In theory yes a jacket could blow away. Any race which stipulates taped seams would also stipulate a hooded coat. If it's bad enough to wear a waterproof you'll want a hood anyway. Even a WP cap would fail a strict kit check, you can get a regatta waterproof for less than £15.
You can spend loads on waterproofs, but it's only worth it if you're going to run in them regularly. I've got a Montane Atomic Dt Stretch, it's a great jacket but I rarely run in it. Luckily it was bought for me as a gift!
The only jacket I run in regularly is my OMM sonic smock, which is ironically a hoodless wind proof! The thing to remember though is you carry this gear in case of emergency to keep you warm if you have to stop running.
Vegan Runner, are you doing the Stanbury Splash? I'm hoping to, although I'm off to a birthday party on the saturday night so we'll see. If you are, I'll make a point of saying hello to compensate for my not doing so at the Giant's tooth!
You can get a 'pac-a-mac' style waterproof from Decathlon with taped seams and a hood for £7.
It's about the size of a gent's wallet, and can be folded in half again at that.
I wasn't doing it but I think I might. I was a bit unsure due to the Northern XC Champs the following Saturday. I don't think I'll be anything more than a sweeper there but it gets the Vegan Runner UK club seen at a big event so I entered. I like the look of this Slash race though. The distance ties in nicely with my training schedule run for that day too. Two things though: 1. Is it suitable for a novice like me? 2. Full kit? Will go out this weekend and get a bum bag, waterproofs and the like but will I need anything else?
I'm probably not best qualified to say, but I would say full kit will mean a set of waterproofs, mebbe a whistle, hat and gloves? That's about what I'll be taking. I think you'll be fine on this one, no doubt you'll finish in front of me again and I'm hoping to give it a go!