A simple one is will the ball stay still on the ground. No problem if it is just the odd gust moving it, but if it consistently moves how are set pieces going to get taken? I'm in Devon at the moment and it was very bad at lunchtime today, at one point the wind was physically stopping me from walking forwards, there is no way you could play football in those conditions.
As Chas also says, safety of the venue has to play a part. I was doing a pitch inspection at a step 3 ground when part of the stand roof came off and landed on the pitch. I already had serious doubts, but that obviously make the decision for me.
You'll get "nanny state" type comments, but stand your ground. I was at a music festival in Spain years ago where the wind was horrendous, if you hadn't properly pegged your tents in they were on the railway line, if you had then every single tent pole would be snapped. It should have been called off, but the Spanish have a much more laid back approach to health and safety than us. Then about 10pm a huge part of the main stand roof came off, luckily it landed to the side of the stage and missed everyone, had it gone forward it would have landed on the crowd, me included. I've never questioned H&S related cancellations since that night.