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phil nw.

Model Output Discussion 01/09/17

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The ECM London ens shows high-pressure building in quite nicely as we move into the 2nd half of the month though with 2 major Hurricanes in the Atlantic this should be taken with caution for now

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Tonight's Ecm 12z ensemble mean indicates a marked improvement in our weather from mid month onwards, especially across the southern half of the uk with high pressure gradually building in from the Atlantic and becoming the dominant feature bringing increasingly pleasantly warmer days with sunny periods and light winds but with chilly nights under clear skies with mist / fog patches and a risk of a touch of frost.:)

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Yes it does look like an ongoing trend for the mid-month rise in pressure Frosty.It will be a welcome change from this early onset of cool and unsettled weather that we are now experiencing nationwide.

Further low pressure moving across the north will extend this chilly and showery spell until later next week.The 3 main models show a similar pattern for next Wednesday before,hopefully, pressure starts to build in slowly from the west as the Azores high ridges towards southern parts. 

This is the GFS take on things,note single figure temps.quite widely at mid-day.

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so a definite chill in the air reminding us of the changing of the seasons.

The ECM mean for day 10,does indeed look promising,especially further south.

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Hopefully we will see something of a day time warm up from that high pressure following this damp and cool few days.

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On my phone so its not so easy to post the charts but take a look at Wednesday 18z that's quite a change from the 12z run in terms of the depth of the low it's gone from a near gale in NE Scotland to barely a breeze

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Squally showers in many places today, perhaps some hail and thunder, and windy in Wales and the south west. dying out later as a brief ridge nudges in  Ergo quite chilly in places tonight before the next low pressure arrives to the NW of Ireland 977mb with associated fronts bringing more rain tomorrow followed by more showers.

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According to the gfs this morning by midday Monday the low is just NNE of Scotland with UK in a showery north westerly. Then follows some very brief ridging once again but by 12z Tuesday a disturbance has formed in the circulation of the main low away to the north west and is just west of southern Ireland tracking rapidly east. Twelve hours later this has developed into an intense little feature 989mb over Birmingham en route to the North Sea six hours later 980mb. Ergo quite a wet evening and night and possible quite windy for a time along the south coast but this very dependent on the precise track and intensity of the low.

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The low continues it's journey east and with the expected amplification of the Azores HP to the west the wind veers to a cool northerly over the UK accompanied by showers. This northerly flow will be cut off to some extent as the high pressure orientates more NE, relegating the jet northwards, and a more settled period of weather becomes established albeit with no great impact on the temps at first

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So in a nutshell a pretty unsettled cool week before settling down by the weekend.

Sidney on the lookout for chionophiles yesterday.

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The ecm is not making as much with Tuesdays low and in fact looks like it keeps it to a small wave tracking across southern England Tuesday evening thus the rain more or less confined there. The key question in the medium term remains the position and orientation of the surface high cell

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Already a strong jet streak piling out of the USA again, this high pressure isn't going to last long....soon be flattened out and windy again. No Indian summer on the way.

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18 minutes ago, mb018538 said:

Already a strong jet streak piling out of the USA again, this high pressure isn't going to last long....soon be flattened out and windy again. No Indian summer on the way.

They don't start until later this month when the northern hemisphere summer ends

Ample time for an Indian summer in October

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The EPS mean anomalies this morning are not indicating any prolonged influence from the Azores HP with the possible exception of the south

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A pretty grotty next 48 hours before some cool northerlies and then the Azores ridging north east for the weekend. Confidence not high for the end of the week as yet

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The main difference at t96 is the low near Denmark

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GFS & UKMO both have it around 980mb whilst ECM has it at 988mb but a bit further east

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A quick look at the London ens mean longer term the signals remain for high pressure to build

In the short term the 12z has slightly increased pressure on Tuesday 00z it was around 1002mb 12z it's now around 1007mb

00z

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12z

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Last night's EPS is certainly not indicating any sustained influence from the Azores HP and has it making a brief appearance next weekend before relegating it quite rapidly south west next week and then probably the proverbial N/S split.

Meanwhile back on the farm. Today starts off pretty good in eastern areas but the next low and fronts are approaching from the west and the latter will track east during the day bringing sporadic rain followed by squally showers.By 00 the low is over Scotland and it continues to move east thus tomorrow in a strong north westerly, perhaps gales in exposed areas, with again squally showers.

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So by midday Tuesday the low has drifted and filled west of Norway with some very transient ridging over the UK but the next depression has formed within the circulation of the main low east of Greenland and is tracking rapidly east and is west of Ireland by that time. But by 00 Wednesday it has deepened to 980mb and is over the Isle of Man with the associated fronts traversing the country with a band of rain. It could also be quite windy for a short period with perhaps severe gales in the west.

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From this point the low continues to track quickly east and with the Azores HP amplifying to the west the wind veers northerly over the UK with showers quite likely and rather cool. But the HP continues to reorientate and ridges more to the north east and brings some more settled weather to the UK over the weekend. But the problem is, as ever. that the centre of the high stays rooted to the south west and thus the energy generated upstream can always run around to the north and threaten the UK as it squashes the ridge .Ergo the north not quite as settled as the south and leaves open the question the sustainability  of any HP influence.

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Edited by knocker
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GEM shows thing turning drier from the weekend with temperatures gradually becoming warmer by day with some chiller nights

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I found some snow and frost in the north at the end of the Gfs 00z..hopefully a sign of things to come as we go deeper into autumn and then into winter!:D:cold:

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The Gfs 6z turns into a more settled run beyond the very unsettled autumnal week ahead with high pressure becoming much more influential, especially across southern uk where the best of the weather would be..and unlike the 00z which brought a very early taste of winter to northern uk by late september with arctic air drawn south, the 6z shows winds becoming southerly, sourced from southern europe / north africa with temps trending well above average..indeed, very warm and increasingly humid further south with a risk of thundery showers and warm air bathing the rest of the uk too.:) 

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Edited by Frosty.
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The GEFS Euro Temp.anomalies for the next 6 days show the effect of this unsettled west/North westerly pattern with the air sourced from the North Atlantic/Iceland area.

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Day 3 and 5 from the latest GFS op run showing this pattern

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The Azores high just moving in towards the weekend which looks like cutting off the cooler air as winds drop off.Daytime should feel warmer but with the payoff of colder nights,possible fog in places.

Edited by phil nw.
corrected text
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An unsettled definately autumnal week ahead for all, with conditions more akin to late October than early-mid Sept. Lots of rain and strong winds at times and feeling chilly, indeed northern parts will struggle to hit more than 15 degrees all week, some places languishing in the 11-13 degree range at times - very very poor for the time of year. Limited brightness as well will make it feel preety miserable.

Tuesday night / early Wed likely to bring the first gales of the season, with a nasty little low pressure system set to track through central Scotland, strong winds on its southern flanks, Irish Sea coastal areas look most prone, with severe gales possible at times, and lots of heavy rain as well.

Thankfully there appears to be a settling down of conditions on the cards as we approach the weekend, as the azores high looks set to ridge in and push away the chilly unsettled n atlantic air, I've my fingers crossed a warm front doesn't spoil the party here on Saturday, I really want a dry day.. for personal reasons. Some spots might see a localised grass frost as well over the weekend.

 

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Major Hurricane Irma is playing a significant role on modulating the Atlantic Jetstream; Very important player in future track of Jose. H/t MV And before anyone asks irrotational wind fields are way above my pay grade.

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Edited by knocker

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And further to a comment I made much earlier the EPS 500mb anomaly in the ext period is still indicating a fairly rapid return to a trough south of Iceland and thus a westerly upper flow and a continuation of unsettled weather, after a brief lull, and temps around average.

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Gales, possible severe for a time, in the Tuesday evening/Weds morning and maybe an air frost in rural areas on Friday :shok: before the Azores ridges in by Sunday.

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Edited by knocker

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The Gfs 12z shows an unsettled week ahead with low pressure in charge,  fresh to strong winds, especially midweek and a mix of sunshine and showers, some heavy with hail and thunder but then comes a change during next weekend as high pressure gradually builds in with drier and brighter days and feeling warmer in the sunshine and lighter winds but chilly nights with a risk of mist and fog patches forming and still a risk of a few showers with breezier conditions across the southeast for a time but generally fine for most of the uk. It then briefly becomes more changeable later the following week, especially across the north / northwest but high pressure again builds in strongly across southern uk later in low res with increasingly fine and sunny pleasantly warm days  / chilly nights under clear skies with mist / fog and perhaps a touch of frost, especially settled across england and wales.:)

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Edited by Frosty.
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