It’s about 4 miles away. I would agree that can make a difference, but the geography is virtually identical.
I still maintain that I was getting accurate daytime readings previously, when the unit was located in the shade. The difference moving from shade to sun is noticeable despite the addition of the fan.
In any case, I will try what you suggested.
I do have some good news to report - my overnight lows appear to have improved noticeably. On Sunday morning I read 0.5 C lower than the metar. Only the second time this month I’ve registered lower, and the other time was only by 0.1 C. I’m still waiting for this morning’s offical low, but I suspect my station was about the same or cooler once again.
I think that having the unit in direct sunlight will increase it opposed to having it in the shade
i think that no matter how much ventilation or fans will change it to the shaded temp…
I have a Stevenson Screen of which is very well ventilated and this too has a degree or so
difference when the sun is directly on it, you can see this on my graph (below) from 10am till
about 12pm between this time is when the sun hits the screen at this time of the year, then
after 12pm you can see where the sun moves away from the screen, you can also see from the
graph that the sun is still out from the solar graph…
Even a Davis FARS has this issue, a fellow member just down the road from me has this same issue
I think the only way around this would be to have it placed in the shade
I’ve had some pretty good results the last few days by relocating the temperature probe to directly above where the air enters the box. I’d almost say it’s good enough now and leave it alone.
I agree. One might wonder how the official metars could be completely accurate if that is the case.
That is quite a large jump. I don’t have anything that substantial, but that may be due to the fact that my shield is in the sun for most of the day. I get a small decrease in temperature around 3:30 PM, but I’m not sure how much of it is natural cooling and how much is due to decreased solar. Probably a combination of both.
On my graph, you can see where it was cloudy at 1st so i would really ignore the temp going up
Look at it coming back down, when it starts thats when the sun is moving away from the screen
its gradual but by about lunch-time the suns totally moved off the screen, so it looks like a 3oC
drop, my screen has very good ventilation from 3 sides, ideally it would be better off in the middle
of the garden but this is not possible (so she says anyway) but i dare say that would eliminate a
lot of that extra temp…
i have a davis vantage pro 2 i bought a day time solar fan kit from provantage for 82 bucks went to radio shack and bought a 4 volt power supply $20 bucks and lowes and bought a 100 ft roll of low voltage wire (the kind for land scape lights) $20 bucks now i have a 24 hr fan for $122.00 bucks been running fine no problems and has got temps where they need to be a lot cheaper the buying a vantage plus unit !!
Today we had a full sunny day so I thought I would post my results.
The shield is in full sun from about 9:30 am to about 3:30 PM. There is little or no spike in the morning, however you can see where the temperature drops off dramatically when the sun moves away late in the afternoon.
For daytime highs I’m running about 1 C higher than the metar, but only on sunny days. Cloudy and rainy days are usually within 0.1 or 0.2 C. I’ve also noticed that I average 0.5 to 1 C colder than the metar on clear nights.
I think you have a very good smooth curve, no deviations - something susceptible to garden breezes and clouds passing will show jumps. I think the values you have a relevant to your particular location and are real. You should be happy with the setup now.
