Hi Matt and welcome to the community! Wind is tricky! We’ve taken a look at a sample of your data and everything looks good in terms of data integrity - your hardware is functioning properly. We need a little more info to help troubleshoot the apparent northern bias. These issues are often due to siting and/or the subtle differences between an ultrasonic anemometer and a spinning cup & vane anemometer.
The most helpful thing would be to point out a more specific time range where you are seeing this phenomenon. And if you can share your Davis station’s data for the same time range, that would help a ton with troubleshooting. Also, if you can provide photos and describe how you have your Tempest installed (as it relates to potential obstructions on your property as well as how it relates to your Davis), that will help.
Hmm. There’s nothing built in to the way the tempest samples wind that would cause it to have a northern bias. The one-minute observations you see at the deepest zoom level are an average of 20 samples (one every 3 seconds). And it’s true that if the direction is highly variable during any particular one-minute period then the “average direction” may not be very meaningful - but it still shouldn’t have a northern bias. To answer your question about the math side of things: when the wind speed is 0 the direction is null (not 0 or 360), and therefore does not affect the average.
Assuming this is during light wind events, is it possible the Davis vane is simply “settling” into facing south? As you probably know, one of the drawbacks to a physical wind vane is that inertia & gravity can prevent it from aligning to the true direction of the wind, especially when the wind is unsteady or very light. A slight tilt from perfectly horizontal can create a position that the vane will literally gravitate toward.
Yes! There is still a bug in the apps in terms of the way direction is averaged as you zoom out (the one-minute 0 speeds are being counted in the direction average as a direction of 0). Thanks for the reminder, @sunny - I will make sure that gets moved up the priority list. That may be part of the confusion here @matt4 - to eliminate that, be sure you are zooming all the way in to the one-minute graph before you compare the data.
Much of the same discussion may apply to your situation, Jim, but I’m glad to hear the Tempest seems to be agreeing with your physical observations now!
PS: I’m quite impressed by your improvement upon the old “wet your finger” technique…