Cumulus Support

Looking at the aerial photograph, I think you have placed the unit about as far away from the houses as you can. I'd have thought that keeping it away from heated buildings would be the top priority. I did some night time comparisons in my garden which is about sixty feet long and in both summer and winter the positions near the house are about a degree warmer - sometimes more in summer when the sun has been on the house. You can see this effect looking at stations near me on weather underground. Some are a degree or two warmer than mine at night, and one in particular goes up about 5 degrees higher than all the others in the locality on a sunny day - and that is in winter at 55N.

I've put my sensor in a place shaded by a fence covered in climbing shrubs on both sides. It can't get any sun, and I'm sort of hoping that the south facing side of the fence being covered in loose plants and leaves will stop the fence from warming and radiating heat back to the sensor which is currently only about a foot away. I know that isn't ideal but it is the easiest compromise for me, though I could move it another three feet away if need be, but I'd have to sink a new post to mount it on.

In the end, people in domestic locations in England - the most densely populated place in Europe, are bound to have to make some compromises from the ideal location of temperature measuring instruments.

EvilV wrote:Looking at the aerial photograph, I think you have placed the unit about as far away from the houses as you can. I'd have thought that keeping it away from heated buildings would be the top priority.

That was my thinking. Further away from that corner means closer to the house and the patio that will generate a lot of heat with the sun on it all afternoon. Whilst the sun will be shining on one fence close to my station it's the lower of the two and the sensor is above and a few feet away from it. Most heat will rise up rather than expand outwards.

EvilV wrote: I did some night time comparisons in my garden which is about sixty feet long and in both summer and winter the positions near the house are about a degree warmer - sometimes more in summer when the sun has been on the house.

Is that C or F? I wouldn't worry about 1C.

EvilV wrote: You can see this effect looking at stations near me on weather underground. Some are a degree or two warmer than mine at night, and one in particular goes up about 5 degrees higher than all the others in the locality on a sunny day - and that is in winter at 55N.

There's a station in Ashton-Under-Lyne - east of Manchester - that's consistently far too warm and I suspect it's located very poorly. Some people just don't know or care about the placement rules. But looking at both our sites tonight all stations are reporting near identical temps. Heavy cloud clearly helps. It will be interesting to see what things look like on a warm spring day assuming we'll get one!

EvilV wrote:I've put my sensor in a place shaded by a fence covered in climbing shrubs on both sides. It can't get any sun, and I'm sort of hoping that the south facing side of the fence being covered in loose plants and leaves will stop the fence from warming and radiating heat back to the sensor which is currently only about a foot away. I know that isn't ideal but it is the easiest compromise for me, though I could move it another three feet away if need be, but I'd have to sink a new post to mount it on.

A photo would help as would a 3D one of your area. If the sensor is in the shade then you should be all right but a photo will help.
I'm going to take some temp readings at the front of my house when it warms up to see if the more open location is adversely affected by the large amount of tarmac and concrete nearby. Should be interesting.

EvilV wrote:In the end, people in domestic locations in England - the most densely populated place in Europe, are bound to have to make some compromises from the ideal location of temperature measuring instruments.

How true!

Finally, there's a Davis VP2 station 10 miles from me that has 24hrs FARS and our max temps today were more or less the same. It will be interesting to see how they differ on sunny days. Not an exact science but the best I have for now.

RayProudfoot wrote:The Davis ISS can't be installed in a Stevenson Screen. This thread is all about shield accuracy and I'm happy with the design of the Davis.

Sorry my bad.

With the sun gaining strength and the skies clear with little wind it was the ideal conditions for a temperature survey in my problematic back garden.

I used a Oregon Scientific unit with the sensor at the end of a long cable so I could hold it at arms-length from my body but in my shade. I took three readings - one next to the ISS (1), another at opposite end of the garden (3) where the ground has been in the shade all day and a third half-way between the two (2) where it's had some sun but not as much as where the ISS is located. Position 2 would be the theoretical ideal location being well away from the house and fences.

Furthest from the ISS - position 3 - the temp was 4.8C. At position 2 - right in the middle of the lawn and not close to any fences it was 5.4C. By the ISS (position 1) it was 6.3C.

So that's a range of 1.5C from the shadiest to the sunniest position.

What to make of all this? It seems no coincidence to me that the longer any position is exposed to the sun the warmer the air. In an ideal world if I placed the sensor in the shadiest position I'd get the most accurate readings. But the ISS is meant to shield the sensor so why is it recording higher temps? Maybe it's the lack of wind? If so then a daytime FARS would probably help.

Davis only recommend a daytime FARS in very hot conditions with little wind but my garden is very sheltered so I think a daytime FARS would make readings more accurate. After installing one if my readings remain higher than official sites then I will consider repositioning the ISS but that means putting it in a less desirable position on the lawn which I want to avoid if possible.

I'm recording this here for my own benefit but if anyone wants to chip in be my guest.

Finally, there is another VP2 10 miles away on the other side of the airport that has a 24Hrs FARS and his readings are identical to the airport's so I'm hopeful that with an airflow over the sensor I will reduce the over-readings but I still expect readings to be higher on calm days because of my sheltered position on a housing estate.

Ray, any chance that you can plant some vegetation between the fence and the ISS? Something like ivy growing along the fence could solve the radiant heat problem.

silverview wrote:Ray, any chance that you can plant some vegetation between the fence and the ISS? Something like ivy growing along the fence could solve the radiant heat problem.

Thanks for your post Chris. Where the ISS is located is the lowest part of my garden and because of the clay soil and permanent shade for 5 months of the year the ground is nearly always saturated. I can't really grow anything within 8ft of that corner unfortunately.

The station has been in the shade now for the last 30 mins and the temperature is now identical to that of the station 10 miles away with a 24Hr FARS. Of course I don't know precisely how that one is positioned. I'm considering writing to him and asking for a visit so I can see how his is setup.

I've established my ISS is in a warm spot but it's strange how the middle of the lawn is warmer than a shaded spot. That could be down to an unscreened sensor on my Oregon of course. For my next test I'm waiting for a sunny day with a moderate breeze. That will be as close as I can get to having a daytime FARS.

The last thing I want to do is reposition the ISS to a spot on the lawn (with all the problems that goes with that) if it's not going to solve the problem. If a daytime FARS will solve the problem with the ISS in its current position that will be the ideal solution for me. Ultimately it may be necessary to reposition the ISS with a FARS fitted. Having spent a lotof money to get my station up and running I'm determined to get things as accurate as I can.

Could you try growing something in containers? A planter or large pots, for example, would overcome the limitations of the soil in that location.

Coincidentally, I am currently struggling with finding a permanent location for my ISS. I'll be forced to make compromises due to having a suburban location, but I can't decide which instrument's accuracy I am willing to compromise.

That's certainly one possibility but it will take time of course before the plants are tall and bushy enough to provide a shield.

Some photos of your location might help us to understand your problem. I've separated the anemometer from the ISS. It's 30ft up attached to the chimney on a 8ft pole to ensure I can capture most of the wind. I don't have any large trees in my vicinity which does help.

Surburban gardens are all about compromise but with knowledge gathered on sites like this you can get pretty good results especially with kit as good as Davis.

Ray, I don't want to hijack this thread. I put the anemometer on our roof, six feet above the peak. I'm happy with that location. The ISS has to stay in the back yard, which is small with large trees. I have to decide whether to favour accurate rain or temperature. I'll likely favour temperature since we get that year round. Calgary is not a very rainy place, although we do get some major thunderstorms in summer. I'll work it out. I may impose on our good neighbours a little. They make some use of our weather website, so it only seems fair.

Chris,

Why not hijack the thread? I did.

Yours is a problem I frequently see from our cousins. The trend of having trees surrounding a house presumably to keep the sun off it is the opposite of the situation over here. We don't have that much sun so we make the most of it when it comes out.

I'd agree with you that temp is paramount and rain needs to compromise. The problem with the VP2 is that the rain guage cannot be separated from the ISS so it's not an easy problem to resolve. The most open location you can manage is best but you already know that. Good luck!

The 24Hr FARS station 10 miles away from me is currently showing a temp 6F higher than mine. Mine is the same as Manchester Airport. How baffling is that?

It's another sunny day in Manchester (not often I say that! ) and I think I may have a solution. I've been taking temperature readings around the garden and I've positioned my Oregon sensor on the fence (see below) and it's showing a temperature within 1F of that at Manchester Airport and the other site that has a Davis VP2 24Hour FARS. Whilst the sun shines on my side of the fence up to lunchtime it doesn't afterwards. And in that position I'm well away from the shorter fence that does get sun on it all afternoon.

So in the next couple of weeks I'll move my station and position the meta-post in the border as close as I can to the lawn and monitor my readings. Hopefully they will be more accurate.

A further update. It seems that the Oregon Scientific sensor I used for the comparison reads 0.7C lower than the Davis. This difference was leading me to believe the proposed new location would be the solution to my problem.

Today was the warmest day of the year with 53F recorded at Manchester Airport and 56F on my station. The wind was quite light and in my back garden there would have been little movement of air around the sensor.

I don't think moving the ISS to the proposed location will make things any better as it will be closer to the taller fence. What I am now thinking of is raising the ISS by attaching it to a taller post. I'm wondering if raising it around 18" (45cm) would improve things as it would be clear of the fences and any outwardly radiated heat. Some heat would rise upwards from the fences but most of it would miss the ISS.

Thoughts?

RayProudfoot wrote:A further update. It seems that the Oregon Scientific sensor I used for the comparison reads 0.7C lower than the Davis. This difference was leading me to believe the proposed new location would be the solution to my problem.

Today was the warmest day of the year with 53F recorded at Manchester Airport and 56F on my station. The wind was quite light and in my back garden there would have been little movement of air around the sensor.

Hope you don't mind the "hijack" but I've been following this discussion with interest over the last couple of weeks since I found it as I have very similar issues with a Davis VP2 in a small (~10m*10m) garden in Worcestershire which is South facing. Therefore, the house wall is facing south & gets the Sun for a large portion of the day. The two sides of the garden are bounded by 2m high wooden panel fences. The end of the garden has a slotted wooden fence with a hedge behind it that is about 2.5m high after cutting. After that, it is essentially open with a wide grass verge, a road then a few houses but mainly open fields. The only real South shield is a ~5-6m high leylandii hedge at the end of the garden of the next door neighbours to the east of me. Pics to follow at weekend.

My station is mounted on a 38mm dia metal pole (rather than a wooden one) and situated at 1.25m above grass in the centre from side to side of the lawn but about 7m away from the house, i.e. more towards the end of garden hedge. Sun exposure is for much of the day, aprt from early hrs while shielded by the tall hedge to the east. Anemometer is on a separate pole just above roof level so is not an issue here.

Details of my measurements are on WU at ICWORCEST25. Mine is the station to the immediate SW of the other nearby one. On the wider field, it can be seen against several others here.

I have also being going through the "Do I fit a daytime FARS or am I getting a true suburban garden microclimate reading?".

RayProudfoot wrote:I don't think moving the ISS to the proposed location will make things any better as it will be closer to the taller fence. What I am now thinking of is raising the ISS by attaching it to a taller post. I'm wondering if raising it around 18" (45cm) would improve things as it would be clear of the fences and any outwardly radiated heat. Some heat would rise upwards from the fences but most of it would miss the ISS.

Thoughts?

My thoughts are that you are correct regarding being too close to one or other fence, you may get a lower max but almost certainly would get higher nightime minima being close to one or other fence. However, raising the ISS would probably give a different reading but which is truer? They probably both would be relative to their positions. Those 2 stations to the due South of me are both roof mounted and the more westerly of the 2 often reads a degree or 2 less than me during pm.

I have come to the conclusion I am in the best location in the garden for night minima and sunshine readings but don't know about the daytime maxima on Sunny days. However, the "best" mounted systems are always away from any shielding such as fences, trees etc (impossible in the average garden) so would get Sun all day but of course also get more general airflow around them that is not affected by nearby house walls etc.

Regarding yours, I would be thinking as far from the house as possible but not too close to any of the fences, which one of your ideas proposed and the idea behind my current mounting position.

I can only wait and see what Sunny warm summer days bring to me and the others in the wider locality and go through exactly the same thoughts as you, i.e. trying the FARS or raising the ISS (but then that has rainfall issues).

All in all a very interesting 'new' hobby.

Hi Pete,

I'm glad I'm not alone in trying to find the ideal site for my Davis kit. It really is exasperating the more you think about it.

Looking at your situation I think you have the ISS in the best location available in your back garden. Mid way from left and right fences and as far away from the house as is possible. Photos will help of course.

There is a station to your south - IWORCSMA1 - that has a FARS fitted and his max was 13.3 compared to your 15.3. Is that roof-mounted as well as FARS-equipped? Hard to say how much of that difference is down to the FARS or the height. Do you have a sufficiently acurate thermometer that you can use to take different readings around the garden on a sunny day? That would help you identify any hot-spots but based on the description of your ISS location I don't think it's in a hot spot.

I think your enclosed garden is mainly responsible for your higher temperature and that doesn't make your readings inaccurate. It's the micro-climate that your garden enjoys. I think you'll find that with a moderate breeze and cloud cover all the stations in your area record the same temps. When the sun comes out is when you see the effect of a micro-climate.

Returning to my station I don't think I can place the ISS where the Oregon sensor is located because it would be side on to that fence (as the solar panel needs to face south) and much closer to it than it is now. The better location would be on the side border where the lower fence is because the solar panel and sensor would be the maximum distance from the fence. I may cut a section of lawn out to accommodate the post and raise the ISS about a foot and then it would be about 4ft from the fence and about 2 ft higher.

One question about your placement. If it's in the middle of your lawn is it a pain to avoid when you mow? The ISS needs to be dead level and I wouldn't want the gardener to keep knocking it.

On the subject of temperature comparisons today's were interesting for me. Manchester Airport - 3 miles to the west recorded 15C and my max was 15.6C. It was often cloudy but the sun did make an appearance on occasions so I'm quite pleased the difference was that low.

But comparing the two for March shows my station to be warmer by 4F or more on 7 days, 2-3F warmer on 7 days and just 1F warmer on 3 days. I'm sure my enclosed garden will be warmer than the exposed airport but not as much as 4F (2.8C). The airport only mesure to the nearest degree C so those differences may be smaller. I think those big differences will have been on the sunniest days. It might be useful for you to keep a record of your max cmpared to that at a FARS Davis station and see how much they differ especially on sunny days with little or no wind.

I'm sure a FARS will help with accuracy but £150 is a lot to spend when you're not sure how mmuch accuracy you will gain.

Regarding higher nighttime minima that doesn't concern me too much because as 6-7 January showed there are huge variations over a short distance. Woodford (official Met Office site) is 3 miles to my east and recorded a low of -17.7C whereas mine was -11.1C. This is more about the local conditions rather than erroneous readings. Woodford is on an exposed field at the bottom of the sloping hill close to the Peak District and all the cold air flows down the hill. Even at my work car park (mid-way between me and Woodford) the temp was -14.

It's all very interesting but also very frustrating trying to get things as accurate as possible. I'll now look at a relocation along the side border and as far aay from that fence as I can get without annoying the gardener!

Hi Ray

I'm not sure that the more westerly of the 2 stations to the South of me, IWORCSMA1 is a FARS station, unless I've missed something on the website. I've 'spoken' to the owner via e-mail & he didn't mention the FARS. It is a '+' station though, i.e. has both solar intensity and UV intensity sensors on the ISS whereas mine only has the solar sensor so ideally, my ISS requires sunny exposure. His station is also roof mounted, as is the other one to his East so this may affect readings on sunny days.

Interestingly, today - a windy, cloudy day over this area has resulted in most of the stations on the larger area map all giving very close readings to each other. There is another station on WU very close to me, just to the NE of mine, IWORCEST27. However, I don't know how it's set or exactly which house it is as nothing such as a high mounted anemometer can be seen but the fact that their pressure reading is about 30mb higher than everyone elses doesn't inspire much confidence in it being well thought out or set up for accuracy. There is also another conventional Stevenson Screen station very close to me although at present, that stations readings are not uploaded to the 'net. I think they used to be via this site - showing as 'Great Malvern' but haven't been since late 2008. Substituting the year, month & day for any of choice prior to Nov 2008 will show the GM reading to compare with the others. Interestingly, when they were uploaded, the readings were often a degree or 2 higher than those for adjacent stations at Pershore & Hereford so it may be that there is a genuine mini climate for Malvern due to the unusual (for England) geography with a hill range rising rapidly from a generally flat plain to a height of about 250-300m higher than the plain. Today, my high temp of 15.8C is identical to that of the Pershore station which may be a small private airfield in that area.

At present, I don't have a separate thermometer to check other parts of the garden, although a simple max/min such as a Six's should suffice for such checks. However, whatever I may get from this kind of comparison, I may wait for a bit to see how my readings compare to others on truly hot days in June/July before doing too much. If I start to get silly readings, i.e. regulars above 32C (90F) on ordinary hot (27 - 29C) days, then I know I need to do something to get meaningful readings. As you say, for winter night minima, it is very difficult to know exactly as lower lying well open areas will always be lower than those in small suburban gardens

Lawn cutting is not an issue as I do it myself . However, I will need to remember the separate temp sensor I have lying on the grass for grass minima, sending data back to the data logger via a Davis leaf/soil transmitter unit.

Incidentally, using Google Maps in conjunction with the Google Earth links in WU, you can get a good idea of the location and general area around most stations, i.e. housing density, average garden size & layout etc. E.g, both those roof mounted stations to the South of me can be seen on Google Maps themselves as well as the general area they are in.