Hello, I am located in Northern Ireland. I have sited a Davis Vantage Pro 2.
Over the last couple of months I have noted that my station appears to record warmer minimum temperatures than most local stations. I am up on a slight incline so I attributed this to cold pooling in valleys.
More recently, in colder weather I noticed that my station was often at least 1 degree Celsius warmer than most stations in my vicinity. What struck a chord in particular was a coastal station being 2c colder than my station, during heavy snow.
This station is right on the coast and had a wind coming on shore. There is no way that this station was 2c colder than my station. This is a common temp difference with this station that I have noticed, infact at this very moment this coastal station is 1.7c colder.
Additionally, I note that my station has a markedly reduced decline in temperatures as cold fronts pass through. While local stations are dropping 4c in 10 minutes my station is dropping 1.5c over that same 10 minutes.
At this point, I am starting to wonder if my garden is naturally a heat trap? I have my station placed on a grass strip just in front of my neighbours asphalt drive way. Unfortunately there is asphalt all over my house. Our front yard is almost 60-70% asphalt, and my neighbours garden is of a similar composition.
In addition to this, if I move my station to the all grass area it would be situated within 30 metres of the asphalt road.
The only place I can situate the station is at the far end of my garden. However, that comes with the station being placed on top of an unstable fence and beneath a large tree.
Is there anything I can do to improve the accuracy of my station? It does have an aspirated fan.
Is it the daytime fan or the 24hr version?
The daytime fan only works when there’s Sun directly on the solar panel, so doesn’t run all the time.
Raising the station may put into cleaner air, but I wouldn’t have though the radiated heat from the asphalt would have had that much affect on the station at this time of year.
Also remember that the temperature sensor accuracy quoted by Davis is +/- 0.5°C, so if yours is reading +0.5° and the coastal station is -0.5° then the difference between the two sites may only be 1°C, which could be quite normal.
My own Davis VP2 is situated fine for everything except the wind. I have a hill to the East, trees from the North around to the Southwest. So I’ve accepted that I record the weather to best quality that my location will allow.
An image of the setup would give us a better idea, the wind could be eddying around the building and that combined with the little heat from the tarmac at this time of year could be your issue. Try to get a shot off most of the tarmac around the station and the house and the strip of grass, please? Like Budgie says, the next best option might be to raise the temp/hum sensor. I had to raise mine up to about 3m i think it is, we try to do the best we can with what we have.
It might also help to check what the local temperature is by some other means. Temperature can and does change over relatively short distances, especially in urban/suburban locations. We always assume that we’re wrong because everyone else must be right, so checking with another device might help you to see that you’re not too far off reality yourself. As an example of this, my local airport is often a few degrees cooler than my station, but that’s because the airport is on the outskirts of town in a wide open area and my station is in the suburban ‘heat island’ surrounded by houses.
I’d agree with other commenters…radiation from asphalt at this time of the year is unlikely to play a major part in the temperatures you’re seeing. Perhaps on very sunny days it might affect things a little, but you’re not too far from me and I’m not seeing many very sunny days at the moment!
Thanks all for your answers. I am not sure if the issue is down to the asphalt or some sort of microclimate in my area.
However, it is an ongoing issue that continues to be a problem for my observations.
I noticed that it came into the fore yesterday when the sun came out. Locally maximum temperatures were around 4-5c, my station recorded a maximum temperature of 7c.
Having gone out and checked my car, which read 4c at the same time. I am convinced that there is some sort of factor that is influencing the station to overread. Right now, even on a rainy day, the station is 1-2c warmer than stations locally.
Given that I have the aspirated fan built in, it is disappointing that the station can’t mediate the affects of the sun.
I am also having problems with the rainfall, in that the station records minimal rainfall… at the moment it has recorded less than 1mm, local stations are consistently recording 5-6mm. Our monthly totals are 20-30mm out! Any suggestions to remedy this?
Rain fall amounts can be just as bad, if not worse.
I would still very much like to see your station setup up close and also a wide area shot please?
As been said above, temps can vary over short distances, example, when I left home it was 7C, about 15 miles away it dropped as low as 0C and large areas of fog.
Seeing your setup would give us a better understanding and would be able to give you better answers, please?
These stations are all within a 5 mile radius of me, to my north, south and east so pretty consistent and unlikely to be out.
The situation with respect to temperature may vary in terms of radiative cooling and wind direction but not yesterday which was a polar maritime airmass. Not a stable airmass.
Could it be your station is correct and all the others are wrong?
It could be that the other station owners are all calibrating their stations to each other…just so they all report the same values.
It’s a bad idea to try to correct your station to others around you, assuming they must be correct.
I highly recommend NOT trying to match your neighboring stations data…trust your data…Davis stations normally provide good data.
Thing is, they have mentioned asphalt and we all know that that is a red flag especially when their temps appear to be overreading compared to other stations, this is why I would like to see the setup to get an idea, whilst Davis are very good, that is only if there are no other factors involved, the mention of the asphalt could be a big player in the issue, take a look at some of the UK max temps though the year, many have been at Heathrow and we all know why that is. So in my opinion, we cannot ignore the asphalt until we see the setup to rule it out or name it as the cause.
For one station I think that’s a possibility. It’s nearly always at least a degree lower than my station despite being at the immediate coast. The only time it’s not colder is with a north wind.
The other stations are all labelled grasscheck. So I don’t know if that infers grass temperature or air temperature?
Straight away, the issue has to be the fence, 100%, even this time of year (winter), warmer months you will also get issues from the ground behind the fence, you really need to be away from that fence are a good few feet above it…
Yep, now I’ve seen the photo, I’ve got to a agree with Bashy. If you can’t move the station, get a longer pole and mount the main station at about the 6-7 foot level, with the anemometer at the top (as high as you can get it).
Assuming the solar panels are aimed roughly South, to catch the Sun, the fence will heat up and radiate heat which the 24hr FARS is then sucking into the heat shield and over the temp/hum sensor.
