Come on GFS... Throw Us A Ridge!Added : Wednesday at 14:45 A few months ago, we had a discussion where we talked about the position of the jet stream and how by simply looking at the charts, you know instinctively whether the overall conditions will be settled or unsettled.
There is no magic to it, the jet stream controls the surface weather by moving high and low pressure areas around. Not just that, but depending on the axis of the jet, the systems will either build, fill or deepen, that's pretty much it.
So, when you get the jet stream to the North of the UK then we tend to be under a ridge with high pressure across the UK. When the jet stream is to the South we are usually under a trough with showers, cooler weather and rain.
So, what about this :-
That's the jet stream forecast for the weekend and here it is for the middle of next week :-
The jet stream is pretty much slap bang across the UK and you can see that it is hardly meandering at all. This is what we call a zonal pattern.
When the jet stream is above the UK then you can expect two things. The first is for low pressure areas to cross in from the Atlantic right over the UK. The second, is where it means the air at height it moving quicker than the air near the surface, this is called upper level divergence and depending on what you have at the surface will dictate the weather.
If it's low pressure at the surface then some wet and windy weather, but if the low pressure has passed through and you have showers, then these have the ability to develop and become a little more widespread thanks to this uplift of air.
If you look at the GFS ► charts for the next week or so, then changeable weather is the overriding pattern. But, the benefit of having the jet stream across the UK (if there is one) is that the weather remains transient with some rain, showers, sunshine all passing through in succession and temperatures remaining not far from the seasonal average.
METEOROLOGIST : MARSH |