Weather wise

I was taking my children to school one of those crisp, clear, cold mornings last week and I encouraged them to breathe deeply and savour the fresh air. "It's come stright from the North Pole," I told them. Then I realised that we were walking westwards and the wind was blowing directly in my face. So if the wind had come from the Arctic, then it must have made a left turn somewhere on its journey.

So I distracted the children with Apple Attack sweets (a hard fruity shell with a mouth-wateringly chewy flavour) and resolved not to talk to them about the weather again until I had looked at the maps.

For much of last week, they (the maps, and, come to think of it, the children too) were a mess. There are several different directions from which air masses typically pass over Britain, and it seemed that they had all decided to meet in our skies at the same time.

What we were not getting much of was a good, honest, cold north wind. The north wind that proverbially doth blow (and we shall have snow) is Arctic air coming to us from the north. Not all north winds are of this type; they may also be warmer, wetter air that has travelled east over the Atlantic, passed over Scotland, then taken a right turn. Since the sea in winter is warmer than the land, the coldest winds come from Polar Continental air masses that reach us after chilling out over Europe.

What seems to have been happening last week, however, was a huge muddle of a cold front of Polar Maritime air coming from the north-west, a warm front of Tropical Maritime air coming from the south-west, and another front of Polar Maritime Returning air, which is warmer air that began in the Arctic, headed south over the Atlantic, was warmed by the water, and is now heading back home to the Arctic.

When cold air behind an area of low pressure catches up with the cold air in front of it, the warm air in the low-pressure area is lifted up and an occluded front results. That is signified on the weather maps by spiky and rounded symbols pointing in the same direction on the same frontal line. There were plenty of those around last week, and also a few of those with spikes in one direction and curves in the other, when warm and cold meet head-on.

With all this muddle going on, no wonder the cold wind was coming from the wrong direction. It's confusing weather for an amateur meteorologist.