Sandaysoft

Hello Matt.j5b,

As Stephen quote, placing the thermo-hygrometer sensor can be a nightmare in some environments, and at some point, you need to accept the fact of not totally accurate readings.

A work around will build a Stevenson Screen like this one http://sandaysoft.com/forum/viewtopic.php?p=40916#p40916, this thread also covers this point. http://sandaysoft.com/forum/viewtopic.php?f=16&t=5447

Good Luck.

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Marco-Luis
YV1HX
Cabimas, Zulia, Venezuela
http://www.twitter.com/meteoven

Thanks both of you for your comments. I do understand it is a problem with getting accurate readings on a wall, but I have to work with what my situation allows in terms of mounting the sensor in that I am limited to the location of the sensors. This is because the better side of the house would be the south side of the house but because of a neighbour with a taller house and many tree next to the house I think that would have a great effect on my wind readings for the worst, which I don't want to do. Also the temp sensor is weather resistant but not waterproof so I am keen at keeping at the house wall.

The sensors themselves are accurate it is just where they are located that makes the problem. I know that the offical practice is out in the open in the screen but for me that something I don't want to do, I do have space that is why my rain readings that I have been doing for many years are correct. The problem is not heat during the day. Before I used the shield it was reading too high by about a degree C but with the shield it is now spot on.

It is the location which is slightly protected that creates high overnight temps because it is not exposed as it should be for overnight temps. I am moving the sensor more and more closer to the north side so as long as I don't get daytime temps reading too high I might be able to get overnight temps correct. Then once I tried everything then I will have to be happy with the recordings. But thanks for the comments.

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Regards, Matt of Brisbane, Australia
Web Site: http://www.localweatherdata.0glo.com

Matt - I am going to presume you are in a brick/brick veneer building? Even sheeting or cladding? Either way your high overnight temperatures will be due to heat soak in the walls during the day which is being released overnight - thus the higher readings.

Being in Brisbane (or that area) your sensor should be on the south side of the house - any other side simply won;t give you anywhere near true reading. The north side - well you understand about that; east it will get the morning sun, west the evening sun.

As I mentioned before if you can't place the sensor in a screen then just use a spot and leave it. OK so the temperatures aren't accurate to 0.1C - but I guarantee the sensor isn;t that accurate either (despite what the manufacturers say).

I had similar situations - my temperature sensor is now on the south side (well it has been since 2000), wind vane located on top of the antenna pole on the north (the clearest location I could find but is still affected by attenuation from surrounding bush and houses) and ther rain gauge on top of the garage opn the north side. IOW - I just picked the best spots available knowing that temperatures WILL be affected by the wall of the house at times (this shows particularly around late Jan/early Feb during our hottest periods); the wind vane will be affected by local conditions and the rain gauge has its best possible location given the bush etc.

If you don't, at some stage say 'I've got the best spot I can' you are going to be forever chasing your tail. Remember - as said before - unless you are an official BOM station, it is an amateur weather station. (no offence meant btw)

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

Kind of you to share your thought so thank you. I am in a low set brick house and I fully understand the sun path and the more sun on north side etc etc ... When it started more detailed records than just the weather and rainfall with a manual gauge in April 2009 I read about the seasons and all that sort of thing. About the heat soaking over night, the north side received sun during the day but less towards the top of the wall as the sun is higher at this time of the year and inside get much warmer during the day, but I did not think that it is the heat from the day. Before I moved it yesterday I had it on the west wall with a garage to the west of this west wall with a patio in between where it was more protected but too protected for overnight temps.

I know the south side is the best side but the cable from the temp hum sensor is only 10 metres so the sensors need to be same area so it is impossible to have wind readings on the north side because that is the best spot and move the temp sensor to the south side because the cable would not reach. Or if I moved the wind and rain sensors to the south side and it may end making it worst and to that would affect Cumulus because the batteries would have to come out and cause more trouble. And then I would have to move it back, that effort it not worth it. I am more interested in weather records without it stopping because all the sensor are moved to the other side of the house. The movement of the temp sensor I have been doing have only been minor movements.

I not just moving the sensor just for the fun of it, I am doing it to get to the closest to being correct and a screen is the most effective method but I can't do that. Is it all right that day time are correct and overnight is about a degree C too high. What is more important overnight or daytime temps, if it gets to a point I have to choose.

I know it is not a bom offical station and not trying make it one because my standards are different. For example my rain gauge is located on the east side on a fence 1 m off the ground about 3 to 5 metres from the back of the house with a large tree on either side of the gauge a few metres away. On the east there is a low tree from a neighbour next to us but is down lives further down. According to bom this is not right because it should be twice this distance but is quite open and I get good results.

I can be sure that I not going just keep chasing my tail, I am getting to the end of the project and once I done my best I will settle for that.

Your comments have been very helpful and your comments have not been offensive. Thanks

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Regards, Matt of Brisbane, Australia
Web Site: http://www.localweatherdata.0glo.com

Matt,

You could ring the Brisbane BOM office and talk to one of their INformation Officers (thnk they still call them that - they used to when I was there). They are (usually) very helpful and can guide you with some really good informaiton and tips.

Couple of things from what you say.

As long as your 'incorrect' readings are consistently wrong (bad choice of words, I know) then the reality is it shouldn;t matter. If they were wrong one way one day, and then wrong theother way the next - that would be a problem - but if they consistently read, say, 1.5 C higher than a manual thermometer - then let it be. Rememebr - you are recording a measurement for THAT location only - not one 10 metres or 1 km away. As long as they remain consistently 'wrong' you will have accurate records for THAT locaiton. If this makes sense?

Rain gauge - have to say you really should think about moving it. The trees will have a dual effect - one is shadowing - so if say, one tree is SE of the gauge and no the day of rain the wind is blowing from the SE, so is the rain, and you are more than likely to be missing rain coming from that direciton because the tree is shading the gauge.

The other side of this coin is, again, depening on wind direction and tree overhang, you are very likely to get rain drops coming off the leaves of the tree and not true rain.

There is nothing to stop you putting your rain gauge on the roof of your house - provided you don't have trees overhanging the roof line I have a flat topped carport/garage, and have put my gauge on the top of the front of it - it lies in line with the gutter on both my and the neighbours house and clear of anything higher than it by about 10 meres on either side (to the N and S are the roof peaks and nothing for over 50 metres to the E and W).

Have to say - from your description it would be rainfall I would be worrying more about being wrong than temperature. Drop me a PM if I can help/assist - but seriously - don't get too pedantic over locaitons unless the readings are so wildly incorrect. Try ringing the Bureau - you might be surprised how they can help.

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

Thanks once again for your help. Regarding the temp readings I have got the daytime temps right but the overnight temps are consistently 1 degree C too high each overnight. This error is quite predictable because when I get a certain temp the error is this certain amount which is constant but would vary with temp at different times of the year and so the actual temp is this. That is how the I calculated the overnight min temp with my first La Crosse station I don't use with Cumulus with my manual records. But as you say if it is consistently wrong then I might have to settle for that. For example I might record 22 for the min and it should be 21. But a few that had good overnight temps have higher daytime temps.

About the rain gauge, it is a manual gauge and I think my description gave the wrong message, I might PM you a photo because the gauge is not too close to the trees as it might seem and I have not had any trouble with the readings. The wind and rain readings with my other La Crosse station I use with Cumulus is mounted on a Greenhouse at gutter level with apart from the roof next to it there is a 10 to 20 metres clearance to trees and buliding around the greenhouse not including the roof with a few lower trees on the west side that don't have a great effect in readings.

If I need some more help, I'll PM you. Thanks so much for your help.

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Regards, Matt of Brisbane, Australia
Web Site: http://www.localweatherdata.0glo.com

No problems.

Just as a rule of thumb for tree - allow at least twice their height all around them before placing any gauges - so it is 10 metres high allow a clearance of at least 20 metres from the tree in all directions - anything inside that is likely to be affected by the tree. Some bureau staffers will even say 3 times...

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Punctuation is the difference between 'Let's eat, grandma' and 'Let's eat grandma'

OK I will settle for slightly off overnight temps and it only affects my Cumulus records and it doesn't affect my manual records that uses the data from the weather station and Cumulus, only the data in Cumulus is not correct.

About the rule of thumb I been aware of that and the rain sensor in use with my two La Crosse stations which it siting on top of the greenhouse at gutter level follows that rule of thumb but the back gauge is average but it seems to record close to the same amounts. I will send you a PM for the Rain Gauge pics. Thanks

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Regards, Matt of Brisbane, Australia
Web Site: http://www.localweatherdata.0glo.com