Just before I quote Malcolm's thoughts (which will be in two parts as he includes more imsges than our forum software can include on a single post), I thought I'd link this diagram showing how Walker circulation, which refers to air rising at one lturde and then advecting to a different latitude prior to sinking, helps define the rough locations of the polar jet and subtropical jet:
It can be seen that air returning north in the Ferrel Cell is the origin of our mid-latitude westerlies - of course, the westerly component of the flow is due to Coriolis which I discussed way back when in this thread. Were it not for that effect, the flow would be due north in the northern hemisphere.
A look at last evening’s short term anomalies to see where we are going with this, if anywhere. The major players remain the weakening Canadian vortex and the strengthening one over northern Russia with the elongated blocking high pressure ridging east >west between Scotland and Iceland
But in a not unimportant supporting role is the upper low in the western Atlantic which divides the flow exiting north east N, America, albeit some of it returns in mid Atlantic to support the strong westerly jet over Iceland, but more to the point it also creates a channel south of the block to the low pressure south of the UK giving it the odd boost and perhaps an indication of future events?
So for the interim it looks like a continuation of a slack pressure gradient over the UK with temps above average but sunshine in many regions interrupted by showery/stormy outbreaks, the detail of which will be impossible to pin down much in advance.
A front/trough, currently lying Dorset > Wash, accompanied by rain, showers/ storms and localized intense rain fall will track north west during the day. Clearer and drier weather behind in the south east where the odd Cb could pop up but remaining pretty cloudy along the east coast and some central areas. Again the best of the weather in the north west.
Thursday sees the large slack area of low pressure esconced over the UK heralding a warm humid day in England and Wales with cloud still the bugbear along the north east/east coast and perhaps central areas of England. Some home grown storms could be triggered where the sun gets going but just to add to the mix more showers/storms will track north west across central southern England and Wales during the day
The general pattern on Friday sees both the Bermuda and Azores high pressures ridging around the cut off lows in the Atlantic as the next phase of the evolution gets underway. On the surface this translates to another very warm humid day for the UK and with the heavy showers/storms extending further north one could pop up virtually anywhere. Meanwhile high pressure is building south of Iceland.
Saturday a drier day in England and Wales, the showers confined to Scotland, but still above average temps but 'cooler' air creeping in in the west as as the low to the west takes closer order and the high pressure continuing to ridge east north of Scotland
Another very warm day on Sunday but although the high pressure is becoming established to the north the low is quite adjacent to the south west so apart from home grown storms being triggered some could still move north from France and affect the south
With the warm, muggy, air associated with the low pressure to the south drifting north over the next couple of days the spread of the unstable atmosphere will be conducive to a lot of storm activity, both home grown given the right trigger (temps) and imported from the continent associated with troughs within the circulation. The storms could occur virtually anyway but more prevalent in Wales and the midlands south today before moving north tomorrow. They could be very intense and where they do occur a distinct possibility of localized flooding. Settling down over the weekend as the high cell developing to the north west takes closer order.
So today some storms probably triggered in central southern regions (forecast sounding) before the more concentrated area tracks north west through southern regions into Wales during the day. There will of course be plenty of sunny intervals elsewhere but the east coast again subject to low cloud and mist.
The showers/storms will hang around in western areas overnight and through tomorrow and gradually drift north into Scotland. It will be another warm day in many areas but not cloudless, and not so much in Wales and the south west and the usual caveat vis the east coast but temps still generally above average.
So as we come to the weekend the pattern evolving sees the the Azores ridging north around the upper low south west of Ireland before curving east north of Scotland. with a very slack gradient over the UK. Another warm day, less so in coastal areas, with broken cloud cover but the showers and any residual storms now really confined to Scotland.
A not dissimilar story on Sunday except much of central and southern England and all western areas will be warm with the north east and eastern areas cooler with the possible ingress of cloud to boot.
Monday sees another relatively fine day but as the high pressure to the north takes closer order as the low pressure retreats a north easterly drift from the North Sea is once again initiated and thus quite a west/east split.
An update on last night’s medium term anomalies as I see them and what appears to be an upcoming major test of the very impressive block
The major players are the north Canadian vortex and associated trough into the north west Atlantic, which is connected to the main vortex N. Russia and cold European trough with in between the European and Azores still combining to formulate the strong ridge running north west into Iceland.
But the orientation of the trough in the north west Atlantic has shifted a tad north east which effectively diverts more of the energy exiting north America south around it, albeit it still diverges in mid Atlantic around the block and down to the Iberian low pressure.
So currently the UK remains in a very slack pressure area with high and low pressure to the north and south so likely the temp will remain above average but leaving the det runs with a lot of niggly regional detail to sort.
But the question is will this transfer of energy and movement of the trough eventually wear down the block? Probably not rapidly?
On to a few more details
Over the next couple of days the UK will largely stay under the influence of the warm, moist, unstable air which is conducive to triggering heavy showers/storms with the possibility where these occur of localized flooding. As the airmass slowly shifts north, thus introducing quieter conditions in the south, then so will the showers/storms.
Currently there is still shower activity over Wales.
whilst, apart from the north and north west, over the rest of the UK a muggy cloudy day dawns, But as heating gets under way convection will be triggered in many west and central areas spreading north and storms could crop up virtually anywhere. Where the sun appears it will actually get quite warm with the usual caveats vis Haar and the eastern coasts.
During this evening and overnight there will be a lull in the storms but another humid night with a lot of cloud around in central areas and the Haar ingressing inland again in the east. But as temps rise again tomorrow more heavy showers and storms are triggered concentrated more on central and eastern regions but spreading north west into Scotland where their could be some very intense stormy outbreaks. Another warm day but 'cooler' weather slipping in to the south west.
The overall pattern on Sunday sees the high cell to the north west becoming more influential with any residual showers mainly in Scotland and the north east but also that means back to a north easterly drift whilst elsewhere another very warm day.
Monday sees a marked west/east split with warmer conditions in the west with the chance of the odd shower but much cooler and cloudier in the east in the brisk north east wind.
Tuesday will be a generally dry and quiet sunny day but still with the west/east bias with more cloud in the latter half of the country
I'm pleased to hear that - storms scared me until an embarassingly late age, and, if we get one close overnight I'm still a touch wary.
Apologies for not posting for a few days - my anxiety hs been bad again and I've been rather busy. I'd like to think I'll be back to posting from tomorrow.
A quick look at the GEFS NH analysis at the beginning and end of the short range from last night’s 1800 run which continues to signal the start of a major transition with the amplification of the ridge over North America and displacement of a vortex lobe/trough into the north west Atlantic whilst at the same eroding the block that has been so influential in recent weeks in dictating the weather over the UK.
Back to this morning
Overnight most of the cloud that persisted yesterday in the south has disappeared as the drier air moves south resulting in a clear start to the day. but in eastern Scotland the north east of England low cloud and mist from the North Sea has once again encroached inland. So today will be a reversal from yesterday with a generally sunny day and warm in many areas, particularly in the south but the cloud could well hang around in the north east.eastern areas and thus depressing the temp. But by late evening more humid unstable air is once again pushing north from France into the south.
The humid air will continue to push north overnight and through Thursday whilst also initiating showery, perhaps stormy, outbreaks along the south coast and the south east. Despite this another warm day in these parts and elsewhere with the usual caveats vis the north east/east although it should be less cloudy.
So the overview on Friday sees the upper low to the south encircled by the ridging of the Azores and European highs thus a fairly quiescent period beckons with the surface low and moist air continuing to push north with more showery outbreaks in the south but generally tending warm and sunny with the possible eexception of the usual areas in the north and east.
Little change from this scenario on Saturday
And the north/south split continues to be the percentage play on Sunday with showery/thundery outbreaks likely in the south and west whilst sunnier and drier in the north with the usual proviso vis eastern coastal areas. But still generally remaining warm over the weekend with temps a little above average
Some time next week, yes. I think the spell we've had with the stronger arm of the jet running so far north and thundery lows drifting up from the continent has been unusual in its longevity, and expecting it to last for much longer would be unreasonable. Thanks to that set-up, the only rain most areas have seen for the past 2-3 weeks has been storm rain which is hit and miss and can be damaging to gardens and crops as opposed to the prolonged but usually moderate rainfall we get from summer Atlantic depressions.