Clear nights Vs Clear Days

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Michael
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Clear nights Vs Clear Days

Unread post by Michael »

Wonder if all 24hrs of the day was counted in 0/8ths etc to 8/8,What,Who and Where would have the cloudiest weather in NZ?
Like this winter we had lots of clear nights but cloudy days.
Gary Roberts
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Re: Clear nights Vs Clear Days

Unread post by Gary Roberts »

Michael wrote:Wonder if all 24hrs of the day was counted in 0/8ths etc to 8/8,What,Who and Where would have the cloudiest weather in NZ?
One candidate would be Oamaru. In fact from the SI east coast up the Waitaki valley as far as Lake Aviemore would get my vote as one of the worst places for constant, near-total cloud cover, day and night.

Fiordland is another. Certainly whenever I'm working at Manapouri power station it always seems to be cloudy at night.

The West Coast and maybe Fiordland as well. Having said that, the sky viewed from Aspiring hut at night on (rare?) fine nights is utterly astonishing, although I last viewed it from there back in the late '90s, early '00s, before the real destruction of Wanaka had commenced.
Like this winter we had lots of clear nights but cloudy days.
That's true. It was a pretty good year for astronomy in NZ (or at least many places in NZ)! :)
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Re: Clear nights Vs Clear Days

Unread post by RWood »

Can't say about nights, but Oamaru ain't the cloudiest town. It is well down the list, but there's quite a few lower.
Of the east coast towns north of Dunedin, Waimate had the lowest sunshine when records were being kept.
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Re: Clear nights Vs Clear Days

Unread post by Gary Roberts »

RWood wrote:Can't say about nights, but Oamaru ain't the cloudiest town. It is well down the list, but there's quite a few lower.
Of the east coast towns north of Dunedin, Waimate had the lowest sunshine when records were being kept.
Waimate is less than 40 km (?) up the highway from Oamaru. The weather patterns tend to be fairly similar. I can believe Waimate would come out tops, but probably not by much.
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Re: Clear nights Vs Clear Days

Unread post by RWood »

I think the proximity of the Hunter Hills may have been a factor in trapping cloud. But there was something odd about the Waimate record, as the values were better in the 60s onwards than earlier. Probably a non-climatic reason for the change. In the Oamaru region there have been cloud/sun records from the Aero as well as at Iona Hospital. The latter recorded significantly more sun (no overlap of records) and indeed during some of the late-60s and early-70s dry periods had some very respectable totals.

On the original point: have never seen any nationwide assessments of night cloudiness vs. daytime cloudiness. For Wellington, however, a study taken years ago showed that early morning and late afternoon were generally a little cloudier than the the middle part of the day, and the same probably applied to the nighttime hours. Probably reflected the frequency of N/NW airflows.
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Re: Clear nights Vs Clear Days

Unread post by Gary Roberts »

RWood wrote:I think the proximity of the Hunter Hills may have been a factor in trapping cloud.
Yes, you often see valleys filled with low cloud while areas outside of them remain clear.
But there was something odd about the Waimate record, as the values were better in the 60s onwards than earlier. Probably a non-climatic reason for the change.
But I'm sure it had nothing to do with somebody fiddling the records to "prove" to the world that the weathermen were wrong and Waimate was a lovely sunny place which tourists should flock to and spend lots of money... :roll:
In the Oamaru region there have been cloud/sun records from the Aero as well as at Iona Hospital. The latter recorded significantly more sun (no overlap of records) and indeed during some of the late-60s and early-70s dry periods had some very respectable totals.
The new weather station in Oamaru, like the old Iona hospital one, is located on an elevated site but much more sheltered than the hospital one. The site was deliberately chosen so that the station would indicate much finer weather than Oamaru actually really gets, because, you know, it'll bring in the tourists.
a study taken years ago showed that early morning and late afternoon were generally a little cloudier than the the middle part of the day, and the same probably applied to the nighttime hours. Probably reflected the frequency of N/NW airflows.
Adiabatic and katabatic conditions are commonly seen on Benmore, with ridge cloud forming during the day then dissipating in the evening as the valley/mountain winds kick in.
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Re: Clear nights Vs Clear Days

Unread post by RWood »

I think the Waimate case was more innocent than that - back at the start of the 60s weather readings didn't get anything like the prominence they do now and the nightly TV temperature competition idiocy hadn't started. It's possible the older Waimate records were disadvantaged by some flaw in instrumentation. Regular checks were done on data files and sites but there wouldn't have been anywhere near enough people to do exhaustive checking. A new device would clarify matters (no sun records since 1976). But anyway, I believe there's some evidence to suggest that many of those eastern locations in Cant'y and Otago are not subject to quite as much fair-weather coastal clag as they once were - though you may find that hard to believe.

Yes, anabatic/katabatic conditions would be important in many inland regions, especially in the SI hinterland with all those mountain ranges.
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Re: Clear nights Vs Clear Days

Unread post by tich »

Might've just been coincidental, but the times I've passed thru Oamaru, it was chilled by a fresh onshore northeasterly. After the areas further north (eg Timaru) were basking in a warm northwesterly airflow. Seems Oamaru might be even more exposed to the northeaster than Chch.
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Re: Clear nights Vs Clear Days

Unread post by RWood »

tich wrote:Might've just been coincidental, but the times I've passed thru Oamaru, it was chilled by a fresh onshore northeasterly. After the areas further north (eg Timaru) were basking in a warm northwesterly airflow. Seems Oamaru might be even more exposed to the northeaster than Chch.
I think Timaru must cop its fair share of that as well. In some of the most easterly-plagued months Timaru's cloud and sun stats. look pretty bad.
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