oxford blue
I realize the term "varying" has a specific meaning. (And thanks for not talking down to me...)
If the "varying" of a six knots wind has "serious implications" on my runway performance, I am probably operating at a runway where I should not have been in the first place, don't you think?
Part of my point is that you should always expect the wind to vary a bit, both from what it was seconds ago, and specially from what it was when the last ATIS was recorded.