Model Discussion - 27th July

[Gibby]

Good morning team. A new week so what can we expect from the models this week.

GFS this morning shows the whole of this week and into the weekend as unsettled as a thundery Low moves North innitially to become encompassed in the general Low pressure complex which staggeres across the UK later in the week from off the Atlantic and away NE later next weekend. High pressure then moves into the UK from the SW by next Monday. The resultant weather would see a week of rain or showers at times, heavy and thundery innitially in the south and east tomorrow. Later in the weekend a NW flow brings cool and fresh air across Britain with rising pressure and dry conditions to all by Bank Holiday Monday. FI this morning shows high pressure throughout with its centre over or to the north of the UK with fine and warm weather in a continental East or SE flow.

UKMO too shows an unsettled pattern much as above with a High pressure centre west of the UK poised to settle the weather down over the UK on Bank Holiday Monday.

The Fax Charts follow the raw UKMO output in as far as they go out until Friday also confirming an unsettled week.

ECM completes the trio in showing an unsettled week with complex Low pressure through the week with a strong build of pressure over the Bank Holiday weekend drying things out and warming things up. As we move further into next week the High pressure cell over the UK weakens as Low pressure slowly erodes it from the west by the end of the run.

In Summary I think we can confidently say that unless things go belly up somewhen through the week the pattern looks more set this morning. So, in essence a fairly unsettled 5 or 6 days likely ahead with thundery rain entering the south and east tonight while Atlantic Low pressure moves in from the west later in the week keeping further rain and showers going. Over the weekend High pressure develops and moves over the UK promising a fine and warm Bank Holiday Monday. GFS goes on to show the best spell since April with persistant high pressure near by while ECM is less keen and collapses it somewhat by midweek next week as Low pressure inches in from the west.

[shedhead]

'better' in what way?... i think location plays a role too... its not been too bad here, i wouldnt want to see a high pressure dominated september, i need rain! plants are really suffering here, leaves are turning early, and as far as im concerned summer is over.

Whilst days are shorter and the sun lower/weaker, we can still have plenty of 'summery' weather in Sept (esp 1st half) and the way the models are now shaping up I think this will again be the case this year. Those who like dry, warm and sunny weather can look forward with far more optimism than for some considerable time in my opinion.

[Nick F]

Well, most models this morning seem to indicate that Bank Holiday Monday will be dry for most (though this may change), as the current trough lurking on our western doorstep eventually moves away NE allowing high pressure to build from the W and SW. But not before an unsettled spell of weather this week with showers or longer spells of rain affect many of us right up to next Monday.

The upper flow looks like remaining quite amplified into the medium to longer range, so I suspect that we may have a few days or more of high pressure beyond this unsettled spell this week followed by another trough moving in from the west as the ridge drifts east later on.

[Thundery wintry showers]

Looking at the GFS FI I'm not convinced that it would be particularly warm for the time of year (highs of 17-21C are suggested when allowing for the traditional underestimation of maximum temperatures, which is about average for early September). The reason for this is that the high is preceded by a polar maritime incursion and no particularly warm air gets caught into its circulation, unlike the aforementioned April 2011 spell when we picked up southerlies originating from a long way south. However, it does look like it would be quite a "sunny" high, due to its arrival being preceded by clear polar air rather than moist tropical maritime air.

Like Nick F I expect the ECMWF to be nearer the mark, with a few days or so of dry, sunny weather with near average temperatures by day and probably one or two chilly nights, followed by the arrival of the nexxt Atlantic lows.

Before that, the fronts moving in from the west look like making slow progress during the next three days, so rather wet and cloudy midweek, but the models continue to suggest a bright, showery and thundery day for many on Friday. Over the weekend there will be some areas of frontal rain about on Saturday meaning showery for some and longer outbreaks of rain for others (most likely in the east of the country) and then Sunday/Monday look like being cool and bright with declining shower activity, the majority of the showers located in eastern areas with high pressure increasingly keeping the south-west dry.

[Gordon]

I see the Met office have redefined their warnings and it's mainly the SE quadrant of the country which is now due any rain of note so I may not see much rain at all as my location is the West midlands is no longer covered by warnings

oh well my Grass will have to be brown just a little while longer

[shedhead]

GFS maintains the theme of a marked rise of pressure as we move into early Sept, so confidence slowly but surely increasing on some long awaited dry, sunny and eventually warm weather.

[Thundery wintry showers]

The confidence is certainly growing on a build of pressure but I retain reservations about duration considering that the prolonged-looking high pressure spell remains out in FI. The scenario of high pressure holding station to the north feeding in an east to north-easterly flow has recurred on two successive GFS operational runs so can't be ruled out. The most likely result of this would be a September 1996-esque west-east split with dry, sunny and increasingly warm weather in the west, but temperatures staying close to normal in the east with increasing chance of low cloud heading in off the North Sea.

The most likely route to a warm dry sunny outlook would be if the high stuck around for a while just to our east allowing warm southerlies in while holding the Atlantic at bay, in a stagnant amplified jet scenario, but my feeling is still towards warmer and more unsettled conditions taking over into the first week of September as the high pulls out eastwards allowing a cyclonic/southerly type in. Meanwhile Friday continues to look interesting for the convection/storm lovers to the south of the Scottish border.

[The PIT]

Agree High Pressure is well out in FI land so a bit early to get excited about it. In reliable time frame it looks like a unsettled spell coming up. There is a possible period of real autumn weather coming looking at the ECM although shown less on the GFS

[Gibby]

Good evening.

GFS tonight shows the pattern as before with Low pressure in charge near to the UK bringing rain and showers across all areas from time to time. This pattern lasts until Saturday when the NW airflow brings a cool showery day on Saturday before dry weather extends NE over the UK through Sunday and Monday. After the Bank Holiday and through FI High pressure dominates the UK gradually migrating NE into Northern Europe but always maintaining a ridge SW from the centre over the UK. The result of this pressure pattern would mean fine and warm weather across the UK with warm sunny days and overnight fog patches where winds fall light.

UKMO is in unison with GFS tonight with an unsettled 4 or 5 days with a large high pressure area moving slowly into Western Britain by Sunday.

ECM is much the same though it may be a day slower bringing high pressure into the UK Bank Holiday Monday.

A change in the weather pattern looks distinctly possible through the coming weekend. High pressure looks like developing strongly and could hang on for a while with the resultant weather becoming warm and settled for most. Even ECM has given a 240hr chart to die for with fine warm weather for all with pressure having finally fallen over Greenland.

[Summer Sun]

Yes a very nice set of charts yet, summer 2011 could yet be resuced by September, Summer is NOT over yet fingers crossed.

[Optimus Prime]

Well in recent years September has been the month which has usually started fine and warm but become noticeably cooler as the month progresses, to be expected really. As pressure is regulated by the changing seasons, some very warm conditions can be had during this seasonal shift.

[Summer Sun]

Well in recent years September has been the month which has usually started fine and warm but become noticeably cooler as the month progresses, to be expected really. As pressure is regulated by the changing seasons, some very warm conditions can be had during this seasonal shift.

Yep, i'd expect the cooler conditions to be felt widly be October, unless something strange happened and we got some unseasonal weather like we did at easter, however i can't see that happening again this year.

[Milhouse]

Once again its the end of August and we are being greeted with HP almost slap bang over the UK. Why does it wait all summer to visit our shores but eventually turns up when things start to cool down. The ECM chart at 240h has upper temperatures of under 5c so i doubt it would be that warm given the air looks to be being sourced from the north but had it occured in mid July we would be looking at widespread low to mid 20s. However we really need the high to hang around for a long time in September to give it chance to pull up some warmer air off the Atlantic or off the continent.

edit: The ECM ensemble mean has uppers of above 5c across the whole of the UK at 240h so i'd say were odds on for a long awaited settled spell and given we will be just at the turn of the month it should still be warm.

[johnholmes]

Its an odd situation! Why?

Well both GFS and ECMWF are fairly set on giving an upper ridge and surface high for the month end, suggesting it might be around for several days.

Its odd because none of the 3 500mb anomaly charts really suggests that upper pattern. The NOAA one has been more consistent with its variation with ECMWF and GFS less so. Its not an infallible guide for sure but its a bit unusual to see the synoptic charts so set on one idea and the anomaly charts suggesting a bit different. It will be interesting to see how the month does end. The anomaly charts would certainly fit with a temporary upper ridge and surface high, maximum of 2 days, but not any longer.

[damianslaw]

Once again its the end of August and we are being greeted with HP almost slap bang over the UK. Why does it wait all summer to visit our shores but eventually turns up when things start to cool down. The ECM chart at 240h has upper temperatures of under 5c so i doubt it would be that warm given the air looks to be being sourced from the north but had it occured in mid July we would be looking at widespread low to mid 20s. However we really need the high to hang around for a long time in September to give it chance to pull up some warmer air off the Atlantic or off the continent.

edit: The ECM ensemble mean has uppers of above 5c across the whole of the UK at 240h so i'd say were odds on for a long awaited settled spell and given we will be just at the turn of the month it should still be warm.

Yes as so often seems to happen as we enter september the weather decides to settle down - too late in my book. Whilst we can still easily achieve mid 20 maxima in early sept, the diminishing light and lowering strength of the sun combined with cooler nights hardly makes for a high summer feel.

It reminds me of those cold northerlies that often occur in late feb/early march when we often get superb winter synoptics but it is a bit too late to feel the full affects of winter..

Back to the charts - reliable timeframe unsettled for all with a slow moving low pressure system gradually moving NE and weakening in situ. Some heavy rain in the SE tomorrow and then for the west on Wed and Thurs followed by a cool showery airstream Friday and Saturday.

Beyond the reliable timeframe all models in agreement of a pattern change as we see heights build strongly from the west ridging across the country and eventually moving east giving rise to the chance of some warm continental air at long last. All along way off, but those thinking this could be the start of a long protracted settled spell as we enter Sept be warned, the atlantic has some real vigour in it at the moment and I can see low heights to the SW quickly crashing into any ridge and spoiling the party..

[Geordiesnow]

Yes a very nice set of charts yet, summer 2011 could yet be resuced by September, Summer is NOT over yet fingers crossed.

Yep a very nice set of charts for the ducks but nothing summery in the charts in the reliable timeframe unfortunately. The low for this week has become more flabby and I got a feeling that it could be a cloudier week than perhaps first thought with showers or longer spells of rain with the risk of thunder. In any sunshine, the temps could reach 20C as the air is not that cool but for most of the time, temps will be struggling in the mid-high teens.

The models agree on the low to intensify and move NE'wards which in turns brings cooler NW'lies into our shores. The GFS has the hpa temp reaching 0C in Scotland so that is certainly a sign we are heading into Autumn and it will feel cool even in the sunshine.

[mushymanrob]

Whilst days are shorter and the sun lower/weaker, we can still have plenty of 'summery' weather in Sept (esp 1st half) and the way the models are now shaping up I think this will again be the case this year. Those who like dry, warm and sunny weather can look forward with far more optimism than for some considerable time in my opinion.

...of course we can have nice warm sunny weather in september, but its autumn, not summer. tws is right to have doubts over the possible high next week, it wont be 'hot' and under pm air itll be chilly at night with that familiar autumnal misty tang to the air in the mornings. its a great pity however that the best and longest spell of high pressure might be coming too late! if it had occured at anytime over the last 4 months it would have resulted in the best countrywide sunny/hot spell for 5 years... at least in deep fi both the gfs and ecm expect it to drift eastwards allowing a breakdown from the south prior to the atlantic pushing in, this IF it happens just might give us a last chance of a thunderstorm.

ps... forget dry weather, i want, i NEED rain, even todays looks like missing me... im losing money now...

Edited August 23, 2011 by mushymanrob

[Gibby]

Good morning. After last night's damp squib how are the charts looking in predicting the next two weeks weather.

GFS this morning shows an unsettled remainder of the week with todays remaining rain in Central and Eastern England moving off later before new Low pressure moves in from the west tomorrow. This hangs around for the rest of the week and start of the weekend before a ridge of high pressure system settles things down over the second half of the Bank Holiday Weekend. Thereafter and into FI weak High pressure over the UK gradually gives way to a more unsettled theme yet again as the Atlantic train picks up momentum with wind and rain for all at times in brisk west winds.

UKMO also shows a period of unsettled conditions until Saturday/Sunday with Low pressure moving in from the West then away NE at the weekend. A NW flow sets up then with the rain and showers through the week and start of the weekend being replaced with drier though none too warm weather for Sunday and Monday as High pressure then lies close to Ireland.

The Fax Charts follow the raw output fairly closely again today with waving fronts crossing slowly east through the rest of the week bringing occasional potentially thundery rain with heavy showers inbetween. It also shows Low pressure moving away over the weekend with an occlusion moving SE Saturday clearing Low pressure away behind in a fresh NW flow.

ECM shows the same sequence of events showing High pressure close by from Sunday. The high itself is shown to be fairly weak at just 1020mbs or thereabouts but seems quite steady, centred over the UK early next week before pulling away North by 240hrs at the same time as maintaining a ridge south over the UK. The weather after this weeks rain and showers would become set fair with sunny spells and moderately warm conditions by day though with light winds the nights could be chilly with fog becoming quite widespread in the early hours of each day.

In Summary not much change in the models this morning apart from GFS in FI. In the shorter term High pressure is shown to develop on all models close to the UK at the weekend though its longevity looks a little more tenuous this morning. However as shown there would be a spell of quiet settled weather with daytime temperatures near or a little above normal by day but with the chance of overnight fog patches in cool conditions. It then falls apart from GFS with wind and Atlantic rain returning as per GFS and as far as ECM is concerned pressure also begins to fall by 240hrs.

[shedhead]

Nothing within the overnight outputs to suggest HP will not become the dominate feature by early next week. It's initial positioning to the west will mean temps will be near or even a little below average at first, but I think it will become warmer as the week unfolds and it should certainly feel very pleasant, even summery, in the sunshine and light winds. Despite the fact Summer 2011 has been poor overall here, it's going to feel a long one if we get a good Sept, having had some cracking conditions 5-6 months ago.

[Weather Boy]

ECM and GFS singing from the same hymn sheet with some very unsettled weather, initially in the south, then transferring further north (although far from dry further south) with -it looks like- Saturday being the changeover day (at least in the south, the bad weather hanging on for 12-24 hours longer in Scotland) between the very disturbed weather and the settled weather which appears to take hold as far as the eye can see, discarding GFS extreme FI.

UKMO, to my eye, has the Low pulling away NE slightly later which, if correct would probably make Saturday a more disappointing day than the other two models.

I do however note two things. Firstly, despite its resiliance, the High seems to lack intensity being progged at only c. 1020. Do any of the more experienced members think that this could be an issue? I wouldn't have thought that it would permit any shower activity except perhaps one or two on its northern flank - what do people think?

Secondly, there is an unusual feature of a small Azores low in both GFS and ECM which both models treat as irrelevant to the UK, as it just stays there. Could that come into play on later runs?

[Nick F]

The ridge arriving from the W/SW by Bank Holiday Monday should hang around for a few days of more next week, though its duration seems a little uncertain and perhaps tenuous given the falling heights from the SW shown on the ECM/GFS 8-10 day H500 comparison this morning:

All depends, I think, on how quickly the trough over the Atlantic advances eastwards towards the UK, if it slows/stalls like 00z ECM, then a cut-off low may form to the SW with the ridge holding across the UK.

[shedhead]

The ridge arriving from the W/SW by Bank Holiday Monday should hang around for a few days of more next week, though its duration seems a little uncertain and perhaps tenuous given the falling heights from the SW shown on the ECM/GFS 8-10 day H500 comparison this morning:

All depends, I think, on how quickly the trough over the Atlantic advances eastwards towards the UK, if it slows/stalls like 00z ECM, then a cut-off low may form to the SW with the ridge holding across the UK.

That looks the most likely evolution to me at this stage. I'm not buying into an immanent Atlantic return, in fact I think it could well be mid month before that happens, at least to any great degree.

Edit: 06GFS very much fits with my thought pattern post this weekend.

Edited August 23, 2011 by shedhead

[Isolated Frost]

06Z GFS brings back a more NW'ly tone with the high further east into the Atlantic next weekend.

[Summer Sun]

Looks increasing likely that the end of August and early September will be dominated by high pressure, becoming warm to very warm at times in the south, as September progress though things will most likely change to more unsettled conditions if you believe the Met Office.

[Frosty.]

At last there is a chink of light at the end of the tunnel with an atlantic anticyclone probably migrating east across the uk during next week but scotland may again miss out on the most settled weather with some unsettled days but further south is looking dry next week but not particularly warm according to the 850's shown on the Ecm 00z but at least the 500mb anomoly charts are changing in favour of an anticyclonic spell with lows tracking further north. This weekend looks cooler and windy or possibly very windy across northern and eastern scotland with showers and longer spells of rain but drier and brighter further south and then as the low tracks away northeastwards into scandinavia, high pressure should ridge in from the west but with the best weather once again across the southern half of the uk according to the Gfs 06z op run. The further outlook is uncertain but the meto seem to think the uk will descend into a more mobile zonal pattern with an increasingly active atlantic sending low after low across the uk as we go into mid september but once again, as has been the case all summer, the warmest, brightest and driest weather will continue to affect southeastern england at times,