What is a sww?!
Embarrassed to ask but I don't know!
Originally Posted by: Quantum
SSW, sudden stratospheric warming.
Simply put, in the stratosphere when a massive warming occurs this can signal blocking in about 1-3 weeks time. SSW is forecast to occur in about a weeks time.
The rough idea of how it works is this:
1) Deceleration of upper level westerlies occurs (or easterly winds develop) this causes the air to compress and heat up extremely rapidally (by 70C sometimes!)
2) I don't quite understand this fully, but so called rossby waves in the lower atmosphere tend to propagate upwards. Westerly winds propagate easily into the high atmosphere, but easteries don't.
3) Therefore easterly winds in the stratosphere prevents lower level westerly winds from propagating above that level, what this means is that the waves get stopped below the original easterly, and this one becomes easterly at a lower level.
4) The process continues with the easterly winds propagating further and further down until they reach the jet stream and weaken it, perhaps pushing it further south.
5) Southern jet allows cold air from the north to make more progress south, so in the UK that would mean cold and snow.
Like I say the whole process takes 1-3 weeks, and 'weakining of the jet' doesn't necessarily mean in the right place for northern blocking and cold/snow for us. But it does increase the odds.
Originally Posted by: idot