Why input height of sky?


Out of all the weather stations, weather flow with sky ask for height of both sky and air?

Why is this? Does sky compensate for lower than stand wind measurment meaning if your at 10 feet then works out what speed it should be at 30 feet then calibrates the wind speed as though you had your sky at the standard 30 feet, so does it add or subtract speed? Depending on height?

Same as air, does it add or subtract and use height for calibration as no other station asks for height on how high you are above sea level?

The Air needs the height so the correct pressure can be calculated.

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But why does sky need height input? Without it may have been it calibrates wind to your height? So if your 10 feet it records the wind as though your the offical 30 feet so uses height to calibrate wind speed?

Meta data, especially the height of the anemometer is a very important piece of information when reviewing meteorological data from a weather station.

Currently, there are no calculations/corrections made that use the instrument height. Although, wind chill values in particular could benefit from an adjustment when a SKY is sited very low.

It was quite a common complaint last winter - some station owners wondered why they weren’t seeing the same wind chill value reported by a local news station (which is most likely using a wind chill value based on an airport weather station sited 10 meters above ground level). Higher anemometer = higher wind speeds = lower wind chill value.


As a future enhancement to the SKY’s wind speed reporting and wind chill calculations knowing the SKY’s installation height can the software be modified to offer a correction to adjust the actual wind speed reading at the installed SKY’s height to the standard of the 10m height? Either +/-. Perhaps a user’s toggle switch to either use the correction to 10m or use at the installed height. Just a thought …

I posted something like this also. If your sky knows the height then would be great if software can adjust for the hieght

dennisrogersx … Yes, I saw your post and I’m trying to reinforce your message in hopes that such an enhancement can be incorporated into the SKY. Good idea!

Let’s hope so. Afterall if it knows the height surely not hard to work out winds at 5 feet and be able to calibrate wind to height?

But physics isn’t that simple that you can apply an simple formula which will fit all installation situation. Especially, the physics of fluids (here air flow) is complex.
Hence, a software option to calculate an approx value at 10m depends strongly on the installation and it’s surrounding.

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indeed wind at lower heights depends way too much on the environment to extrapolate to wind speed at 10m height. The general formula is also non linear, which would make it extra inaccurate.
Inputting the height as meta data might be useful if someone wants to do an analysis and just discard all the stations where wind isn’t measured at 10 m height above the ground. (which would probably be better then to incorporate extrapolated measurements that just pretend to be taken at 10m height)

dsfg and sunny thank you for your explanation of the “physics of fluids” and “non linear” formulation as they apply here. Perhaps a different approach. Request WeatherFlow if they can incorporate a “calibration” input option for wind speed where the user can apply a “calibration” factor to the SKY wind speed, if desired. Case in point. A user currently has a non SKY anemometer mounted at 10 meters taking wind measurements. As an example, let’s say that the wind speed at 10m is 25 mph but the SKY is mounted at 10 feet in the same location and is measuring 21 mph which is ~ 19% difference. The user also tracks varying wind speeds being measured at the 2 different heights and comes to the conclusion that there is an average difference of ~ 19% between the 2 different heights. So the user applies a factor of 1.19 to the SKY wind speed output to “estimate” the wind speed at 10m. Obviously, this is not a “true” wind speed at 10m but an “estimate”. Why would someone (me) want to do this? For a few reasons. At my location wind gusts of 70 mph occur and mounting the SKY at 10m (~33’) might very well generate false rain readings. Also in the winter I don’t want to have to climb a roof or take down a 33 foot pole, if needed. I could use 2 SKYs but don’t want to have to purchase another (one for wind, one for rain). So just a “calibration factor” option for wind speed. That approach wouldn’t alter the design of the SKY and it would be up to the individual user to use it or not. Just a thought.

That’s yet another thing that weewx can do for you, if you want a self-hosted software solution.

But I’d suggest not doing it in this case. The Sky measures what it measures, wherever it’s at. As long as that’s an accurate measurement, you shouldn’t have to change it.

unfortunately it will be way more complicated then just a calibration factor. Because of a strong non linear behavior, you would need a different calibration factor for different wind speeds (or use a model that does that for you), also depending on your location, you might need to have different calibration factors for different wind directions. That could end up with many parameters. All those parameters need to be determined and you would need a good amount of measurements for all these conditions.
It can be done, and you could try to do it yourself, as the data is available to you, but generally it isn’t very easy. (but probably slightly less hard then I just described ).
For the bulk of the weatherflow stations it would be impossible, as there is no reliable local data to calibrate to. But in your specific case with the extra anemometer, it could be done.

to give you an idea of what is involved at heights up to 10m, you might want to have a look at this article https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1655&context=abe_eng_pubs

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Thank you all for the education. My WeatherFlow system arrived today and the SKY/AIR will be mounted tomorrow. Will see what kind of wind speed numbers are reported as compared to my existing Davis VP2 Pro unit.

You should find pretty strong agreement if they’re sited very close together, after the usual few days or couple weeks for the CL tunings to get applied to your WF gear. The WF seems to detect light breezes better, as you’d expect, but otherwise they seem the same basically to me so far.

New owner here - so we’re asked to put in the height of the Weather Station…
… so do I measure from the ground level to the base of the actual Tempest not including the mounting unit or to the top of the Tempest, or some other place?
Might as well be précis if I’m going to get my measure out…

There is not going to be a perceptible difference between the top and bottom of the Tempest device itself. Since the solar panels and battery are at the bottom portion I’m assuming the pressure sensor is in the vicinity of the solar shields in the center, so if it matters to you, measure to that point.

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I measured mine to the bottom of the tempest as inputting height i think you can only go to the nearest .5 meters when inputting height so don’t need to be exact as you cannot input exact hieght. If your near enough wont make any difference

When using imperial units it accepts to the tenth of a foot so I’d be surprised if it doesn’t take at least to the nearest decimeter if not centimeter.

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