Metservice "your weather" temps

[midgrove]

Some of the temperatures in Wellington area seem way too high. Are these sensors located in greenhouses?
(Upper Hutt area 36 deg last 2 days). When I first set up my weather station on light wind days the temps were very high until I built a proper screen.

[NZ Thunderstorm Soc]

Could be temperatures taken in direct sunlight?

[kiwisk8er]

My weather station on there shows higher temps because it just has the temperature cover that came with the weather station. I need a Stevenson screen but have no skills to build one. But it doesn't read 36 degrees, usually a couple of degrees higher than Kelburn.

[Tornado Tim]

This is kind of why I am not joining, there isnt any quality controls...

I would have thought they would accept stations if they meet WMO standard (Height, placement etc).
CWOP puts alot more weight on WMO standards before joining, and yet I had to withdraw from that network unfortunately due to companies scraping off the data for profit.

[melja]

I find them very good as a general over view of whats going on.

[Razor]

I find them very good as a general over view of whats going on.

Agree, the outliers are pretty obvious, and its good to see all the sites I look at one by one in one spot

[Richard]

I find them very good as a general over view of whats going on.

I dont think they are because when i brought my weather station i first had the censer in what i thought was the ideal location - out of direct sunlight, good air movement,no radiating heat from buildings paths etc and at 1.5m above ground. Because i was comparing the censer to the mercury gauge along side it that fact that i noticed a similar reading i thought that that location was fine,now that both are in a screen i'm not getting the higher readings that i was,so in other words those 'cheaper' weather stations DO to be housed in screens and thats why i think we are seeing such wide variations in temperatures on the MS 'my weather'

[Richard]

I find them very good as a general over view of whats going on.

Also that only works in urban areas if there's enough of them scattered about

[Nev]

I read of some people making little hats above their shields as added protection from direct sunlight, e.g. a frisbee covered in tin-foil.

Thought these comments from an Irish weather forum a few years ago might be worth a read…

Air Temperature

When measuring air temperature you will definitely get what you pay for and with some of the budget-priced stations on the market, the radiation shielding can be exceptionally poor. The purpose of radiation shields is to reflect solar radiation away from the temperature/humidity sensors and also to keep a good airflow running over the sensors. With some stations, the radiation shields do not perform well and as a result, the air temp is over recorded. At the end of the day, we want to measure Air temperature and not apparent Solar temperature. There is a huge difference between the two.

For example this is an experiment I carried out while living in a housing estate: -
I had a Davis VP1, a second VP1 temp sensor that was unshielded and a La Crosse brand.

One summer’s morning, I placed all three side-by-side and very quickly the unshielded sensor was measuring 9°C higher than the Davis VP1 and the La Crosse 3°C higher than the VP1. When the unshielded Davis VP1 sensor had its radiation shield replaced, the temperature it recorded quickly came back into line with its shielded counterpart.
The La Crosse however had a different type of shield. Due to its construction, the sensor was virtually enclosed in the housing and had a more restricted air flow, basically creating its own little greenhouse and over-reading the temperature. I stripped the La Crosse sensor down and placed it in Davis VP1 housing and afterwards, the sensor reading dropped to just 0.7°C higher than the Davis readings. This was all due to the better airflow created by the design of the Davis radiation shield. This experiment was carried out 10 years ago and the La Crosse brand has improved its shield since then or so I believe.
(NB: Davis Vantage Pro2 is within ± 0.2 of Standard meteorological equipment which I measure officially along side my Vantage Pro2)

If you are experiencing problems with poor radiation shielding, a simple solution is to move the shielding or housing out of direct sunlight and this will immediately eliminate the problem. Alternatively, some of IWN members have constructed their own louvered Stevenson Screen's and placed the temperature sensor including the housing/shielding inside thus maintaining an airflow and eliminating direct solar radiation. This solution is not for everyone though, some of us will lack the carpentry skills to complete this task and the screen can be expensive to construct.

[NZstorm]

Temperature is possibly the hardest weather parameter to measure accurately. Its not easy setting up a weather station that will represent the district rather than the back yard.

[Manukau heads obs]

plastic white pudding bowls upside down with 3 rods up through them to separate them and the lower ones a hole in the middle to place the sensor up into works well

[Nev]

plastic white pudding bowls upside down with 3 rods up through them to separate them and the lower ones a hole in the middle to place the sensor up into works well

Depends on the plastic. Also a lot of plastics break down after prolonged exposure to UV. The upturned plastic saucers from flower-pots painted white works better (assuming you can find the right shape).

[Manukau heads obs]

UV is hard on plastic here in NZ thats for sure. Alot of the cheaper weather stations suffer from that problem

[David]

UV is hard on plastic here in NZ thats for sure. Alot of the cheaper weather stations suffer from that problem

The radiation shield of my Davis station is quite weathered now actually, the white plates have become a tiny bit yellowed and slightly rough-textured in areas. NZ sun is harsh alright!

[Tornado Tim]

Have a look at this:
http://www.nzherald.co.nz/wanganui-chro ... d=11393403

Picture shows Lacrosse Weather Station with a Standard Radiation Shield, she says she gets warmer temps in the day than the Metservice Weather station, thats probably due to the poor radiation shield on it....

Its funny as people treat $150-$300 weather stations as absolute fact.....

[Manukau heads obs]

yeah, I made a post on their FB page about that article about basicly that

[David]

I had a cheaper station like that 2008/9 before getting my Davis. It would frequently read more than 3 degrees too high when shifted into sunlight, so I had to shade it as best as I could...

[dizzy]

This is kind of why I am not joining, there isnt any quality controls...

Tornado Tim, they have a button on the YourWeather page which allows you to toggle between the MetService stations alone (which would be properly maintained to WMO standards), and the other stations owned by members of the public. I don't think that the data provided by the public is used by the MetService in their models or anything. It's more just a public interest thing.

And it's usually fairly obvious to pick out the outlying values. I've noticed that, particularly with pressures, there are a few stations that consistently show pressures that are up to 10 hPa higher/lower than those surrounding them. I wondered why this would be, and thought maybe it was to do with the person not knowing their altitude accurately? I don't have a weather station of my own, but I assume that to calculate mean sea level pressure, you'd have to enter in your altitude at some point when setting it up?

[Tornado Tim]

This is kind of why I am not joining, there isnt any quality controls...

Tornado Tim, they have a button on the YourWeather page which allows you to toggle between the MetService stations alone (which would be properly maintained to WMO standards), and the other stations owned by members of the public. I don't think that the data provided by the public is used by the MetService in their models or anything. It's more just a public interest thing.

Yes I understand that, but my station wouldnt be classified as a Metservice station. Even though its sited at WMO requirements (and has a FARS etc).
It would be left in the ballpark of other cheap stations in the neighbourhood. Which I would have thought Metservice would want the network to be as accurate as possible....

I don't think that the data provided by the public is used by the MetService in their models or anything. It's more just a public interest thing.

Exactly, there is no practical purpose of pushing your data to the service, its only a strategic tool to drive more and more traffic to the Website in order to get more money via Ads.

There is an expression that identifies this quite well: If the service is free for you to use- you are the product.
IE: They will make money off your data.....

[Manukau heads obs]

there are though MS stations that show up on this system that are not normally available , which is cool

[dizzy]

but my station wouldnt be classified as a Metservice station. Even though its sited at WMO requirements (and has a FARS etc)

That is a fair point, maybe they could make a way of adding some sort of info tag to the station, so those who are really interested could see what kind of standards the station is kept to.

Exactly, there is no practical purpose of pushing your data to the service, its only a strategic tool to drive more and more traffic to the Website in order to get more money via Ads.

That is also a fair point... Though I do recall in the news not so long ago, Philip Duncan was having a go at MetService for only providing three hourly observations to both him and the public. Now they're providing their own up to the minute data (along with other data). While they might be making money off the ads on the website etc. people can still view it for free. It's the advertising companies paying. It seems to me like a good way to provide the data that Mr. Duncan campaigned for, while helping to pay for the maintanence etc. of their stations with the advertising money.