I have sometimes heard people say wind power is reliably predictable, but have never looked into the issue before, mainly because some of the people I have heard make the claim are not likely to be stupid enough to have this wrong.
It’s relatively easy to check the issue courtesy of the Irish electricity grid. Ireland has both a relatively high wind penetration (greater than 11% of electricity) and freely available data on forecasted and actual wind generation. Below are screenshots from their website in the last three days:
This looks a pretty decent fit. What about the entire year so far? Comparing actual with forecasted wind generation shows a very strong fit (statistics note: correlation coefficient of 0.95 and R^2 value of 0.9 in a linear model.) Looking at individual time periods back this up further. So, it looks as if wind power is reliably predictable (at least in Ireland).