When we have extremely high winds for a few days, I've noticed that some if not all of the bowls are a bit low. I can hear the winds coming in the vents and the water in the bowls actually moves a bit when high winds are present. We average 10-15 MPH winds as it is and 25 MPH happens quite often as well. I have seen this occur, yet others say they never heard of this. Can high winds affect the water level?

Its called the VENTURI EFFECT.
When the wind blows across the top of your toilets vent pipe, it tends to pull air out of the top of the vent pipe.
This creates a reduction in air pressure in that pipe.
The resultant effect is that the air pressure on the water in the toilet pushes down on that water [which was held steady by the same pressure outside] and lowers its level by pushing it down and over the waterfall created by the U bend. Does this answer your question? Regards, Tom

It does answer my question Tom thanks. While I did not know that there was an actual term for this, I have seen it many times before especially in our current house which has constant winds. I only asked the question because when I said that winds cause our levels to drop, I got the... ooooook look. I figured who better to answer the question than a professional. Thanks again.

Ton cut back on the "venturi effect" you might consider installing vent caps, (see image) Good luck, Tomk

Tom is correct and for those who ever took physics it is also the Bernulli Principle. One of my students once sai, "oh, I get it, the wind blows and this sucks. " Never cared for that kid.