NZ Weather Forum

Hi there, I am trying to find the hottest and lowest recorded teperatures in Twizel for a tour I will be running, I hear temps as low as-18 but that has ben a few years ago and unoffically as high as 44. Would really love to know the answer to this and also if anyone has any comments about the weather has changed since the hydro lakes were filled, I rememebr someone telling me when they were working on the development it could be 26 by 6am in summer and that it is not so hot anymore and that there is more hoar frost and fog. Can anyone help me out?

There's free access to NIWA data now - see the thread on "National Climate Database Now Open for Access", where you can read about it. Gary Roberts will confirm for you that the highest maxs. recorded there officially are nowhere near 44C [he refers to temp. readings taken in the likes of heat sinks like the Twizel mall!], more like 32 or 33 I would guess. Were you in Twizel in 1982? There were some lengthy freezing fog incidents in June/July that year.

I just looked up their data - 3 different sites covering the period 1972-2001, nothing in their records since then. The extremes for that period were: 33.4C on 6/2/1973 and -14.7C on 5/7/1975.

any comments about the weather has changed since the hydro lakes were filled

I would have thought there would be no change to the Climate of Twizel with the filling of the Lakes as the Lakes are very small.

Thanks for that, I have only been since 2001 and 9 years before that in Mt Cook. The 44 I had was from someone temperature gauge in the shade of their house and that was last year and I would guess that would not be very accurate. Yes, I would imagine that the temp from the Market Square would be hotter due the buildings and concrete around it. It is very hot at the moment late twenties I think another great day with some beautiful cirrus on display. Also thanks about the lakes being too small to really influence the weather, I was not sure whether the extra water froman larger pukaki and the Ruataniwha and Benmore evaporating would have an influence or not.

I was not sure whether the extra water froman larger pukaki and the Ruataniwha and Benmore evaporating would have an influence or not.

There's bound to be more early morning Mist/fog close to the lakes.

My car told me it was 41 last summer while down at falston(benmore) camping and its normally correct, i would say that it gets into the mid 30s with out to much trouble down there.

I don't think there's a lot of useful information obtained from car thermometers.

I wouldnt say that at all, it allways has the same reading as my work weather station when i get to work but is only accurate when moving with out the heat soak from the engine.

It must have got to nearly 40 degrees in the Basin in the last 50 years. Its not much different from Alexandra, a little more elevated, slightly less sheltered, but as barren and cloudless and Alex has got to 38.

Edited to correct inaccuracies...

Much higher altitude still counts. There's no accepted record reading for Omarama, Twizel or Tekapo which exceeds about 33-34C.

Yeah bit of a micro climate in the Mackenzie eh,some of those sheltered inland basins and valleys must craack the mid thirties.Used to camp at places like Ruataniwha/Benmore.Stinking hot in January.Doesnt seem to happen as much anymore,maybe La nina will change that this year.

spwill wrote:

any comments about the weather has changed since the hydro lakes were filled

I would have thought there would be no change to the Climate of Twizel with the filling of the Lakes as the Lakes are very small.

The central otago lakes (dunstan and roxburgh) have a known effect. Intoducing a relatively static body of water occupying considerably more area than a river would have before it will always have some sort of climatic effect, especially in areas as dry as the McKenzie/Central otago.

What effect(s) are you claiming?

RWood wrote:What effect(s) are you claiming?

generally a moderation in climate around the peripheries of water bodies, and associated flow on effects, localised winds etc.

Best example is the effect on frosts and snowfall.

generally a moderation in climate around the peripheries of water bodies, and associated flow on effects, localised winds etc.

Best example is the effect on frosts and snowfall.

Yes temp moderation,more mist and fog along the lake shore lines is obvious but how far out from the waters edge would be impacted.

I suggest that in the case of Alex, Clyde and Cromwell there has been no "temp moderation" due to the increased levels of rivers/dams/lakes.

I have no statistical facts. Clyde sits below Lake Dunstan, which sits along a narrow wind gap between large open areas ie the Cromwell-Wanaka-Hawea-Tarras plains and the Alexandra Basin. Where lower pressure in Alex, or faster heating, or some other effect there draws or pushes air in from Cromwell, it flows over 15 or so kilometres of Lake Dunstan and is thus either cooled ( in summer) or warmed (in winter). The amount of heat transfer may be fairly significant. I heard somewhere, I'm sure of it, that Clyde old-timers have noticed a more moderate climate post-Dam, especially cooler summers.

Likewise, when the air is going up the gorge from Alex to Cromwell, Lake Dunstan would do some work to it. I suspect the penisula portion of Cromwell, around the area where the rivers meet, would also have a large enough expanse of water around it to have a moderation effect in still conditions. In winter warmer lake air might rise and circulate over the edge of the town.

Again, in still times, particularly at night, katabatic flows coming gently down the 1000 metre walls along the gorge would land on Lake Dunstan and find it either warmer or cooler than themselves and potentially move off to either end of the lake in a different form to how they would have been when just the cantering Clutha was there.

I'm also wondering, in the case of Cromwell, if the low level winter sun bouncing off the northern expanse of the lake and into town, lifts the temp slightly. Also, in summer the lake covers land right next to Cromwell that would have been heated way up, and not cooled down until well into the night, hence without that land radiating heat, summer evenings may be cooler.

Sounds interesting, but I think you'd have to have some data from a longterm site to test any theories. I'm always sceptical of "old-timers" because it's been demonstrated time and time again that weather memories, like other kinds, are always selective.

Yes the old timers just about everywhere will tell the weather has changed.
Those Otago river valleys are mostly narrow so I could well see some local climate change Temp/ mist /fog for some locations like Cromwell.

I remember speculation that fogs in Alex. had increased in number since the Roxburgh dam was built in 1956 but have never seen any followup, or evidence that this happened. Andy would be too young to remember.

there has actually been a fair bit of academic reseach done on lake dunstan, slightly less on roxburgh. And many of the effects sw_windblow has listed are believed to have resulted from the formation of dunstan.

Thats the narrow end of the wedge as far as the impact of those dams goes, wretched things.

I've never seen a NIWA or MetService paper on it though - and there aren't many of their papers that I haven't seen.

The Metservice and NIWA aren't the extent of NZ's climatological and meterological research... thin end of the wedge if anything. Blair Fitzharris from Otago University would be a good start.

Feel free to point to any references, I'd like to see anything on the subject. I've met Blair several times over the years and don't remember the subject being raised, or covered at any conferences.