I have to admit, I don't usually bother playing if its too windy. I have a relatively high toss, and there's nothing I dislike more than a ball being pulled out of position when serving or when there's a cross wind that pulls what would otherwise be a winner outside of the court. Turns everything into a random lottery. 10 years or even 5 years ago, it wasn't easy to get an accurate assessment of windspeed (I'd just look at how much the trees were waving around) but these days, the Android weather apps for example are fantastic and give hour by hour readings of weather including wind speed. At the moment, its 19mph outside and the tree branches are waving about all over the place even at the lower levels. What do you consider to be too windy to stop you from arranging a match?