I have my La Crosse 3600 temp sensor under a clump of trees and it is also shielded with the standard ventilated shield. I can’t be definite yet, but it is possible I am getting low temperature readings during high temperature periods.
One person actually emailed me to say that the temp reported on my site is low compared to his reading (have no idea of his setup). On that day he was reading 37 deg C and I was reading a max of 32 Deg C. Today I had a max of 35 deg C and other stations at my altitude in the area where reading in the 37 - 38 range ( a few stations higher up than me where showing similar readings to me). Funny thing is I have a Thermor unit also mounted on the ground and in the shade and it is reporting very similar temperatures to the La Crosse sensor.
Could placing the shielded temp sensor in the shade create lower readings than having the shielded sensor in the sun ? It was also fairly windy day, so perhaps the sensor was over ventilated, creating a kind of wind chill factor ?
The station is used by a few people around the area so I really want to get things as accurate as possible.
Wind chill is simply how much colder it feels to humans and is not a temperature reading. I don’t know your station details, but I would almost suggest that your nearby stations are perhaps not properly shielded and you are in fact more accurate.
I have a OS928 and until I placed it in an aspirated screen it was peaking to a higher temp when diectly insolated.
The position you describe could actually give a higher rather than lower reading if it is receiving radiated heat from the ground.
The lowest outdoor sensor in general is
rigth. The art of outdoor temperature
measurement is avoiding too much heat,
not being too cold.
Of course, defects excluded.
Easy to check with a second thermometer
on a cloudy day or inside home.
The only way a thermometer outside may
be too cold is when the internal sensor is
wet and wind is chilling it.
There is one possability that could cause lower readings and that would depend on the area under the clump of trees.
What comes to mind is a micro-climate that is cooled by evaporation. :roll:
Evaporation either from the tree’s leaves or moisture from the ground.
You know the way it feels when you walk in a rain forrest.
Apart from the guy that email me (his temp seemed way to high anyway) the other stations I am comparing with are Bureau of Meteorolgy stations, so I would be a little bold to suggest that my little La Crosse is right and they are wrong !
Night time temps seem to compare well, just the daytime seems to be a degree or two down on other ‘official’ stations.
The trees are Eucalyptus trees and the ground is rock solid clay and slate, so there is plenty of airflow and no moisture, atleast not today … unfortunately we have only had 11 mm all month
Anyway I will keep comparing data, just wanted to make sure that I wasn’t giving it a double dose of cooling by putting it in the shade with the shield on it also.
I sometimes think that we put too much faith in the accuracy of our sensors.
I bought two extra sensors and placed them both alongside the main sensor in the study and in the area the main sensor is sited. There was a discrepency of almost 1.5C between the three when tested for about two hours in each location.
I set the offsets in WD so that the two extra sensors matched the thermo/hyg which is used as my datum.
If you read the fine details of the specs, you may find that the tolerances vary within different temperature ranges.
It can be difficult in some residential situations to find optimum sensor placement but if you want to compare your site with other “official” sites then the standard is to have the sensor shielded (preferably aspirated) and in the sun. Keep in mind that you can sometime see differences in temp/hum/wind in stations that are relatively close and it just might reflect the local microclimate and not necessarily indicate a bad sensor.
Yes, I have used that guide to setup my station so far, it is fantastic, I have learned heaps from it. It gives 8 points for putting a shielded sensor in the sun and only 6 for putting a shield sensor in the shade. But I thought the reason for that was down to ventalation.
The temp sensor is mounted on a hill about 150 metres behind me here. It needs to be there becuase that’s the only reliable location to measure wind. I did have it out in the sun at one point and it seemed to compare more favourably with other stations around here, but then read on here a comment about the 3600 having a bad shield and that it needed to be in the shade … so I move it.
Today it is overcast and temps seem to be much more comparable. I’ll keep collecting data and expirimenting. An added complication is that I live in the foothills to an Apline area at about 300 Metres altitude, the altidude of other station varies from almost sea level right up to 1800 metres.
