Red sky in the morning…

I took an unscheduled stop on my cycle in to work this morning to take some photos of the amazing altocumulus that was over my patch of West London. Here’s a quick snap:

And here’s another looking straight up, it was lovely and fuzzy:

Anyway, it got me thinking about the old saying “Red sky in the morning, sailors take warning. Red at night, sailor’s delight.” This relates to the Norwegian model of fronts, which is summarised by this figure below:

So the saying kind of works because, if you see some altocumulus then it is quite likely to be at the leading end of a warm front. This means that some bad weather may be on its way. Sure enough, here’s the current Met Office forecast (though I doubt that this was constructed by looking up at the clouds!):

The other question that comes up here is: why is the altocumulus red? The quick answer is that its at about the right height to pick out the red light that is scattered from the sunlight that is travelling through the atmosphere at a particular angle in the mornings and the evenings but see here for a more complete discussion.