Jet stream heading south again. Will it be as bad as before?
Over a week ago I broke the news that the jet stream was finally going to head northwards having been stuck south of the UK for months bringing record-breaking rainfall.
Torrential rain brought frequent flooding only months after much of England experienced drought conditions and faced growing concerns that water restrictions would become essential to manage our water resources through the summer.
Last weekend, much of the UK enjoyed some warmth and sunshine with the fine weather and heat continuing all week for England and Wales. Yesterday the temperature reached 30.1C at St. James Park in London, making it the hottest day of the year so far.
Scotland and Northern Ireland haven’t been as warm, but after some rain at the beginning of the week, the weather has settled down here as well with some welcome sunshine.
Whilst most of us would like the summery weather to continue, it does look as though the jet stream is going to return southwards at the end of the week.
You’re probably thinking that this means a return to the perpetual rain and cloud that we experienced before. Well, not exactly. This time there’ll be some notable differences that will mean whilst the weather in the coming weeks is more changeable, it’s unlikely to be as bad as before.
Jet stream not as active
When the jet stream is very active and travels at high speed, low pressure systems form more frequently and are deeper, meaning that they produce heavier rain, more cloud and stronger winds.
However, when the jet stream returns southwards in the coming days, generally, I don’t think that it will be as active as before and travel more slowly.
As a result of this, low pressure systems will be pushed towards us more infrequently and tend to produce less in the way of heavy, persistent rain. The rain will tend to take the form of showers, which means that there’ll be some sunshine in between.
Jet stream wriggling around rather than getting stuck
Another difference from the past few months is that when the jet stream returns southwards, it’s unlikely to get stuck in exactly the same place as it was in recent months.
In the coming weeks, it looks set to wriggle around which means that the weather will be more changeable. In effect, rather than continual low pressure, there’s a better chance of ridges of high pressure in between.
This will have the effect of producing some decent days with sunshine, interspersed with showery days with a bit more cloud.
Temperatures are likely to be close to average at 16-20C for Scotland and Northern Ireland and 18-22C for England and Wales. But given that the sun is still strong at this time of year, if there’s little wind and not too much cloud, it’ll feel pleasant enough.
London 2012 opening ceremony
One headache for us weather forecasters is that the process of the jet stream heading southwards again is occurring on Friday, which of course is when the opening ceremony of the Olympics is taking place.
Whilst it looks like it’ll be a warm evening in London on Friday with temperature of around 22C, there is still the possibility of a shower.
Based on the latest forecast information, I’d say that the risk of catching a shower for the opening ceremony is around 40%.
In the meantime, you can stay up to date with the latest forecast on the Channel 4 Weather website and I’ll be tweeting regular updates on Twitter – @liamdutton