The great volcanic ash cloud forces in northern ireland

Make no mistake this is still a very small eruption. If the neighboring volcano Katla erupts with the volume of the last eruption (0.7 cubic km of Tehran/ash), the effects may be much more serious for UK air travel than we are seeing currently.
Something doesn’t quite add up with this volcano!
I am a little confused over the explanation for the reason for the severe distribution being a combination of very rare events. We are told that eruption episodes in Iceland occur every 3 to 5 years and can last for period of days to months. As a very rough order of magnitude calculation let’s assume the following: Significant eruptions occur every 4 years and last for 30 days at a time. This means that since say 1970 there have been around 10 such eruptions and therefore an exposure to around 300 eruption days.

To allow for any the effect of weather patterns (including wind direction) locking into a pattern we can assume we have only suffered 1 day of ash exposure so far. This would tend to imply that the current wind direction is very rare indeed i.e. a 1 in 300 chance of it occurring.

I seriously doubt that the current wind direction is that rare and therefore there must be other factors I have not considered which truly make this a very rare event. Alternatively it may be that our policy of closing airspace as a reaction to these events is relatively new. Is this just a taste of what’s to come?