Astronomy Weather

I have an unhealthy pre-occupation with the weather, and spent far too much time trying to work out what the weather will be likely to do tonight, or this weekend.

Is it going to be worth observing? Or am I free to make alternative and more social plans for my time? These are the questions that we astronomy types must try to answer every day. This page is a small selection of links that I often visit when making these choices.

Most amateur astronomers soon end up being expert weather forecasters as well. As you keep feasting on weather reports, you rapidly learn the basics of weather in your locality.

I live in the UK, and, as such, these are my thoughts on the British weather. I'm not giving forecasts here... just some observations on how it appears to work.

  • First of all, British weather seems to exist in two basic states. You've either got systems swinging across the atlantic on a regular basis bring alternate clear and wet spells, or, the weather system gets blocked by high pressure over europe, and not much seems to happen.
  • On balance, I think I prefer the first case, because blocking systems can be very nasty. When blocked, the weather you actually get varies a lot.
  • For example, if the blocking high is to the south west of the UK, its going to be a very moist high. This brings that most hated of British weather conditions - the anti-cyclonic gloom. This is basically a big wet mass of air anchored over the UK and not going anywhere. Crap for astronomers.
  • On the other hand, if the high is to the North West - ie coming from greenland then fetch your telescopes for some clear dry weather!
  • A high to the north east can bring either. However, in the winter, a high to the north-east has two effects. It blocks the atlantic systems, but it can sometimes allow very cold air to the east (ie Russia) to get pumped across the UK bringing snow to the east of the UK.
  • More often than not, a blocking high is a bad thing as the transparency seems to deteriorate the longer it is there. The only good thing is the blocking high can give very steady air for planetary observations. Big wow. 9 planets versus zillions of DSO.
  • So, as I said, I like a nice varied flow of altantic systems because it normally gives you some clear skies, as opposed to a blocking system that could give you great conditions, but, more often than not, gives dreadful astronomer weather.
  • You may recall the absurdly hot summer in 2003. This was cause by a huge blocking high parked over Europe which didn't move for weeks on end. This big pool of hot air made for some great seeing conditions in the Mars opposition.
  • British winters become a battle between the blocking highs and the altantic systems, with the occasional blast of frigid air from the north thrown in to keep things interesting.
  • As the altantic systems rush in, they push the very cold air in eastern europe further back to the east. As the energy in the depression dissapates, the cold air swings back to the west. If it reaches far enough west, you get some cold weather in the UK.
  • In recent winters the cold air has not reached far to the west, but its kind of like sitting on a beach wondering if the next wave is going to reach you.

Important Weather Links for Astronomers

There are a lot of weather sites out there - here are a few.

Weather Outlook
The Met Office
Meteosat Images/Movies
Weather Web