Around the country headteachers, as usual, contemplated the prospect of a white Christmas with excitement. Nothing to do with seasonal goodwill, nostalgia or Ladbrokes. As the flakes drifted down, one thought above all others will have caused them to smile: it’s snowing, and it’s not during term time.

The National College for School Leadership could devote a whole module to the complexities of running a school when there is a threat of snow. Yet the topic is almost taboo, for it exposes the head’s vulnerability like nothing else. Fire, flood or financial meltdown have far more lasting repercussions, but everyone understands and rallies round. Heads are used to being held responsible for things over which they have little control: pupil misbehaviour in town, parents parking cars in the local streets when picking up their offspring, and carnage at the latest sleepover while mum and dad were in Majorca.

So why is snow different? It’s sheer bloody- mindedness, that’s why. It usually starts with the meteorological Jeremiahs on the staff. They will let it be known that there is a threat of snow “later this week”. You then listen to every weather forecast, ring the Met Office every 10 minutes and log on to any website that might give you a precious tip-off about timing.

But snow is perverse, and geographical factors make predictions a hazardous business.

There is simply no good time for it to begin. If it comes in the evening, there is nothing to be done. It might melt overnight or it might still be there in the morning. Snow on the ground as you wake means deputies on the phone early. “What are we doing boss?” “I haven’t a clue!” you inwardly scream. You decide to close the school and the greatest thaw since records began clears the snow by 9.30. Your rival down the road has done his Captain Oates bit and stayed open. Meanwhile, you know that the staff and pupils are laughing their heads off. The LEA launches an inquiry about procedures to be followed when closing the school early. You vow that next time it will be different. And it is. Invoking the Dunkirk spirit in your determination to keep the school open at all costs has inevitably led to the onset of a 1947-style blizzard of rules and procedures from the authority. Then comes the real thing.

Pupils and staff chorus their approval of this exciting development, usually within earshot of the head. “It’s snowing!” Everybody loves it apart from you. By lunchtime the switchboard is white hot and every mobile in the school is trilling messages of impending doom. The head of French bangs on the door to tell you that her husband has been on the phone to say there are 15ft drifts in their road and if she doesn’t leave now he cannot answer for the consequences. School buses arrive unannounced in the car park and the drivers tell you they’re going now or not at all. The local radio station has gone into overdrive; this happens but once a year and they are going to make the most of it. A fight breaks out on the school field as Year 11 exploit their last opportunity to sort out Year 10, who are busy trying to do the same to Year 9.

It could be worse. Imagine this happening during an Ofsted inspection. Or what if unauthorised closure of the school became part of the league tables? Makes you say a quick and guilty thank you for global warming.

Dennis Richards is head of St Aidan’s C of E high school, Harrogate