Nice start to your analysis, and I agree with two (or more) posters above, fleshed out a little:

- Average wind speed does not usually give a good picture of total available wind resource; your actual resource will usually be quite a bit higher once the cube factor of speed is taken into account (usually about twice, but YMMV). It's best to use things like "% of time above x wind speed" such as in the chart in your post. For example, in this case, you know that more than 30% of the time for 4 months, you have at least Beaufort 4 winds (look up what that means; I'm too lazy at the moment).

Also, you need to know what height the average wind speed is for. Usually, unless the info is specifically for wind generators, it's at 3m (10 feet), so your average wind speed at your tower height will be higher (for your relatively flat - I assume relatively treeless locale - you can use the 1/7th power law, i.e., wind speed at x height = wind speed at y height * (x/y)^(1/7)).

- Even if the math doesn't work out quite right, go ahead and do it, and start small (7-10' diameter). You will have gained valuable information about your wind resource and your abilities, and you will have had a lot of fun !

Never underestimate the value of doing a project like this; it's much more than what you will save from your power bill, even if it is a fact that you will always underestimate the cost by a factor of between 2 and 10, depending on your savvyness.

• Do not necessarily believe the "big guys" who say that "wind power doesn't work for 'x' locale because...". For the overhead they are dealing with, that may be true for them vs. placing it in another location such as a mountain pass, but you are dealing with very different criteria, and you are in control of your overhead and how much value you place on it.
• Unless you are in a place with quite consistent winds, I always recommend a few solar panels to augment a wind generator. Consider installing about 100-300W, and starting your system with solar, which is quite a bit easier than a wind generator and gives you a good idea of how hands-on you want to be and how much you like making your own power. When you want more power (and people usually do, it's addictive !), start on the wind generator, and start small.