In Depth Model Discussion, Analysis and Summaries

[Evening thunder]

Looking like GP's idea of a cooler end too April is dead in the water and the warm to very warm dry weather to continue.

Maybe not though if the 00Z ECM has it's way. Although I think I missed him saying he expected a cooler end.

UKMO looks similar to the ECM at T+144 as well. I can't really offer a more technical post though..

[Eugene]

I think most places should be OK for this summer. Yes, they'll be hosepipe bans and obviously it'll have a disasterous effect on agriculture, but as far as people keeping their water supply goes, we should be OK this year.

Now, if we were to repeat the 75/76 pattern and had a dry autumn/winter 11/12 followed by another intense heatwave and drought through summer 2012, then next year would be looking far more serious. That would take quite some doing, though.

Gavin looking at GFS 00Z FI the high looks like retrogressing northwards with southerly tracking lows if this continued into the summer no worries about hosepipe bans, dont know about you but i am feeling winter 2011/12 could be a very cold one

[Glacier Point]

With the current global ocean-atmosphere coupling showing no signs of rapid transition for at least a month, I tempted to suggest here that rainfall for the next four weeks looks in short supply which is only going to compound water resource issues going forward.

Whilst sea surface temperatures in the Equatorial Pacific have weakened consistent with a fading La Nina episode, the atmosphere is still displaying all the traits of a strong Nina. High impact weather events such as tornado activity in the southern US and our strong anomalous ridge over NW Europe are all consistent with a spring La Nina.

Total and relative angular momentum have fallen to much below normal levels indicative of a strong easterly (weak westerly) tendency in global winds. Renewed trade wind surges are occuring in the Pacific whilst the extratropical circulation is characterised by anomalous high pressure belts consistent with a low angular momentum (La Nina) base state and the lagged influence of a persistently cold polar stratosphere in February and March. The latest relative angular momentum data places nearly -2SD, which is solidly La Nina-like and the Global Wind Oscillation is in phase 2 having undergone a rapid and amplified orbit earlier on in April on the back of a bout of westerly winds and MJO wave.

The general longwave pattern is very consistent with GWO phase 2 plots depicting anomalous ridges centred over the Aleutians and Scandinavia. The strong ridge centred further west over the UK is in part derived by this and low heights over Greenland. The troughing in the Atlantic is also well depicted by this phase of the GWO.

Tropical convection remains somewhat depressed and centred in the far western Pacific consistent with the atmosphere 'getting stuck' an unable to effectively migrate eastwards against the La Nina wall of easterly trades. Should tropical convection continue to manifest itself in the western Pacific, this would have the effect of maintaining the status quo.

Of note however is the development of a westerly wind burst throughout March and April centred around 140E . This may fall back a little in the coming weeks although this may be of interest for those interested in a warm June as this is when we should next see westerly wind bursts and MJO activity increase. For the time being, MJO activity looks to be weak and incoherent.

With little tropical convection and trade winds increasing, there seems little to move the atmosphere on from its low angular momentum base state. Phase 2 GWO is favoured for a sustained period of time. Composites for phase 2 in April and May continue to show the influence of high pressure around the UK. Potentially the weakening of the polar vortex may allow some extension of the ridge further north although it should be noted the composites maintain low tropospheric heights over Greenland. At best I think the weakening of the polar vortex should allow for the mean ridge to position itself further north and west than shown but not by much and we need to remember that the delay of the polar vortex break-up is may be coming too late to impact the pressure pattterns which have become ensconsed. A phase 2-3 type orbit of the GWO looks the more likely into May.

Composites for GWO Phase 2

April

Composites for GWO Phases 2 and 3

May

So the extended outlook looks to be characterised by high pressure centred close to the UK maintaining dry conditions and lack of meaningful frontal activity. Above average temperatures also look likely to persist over much of the UK.

Edited April 18, 2011 by Glacier Point

[Kentish Kiwi]

So the extended outlook looks to be characterised by high pressure centred close to the UK maintaining dry conditions and lack of meaningful frontal activity. Above average temperatures also look likely to persist over much of the UK.

Another brilliant post GP. Certainly not what those hoping for any meaningful rain in the medium term would be hoping to hear.

In regards to the bolded sentence; what are your thoughts about the possibility of the current high moving far enough north to bring in a rather solid looking easterly/north-easterly (as has been hinted at several times by the GFS/ECM) and its effect on temperatures, particularly for the eastern side of the UK? ie. is it very likely?

[Alex]

Hi GP another good post, so it seems May looks good, can I be greedy and ask whats the best an most likely outcome for June based on current scenario, are we looking at a dry warm June if we keep hold of +qbo?

[Glacier Point]

Thanks.

The slight retrogression of the mid latitude high is possible and would fit the notion of the -NAO trying to re-establish itself after the depressing influence of the +AO is lifted somewhat. However, note what the GWO composite for May phase 3 is trying to tell us, high pressure to the south which, allowing for this being slightly further north, would put the ridge slap bang over the UK or just to the north so some influence of easterly fetch to the far south but I wouldn't make too much of this in the grand scheme if things.

Hi GP another good post, so it seems May looks good, can I be greedy and ask whats the best an most likely outcome for June based on current scenario, are we looking at a dry warm June if we keep hold of +qbo?

As you rightly point out, the +QBO should do us fine weather fans a favour and prevent any sudden downwelling easterly wave from being started (this is the key difference to 2007), which should mean that blocking over the Arctic this summer is much less prevelant.

If we start to see westerly wind bursts increasing in late May (and MJO forecasts going for a strong wave in early May) , I'll start to bang the drum for a flaming June.

[Kentish Kiwi]

Thanks.

The slight retrogression of the mid latitude high is possible and would fit the notion of the -NAO trying to re-establish itself after the depressing influence of the +AO is lifted somewhat. However, note what the GWO composite for May phase 3 is trying to tell us, high pressure to the south which, allowing for this being slightly further north, would put the ridge slap bang over the UK or just to the north so some influence of easterly fetch to the far south but I wouldn't make too much of this in the grand scheme if things.

As you rightly point out, the +QBO should do us fine weather fans a favour and prevent any sudden downwelling easterly wave from being started (this is the key difference to 2007), which should mean that blocking over the Arctic this summer is much less prevelant.

If we start to see westerly wind bursts increasing in late May (and MJO forecasts going for a strong wave in early May) , I'll start to bang the drum for a flaming June.

Appreciate the reply GP and certainly what I was hoping to hear to support what those two May GWO composites were illustrating, good to know any potential and sustained northwards retrogression of the HP cell doesn't have too much support from the teleconnections.

Also quite an exciting prospect you paint in regards to June, particularly glad to note the differences with 2007...

[Jezzer]

Thanks.

The slight retrogression of the mid latitude high is possible and would fit the notion of the -NAO trying to re-establish itself after the depressing influence of the +AO is lifted somewhat. However, note what the GWO composite for May phase 3 is trying to tell us, high pressure to the south which, allowing for this being slightly further north, would put the ridge slap bang over the UK or just to the north so some influence of easterly fetch to the far south but I wouldn't make too much of this in the grand scheme if things.

Hi GP, I've been keeping an eye on your comments over the last few days as I'm entering possibly the most nerve-wracking period of forecast watching that I've ever done. Usually I'm obsessed with Glastonbury's forecast and will be in a couple of months. But before then I've got something even more important. I'm getting married on Saturday May 14th in Gloucestershire and am obviously praying for a dry, sunny day!

Judging by your comments the signs look positive but I'd be interested what you think may occur in that particular neck of the woods around mid-May.

Many thanks

[The PIT]

Looks like one of the driest springs on record then plus a warm element to it as well.

[geoffw]

any initial thoughts on july or august GP?

[Gavin P]

Gavin looking at GFS 00Z FI the high looks like retrogressing northwards with southerly tracking lows if this continued into the summer no worries about hosepipe bans, dont know about you but i am feeling winter 2011/12 could be a very cold one

Good heavens, I've not even started to think about next winter yet. It would be quite something to pull off a fourth cold winter though....

GP, assuming this anticyclonic spell ever breaks down, what teleconnections should we be looking for to hint at a fundamental shift in the pattern?

Edited April 20, 2011 by Gavin P

[damianslaw]

Would like some thoughts from experts of upstream signals as we head into May - i.e. teleconnection forecasts, state of strat, state of polar vortex which seems to have been stuck like a broken record for weeks and weeks now - surely it must be weakening now..

On a more general note it is a pity once winter is over this thread and the model discussion thread quitens down markedly with very few senior forecasters and experts posting thus making it very difficult for amateurs like myself to understand longer term pattern changes.

[Glacier Point]

Good heavens, I've not even started to think about next winter yet. It would be quite something to pull off a fourth cold winter though....

GP, assuming this anticyclonic spell ever breaks down, what teleconnections should we be looking for to hint at a fundamental shift in the pattern?

An indication that the core of tropical convection is shifting further east than it has been which should go hand in hand with the trade winds weakening and atmospheric base state moving away from the La Nina that we've been locked in since October.

Speaking of which.....

Here is a stunning example of what a fundamental influence deep tropical convection (cloudiness and thunderstorm activity) has on the pattern of Rossby Waves.

Take a look at the seasonal 90 day anomaly for outgoing longwave radiation. The centre of tropical convection (purples and pinks) is shown nicely in the Indo-Pacific region. This loosely teleconnects to the MJO phase 6. Also shown nicely is the strong area of +ve OLR around the dateline which is consistent with a La Nina episode.

Now, composites for MJO phase 6 for the winter when we have a La Nina in place:

For the last 90 days, the H5 anomaly pattern looks like this:

Spot the difference.

Moving forward, if we stay roughly where we have been, angular momentum will be low and consequently the summer will be poor. However, if we begin to see westerly wind bursts in the far eastern Indian Ocean and west Pacific increase in strength and frequency, and the location of tropical convection change, the atmosphere should go along with this and we will see angular momentum begin to rally away from the Nina base state towards much more neutral conditions. At the moment, there are hints that we are seeing the latter. This would set up the Rossby Wave pattern to be more pre-disposed towards high pressure in the North Atlantic and NW Europe.

Edited April 21, 2011 by Glacier Point

[Alex]

Hey GP, shorter term u think May Will continue with the mostly settled conditions with ridges of pressure continuing to settle slightly to the east of us?

[Glacier Point]

If anything Alex, I would say ridges more inclined to be centred just to the west and north-west as well as a separate cell to the south.

[Alex]

Not great then for temps if we have higher pressure to west. However higher pressure to the south will mean southwesterlies which could bring warmth ESP to inland southeastern areas. But it sounds generally settled as I doubt too much Will get to us if we have a blocking high to our west or south. Correct me if I'm wrong.

[Gavin P]

Many thanks GP.

[damianslaw]

If anything Alex, I would say ridges more inclined to be centred just to the west and north-west as well as a separate cell to the south.

A ridge in this position would essentially mean a continuation in the dry conditions but cooler than of late with winds predominantly from a cooler north-east quadrant as opposed to south to east quadrant as we have seen in recent weeks. Eastern parts could be dissapointed with lots of low level cloud and drizzle.

It also suggests a split jet with spain suffering from low heights and low heights being forced to track far to the north and then into scandi - some of these may influence us as heights ridge further NW from time to time, it doesn't sound like we will see much atlantic influence or any low height influence to our SW provided we keep a separate cell to the south, though if this is more southerly or southeasterly we could pull in some wet conditions for the south from time to time.

Such a pattern is quite common for May - the atlantic is traditionally at its quietest now and we are much more likely to see northerly and easterly airstreams take hold, those westerlies tend to resurge in June as SST's over the atlantic increase causing greater temp gradients and enhancing low developments.

[lukemc]

A ridge in this position would essentially mean a continuation in the dry conditions but cooler than of late with winds predominantly from a cooler north-east quadrant as opposed to south to east quadrant as we have seen in recent weeks. Eastern parts could be dissapointed with lots of low level cloud and drizzle.

It also suggests a split jet with spain suffering from low heights and low heights being forced to track far to the north and then into scandi - some of these may influence us as heights ridge further NW from time to time, it doesn't sound like we will see much atlantic influence or any low height influence to our SW provided we keep a separate cell to the south, though if this is more southerly or southeasterly we could pull in some wet conditions for the south from time to time.

Such a pattern is quite common for May - the atlantic is traditionally at its quietest now and we are much more likely to see northerly and easterly airstreams take hold, those westerlies tend to resurge in June as SST's over the atlantic increase causing greater temp gradients and enhancing low developments.

Just of a matter of interest Damien what are your thoughts on this coming summer do you think we could be in for a good summer this year in the first half at least? It would be nice to get a sunnier summer this year especially considering recent summers in our part of the world (NW England) have been rather dull especaily in the latter half so I really want to see good sunshine levels distributed thoughout the summer this year.

Luke

[damianslaw]

Just of a matter of interest Damien what are your thoughts on this coming summer do you think we could be in for a good summer this year in the first half at least? It would be nice to get a sunnier summer this year especially considering recent summers in our part of the world (NW England) have been rather dull especaily in the latter half so I really want to see good sunshine levels distributed thoughout the summer this year.

Luke

I'll leave summer forecasts to the experts. As a rule of thumb here in the NW we are far more likely on average to see sunny settled conditions during May and June than we are July and August. I never rate August up here, it can be a very wet month despite any warmth.

Recent summers since 2006 have followed a general distinct pattern, with June on the whole the best month for warmth and sunshine, July the wettest unfortunately and August the coolest and cloudiest though not necessarily that wet. We have had some great weather in April and May at times in the last four years.

I will be surprised if we see a summer as wet as 2007 and hopefully July won't be as wet as the past four.

[Alex]

If we see a westerly burst then yes a nice June as GP comments. it's more likely right now!

[The PIT]

Okay it looks like both the AO and NAO are going negative what will that mean for us ???

[Uncle_Barty]

Northern blocking and a more southerly-latitude tracking jet, so another 2007 or 2008? I hope to god that is not the case.

What do you think, GP?

Edited April 29, 2011 by Jim_AFCB

[snowlover2009]

Okay it looks like both the AO and NAO are going negative what will that mean for us ???

Blocking over the north and Greenland, would not be brilliant at all for summer. Would potentially be a washout of a summer.

My thoughts on a decent summer since 2006 has changed dramatically recently, I am calling a very wet summer to be honest. The best of the weather to the south-east of europe, I don't think the rest of europe will escape it, we saw how wet it was in Spain so far this April.

[lukemc]

Blocking over the north and Greenland, would not be brilliant at all for summer. Would potentially be a washout of a summer.

My thoughts on a decent summer since 2006 has changed dramatically recently, I am calling a very wet summer to be honest. The best of the weather to the south-east of europe, I don't think the rest of europe will escape it, we saw how wet it was in Spain so far this April.

Could this qualify as the first "summer is over" post for 2011 - over 4 weeks from the start of meteorolgical summer with the full 3 months of summer ahead of us?!? LOL - only kidding!!

On a more serious note what makes you think that this coming summer will be a poor one? Do you have any evidence - statistical, model related or other to suggest this? Even if we did get a poor summer I certainly cannot see the coming summer being as bad as 2007 as far as rainfall was concerned the summer of 2007 was exceptional and it could be a while until we get another summer as wet as that. If anything, we are overdue a drier and sunnier than average summer especially in the North West were I live. I could not stand another summer like 2007 though and I really hope that you are wrong in your predictions.

Do you base your prediction on the theory that a warm April is more often than not followed by a poor summer? I don't think that can be statistically backed up - as Mr Data and the likes have quoted in the past there have been warm spells in April that have been followed by poor summers like 2007 and 1987 but there have also been warm spells in April that have been followed by decent or very good summers like 1984, 2003 and of course the famous example of 1976 - so I still don't buy that theory.

Yes this summer may turn out either way but I think it is a bit premature to effectively write off the coming summer more than a month before June 1st - yes the NAO may be turning negative but there is plenty of time for things to change in your favour if it is a good summer you are after. If you feel that there are compelling signals for a washout summer please feel free to explain why you think that may be the case.

Luke