Model Output Discussion 31/07/14 onwards.

[tallsmithy]

Hello!

 

My first post after being an avid reader of this forum for some time, and being a fan of late summers Im very much looking forward to this upcoming settled spell. STUPID QUESTION ALERT - At what point does pressure become low pressure in terms of millibars? Around 1000? Ive never been sure of the exact figure, if there is one?

 

Leigh

[Summer Sun]

Another settled and warm update from UKMO this morning

 

 

The south should see temperatures into the mid 20's during the 2nd half of next week and the low 20's for northern parts of England

[knocker]

Hello!

 

My first post after being an avid reader of this forum for some time, and being a fan of late summers Im very much looking forward to this upcoming settled spell. STUPID QUESTION ALERT - At what point does pressure become low pressure in terms of millibars? Around 1000? Ive never been sure of the exact figure, if there is one?

 

Leigh

 

No exact figure just that all the pressures adjacent are higher. Ergo you could have a slack low pressure area of 1010mb.

[carinthian]

Hello!

 

My first post after being an avid reader of this forum for some time, and being a fan of late summers Im very much looking forward to this upcoming settled spell. STUPID QUESTION ALERT - At what point does pressure become low pressure in terms of millibars? Around 1000? Ive never been sure of the exact figure, if there is one?

 

Leigh

Welcome tallsmithy, its always nice to see your location if you can add it please ? Ave global atmospheric pressure is 1013mb, so I would say anything above about 1015 mb could be classified as high pressure, whether transient or centred .

[knocker]

Welcome tallsmithy, its always nice to see your location if you can add it please ? Ave global atmospheric pressure is 1013mb, so I would say anything above about 1015 mb could be classified as high pressure, whether transient or centred .

 

It wouldn't be if the adjacent pressure was higher.

[ANYWEATHER]

I assume that those charts haven't changed in the 15 mins odd since you posted them, and to my eye they don't even slightly support what you are saying, Ian. The final chart could arguably see a breakdown if one imagines what could happen beyond that, but that's anyone's guess really. Do please explain if you think I am wrong. You do always seem to be determined to look on the unsettled sign of the charts even when they are resolutely saying the opposite. Gets a bit wearing, especially as you are not alone!

Im afraid, if you don't like what the models are saying then its as simple as don't look at them. Your comment Im afraid is a little bit harsh, Im only stating what the models show. The model output is still rather mixed, with high pressure trying to get a foothold, but there are lots uncertainties regarding the detail. Gone is ,the output from a few days ago where models were indicating plain and simple high pressure......slap bang over the uk,

[Man With Beard]

Im afraid, if you don't like what the models are saying then its as simple as don't look at them. Your comment Im afraid is a little bit harsh, Im only stating what the models show. The model output is still rather mixed, with high pressure trying to get a foothold, but there are lots uncertainties regarding the detail. Gone is ,the output from a few days ago where models were indicating plain and simple high pressure......slap bang over the uk,

It's fair to say that today's ECM is a slight downgrade from recent charts. It's still settled (though not wall to wall sun), it's still warmer that average but it does show how a chart that would be hot and sunny may not be so in September - at this time of year, you need extra things to do right to get heat. For example, an easterly or a southerly will be hot in July, but an easterly might not be hot in September if the rest of Northern Europe is cool - the sun no longer has the power to heat things up quickly. And that's where we're at with the ECM today.

 

Having said that, the ECM this morning does not represent the other charts. Looking at the 500mb anomalies in the mid-range, GFS and NOAA do not have the disturbance that ECM has:

 

http://mp1.met.psu.edu/~fxg1/ECMWF_0z/hgtcomp.html

http://www.cpc.ncep.noaa.gov/products/predictions/610day/500mb.php

 

so odds are still on something a little bit warmer and settled that ECM

Edited August 29, 2014 by rjbw

[knocker]

It wouldn't be if the adjacent pressure was higher.

 

If you want to talk in general terms then the logical way to go would be to take the mean sea level pressure for the earth, 1013mb, and whether the pressure was above and below the mean. I'm not aware that this is the official position.

[johnholmes]

Been away for several days with an occasional peek at synoptic and anomaly charts. Certainly the anomaly types have changed in that time. Now much more towards a more settled set up, but not having got the whole set over the past 6-7 days I am not sure if this 'settled' upper pattern I've quoted is a short lived idea or longer term.

I need to see 2-3 days of them to make any prediction but it is looking reasonably hopeful, for most areas, I would have thought, once this weekend is out of the way?

[William of Walworth]

I haven't checked the most recent output in as much detail as I'd like, but re the above disgreements, may I gently suggest that the idea of some sort of breakdown for next weekend (that of Saturday 6th Sept) is far from nailed on yet. Not supported by all the models anyway. May happen, may not, we all now that as ever, there's plenty of time for positioning and detail to change between now and then.

Edited August 29, 2014 by William of Walworth

[mushymanrob]

well the longer term outlook appears to be pretty good. after this weeks expected high pressure drifts eastwards the 8-10 day anomaly charts suggest the jet on a northerly track leaving the uk on the warm side and high pressure never far away.

 

 

both the gfs 06z and ecm 00z appear to suggest that next weeks high drifts eastward, followed by abit of a col, or perhaps a thundery low, before the azores high ridges in to replace the exiting high.

 

 

not so sure about sunshine levels in the coming week, and hence maybe why the uppers now arent expected to be quite so high so early (10c isobar). the fax suggests a lingering cold front embedded in the building high

 

 

 

before hopefully a southerly/southeasterly draft will shunt that north and allow the real warmth to cover the uk as per this from the gfs 06z

 

 

into deep fi, and if the gfs is to be believed then the first half of september at least will be high pressure dominated and warm.

 

 

so september 2014 is shaping up to be possibly a very warm, dry, settled one, at least indications would suggest that for the first half.

[knocker]

Bit puzzled mushy as to why there is a connection between sunshine levels and the 850mb temps. I'm obviously not picking up what you mean.

[summer blizzard]

Bit puzzled mushy as to why there is a connection between sunshine levels and the 850mb temps. I'm obviously not picking up what you mean.

Lapse rates and instability I imagine. For sunshine you don't want uppers to be matching sea temps in the Oct-March timeframe.

Its still September so the sun should melt that front.

[mushymanrob]

Bit puzzled mushy as to why there is a connection between sunshine levels and the 850mb temps. I'm obviously not picking up what you mean.

 

 

 

oh, yeah... sorry, i didnt mean to suggest there was a connection but thats what i incorrectly posted. its the straggling cold front that appears to be perhaps further south and more of a feature that would introduce more cloud, and cooler uppers on its northern flank. the op runs failed to show this front obviously, but previous runs had the 10c isotherm across the country earlier then the current runs suggest, i read that as the cold front not being as strong, nor as far south as the current fax suggests.

 

hope that makes sense.

[knocker]

Yep no probs.

[Tamara]

Its a case of watching over coming days for consolidation of any hints beyond the 7 to 10 day period for the atlantic to de-amplify in accordance of relaxation of the prevailing pattern.  A modest warming trend is still indicated in the longer term London ECM ensembles to reflect the possible background changes as discussed further out (and as illustrated previously by others in the thread, this is reflected by GFS data)

 

At least there are some hints that the last period of August may well produce something of a return of more settled summer weather with temperatures returning from slightly below average to closer to average and perhaps slighly above as the Azores high is allowed to ridge eastwards, eventually, from its retracted and amplified westward position. Taking into account the first 10 days of August (which, although increasingly changeable, was reasonably acceptable and quite warm for many up to the arrival of Betha this weekend) then an improved last week or so of the month would put August into a positive context as not being by any means a write-off or wash out month and nothing comparable with, say, 2012 - albeit a step back from the upward momentum through and into the mid part of summer

Highlights of previous update copied for continuity and assessment of progress since midmonth. The pattern has evolved quite well along the themes suggested with warmer, quieter and more settled weather arriving next week to mark the official start of autumn - a few days to a week later than was hinted at long range

 

If we look at our upstream observed and forecasted jet stream profile once again we can see the changes that have occured across the Pacific and have de-amplied the jet stream downstream across the atlantic as mooted in longer term evolution in the last update. The PNA has steadily returned more neutral/negative and this has lowered the High pressure anomaly in the central/ west atlantic and the meridional looping jetstream has split flow replaced with the bulk of the jet stream heading to northwards of the UK. This is also in tandem with energy transport across the pole and the AO turning negative as a first response to seasonal cooling changes across the polar stratosphere. This is quite to be expected though, and has no bearing whatseover on later autumn and winter prospects.

 

 

 

The formerly retrogressed and amplified Azores High is flattened and pushed eastwards and we are set for a string of sub tropical ridges to extend across our mid latitudes through next week

 

As ever in the UK, transitions of pattern are never straightforward and this is a case in point at the end of the weekend/ start of next week as a decaying front (giving wind and rain over parts of N UK on Sunday) presents a spoiler across southern UK in the form of cloud cover and a little residual rain before the migrating High pressure cell squeezes final life out of it. The rest of the week looks very pleasant with warm hazy sunshine - all the more enjoyable for some perhaps with the sun that much lower in the sky than a couple of months back and the heat moderated accordingly and less sapping. The other fly in the ointment are further fronts brushing the far NW as the jet stream carries them across the NE atlantic. However, the fine weather looks set to extend from the south across many parts through next week

 

The EPS members fully advertise this generally settled pattern at the mid point of next week.

 

 

What about the further long term outlook through the end of next week and beyond?  Lower pressure profile to the north of the UK looks set to prevail as further mid latitude ridging is likely to try to renew fine weather further south with perhaps only a minor hiccup (perhaps?) occuring in between times towards next weekend. We have to watch for further ex tropical storms to provide curveballs to proceedings and also it is quite conceivable that upstream patterns may once again try to retrogress the pattern slightly once more. In this way, we might see mid latitude ridges erode across central UK and edge westward enough to allow the more changeable atlantic conditions in NW'ern most parts to edge further south later next weekend and the start of week 2.

 

At this time though the longer term London ECM ensembles show quite warm and relatively dry conditions holding on in the south out to week 2. The peak of the warmth indicated through the middle and end of next week as the mid latitude cell passes just to our east (as was suggested in those above pasted mid term stamp/map ensembles)

 

http://www.weathercast.co.uk/services/ensemble-forecast.html

 

I think next weeks more summer like pattern will be a very welcome return for many - the below average temperatures such as we have seen in that cool August spell can wait a couple of months or so yet when they will be received much better

 

Edit: The key as usual is not to be influenced by individual model output

Edited August 29, 2014 by Tamara תָּמָר

[h2005__uk__]

GFS is keen for Friday to be the hottest day, although there's quite a contrast in the maxes between today's 06z run and the 12z run!

 

06z:

 

12z:

[Man With Beard]

ECM and GFS starting to agree on next week - settled conditions, not wall to wall sunshine but sunny 'spells' expected - the orientation of the High no longer favours a southerly draw, but rather an easterly, meaning temperatures slightly above average for most but not exceptional 20-23C being highly likely, maybe a stray 25C in spots favoured in easterly set-ups (of which my back yard is one :] ). A tad disappointing for those hoping for one more hot blast, but pleasant enough.

Hints at retrogression later on, one to watch, certainly a possibility given the set up by T144 - quite a chilly prospect if it happens given the cold pooling up to the north.

[summer blizzard]

Euro tonight is glorious with the high retrogressing through the run. This firstly brings a north east component to the wind so a cooler source but it also means that the end game would be a northerly most likely. In the meantime it would be sunny but not quite as hot with probably chillier nights.

 

[ANYWEATHER]

Ecm a lovely run for cold lovers if it was winter....! Cant see why the met office updates say unsettled conditions from next weekend, perhaps they no something we dont!..

[Blessed Weather]

In my view the ECM is a disappointing backtrack tonight on the warmth promised from runs over the last few days. Tonight the +10c isotherm on the 850 hPa charts only briefly touches the UK right through the run. Yes it's still a settled week (after ex-hurricane Cristobal's straggling front clears the UK on Monday) and pleasant enough with decent temps in the low 20c's but not quite what recent runs had promised. As posts above suggest, at the end of the run ECM taunts us with the prospect of a rather cool blast of polar air running down from a high forming to the east of Greenland. Cold lovers would indeed be cheering if it was January!!

 

ECM 850hPa chart tonight for Monday 8th Sept:

[knocker]

The anomalies look in fair agreement for next weekend with the HP to the NW and the jet running around it facilitating the maintenance of the HP. Temps slightly above average.

 

[Captain Shortwave]

ECM and GFS starting to agree on next week - settled conditions, not wall to wall sunshine but sunny 'spells' expected - the orientation of the High no longer favours a southerly draw, but rather an easterly, meaning temperatures slightly above average for most but not exceptional 20-23C being highly likely, maybe a stray 25C in spots favoured in easterly set-ups (of which my back yard is one :] ). A tad disappointing for those hoping for one more hot blast, but pleasant enough.

Hints at retrogression later on, one to watch, certainly a possibility given the set up by T144 - quite a chilly prospect if it happens given the cold pooling up to the north.

Another example of ridging being overdone by the models in the mid-range, in this case the surface conditions look very similar, but the thicknesses within the high and hence the heat provided has been downgraded quite dramatically, this means a much weaker and flabbier high with mild to warm conditions compared to the heat projects a day or so back. Still September should start on a decent note.

The models are struggling from next Friday onwards as they handle the incoming Atlantic trough, the solutions differ greatly from this mornings suite, so worth waiting on that, though settled does look like being the consistent thing, just where the high will end up being centred is the question.

ECM ens show that the ECM op has again potentially overdone the retrogression, UK high favoured

So fine and warm with good sunny spells once any troublesome fronts are cleared at the start of next week. Morning mist and fog could be an issue with potentially some chilly nights too in rural areas. The UK high solution is also favoured on the GFS ens for week 2.

Edited August 29, 2014 by Captain shortwave

[knocker]

Sorry not quite with "thicknesses within the high and hence the heat provided" CS. I'm aware that thicknesses are a function of temperature structure but I'm struggling with the hence the heat provided bit. Unless you are saying the later thicknesses are an indication of a cooler air mass

[Captain Shortwave]

Sorry not quite with "thicknesses within the high and hence the heat provided" CS. I'm aware that thicknesses are a function of temperature structure but I'm struggling with the hence the heat provided bit. Unless you are saying the later thicknesses are an indication of a cooler air mass

Fair enough, it is odd that as we have got closer to the next week,  the 850s have been diluted dramatically whilst the surface charts have remained pretty similar. Either the northwards push of the warm air is not as strong as it was previously predicted, or something else is going on. 

Edited August 29, 2014 by Captain shortwave