From High Pressure to Low Pressure…

30 May

Well it goes without question that the final week or so of May has produced some of the best weather of the year so far.  Many areas have enjoyed the persistent effects of high pressure across the country, bringing some prolonged spells of very warm, if not hot, sunshine.  Clearly a strong ‘taste’ of summer for many, however, it is all about to change and unfortunately timing with the onset of the first week of the first summer month.

So before looking forward, it is of worth to highlight and review why we have had such settled conditions.  This will help give a comparison to the up-coming changes.  The below is an analysis of the jet stream from this past weekend with information and comments as to why the weather has been settled and very warm;

If you compare the above image and analysis to the below image, which is the UKMO surface analysis chart on the 26th of May, you can see that a well established and large area of high pressure (1035mb) is centered just to the north and north-east of the UK and clearly maintaining very warm and settled conditions;

http://www.wetterzentrale.de/archive/2012/brack/bracka20120526.gif

So, where do we go from here and why is the weather changing?…

Clearly to get a change in the weather we have to see the above synoptic patterns change and that is what is forecast to take place over the course of the opening week of June.  High pressure is forecast to be replaced by lower pressure and more unsettled conditions and, as usual, this can often be seen and explained within the upper atmosphere;

Now transferring the upper analysis to lower levels and you can see this very well indeed.  Using the GFS ENS (ensemble) mean as the example, note how by Tuesday the 5th of June low pressure is evident at surface levels to the east and north-east of the UK and the upper level low on the above image is directly related to that surface low pressure in the middle of the North Atlantic;

The natural progression here is for the surface low pressure in the central North Atlantic to head toward the UK from the west or south-west, as the minor ridge of high pressure in-between both systems is eroded.  This is what is currently forecast to happen and I have high confidence in this event taking place given good model agreement and consistency within the forecast models for this to happen next week.  So jumping ahead a few days and you’ll note that by the middle and latter half of next week the low pressure to the west and south-west of the UK has moved up into the UK to bring a cyclonic pattern across the UK;

So, there we have it.  From high pressure to lower pressure in approximately a week or so. Just to reinforce this prediction, find below 3 main forecast models GEM (Canadian model), GFS (USA, NOAA mode ) and the ECMWF (Reading, European model) . As you can clearly see despite some variations over the synoptic patterns, all 3 models by the middle and latter half of next week have low pressure affecting the UK;

As is often the case with the weather across the UK, it never stays the same for very long.  I think many will admit and acknowledge that the weather of late really has been stunning and many have enjoyed it, particularly seeing that for a change the excellent weather persisted into this past weekend as well.  However, given the above analysis it is safe to say the first official summer month is not going to get off to a good start and given the longer term analysis for the remainder of June I wouldn’t expecting a ‘flaming June’ either at this stage across the UK.

It’s a case of don’t shoot the messenger, but get ready for a significant change in the weather over the next 7 to 10 days…

Regards to all,

M.

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