UK meteorology

There appears to be a rather complex set-up at present with two different possible evolutions beyond the middle of next week. After the Bank Holiday weekend (see video in previous post) it seems likely that the first half of next week will see high pressure in the northern North Sea moving west (retrogressing), such that, by the second half of next week, the high will be centred around Greenland. As this retrogression occurrs, a north-easterly is expected, which would bring cooler air but stronger sun, so actual temperatures at ground level would be variable for the southern half of the UK, with the warmest conditions in the far south-east. Further north and west, conditions may be more consistently warm but possibly cloudier. Where the doubt emerges is in the evolution next weekend - if the ridge associated with the retrogressed anticyclone (High) lies on a north-west to south-east axis, winds in the south east will be more easterly, bringing warmth (possibly high teens); if, however, the ridge is oriented north to south, it will lie to the west of the UK, leaving areas away from the far west in a cold and potentially pretty unsettled northerly flow.

EDIT: Further to the above, here is the view of an experienced Netweather member who posts model-based overviews (emphasis in bold is mine):
Morning all
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Didn't expect to have to scrape ice off the car this morning but this final hurrah of winter is now at hand and on its own way out to be replaced by, well, a confused weekend. Perhaps best in the north and east but the details still to be worked out.

Yesterday, the models were strongly in favour of a build of pressure to the NE gradually transferring to the NW over time but there were many permutations and much to resolve.

This morning's output takes us to the early hours of Sunday May 7th:

Starting with the GEM 00Z at T+240:



Quite a simple story this morning. After a brief unsettled hiatus through the early part of the coming weekend, pressure builds strongly from north and south on Tuesday and the northern HP becomes the dominant feature first to the NE of the British Isles and then retrogressing to be centred over Greenland but with a ridge SE back to the British Isles. The air flow over the British isles is sourced from a long way north so this would be a cooler NE'ly but the weather would be fine for most and the further west the better in terms of sunshine.

ECM 00Z at the same time:



Some subtle differences to GEM - note the orientiation of the Atlantic trough - but the net effect is much the same. The HP starts in the northern North Sea but retrogresses to Greenland with the ridge more ESWE and that means a more defined NE'ly for much of the British Isles sourced from some cold air over Scandinavia and NW Russia. Dry weather dominates the British Isles with the best of the weather in the west and north west.

GFS 00Z OP at T+240:



Subtle differences again starting with the Atlantic trough which is further south and with a different orientation to the GEM and ECM. The HP evolution is broadly similar though GFS creates a small LP to the far north which runs east into northern Scandinavia before sinking south. This cuts off the relatively warm E'ly and introduces a weak NE'ly flow but pressure falls across the south of Britain as LP moves NE from Biscay so by T+240 the south would be unsettled with rain or showers at times while the far north and north west holds on to drier conditions.

Little changes further into FI with pressure always high to the north and low to the south and the wind flow oscillating between a warm SE'ly and a cooler NE'ly. The south would be vulnerbakle to showers or longer spells of rain while Scotland stays largely dry.

The Control brings the trough up into the British Isles in furthest FI.

The 00Z GEFS at T+240 show strong agreement for the overall evolution and for strong HLB to the north and north west. The position and orientation of the trough has a number of variants but the majority produce a NE'ly flow of some degree.

In summary, while the details of the weekend may still need finalising, the trend to build strong heights to the NE early next week is confirmed this morning. All models take these heights toward Greenland though with varying orientation of the ridge. Some bring the ridge back SE over the British Isles keeping us broadly dry and fine while others keep the ridge further north allowing pressure to fall to the south and less settled conditions to encroach from the south and south west.

The net effect is, after a brief warmer E'ly interlude to swing winds to a cooler NE'ly direction.
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Count of Undolpho said:
Enough coal/need more coal dilemma still on then? Poop!
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Possibly, I'm afraid. I did find the analysis in the threads rather confusing, in all honesty, as posters seemed to be contradicting themselves and each other. I think the set-up is fairly certain out to the middle of next week, though; it's thereafter that the uncertainty really takes effect.
 
To clarify, the question for later in the period is outlined in the post I quoted - when that member discusses the GFS output, he mentions that it would allow low pressure to our south-west to drift north-east 'under' (to the south of) the retrogressing high, which would allow it (the low) to link-up with a longwave trough over Scandinavia and the Baltic states.
 
Quick model discussion for the next couple of weeks, with the caveat that I'm basing this on a review post from Netweather rather than several pages of model discussion due to time factors.

As high pressure over Scandinavia retrogresses (moves east-west against the prevailing flow), the current unsettled south-easterly flow seems likely to be replaced by a chilly, cloudy but mainly dry north-easterly from the weekend onwards. In these sort of set-ups, the warmest and brightest weather is usually in the west, often with low cloud and occasional drizzle on and just inland from the North Sea coast. As the breeze sets in, one model (the GEM) suggests that there may be a gradual but short-lived encroachment of low pressure from the Baltic, possibly bringing something more unsettled, before the high drifts across southern Greenland and into the western Atlantic; most unusual and an indicator (without me even having to check data or do further reading) of how quiet the jet is at present. From the middle of next week, the drift of the high may open the door for low pressure to movee in from the south-west as the weak jet shifts to our south, bringing possibly quite autumnal weather for mid-month, with the indication at the end of the model runs, that high pressure over the far south-west of Europe (to the east of the famed Azores High which will actually be replaced by low pressure over the Azores archipelago) may eventuallly ridge over the southern UK into the second half of the month, but this is a very weak indication due to the timeframe being so far off as I type.

Not all the main models agree with this synopsis, however; ECM places us on the western fringes of general European low pressure, with an unstable flow bringing hefty showers by day and clear, chilly nights arounf the middle of next week, whereas GFS shows the fringe of the Euro low to our north-west, with a shallow area of high pressure over the Low Countries, which would infer warmer, more settled conditions in the south east and cooler weather with showers further north and west.
 
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Brief model conclusion from Netweather member regarding this morning's computer runs is that the anticyclone currently to our north will indeed retrogress (head westward), allowing a brief spell of unsettled weather at the weekend as low pressure from the Azores (which has displaced the normal Azores high) swings in from the south-west. It appears that this will weaken rapidly as a longwave ridge develops, bringing high presure from the north-west, hoewever, this seems likely to be short-lived as well. Beyond there, the models diverge:

Scenario 1 sees a low pressure cell heading south from Iceland, which joins the low pressure currently around the Azores to generate a meridional pattern of a mid-Atlantic ridge and western Atlantic trough, under whose influence the UK would find itself later next week; however, in this scenario, the lows retrogress, shifting the longwave trough into a mid-Atlantic position and allow much of the UK (in particular the south and east) to come under the influence of high pressure associated with a longwave ridge over southern and central/eastern Europe.

Scenario 2 sees the Azores low extending north-east across rance, merging with the remnants of the vortex over Scandinavia and the low moving south from Iceland to form a large, broad-wavelength trough over much of Europe by the second half of next week. GFS in particular emphasises this evolution and. due to rthe persistent merged lows converging on western Europe, when the Azores High des re-establish itself, it is only able to ridge due notrth into the Antlantic, as opposed to north-east through western Europe as it normally would. This suggests, contrary to the ouput described in scenario 1, that southern areas of the UK would stay in an unsettled Atlantic-derived airstream through to mid-month.
 
Well variable describes this weekend.
Dull and cold in Wharfedale Saturday morning, dull and cold in the Lune Valley on Saturday afternoon down jacket and earflaps down.
Blazing hot sunbathing weather Sunday morning in the Lune Valley, dull and cold in Wharfedale in the afternoon.
 
Count of Undolpho said:
Well variable describes this weekend.
Dull and cold in Wharfedale Saturday morning, dull and cold in the Lune Valley on Saturday afternoon down jacket and earflaps down.
Blazing hot sunbathing weather Sunday morning in the Lune Valley, dull and cold in Wharfedale in the afternoon.
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It's been unrelentingly cold, dull and windy down here for days now. Apologies for the lack of updates - anxiety has hit me again.
 
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