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Short range model discussion - into 2018


Paul

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Posted
  • Location: Camborne
  • Location: Camborne

As stated previously the transition to a high pressure regime in the short and medium term (and possible longer) has been pretty much nailed on for a while now. But still to be determined is the precise orientation of the high cell which will influence the regional temp and cloud distribution. There are other players in the mix that cannot be ignored such as the major trough in the north west Atlantic, with still a fair amount of energy exiting the eastern seaboard south of it, and our old friend the Iberian upper low.

Meanwhile, before the high pressure amplifies to the west and moves over the UK late Wednesday into Thursday, the weather will be strongly influenced by a front currently straddling the country, denoting the boundary between the cooler/warmer airmass, on which a wave is forming away to the south west of Ireland and is tracking north east.

to a bit more detail.

Last night really a story of two halves with north quite clear and the south more cloudy and humid with the odd patch of drizzle. This continues through today but where the cloud does thin and break it will get quite warm in the south. Further north after the clear start rain from the aforementioned wave will reach N. Ireland by midday and track east across Scotland through the rest of the day with some heavy bursts on occasion. A very noticeable temp differential either side of the front.

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As the wave moves away to the east the cold front  and rain band will track south again with the rain fizzling out along the way and the cooler air follows in it's wake but the south will again become quite warm, certainly in comparison to the north

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Edited by knocker
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Posted
  • Location: Camborne
  • Location: Camborne

I've had to split the above post as somehow I managed to post it prematurely and at some point it was going to stop me editing.

So but 00 Thursday the front is just clearing the south coast which heralds a cooler breezier day, with maybe the odd shower along eastern regions, as the high pressure ridges in from the west.

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As the high cell becomes established Friday and Saturday will be dry, and reasonable sunny, apart from perhaps the far north of Scotland where a front is lingering.

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Posted
  • Location: Camborne
  • Location: Camborne

Regarding rainfall which may become an issue over the coming weeks. The EC46 update last night gives a very negative anomaly out as far as the beginning of August albeit moving closer to average later in the period. The bottom line is not much rain in the next 6-7 weeks according to this.

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Posted
  • Location: Camborne
  • Location: Camborne

It would appear that one of the key features in promoting the surface high cell into a favourable position vis the UK occurs quite early in the piece, something that was noted in an earlier post.

At T90 the major trough in the north west Atlantic and the energy exiting the NE seaboard south of it partially disconnects the Bermuda high pressure ridging north east  As the whole caboodle moves east, putting more pressure on the ridge adjacent to the UK, it actually facilitates the reinforcement of the latter by promoting the amplification of the European high pressure east of the Iberian upper low as the main European trough is also pushed out of the way. Ergo a much better alignment of the surface. That's the theory anyway.

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And this strong thermal gradient, roughly orientated SW > NE across the Atlantic, is not unimportant as it keeps the strong high cell favorable positioned over the UK. At the moment anyway

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Posted
  • Location: Camborne
  • Location: Camborne

As can be seen not a bad day over most of the UK at the moment, albeit the temp variation either side of the front, but also as can be seen some rain into western Ireland. This courtesy of the wave which will track NE during this evening and overnight taking the band of rain with it and by dawn this will be starting to edge south as the southward journey of the cold front gets underway

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Edited by knocker
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Posted
  • Location: Camborne
  • Location: Camborne

Today completes the transition into the new regime which is very likely going to evolve into a high pressure dominated period and a very warm, quite possible hot, spell of weather next week.

Currently the wave and cold front are orientated across Scotland and northern England with the high pressure amplifying to the west. Thus the rain associated with this is effecting these areas but slowly moving south along with the front. This movement will continue through the day with the rain fizzling out before clearing into the channel by this evening,

Without wishing to labour the point it is not without interest to compare this to the environment that pertained at the beginning of the 2003 heatwave.

Quote

August 2003 opened with the British Isles within the circulation of a deep depression over Iceland, the cold front of which made slow progress south-east across England during 1 August, becoming stationary and weakening over the English Channel on the 2nd as pressure rose over England and Wales. The intensifying ridge blocked the approach of further frontal systems from the Atlantic as pressure continued to build. By 4 August the ridge lay across the North Sea, allowing a thundery trough to affect western districts on 4 and 5 August. As the ridge over the North Sea persisted and built into an anticyclone, very warm continental air was advected from the south-east into southern England and Wales from the 5th, spreading further north and west over the next two days

Thus the partly cloudy and humid conditions in the south will slowly give way to a cooler airmass but not before reaching some very respectable temperatures in the south east. Behind the front much cooler air as stated giving a very marked temp contrast and later in the day some frequent and heavy showers over Scotland courtesy of a trough embedded within the circulation.

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So overnight and through Thursday high pressure builds and moves east establishing a cooler northerly airstream over the UK resulting in sunny intervals with the odd shower around mainly in Scotland. Temps not as warm as of late but perfectly reasonable.

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Over the three days Friday > Sunday the next crucial stage of the evolution develops and it's worth a quick look at the 500mb charts for those days ti get an idea of the direction of travel

By 1800 Friday the major trough to the west is disrupting the NE ridging of the Bermuda high and putting pressure on the ridge adjacent to the UK with the upper low west of Iberia in a very strategic position.

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The pressure continues over the next 24 hours as the whole system moves east but crucially this also involves the European trough which allows the amplification of the European high pressure east of the Iberian low which helps consolidates the ridge over the UK

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By 1800 Sunday the Bermuda high is getting back in business warding off the attentions of the trough and thus consolidating further the influence of the high pressure in the eastern Atlantic with the tight thermal gradient orientated north east across the Atlantic and away to the north west of the UK.

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On the surface this results in the surface high cell drifting slowly east, and taking up a different orientation, with the UK under light winds and getting warmer as the weekend progresses.Dry in most areas but the odd spot of rain around over N, Scotland with frontal systems swinging by in close proximity.

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Edited by knocker
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Posted
  • Location: Camborne
  • Location: Camborne

The front will continue to move south and eventually clear the south coast later this evening leaving most places with a cooler and far less humid night. Apart that is in Scotland where the heavy showers, perhaps thundery, associated with the trough will continue a while and one or two may still crop up during the night. A fairly fresh northerly breeze down eastern coastal regions.

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Posted
  • Location: Camborne
  • Location: Camborne

Today heralds the start of the new regime with the UK in the eastern quadrant of the high cell to the west. Thus a much cooler night, and day to come, in the quite fresh NW/N wind which could reach near gale in the north east. But it will be dry and sunny in most places once lingering cloud has cleared the south (can be seen on the 0300 WV as also can the shallow low to the south west) with just the possibility of some showers across Scotland and the north east region. Even these will fizzle out during the evening and overnight which will again be clear and quite cool.

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The overview of the next few days is that the high cell moves slowly east over the UK whilst at the same time taking on a different orientation (explained in earlier posts so need for repetition) accompanied by a slow rise in the surface temps. This is quite well illustrated by running the 850mb temp anomaly and streamline charts through Friday > Monday.

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A bit more detail

Friday

Generally a sunny day and warming up a tad after a cool start with the winds a tad lighter.

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Saturday > Monday

Sunny and warm in most areas the only exception being Scotland, particularly on Saturday, where it will be cloudy with patchy rain and quite windy as fronts slip past north of the high cell.

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For what it's worth my observation of the morning is that although the very warm, hot, period next week is a slam dunk, the trough in the north west Atlantic and the continuation of energy exiting the eastern seaboard south of it still has an important role to play in the orientation of the high cell effecting the UK. Along with the ubiquitous Iberia upper low of course.

 

Edited by knocker
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Posted
  • Location: Camborne
  • Location: Camborne

Completely irrelevant to the forthcoming evolution but a very nifty example this morning of displacing the high cell and introducing an easterly wind component that advects much cooler air a long way inland and to quite high levels in the lower atmosphere under a very warm airmass

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