wow - nice photos everyone and definitely lucky for some!! 8)
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Re: Polar Outbreak starting 07/06/2008

Unread post by Manukau heads obs »

great photos John (and others), really shows how heavy it was !
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Re: Polar Outbreak starting 07/06/2008

Unread post by Janos »

Snow level came down to just under 100meteres over night...hills around Dunedin are covered and I suspect most of the hill suburbs will be white.
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Re: Polar Outbreak starting 07/06/2008

Unread post by Janos »

http://homepages.ihug.co.nz/~Sgf.hyland/home.htm
Heres a link to Gerards web cam...
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Re: Polar Outbreak starting 07/06/2008

Unread post by David »

I see the Castle Hill weather station in inland Canterbury has recorded a low of -9 degrees this morning!
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Re: Polar Outbreak starting 07/06/2008

Unread post by NZstorm »

the fact the barometer did not rise after the front went through suggests to me that a low developed over the canterbury area, in behind the front, in the lee of the mountains, and so you ended up with the dropping barometer cooling the airmass
Some mesoscale effect was going on there for sure Brian. The modelling I looked at in the previous day or two didn't signal 5cm snow to sea level in Timaru from the cold front. The trough was very sharp and quite active and this would have generated its own cooling as well.
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Re: Polar Outbreak starting 07/06/2008

Unread post by melja »

Here is rangiora at 3.30pm,we had a good 6-7cm before it stoped.
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Re: Polar Outbreak starting 07/06/2008

Unread post by Janos »

A couple of photos of "not much snow"...
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Re: Polar Outbreak starting 07/06/2008

Unread post by gllitz »

Would be interesting to see a chart showing the distribution of the snowfall amounts around Canty/SI....would this be something the M/S would do, or someone's personal project? :-)...yeah, was wondering if that was an upper level low developing behind the front as it passed...the radar loops and sat loops showed something trying to form, but oh well...
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Re: Polar Outbreak starting 07/06/2008

Unread post by spwill »

The modelling I looked at in the previous day or two didn't signal 5cm snow to sea level in Timaru from the cold front. The trough was very sharp and quite active and this would have generated its own cooling as well.
A bit of a supprise that low level snowfall on the Front over Canterbury , the frontal snow level for Otago was 300m. Looks like the Front became more active and slowed over South Canterbury.

I'm in Mosgiel, light snow cover here turned very icy this morn, warming up now.
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Re: Polar Outbreak starting 07/06/2008

Unread post by Smeagol »

Did anyone catch 3 News last night? The last shot of the snow on the news looking down the road was shot from right outside my house.
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Re: Polar Outbreak starting 07/06/2008

Unread post by TonyT »

The models were predicting around 20mm for Canty for this event, which using the 10:1 rule of thumb should have resulted in 2cm of snow, but as others have noted, the flakes were very large, so I'm not surprised that there ended up being greater depths. This snow was nothing like the fine dry snow we are used to seeing in the mountains. The snow is still melting in my raingauge, but I'm only up to 14mm so far, and thats from snow which was 5cm deep in the open. The models were always showing air which would be cold enough for snow to sea level for days before the event, its just that they didnt show it arriving as quickly as it did.

It was interesting to note that we had some light showers here in Amberley between 11 and 12 yesterday morning, well ahead of the wind change which came through at 12.40. The showers were extremely light, and at times appeared to be falling out of a blue sky above, being blown some distance sideways by the gusty westerly wind. So there was enough instability ahead of the front to generate some very light precipitation. Temp at 12noon was 16 deg, by 2pm it was 3 deg and by 2.40pm sleet had turned to snow.

That temperature drop is pretty extreme, not so much in terms of the delta (a drop of 13 deg or more is also quite common with summer SW changes), but in the fact that it got to just 3 deg so quickly. 3deg is an unusually cold mid afternoon temperature for here on any winters day, let alone one which had 16 deg just 2 hours before. So I would suggest that the low level cold air surged along the east coast very rapidly, more rapidly than the models had predicted (understandable given the resolution of the models, and the fact that this was probably a meso-scale event which "slipped through the cracks" so to speak).

The cold air undercut the frontal rain band as the front moved into the lee trough, so the snow level dropped much more quickly than any of us had anticipated. The strong westerly flow ahead of the front probably had a lot to do with it, creating a substantial lee trough which sucked the low level cold air up the coast faster than might usually be expected. The lee trough was also probably more unstable than it often is. Normally this wouldnt be much of an issue (or even noticeable), but in this case the air was so cold behind the front, that it resulted in snow at the surface rather than rain.

If you look at the predicted pressure, temp and rainfall values the models had in the last few days, I think they did an excellent job, the only thing they didnt capture was the speed of the cold advection.
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Re: Polar Outbreak starting 07/06/2008

Unread post by tich »

I'm not that surprised at what happened yesterday - I recall it occurring several times before, an extreme example being the big snow of June 2006.
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Re: Polar Outbreak starting 07/06/2008

Unread post by tidd66 »

We got of very lightly (pity) in Gore no snow on the ground this morning apart from a few snow flakes there was nothing to get excited about. Might move to Canterbury you have way more snow than us the last few years.
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Re: Polar Outbreak starting 07/06/2008

Unread post by NZstorm »

On Friday evening 6pm I noticed the temperature at Campbell Island was already freezing, 6 hours ahead of schedule. I guess that was the early warning sign that Saturdays front was going to be in a colder environment than the modelling was indicating.
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Re: Polar Outbreak starting 07/06/2008

Unread post by Janos »

Thats a great explanation thanks Tony T again it shows that natural forces are so unpredictable.
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Re: Polar Outbreak starting 07/06/2008

Unread post by mikestormchaser »

yes beautiful morning here in Christchurch, what a day yesterday with that snow and sleet, was awesome last night espeacially that good we shower we had when the rugby started.
Port hills are niely covered today right down to about 250m might take wee drive up there again and see how much they actually got.

cheers
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Re: Polar Outbreak starting 07/06/2008

Unread post by NZstorm »

I recall it occurring several times before, an extreme example being the big snow of June 2006.
It has happened a few times in recent years but the 2006 event was something different, that was a warm advective snow event. The energy for that one came in from the north Tasman Sea, hence the 80cm in Fairlie.
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Re: Polar Outbreak starting 07/06/2008

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Jeffs only got down to -1.3 and its 5.7 at the moment.. brr!
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Re: Polar Outbreak starting 07/06/2008

Unread post by spwill »

The models were always showing air which would be cold enough for snow to sea level for days before the event, its just that they didnt show it arriving as quickly as it did.
Yes, the very cold air with the sealevel snowfall for Dunedin was with post Frontal Cb however the sealevel snowfall in Canterbury was with the Front. Snow level with the Front over Dunedin area was 300m.
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Re: Polar Outbreak starting 07/06/2008

Unread post by southernthrash »

Tony - 10:1 would equate to 20cm of snow from 20 mm rain...

Went snowboarding in Dunedin today, up at halfway bush, cover of about 5cm with drifts of 30+ in places. We had a dusting of snow down to pretty much sea level on the ground this morning, and it was very icy, but has warmed up quickly and the snowline is probably around 300 m now.
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Re: Polar Outbreak starting 07/06/2008

Unread post by Manukau heads obs »

Tony - 10:1 would equate to 20cm of snow from 20 mm rain...
thats the way I take it works too :mrgreen:
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Re: Polar Outbreak starting 07/06/2008

Unread post by Storm Struck »

Still plenty of snow well frozen snow on the ground especially in shady spots, although occasionally i will hear a thud or a scraping noise as ice falls off a tree or roof :D .
It seems as though Christchurch city acted as a heat box with obviously more warmer concrete surfaces not allowing much snow to settle, this was evens slightly evident here with the snow melting away fast on concrete surfaces here.
If you drive north from about Marshlands,Papanui area northwards snow becomes visable on the ground.
Sent a photo into the press of the snow so i am not sure if it will make it into the paper but it was worth a shot.
Interesting to note it turns milder NW later in the week not that anything cold is following, but if a trend starts developing like this for winter we could be in for a few snowfalls :-k .
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