shear vs. sheer. I guess it all depends on whether you are from the UK or the US, whether you're a native English speaker or English is your second language, whether it's late at night or not, whether your typing skills are up to scratch or impaired by alcohol intake etc.
In any case, I do apologize to US English speakers, and apologise to English English speakers for my mistake.
Although my dictionary gives a second definition for "sheer" as well - to swerve from a course. So arguably a wind shift could also be called a windsheer instead of a windshear.