Well the first official summer month is well and truly up and running and no doubt the phrase "flamin' June" has already been uttered up and down the country, but clearly not because of sunshine and heat, but because of torrential rainfall and very strong and unseasonal wind speeds!...
What isn't a surprise however, is the change to more unsettled conditions. At the latter half of May I took my usual look at the potential trends for the forth coming month and at that time there was a clear signal that the significant heat and sunshine that was evident during the latter stages of May would not continue into early June. This full discussion with thoughts for June can be found at the below link and in fact some of the forecast charts discussed at the time are matching the actual synoptic conditions of present day very well indeed!
Today's blog is taking a more specific look or advancing on the above blog to provide some additional answers as to why the unsettled conditions are now present and how long they are likely to last.
As usual, one of the best places to start is the jet stream;
This jet stream pattern can then be followed down to more surface levels, which using the below surface chart clearly shows where the main area of low pressure is to the West and South-west of the UK;
Note how the Azores high pressure is being held well to the west and south-west of Spain and Portugal. This is a text-book sign that the jet stream is dominant just to the north of it and suppressing what is meant to be a feature of the weather much further north and east, affecting France and the UK during the summer, for example. It's clear to see that across the UK and also within the Central-North Atlantic low pressure is dominating the weather.
So is this likely to change...Again lets take a look at another jet stream chart but into next week;
As I have highlighted before, once you progress beyond a certain time period, it becomes important to look for broader trends in the synoptic evolution rather than the details. Just as a re-cap, troughs in the jet stream indicate unsettled and often cool conditions, whilst ridges signal higher pressure at surface levels and clearly warmer and drier conditions. Now unfortunately the variety of forecast models continue to signal a trough-type pattern across the UK until the middle of the month at the earliest with model agreement and also consistency. As a result we are likely to be 'stuck in a rut' now for some time with predominantly unsettled conditions dominating the weather.
The second half of June may well signal a change however. Some longer term forecast models and information do signal a pattern change with the jet stream changing to allow more ridging and hence higher pressure to affect the UK and one particular model, the GFS ENS, highlights this well;
Note how the Azores high pressure is being allow to build North-eastwards towards the UK in what is a perfect example of how the Azores high pressure can bring the UK some of it's best summer weather conditions, particularly if the high pressure builds across the UK and then becomes slow-moving as well. I did highlight within the last blog (link at the top) that the second half of June could well see an improvement in conditions and given the latest forecast data I stick by that prediction. So June could well turn out to be a month of two halves to say the least, the first being particularly poor, but with the potential for better weather in the second half.
I'll take a closer look at the second half of June and into early July later next week, but for the time being you'll have to keep the BBQ covered, the patio furniture fastened down and the summer shorts and t-shirts on standby, as low pressure is here to stay...
Regards to all,
Great stuff. Thanks Matt.
Thanks Matt - an excellent and informative post - describes things very well indeed.
Quality assessment Matt - Cheers
Thanks Matt. It been very boring since 1st June but I notice your jet stream chart over Canada are not effected like us, it further north which it should be over Iceland/Greenland regions here. If northern blocking was there it should also sent the jet stream further south over N America, Europe, Russia and China giving out bad summer everywhere too.
Thanks Matt, an excellent post.
I think I understand how the 'jet' drives the various weather systems which affect us, but what influences the way the jetstream behaves and how it is 'steered'?
A good question Beaufort. My understanding is its all to do with temperature gradients in the troposphere for both the polar front jetstream and the subtropical jet. This influences the positions of the Hadley and Ferrel and Polar cells and the steepness of the temperature gradients at the boundaries. Add in the coriolis force, and factors such as angular momentum, and you have the classic meandering pattern of the jetstream. So..its a bit of a chicken and egg situation with one affecting the other. Yes..the jetstream drives the weather on a synoptic scale..but the weather can have an effect on the hemispheric developments. Confused? well lets not mention Gravity waves and surface frictional drag. For further light reading try
I was under the impression that the Jet Stream is taking a southerly route at the moment because of blocking. In the hot spell in March it twas taking a more northerly route because of blocking. My question would be about the nature of these 'blocks'