UK meteorology

Malcolm's thoughts on the 21st:
Today marks the transition to the next phase of this fine spell of weather (not forgetting that this hasn't, and isn't the case, in N. Ireland and north west Scotland). as the amplifying north east of the Atlantic ridge disrupts the main trough and forges a corridor to the Scandinavian high pressure. This essentially sets the pattern for the next few days and through the holiday weekend with high pressure to the north and north east dominating proceedings and with an unstable low pressure area to the south an easterly regime over the UK is set in motion with the Atlantic trough relegated to the west by the aforementioned corridor.



The detail for the next few days.

Today - The front and band of rain is still affecting N. Ireland ans western Scotland and will continue to do so through the day and evening with some heavy pulses traveling along it whilst elsewhere after a clear night another warm, very warm, day beckons once fog and low cloud has receded from eastern coastal areas although it will still be a tad cooler here. But cloud will bubble up in central southern and western areas that could lead to isolated thunderstorms.







By Tuesday there is a new high cell north of Scotland where the decaying front is still lingering albeit the rain has died out but temps around the region remain depressed Elsewhere Another very warm sunny day with again the chance of thunderstorms in the south. The usual caveat vis temps along coasts, particularly the east coast with the onshore wind.



By Wednesday the center of the high has shifted northeast and whilst warm and sunny conditions continue to dominate in many areas with again the risk of thundery outbreaks, temps in northern Scotland and eastern coastal areas decidedly cooler in comparison.



On Thursday the aforementioned 'corridor' to the west is in full swing and with the low pressure to the south pushing north a trough does likewise bringing more concentrated convective outbreaks to the south and west in the freshening easterly wind.





A similar story on Friday vis the risk of thundery outbreaks in the south and again another warm day but with a definite westerly bias and cooler in the eastern half of the country with possible some low cloud and mist along the coast.



The rainfall distribution reflects the above - hopefuly

 
Malcolm's post for the 22nd:
The rain that has been plaguing north west Scotland will finally peter out today but still leaving a legacy of cloud which will gradually thin out from the south west. But low cloud and mist over eastern Scotland will persist, and even own as far as north east England, and this will depress the temp in these areas whilst further south it will generally be another, warm, sunny day which again could trigger some downpours.





Overnight the low cloud and fog will become quite extensive over the eastern part of the country but clearing quickly in the morning but still much cooler along eastern coastal areas in the on shore breeze whilst elsewhere should be another warm and sunny day, albeit still the possibility of the rogue shower. Out to the west south of Iceland an active front sits thanks to temporary foray from the upper trough to disrupt the SW/NE high pressure 'corridor'



I say temporary foray because by Thursday high pressure is once more surging north east west of Ireland whilst whilst a trough in the low pressure to the south pushes north bringing rain to the south, perhaps some convective outbreaks embedded? and at the same time initiating a quite brisk easterly over the southern half of the country. So still quite warm but again cooler along eastern coasts.



The band of rain/showers continues to push north overnight and through Friday whilst the high cell to the west moves north east, all of which accomplishes two things. A variable temp spread over England and Wales and of course the east coast as the brisk easterlies have spread themselves further north



The trough continues north through saturday but is of little consequence by now whilst the high cell is now west of southern Norway (the alignment of this over the next couple of days is quite important) whilst down south the low pressure is pushing north along with some convective activity which could well bring some heavy thundery outbreaks to the south and west. This scenario introduces quite a spread of temps across the whole of the country but the jockeying for position of the main players High to the NE and low pressure to the SW) has introduced warmer air into the for south.



 
Malcolm on the 23rd:
As we move through the end of the week and into the holiday weekend an overall summary of dry, warm/hot and sunny would not be out of order but must come with a couple of caveats relating to the specifics of the daily analysis. They are the regional temp variations and range and intensity of any convective activity, whether home grown or imported from the continent

Today. It has been a clear night for most but the low cloud.mist eastern Scotland and the north east yesterday did spread further south and inland by this morning. This will burn back as the sun rises but will still affect NE/E coastal regions throughout the day so whilst elsewhere will experience another warm and sunny day temps in these regions will be depressed. Again there may be a few showers bubbling up in the south east this afternoon and late in the evening a more concentrated batch will arrive from the south east.







The concentrated band of showers associated with the trough will continue to track NW across southern England into Wales through Thursday and some of these will be heavy with the odd thunderstorm So although another warm day is on the cards a fair temp variation denoting the specific analysis as be seen on the temp chart.







A quick look at the general pattern on Friday finds the Azores> Scandinavia corridor and the cut off upper Iberian low in good working order.



and specifically the high cell is creeping NE to the NW of Ireland and the trough north over England and wales producing sporadic heavy bursts of rain all of which, on a basically warm day, does again produce some marked regional temp variations



By 1200 Saturday the high is north of Scotland and with low pressure pushing north the gradient tightens resulting in the easterly winds increasing a tad and thus on another warm day, warmer air has now arrived in the south,eastern regions will again be adversely affected temperature wise. Still a chance of the odd shower in the south.



Sunday a generally warmer day with the usual east coast caveat and elsewhere if sea breezes kick in, and a chance of thundery outbreaks in the south

 
Malcolm's thoughts:
For this period the UK will essentially stay withing the circulation of the low pressure to the SW/S and thus a moist, unstable, airstream from an easterly quadrant. Temps remaining above average but cooler in the east with a fair amount of sunshine with a westerly bias but but showers and storms, sometime in concentrated bands, will affect many areas at times.

Today.

After a generally mild night the low cloud and mist affecting many areas will gradually retreat to the eastern coasts (hopefully) leaving a sunny but a tad cooler day than of late, But storms currently over Holland will swing west along the south during the day with possible some intense localized rainfall if you are unlucky to catch one. This evening the low cloud and mist will start to return inland as another band of showers starts tracking north east across the SE and the North Sea.







The murk may well hang around a bit in eastern regions as the line of showers and the odd storm cross eastern and central areas during another warm day so sporadic sunshine unless you in western areas, particularly western Scotland.







By Thursday the next phase in the evolution is underway with the cut off upper low to our south west boosting and re-orientating the surface low which will increase shower activity in general, with the odd storm, but may also negate the east coast malaise on another warm day.



On Friday the slack area of low pressure covers the UK with again a fair bit of showery activity whilst out to the west the Azores high is ridging north quite strongly between the cut off lows.





Not a lot of change on Saturday but the high pressure transition continues apace with, something I've touched on previously, a strong westerly jet in the tight thermal gradient north of the high pressure.



 
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:
Jetcrosssection.jpg


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.
 
Malcolm part 1:
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.



Today

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



 
Part 2:
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


The ecm very similar/ Thursday/Friday



 
Malcolm part 1:
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.







 
Part 2:
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.

 
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