Home weather stations

[Joel Wright]

I was down at Farm and Fleet the other day, and they had a La Crosse weather station on sale for $229. I couldn't pass up the deal so I bought it. It has all wireless solar powered sensors. The anemometer has cups instead of the crappy "fan" design some others have. It measures everything from dewpoint to barometric pressure, along with a wireless rain gauge.

So far the only thing I am not too happy about is how slowly it updates. It seems to only change once every three or four minutes. According to the user guide it reports the maximum windspeed during each three minute time span. I have the anemometer mounted about 3 feet above the garage roof peak on a 3" PVC pipe. (This worked excellently by the way). Another thing that bothers me is it seems to be underestimating the windspeed. The anemometer is operating fine mechanically. I wonder if the unit is reporting the current windspeed at the time the signal is generated, instead of reporting the 3 min max the manual states.

Also, in testing the rain gauge, it took over 10 minutes until the head unit displayed anything in the gauge. I'm hoping the solar powered battery was just still not charged up.

Has anyone else had any experience with home weather stations? What are some of your pet peeves and positives for your station?

I've heard the Davis units are the best, but since I saw this one so cheaply on sale, I couldn't pass it up. I guess you get what you pay for.....

 

[Jeff Wear]

Originally posted by Joel Wright
I have the anemometer mounted about 3 feet above the garage roof peak on a 3\" PVC pipe. (This worked excellently by the way). Another thing that bothers me is it seems to be underestimating the windspeed. The anemometer is operating fine mechanically. I wonder if the unit is reporting the current windspeed at the time the signal is generated, instead of reporting the 3 min max the manual states.

How many stories is your house? Are there a lot of trees surrounding your property? It might just be a matter of exposure - anemometers at weather stations are 33 feet above the ground and generally give out higher readings than those in residential areas. I had an anemometer on the top of my parents one story house and it never gave readings quite as high as those at the area airports.

 

[Joel Wright]

Originally posted by Jeff Wear
How many stories is your house? Are there a lot of trees surrounding your property? It might just be a matter of exposure - anemometers at weather stations are 33 feet above the ground and generally give out higher readings than those in residential areas. I had an anemometer on the top of my parents one story house and it never gave readings quite as high as those at the area airports.

I ended up modifying it a bit this afternoon. I picked up a 10' long 2 1/2" diameter PVC pipe from the hardware store and mounted that on the garage peak. It measure out to 24'. It was about 16' before. It's also free of the turbulance generated by winds near the peak. The surrounding area is pretty void of trees. It seems to be working MUCH better now.

 

[Carrie Halliday]

I have had my Davis Vantage Pro for a year now. I love it! My concerns are that I only have my anemometer at about 17 feet (on PVC that is mounted to the fence). I wanted to mount it at 33ft but a tree on the NW side of the best spot would obstruct it. So...it stays mounted on the fence. I do have my rain bucket on the fence and it is doing well...the squirrel is leaving it alone so far.
Another concern is that I have missing data. Sometimes it will not pick up data for 15min-3 hours. Moving the base unit does not help. Can get irritating.
Don't buy the WeatherLink software to link up to Wunderground. I have never got it to work! $150 down the drain. Very maddening.

 

[B Ozanne]

I have two Vantage Pro systems. I just got the one with the extended range and it works great. The sensor is located across the street and reception is no problem. I am using the Davis software to archive data and view it on my computer, I haven't tried publishing it to the web yet.

One of my anemometers is located about 30 feet in the air on top of an old windmill. It really makes a difference being that high. It may be windier up there, but that is the offical height for placing an anemometer.

Your anemometer is probably working just fine. I'm trying not to get on my soapbox right now, but most people are horrible at estimating wind speeds. Even very smart meteorologists. It is common to think the wind is stronger than it really is. BTW, it never goes the other way, nobody ever estimates on the low side.

 

[Joel Wright]

Originally posted by B Ozanne
Your anemometer is probably working just fine. I'm trying not to get on my soapbox right now, but most people are horrible at estimating wind speeds. Even very smart meteorologists. It is common to think the wind is stronger than it really is. BTW, it never goes the other way, nobody ever estimates on the low side.

My anemometer now sits about 24' up after I modified it. Do you think there is much difference between 24' and 33'? There's nothing at all around to obstruct it. It seems to be operating very good now. I'm just wondering if there really is that much of a difference in just the 9'.

 

[Glenn Rivers]

Anamometer heights and wind speeds

For Joel Wright.....Is there any way you could post pictures of what your exposure looks like in different directions?

When the wind is relatively strong, or there is not much heat flux from the ground or a thermal inversion, the wind profile will tend to be a logarithmic function with height, provided that the aerodynamic roughness is essentially uniform for some distance upwind.

There is a famous equation that relates wind speed with height for the above conditions:
U(Z) = Ln[(Z/Zo)+1]*(U*/K)

U = mean wind speed at height (Z)
Ln is the "natural logarithm function" having a base of 2.71828 instead of 10. (To convert to Log10 just multiply the Ln function by 0.4343)
Zo = roughness length. This is the height at which a logarithmic profile extrapolated downward goes to zero. Estimating its value takes some experience, but it is usually not more then than 10% of the height of the physical roughness elements..i.e. trees buildings, grass, tarmac, ripples and waves on water etc. acting on the wind. Zo can be less then 10% of the height of the roughness elements if they are too widely spaced, or too closely packed.
U* refers to "friction velocity" and is equal to the square root of the wind stress divided by the air density.

An added complication is that the apparent height at witch the winds go to zero (based on measurements above the roughness elements) does not equal the ground surface, but rather an apparent "zero-plane" displaced a good fraction of the height of the roughness elements above the ground. A classic value for the zero plane displacement is at a height of 0.6 times the height of the roughness elements, but this fraction varies a good deal with factors such as the packing density of the roughness elements.

K = the "Von Karman" constant, considered to be near 0.4

Typical values of Zo:
Mature Hardwood forest...1 m (3.3 feet)
One story bungalows with sparse trees.....0.3 m (1 foot)
4-5' high corn....0.1 m (0.33 feet)
4-6" high grass and weeds....0.01 m (0.033 feet)
Plowed or furrowed field.......0.01 m (0.033 feet)
Typical tarmac or concrete....0.0001 m (0.00033 feet)

Ratios of (U33/U24):
For Zo = 0.3m and Zero plane 8' above the ground....1.24
For Zo = 0.1m.....1.07
For Zo = 0.01m...1.05

These ratios refer to wind speeds averaged over periods of 1 minute or greater. The ratios for gust speeds will be smaller.

I hope this will be helpful.
Best regards...Glenn Rivers

P.S. if you would like, I could try to find a site with this stuff.

 

[Joel Wright]

Thanks a lot Glenn. Pretty cool stuff.

I have a picture of my anemometer, but I don't have a webhost at this time to post it.



Now that it's been a few days and I've observed more wind readings, I've found it's actually pretty acurate. I realize since I am in a neighborhood with scattered trees that will cut down accuracy somewhat. I'm very happy that there are virtually no trees for about a block from west to north-northwest. So if a big storm blows through it should be very accurate, as most of the time strong wind blows from that direction.

-Joel

 

[Tom Burgess]

I use the Oregon sci. Stations Have both wired and wireless. I will not buy anything else. The wired station updates about every 10 sec. T wireless station is slower to update but loss of the wires offsets the delay
8)