As a long time windsurfer who has used iWindsurf since its infancy I am very sensitive to wind speed.
Ever since I got my WF setup I have been increasingly curious about the accuracy of the wind speed data.
Yesterday we got a storm that really illustrates the problem.
I was seeing a peak wind speed of 62 mph while the average wind speed was about 6 mph.
Typically, the ratio of peak to mean wind speed is no more than four while my WF showed a ratio of 10 for this data.
This cannot be correct.
I believe the peak of around 60 mph, other stations were showing that but my station was showing an average of 6 while other stations were showing averages of around 20.
Explanation please…?
Seems like a simple 4th grade math thing for you to see if the average of the observations across a desired timeframe lines up correctly. Query your data and toss it in a spreadsheet.
Sonic anemometers take discrete, nearly-instantaneous samples and therefore will generally show higher gusts and lower lulls than the cup anemometers that you may be comparing to. For example, a very brief gust of wind won’t accelerate the cups to the speed of the gust. And inertia maintained by spinning cups could raise the average.
Also, it becomes very difficult for sonics to sample wind speed in rain. Anything that comes in between the signal path could disrupt it and skew the reading, like raindrops. The software does a great job at processing the raw data and performing quality control.
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@edtimm it was raining throughout these readings in question, correct?
Hi @edtimm Ahh, very good question. We’re all long-time windsurfers and kitesurfers too. Most of us are engineers and meteorologists who specialize in wind measurement…so anemometers are very dear to us. 
In this case, we think you might be getting fooled by the temporal resolution of your graph view. The graph you posted above is displaying 3hr data. Please see Data archive buckets explained for a more complete explanation of data binning. Each 3hr data point for wind includes the avg wind speed over the 3hr duration, the lowest recorded instantaneous value during that 3hrs is displayed as the lull, and the highest recorded instantaneous values during that 3hrs is displayed as the gust. With such a large timeframe, you can easily see why the avg would not appear roughly the mid-point between gust and lull. Rather, at the 3hr resolution the data present actually is telling you the highest and lowest obs during that time and the avg over the duration.
Try this: zoom into the 1min temporal resolution and you will instantly see what you perceive to be a more “sane” range / correlation between gust | lull | avg. Here is your station from today 4 Oct as example:
To echo what @WFstaff said (a degreed meteorologist on WF staff) … if you compare a quality sonic anemometer side-by-side with a traditional spinny cup anemometer…you will likely notice differences due mainly to the inertia in the spinny cups. A sonic is more capable at measuring the actual instantaneous wind speeds without the false influence of inertia, old bearings, etc. It’s challenging all of us to re-cast how we evaluate wind speed data.
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Now that makes some sense.
Here is the expanded data and it shows the more typical 4:1 ratio of peak to mean.
I choose my sail size based on the average wind and let the sails deal with the gusts.
If I were to use the WF average, it is so low in a changing wind environment that I’d never sail.
A three hour averaging time for the displayed average wind is highly unusual and misleading.
Typically, I see 10 minute average data from most weather stations.
Is there a way to change the displayed average from 3 hours to 10 minutes?
This discrepancy has little to do with instrument response times and everything to do with averaging times.
Yes. As explained here: Data archive buckets explained the data is available in 1min, 5min, 30min, 3hr, 1day temporal resolutions. Just click on the " - | +" toggles to zoom in or out to what you want.
Exactly. Once you know the math, it’s obvious. Keep in mind, instrument reporting intervals play a huge role in how many obs are used in the calculated average. Your SKY records an instantaneous observation every 3seconds.
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Thanks.
I know I can toggle the graph but can I change what I see on the dashboard as the average to a 5 minute from a three hour?
The main dashboard displays the instantaneous “rapid wind” 3sec ob in the round dial and the current 1min avg. All data in the dashboard is 1min data unless otherwise noted.
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