Model Output Discussion

[Summer Sun]

This coming weekend especially : 12z models seem to me to suggest something of an W / E divide, or more to the point a SW / NE divide, largely. For Saturday in particular.

I know temperatures (at this stage) don't look very likely to be warm for most places til after the coming weekend, but in the W / SW at least, there seem to be a much higher chance of drier conditions this w/e as the HP just starts to influence those regions by Sat and Sun.

Also, in the coming days' putput and still talking about the forthcoming w/e, we stil have time for small yet possibly? significant tweaks in synoptic positioning -- changes to the exact timing of when the Low starts to move away significantly, could alter conditions on the ground a fair bit, in some places.

Just seen this one, surely you mean as JULY comes to an end

Don't give more ammunition to the August/summer writers-offers than they'll find for themselves

Sorry about that typo error, i was thinking of what August maybe like and typed it instead of July

[ANYWEATHER]

GFS or Giving False Summer, is at it again in FI,

http://www.wetterzen...s/Rtavn2161.png

http://www.wetterzen...s/Rtavn2401.png

Before pressure slowly fall as July comes to a close

http://www.wetterzen...s/Rtavn2881.png

Ahh , Gavin, glad to see you are now viewing the model output with some caution, and not at face value!!

[johnholmes]

I honestly don't know if there is an error with the chart, or I am just interpreting the information very wrongly. Would really like John Holmes to shed some light on this, as I believe he is the best guy on the forums to deal with this matter.

there is no error but how to explain it simply or indeed at all, regarding heights/temperatures over a land mass of several thousand feet is beyond my brain cells at the moment. But I will try and answer the question as well as I can EVENTUALLY!

[Thundery wintry showers]

The GFS suggests a mostly dry sunny weekend albeit rather chilly, with high pressure ridging into the south-west and with a north-westerly flow there shouldn't be too much cloud off the North Sea in eastern areas:

However, UKMO at T+144 keeps the low stubbornly out in the North Sea with a pronounced northerly- probably cooler and cloudier generally:

I think this weekend is still quite hard to call at the moment.

[Summer Sun]

ECM has the low sitting out in the north sea which could bring rain to eastern areas with pressure ever so slowly rising from the south west, as TWS has said this weekend is far from certain. That low could have a big say if it stay's closer then there would be plenty of rain around.

http://www.wetterzentrale.de/pics/Recm1201.gif

Edited July 18, 2011 by Gavin D

[Thundery wintry showers]

Yes, good point Gavin, some earlier runs did have that low funnelling a belt of rain southwards across a large area of the country, so "cool and cloudy" could potentially end up being an understatement if the low ends up far west enough. I have a feeling that the UKMO/ECM are over-egging the low, but on the other hand GFS vs UKMO/ECM clashes have a strong track record of going the way of UKMO/ECM.

[J10]

This coming weekend especially : 12z models seem to me to suggest something of an W / E divide, or more to the point a SW / NE divide, largely. For Saturday in particular.

I know temperatures (at this stage) don't look very likely to be warm for most places til after the coming weekend, but in the W / SW at least, there seem to be a much higher chance of drier conditions this w/e as the HP just starts to influence those regions by Sat and Sun.

Also, in the coming days' putput and still talking about the forthcoming w/e, we stil have time for small yet possibly? significant tweaks in synoptic positioning -- changes to the exact timing of when the Low starts to move away significantly, could alter conditions on the ground a fair bit, in some places.

Just seen this one, surely you mean as JULY comes to an end

Don't give more ammunition to the August/summer writers-offers than they'll find for themselves

Definitely looks a SW/NE divide, probably giving at least decent conditions here, you could say the best of a bad lot, however no sign of really good weather to be honest.

[William of Walworth]

GFS swinging into line with the way ECM and UKMO tend to view things -- there's a pretty long track record of that happening and it therefore makes caution essential.

However as you and others have also said, exact positioning is both of major importance and very tough to predict at this stage. I have a hunch, call it stubborn optimism, that they might be overdoing that low and its closeness this time - there's certainly been occasions, even in pretty unsettled summers, when the vigour of predicted lows ends up being downgraded nearer the time, and plenty of history of repositioning too.

In short, and as ever, we don't even know on Monday evening what'll happen come Saturday, but to me West and SW still look best/least exposed. Even in the more Low influenced output.

Definitely looks a SW/NE divide, probably giving at least decent conditions here, you could say the best of a bad lot, however no sign of really good weather to be honest.

We'll be in Devon not Wales come the w/e, for reasons you can guess! but that's how I'm seeing it, definitely, and both areas seem more likely than not to do better in escaping unsummeriness than in the East.

ETA : And yes, you're right, no great shakes for actual wam summer weather by the w/e, even in the West, but I'll take the West over the East coast any time as things currently stand, For us dryness in summer can be more important than warmth .

Edited July 18, 2011 by William of Walworth

[Summer Sun]

ECM at 144h at 500hp ain't work so skipping to 168h thing's do slowly improve as the pressure rise continues,

http://www.wetterzen...cs/Recm1681.gif

http://www.wetterzentrale.de/pics/Recm1442.gif

144h at 850ph appears to have the low sinking south wards this is shown better above, it could affect the far south and east if it stayed close enough.

By 192h the pressure is shown to really rise with 1020 over all the uk and 1025 just clipping the west

http://www.wetterzen...cs/Recm1921.gif

216h has the pressure even higher 1030 over Scotland with 1035 also developing but most likely staying away.

http://www.wetterzen...cs/Recm2161.gif

So a pressure rise is been agreed by GFS and ECM slightly different set-up's but there could be a warmer spell next week and if GFS is to be believed this only looks brief as pressure looses its grip by late July.

Edited July 18, 2011 by Gavin D

[William of Walworth]

Am I just a hopeless optimist in being somewhat suspicious that a pressure rise that strong IF it verifies in FI and IF it comes as near to the UK as that in FI, can be pushed away so easily?

[knocker]

there is no error but how to explain it simply or indeed at all, regarding heights/temperatures over a land mass of several thousand feet is beyond my brain cells at the moment. But I will try and answer the question as well as I can EVENTUALLY!

And mine John but a touch of simplistic thinking. The RUC sea-level pressure model works something like this.

The 700 mb temperature, not station temperatures, are used to estimate an "effective" surface temperature. The model extrapolates this 700 mb temperature to the station elevation using the standard atmospheric lapse rate. Although it seems crude, studies have shown that it preserves geostrophic continuity better than other methods. However this may cause problems:

1. The forecast sea-level pressure will not respond to diurnal variations as strongly as expected.

2 Unusual lapse rates (such as inversions, very cold air masses, and very unstable environments) may cause unrepresentative sea level pressure patterns.

So I'm wondering whether the extrapolation method of a known temperature is used with the GFS? The usual caveats regarding accuracy will apply.

Edited July 18, 2011 by weather ship

[January Snowstorm]

Things are looking a bit brighter thie evening, pardon the pun.

A decent last week of July is now within our grasp.

Will it upgrade into a Summer heatwave or dwindle away to nothing.

The form horse is the latter, but have no mistake the ECM is only a nudge away from Nationwide sunshine and 30C!!

[Summer Sun]

So ECM has delivered a set for very warm and sunny charts from 144h and beyond, can we believe this and think ECM is onto something or is it just teasing us? Hopefully it's onto something for next week onwards, fingers crossed.

[Gibby]

GFS tonight shows Low pressure very slowly moving away east and filling over the next three or four days with the current showery setup becoming more confined to eastern areas late in the week and over the weekend. A ridge of high pressure approaches the west over the weekend meaning dry and brighter conditions but still relatively cool weather. Early next week weak disturbances move down over the UK in a NW flow before pressure builds more strongly in the lower resolution part of the run showing warmer and drier weather for all with variable cloud cover and lighter winds than of late.

UKMO follows a similar trend as Low pressure exits east taking many of its showers and rain with it by the end of the week. However a retrogressing Low moves SW into the southern North Sea by Sunday strengthening the Northerly flow over the UK again and heightening the risk of showers or rain, especially near the east coast.

ECM follows the UKMO route in bringing a retrogressing Low into the Southern North Sea by Sunday then in the following days sinking it South over Europe while pressure builds northeastwards across the NW by Monday. Then in the last few days of the run High pressure moves Northeast towards NW Britain with a light NE flow over England and Wales. After a showery week and weekend in the east the weather would steadily settle down next week with some warm sunny spells and dry weather for all. temperatures would recover to normal or above with perhaps some very warm conditions towards the southwest with time.

Tonight its ECM's turn to do a flip with a large Atlantic Anticyclone settling the weather down and warming things up over the UK next week. GFS suggested this evolution 24hrs ago and flipped back this morning so cautious optimism should be where we are at tonight. Tonights GFS shows a half-way house with high pressure staying to the SW while being close enough to give some pleasant weather in the south at least at times, more so in FI. We now need this trend to be maintained in the upcoming runs and spread to cross model agreement before we should get to excited. Nevertheless, its definately a step in the right direction tonight.

[johnholmes]

And mine John but a touch of simplistic thinking. The RUC sea-level pressure model works something like this.

The 700 mb temperature, not station temperatures, are used to estimate an "effective" surface temperature. The model extrapolates this 700 mb temperature to the station elevation using the standard atmospheric lapse rate. Although it seems crude, studies have shown that it preserves geostrophic continuity better than other methods. However this may cause problems:

1. The forecast sea-level pressure will not respond to diurnal variations as strongly as expected.

2 Unusual lapse rates (such as inversions, very cold air masses, and very unstable environments) may cause unrepresentative sea level pressure patterns.

So I'm wondering whether the extrapolation method of a known temperature is used with the GFS? The usual caveats regarding accuracy will apply.

yes something along the lines you show Fred but I still cannot see how to explain the 850 mb chart for areas like Greenland, height or temperature wise.

I suspect I'm going to have to eat humble pie and send NOAA an e mail!

[Jason T]

fingers crossed time i guess, Praying that the ecm run is on to something and we head into the reliable. This will be a welcome for all.

[ANYWEATHER]

This is one reason not to put much faith in any model right out to T240 or in fact less time than this....One 00zECM lousy for Summer lovers and one 12zECM Great for Summer lovers.. :lol: :lol: :lol: :lol: :lol:

[Kentish Kiwi]

This is one reason not to put much faith in any model right out to T240 or in fact less time than this....One 00zECM lousy for Summer lovers and one 12zECM Great for Summer lovers.. :lol: :lol: :lol: :lol: :lol:

Yes, a huge difference in the +240h charts on the two ECM runs. Just goes to show how uncertain things are even in such 'medium' time frames. However I would say that the 12z run seems to show more support for what yesterdays ECM runs were developing into. Would be interesting to see which of the runs those 500hpa mean charts JH etc. have been posting show support for...

[Costa Del Fal]

The ECM 00z mean supported a more high pressure outlook than a low pressure one in which the 00z operational was fairly unsettled however it would seem this is not the general trend of the ECM lately with more settled weather still the main idea. The 00z cannot be dismissed however because its quite possible given what weve seen recently!

[Jason T]

Best time for a new thread me thinks..as we are in the will it or wont it scenario any offers.

[Uncle_Barty]

Worth noting that in the past week, the MJO has moved quickly through phase 1, then phase 2 - the latter in 3 days flat to the 16th and looks to be about to move into Phase 3.

Composites for July suggest a height anomaly centred west of Ireland but also exttending over the UK into the near Continent. For August the suggestion is for the height anomaly centred north of Scotland.

[Kentish Kiwi]

Worth noting that in the past week, the MJO has moved quickly through phase 1, then phase 2 - the latter in 3 days flat to the 16th and looks to be about to move into Phase 3.

Composites for July suggest a height anomaly centred west of Ireland but also exttending over the UK into the near Continent. For August the suggestion is for the height anomaly centred north of Scotland.

That would seem to fit nicely with the ECM's idea then and possibly provides the 12z with more impetus...

[Costa Del Fal]

On the NOAA site there seems to be fairly good agreement of the NAO to finally go positive to between 0 and 1 which whilst isnt much, it could be the first time it goes positive since late May/very early June. The AO looks like trending towards neutral.

Not massive but hopefully some sign of something a little more settled becoming possible.

[Evening thunder]

I would send an e mail to NOAA they are very good at replying usually. I should know the answer but for the life of me at the moment I cannot quote what the height actually is-sorry

Thanks John, I might do that I was just curious as to how it works.

I would hazard a guess although i stand corrected that its the same logic applied to surface pressure charts, i am 600ft above sea level so the pressure level would be lower where i live than suggested on the charts because they are not really surface pressure charts they are sea level pressure charts and they show what the pressure would be if there was no mountain range and we were on a plain. I would guess the same logic applies to the upper 850 temp charts, it is what the temp would be at the 850hpa level if there was no mountain or ice block.

Thanks for that, you may well be right there. I hadn't thought of the sea level pressure charts and that it might be the same for 850hpa temps.

Hey Stormmad, great post.

I don't think they visited the coast, they went to Lapland, unsure how close this is to the coast though. I can't remember if it was Lapland either, but it's where santa is.

Thing is, those charts are showing the air temperature, and I can't see the air temperature being -25C in the height of summer, and where as slightly further North, sea ice is melting. Surely if it can reach -25C in Greenland in the height of summer, then it can only be even colder further North?

Regarding the 850's I thought that they were taken at a set height above sea level, meaning that in places the 850's would be as cold as the air temperature meaning that the 850's would be as low as -25C?

I honestly don't know if there is an error with the chart, or I am just interpreting the information very wrongly. Would really like John Holmes to shed some light on this, as I believe he is the best guy on the forums to deal with this matter.

Ah my mistake for automatically assuming it would be the coast, although Lapland is in Northern Scandinavia though instead of Greenland. The funny thing is they seem to be getting more warm weather than us this summer (and probably last year too). I've been there myself in Feb 2007, was lovely!

It does seem a bit surprising, though I guess as the sea ice is at sea level and the ice sheet up to about 3000m in places it may not be that surprising if as a crude approximation air temp on average falls by about 1C every 100 metres. To be honest I'm not sure on what 'normal' temps on the ice sheet are.

I thought that too regarding 850hpa temps, which was partly what puzzled me, but sorry to people if it seems like I'm making a mountain out of a mole hill.

[damianslaw]

Various options for late July from the models today. ECM keen on bringing something much more settled, whereas GFS and UKMO are siding more with continued changeable conditions.

Too early to call at this stage. Much will depend on what happens at the end of the week, should we see retrogression of the low pressure into the south north sea, this will set up a much better position for a dry settled warm spell thanks to building of heights to our N/NE, whereas a slack northerly flow as shown by GFS does not bode well as this will maintain low heights to our NE and thus instead we are more likely to see weaker heights develop to our SW enabling the trough to attack from the NW again - very much a continuation in the overall pattern of the summer so far.

On a personal note, I would prefer GFS to ECM not because it promises changeable weather next week, but simply it will mean a relatively good weekend, whereas ECM paints another poor picture for this weekend with cool windy showery conditions, east coast would do very poor. It is good weather at the weekends which really counts at this time of year.. the next 3-4 weekends in my book are the pinacle of the summer and are those which leave the most lasting impression on how we rate the summer just gone.