A Change in Weather Pattern

[Gary Roberts]

I think its more to do with the temperature of the airmass coming from the Tasman sea Jason, if the snow were the main factor then all winter NWers would have the same temperature.

There is little snow on the divide. What small amount fell was washed away by warm rain a few weeks ago and virtually no new snow has fallen to replace it.

On top of that the temperature has jumped and it's not wind-related: there has been very little wind all winter and there's not much wind now either.

However to add some support to Jason's assertion to some extent, when you're up near the divide the wind coming down off it is cold, not warm.

We might get a last-gasp event, such as an inch or so of snow in August, such as we did in 2005 (I think it was) but like that time it won't last half a day as the ground temperature is way too high.

The winter-proper is over. It finished around the end of June or beginning of July. This is now just the long run up to spring. Same as the last few years.

[Manukau heads obs]

its also to do with the ridge of high pressure too i would say
-> a stable air mass does not want to cross the southern alps (which leads to the strong winds in places like wairarapa), but when its forced too, its compressed alot, and that helps to heat it up (more so than an unstable air mass)
(along with the fact its a high moisture fed airstream, coming from the NW tasman sea, and its that loss of moisture on the west coast that gives alot of the heating too (latent heat)

[Manukau heads obs]

what you guys should be saying is, the SI is currently getting a spring like weather pattern

[Lawrence]

Well I've been sitting here for two days watching this low develop and am as stumped as M.S. but looking at it historically and remember that I have to reverse everything the other way as I'm a pom,I can only come to the conclusion that this is going to be a deepening low which will hit the south Island between Graymouth and Hokitika at a best guess ,the next thing is as it moves away to the east it will still have some momentum I think to pull in some cold wintery conditions to the east coast about Tuesday.I do agree that this might be an equivalent event to the North Islands which has just passed,but it's a bit too early yet to be certain

[gopolks]

I think Weather for late Sunday into early Tuesday has got everybody stumped.

Some scoures are saying Heavy Rain and Southerlies.

Some are saying NE winds light rain and temps of 15 degrees.

I have lived in chch all my life, and everytime there have been NW days in the middle of winter, with temps in the high teens, we have gotton some nasty stuff following it. I dont ever recall a NW pattern to be followed by NE???

Very strange indeed, but either way, its going to be fun to see what happens.

[Manukau heads obs]

the latest ecmwf sure has changed its tune for next week from what it had
this latest polar high it has as moving steadily away to the east (after firsting kicking up a fight and creating a squash zone over the SI), with W or NW winds over nz next week instead of cold SE winds....hummm!

[mikestormchaser]

I think Weather for late Sunday into early Tuesday has got everybody stumped.

Some scoures are saying Heavy Rain and Southerlies.

Some are saying NE winds light rain and temps of 15 degrees.

I have lived in chch all my life, and everytime there have been NW days in the middle of winter, with temps in the high teens, we have gotton some nasty stuff following it. I dont ever recall a NW pattern to be followed by NE???

Very strange indeed, but either way, its going to be fun to see what happens.

yup

[NZ Thunderstorm Soc]

the latest ecmwf sure has changed its tune for next week from what it had
this latest polar high it has as moving steadily away to the east (after firsting kicking up a fight and creating a squash zone over the SI), with W or NW winds over nz next week instead of cold SE winds....hummm!

ECMWF have been vague after the first, few days of their forecast, lately
Another 50mm dump in Canterbury does looks likely early nexy week
JohnGaul
NZTS

[Gary Roberts]

what you guys should be saying is, the SI is currently getting a spring like weather pattern

Winter is effectively behind us, or at least it is in the Mackenzie, so we're heading into spring.

[Andy]

Winter is effectively behind us, or at least it is in the Mackenzie, so we're heading into spring.

The Hoar frost conditions of last week are of a distance memory. Temps reaching the mid to late teens, since last Sunday.

[gllitz]

The Hoar frost conditions of last week are of a distance memory. Temps reaching the mid to late teens, since last Sunday.

Ah well, no more curling competitions for another year then!

[gopolks]

Well who would of thought it. Our lovely North Westeries are going to be replaced by cruddy NE, I would of put money on it, that we would of gotton something nasty.

[spwill]

Winter is effectively behind us, or at least it is in the Mackenzie, so we're heading into spring.

So what has 07 Winter been like so far? looks to have been colder than normal for the South Island and warmer than normal for northern NZ. Niwa summary for july will be interesting.

[Gary Roberts]

So what has 07 Winter been like so far? looks to have been colder than normal for the South Island...

Nope, at least not in the Mackenzie. It was significantly warmer than last year and around the same as winter 2005. (Or was it 2004? I forget...)

Possibly a few more cold days but only because we had some snow on the ground (albeit bugger-all), unlike 2004 and 2005 where there was almost no snow at all.

...warmer than normal for northern NZ. Niwa summary for july will be interesting.

I don't know about up north.

[gopolks]

Still lovely and warm in chch.

19.1°C
Heat Index 25.5 °C
Wind Chill 25.0 °C

Humidity: 40 %
Dewpoint: 5.2 °C
Wind Speed: 0.0 km/h
Gust Speed: 0.0 km/h N
Gust Last Hour: 8.0 kmh NNE
Barometer: 1012.7 hpa (Falling slowly)
Today's Rain: 0.0 mm
Days with no rain: 5 days
Sunshine Today: 02:57
Time of Last Lightning: 13:01:58 2007/07/27
Last strike recorded: 430 KM @ 289°


Conditions
Partly cloudy/Dry

[spwill]

[quote][/quote]Possibly a few more cold days but only because we had some snow on the ground (albeit bugger-all), unlike 2004 and 2005 where there was almost no snow at all[quote][/quote

The better measuring stick for winter in the Mackenzie is frost rather than snow. Snow in Omarama is fairly rare as you have no doubt discovered. I'm picking your winter has been colder than average.

[RWood]

For June (from NIWA summary): temps 0.5C below over most of the South Island, and at least 1.0C in Otago.

July - wait and see.

[gopolks]

I guess its the frosts that did this for chch.

[Michael]

Lots of sun in Hokitika greymouth and Fiordland

[Gary Roberts]

The better measuring stick for winter in the Mackenzie is frost rather than snow.

It's true that we did have more frost/rime ice this year than the last three.

Snow in Omarama is fairly rare as you have no doubt discovered.

Omarama receives only a little less snowfall than most other places in the Mackenzie, if at all. There are times when we get snow while Twizel and Lake Tekapo don't. The altitude difference isn't great, less than 300m at most.

The fact is that NZ gets stuff-all snow, and the last few years we've had stuff-all of stuff-all.

I'm picking your winter has been colder than average.

That would depend upon the number of years being averaged. This year was barely colder than the last five, if at all colder. Again that's likely to be because of the small amount of snow on the ground. Last year's temps were lower by as much as 5 °C. (2006 low was -14 °C-ish while this year was only -10.5 °C.) 2004 and 2005 had the odd cold day, but overall were much like this year, sans the snowfall.

If the average is over a long period then I couldn't even guess as I haven't lived here a long time, although again I suspect we'll see that there won't be much difference. I could be wrong though.

[Dean.]

Omarama is around 400 metres above sea level,Tekapo around 700 metres.Fronts moving up the central South Is tend to split around the Lindis Pass/Omarama area,leaving a sheltered area over the central Mackenzie area.So in Omarama snow would be more common from these events,than Twizel/Tekapo whose snowfalls would be more common from warm advection snow,or cold westerly fronts?.Thats just from past experiences of mine when staying up there.One of my favourite parts of the country by all means.

[NZ Thunderstorm Soc]

Next week looks likely there will be a change in the current weather pattern with a westerly-ish flow developing over NZ, with an anticyclone moving into the Tasman Sea replacing the recent developmentation of low pressure systems there.
However, resistance of the anticyclone over the lows, may weakon next weekend with another low pressure system returning, unfortunately.

JohnGaul
NZTS

This anticyclone has now moved away to the east.
It looks as though, with this new developing low, it's like " Hey. Wait for me" as if with the projected development of this low, he was missed out on the recent ECALs and he is trying to catch up with his previous mates in this weather pattern

JohnGaul
NZTS

[TokWW]

Yeah - with some more muddy Nor-Easters to the NI... Then the two Lows merge
and the SI catches up and gets the Nor Easters too after the NWesters

[RWood]

Omarama is around 400 metres above sea level,Tekapo around 700 metres.Fronts moving up the central South Is tend to split around the Lindis Pass/Omarama area,leaving a sheltered area over the central Mackenzie area.So in Omarama snow would be more common from these events,than Twizel/Tekapo whose snowfalls would be more common from warm advection snow,or cold westerly fronts?.Thats just from past experiences of mine when staying up there.One of my favourite parts of the country by all means.

Which might indicate part of the reason the Tekapo area is about 5-10% sunnier than Omarama, even though its rainfall is a little higher with the Alpine overspill being closer.

[Gary Roberts]

Which might indicate part of the reason the Tekapo area is about 5-10% sunnier than Omarama, even though its rainfall is a little higher with the Alpine overspill being closer.

Nope. It has more to do with topography than altitude. When the prevailing W/NW wind is blowing, a low cloud shear line forms along the edge of Lake Pukaki, caused by the immediately adjacent Ben Ohau range which happens to be aligned with the Lake.

Areas south of that line are to some degree sheltered from the wind which prevents the low cloud layer from being disrupted, so cloud covers the area south of that line and it is blown away north of it.

Also there are two common inversion layers which form over the Mackenzie: one around 600-1000m and the other at approximately 1,300-1,700m. Obviously when you are below those you are under cloud. Get above them and it's usually fine.

At 720m Lake Tekapo township occasionally just squeaks out above the lower one, but not often. If the low altitude layer is the only one present then Tekapo has a slight chance of being in sunshine when the more southern areas haven't. But if only the higher altitude layer, or both layers, are present, then everybody below those altitudes has overcast skies.

I've been driving up Benmore Peak and been between the two layers and it's a fascinating sight. Crystall clear air between two seemingly-endless cloud layers. The main divide looks like a wall, as it disappears from view into the upper layer. Then you break out of that and into clear blue sky and the only thing you can see is the tops of the higher mountains, such as the Alps.

In those cases everything else is clouded in. Lake Tekapo's extra 300m of altitude has little to do with its slightly higher rate of clear skies. Mostly it's due to that shear line along the Pukaki-Ben Ohau Conversion Zone© (I just invented that name). If the Ben Ohau range and/or Lake Pukaki weren't aligned the way they are there would be even less difference in the number of clear skies the two areas experience.

These are things you notice when you are building an observatory at 1,900m. But anyway we were discussing other wind-related myths...