Glastonbury weather prospects
Just over a week now until Glastonbury 2013 kicks off so we area reaching the range where computer models start to firm up their predictions and hopefully allow increasingly accurate weather forecasts to be made. Nonetheless, there is still plenty of time for things to change significantly, so the best advice is to keep checking the latest weather forecasts. On TheWeatherOutlook the direct link to the 16 day forecast is:
The 10 day forecast which provides a nice summary as well as the daily details can be found here:
So what’s the score?
The news is mixed. At the moment it looks as though after unsettled weather this weekend high pressure will be building from the Azores towards south west Britain during the first half of next week. This gives the Glastonbury area a good chance of some decent weather during the early part of the festival. I wouldn’t expect wall to wall sunshine or blazing heat, but fairly typical British summer conditions rather than the washout we’ve seen at some festivals in recent years. During the second half of the week confidence in the forecast falls off as you’d expect at this range, but it does look as though we could see the area of high pressure beginning to slip away bringing an increasing risk of wet weather further south across Britain by the weekend. Having said that I’ll quickly qualify it by saying that quite a lot of computer model runs show pressure remaining high over the south of England which would increase the chances of it remaining dry. At this stage my gut feel is that the weather taken as a whole during the festival period won’t be too bad and won’t be the focus of the festival. To summarise, not a heatwave, not a washout, but please remember there is still time for the weather forecast to improve or deteriorate!
I’d like to look at the charts to make up my own mind!
If you’d like to look at the weather prospects in more detail then check out the chart viewer on TheWeatherOutlook. This gives you access to charts generated from the GFS model which update every 6 hours with the last 4 runs always available for you to view. Select GFS 0z, GFS 6z, GFS 12z, GFS 18z and then the chart and time step you would like to view. When you open the chart viewer the latest GFS run is selected by default. The chart view page is:
You can also view charts from the latest ECM model run. Select ECM and then the chart and time step you would like to view. It can be useful to see whether this is showing a similar picture to the GFS at the same time step. If it is then confidence in that being the outcome is higher.
The GEFS is also well worth looking. Select GEFS and then a location. Cardiff and Plymouth are good ones to look at for Glastonbury at this range. You’ll see a plot showing you the 850hPa temperatures (temperatures at about 1500m above sea level) and most importantly the rainfall forecasts on the lower half of the plot. The GEFS consists of 21 runs and the plot shows each of these as well as the mean of them all, and the GFS run so you can see whether it is consistent with GEFS runs. If it looks wildly different then confidence in it being correct is reduced. Look out for rainfall spikes on the lower half of the plot and see whether there are more or less of these in the coming days. The GEFS plots are regenerated every 6 hours.
If you’d like more information use the Contact link near the top of the page.
Tue, 18 Jun 2013 09:56:06
Heatwavelet this week?
If you’ve been reading my posts and checking the forecasts on TWO in recent days you’ll know there’s a chance of it turning very warm for a time this week but there has been a lot of uncertainty. Even now nothing is definite but the odds have continued to move towards Wednesday bringing the potential for a heatwavelet before it cools off through the second half of the working week. The main reason for the forecast uncertainty is that the plume of warm air moving north out of southern Europe is centred well to the east of Britain. The core of it heading for Germany with very warm weather in eastern France and much of Poland, but England sitting rather uneasily on its western edge.
The plot below shows forecast temperatures at about 1500m above sea level on Wednesday with the darker orange and red shadings over Germany showing where the warmest air is expected to be. It’s not really an unusual set-up . In the same way that winters in Germany and Poland are usually colder than ours they also have warmer and sunnier summers because of their position further away from the Atlantic. Nonetheless very warm air is shown in the south and east of England with the 15C 850hPa level isotherm just making it across the English Channel. As a rough approximation you can add 10C to 15C to the 850hPa value for inland areas (not over the mountains) where the sun is shining to get an idea of the temperature down at ground level which we experience. That all sounds quite promising, and it is. But….
We’re on the edge of the warmth and as I said that temperature calculation only applies if the sun decides to show up. Unfortunately it does look as though you’ll need to head further east to Germany if you want wall to wall sunshine. On the western edge of the heat where we are there is likely to be a fair amount of cloud developing and the potential for thunderstorms possible too. Despite this I’ll finish on an optimistic note with the latest GFS temperature chart for Wednesday afternoon which has just become available in the last few minutes. It speaks for itself with very high temperatures showing in the south and east of England. A heatwavelet not a heatwave? I called it that because despite the uncertainty about Wednesday I am very confident that the warmth will be shunted away to our east during the second half of the week with mixed weather returning.
Mon, 17 Jun 2013 10:34:44
80F in the south next week? – HEADS UP 2
Still not certain about the weather details for next week, but it’s continuing to look as though we could record the highest temperatures of the summer to date in the south. It’s not a given though, and some of the computer model runs in the last 24 hours haven’t been keen on the idea. On balance I think it’s more likely to happen than not.
The GFS chart below shows forecast 850hPa temperatures and thickness values for Tuesday afternoon. The 850hPa temperatures are those found at about 1500m above sea level. Thickness values give a measure of how warm or cold the air is with high thickness values indicating warm air. As a very rough guide the 528dam line in winter months can indicate it will be cold enough for snow, and in the summer months 564dam can mean heatwave conditions. On this chart the 564dam line is across southern England and the 850hPa temperatures are up to about +14C. Taken together these are pointing towards it becoming very warm for a time. As a rough approximation you can add 10C to 15C to the 850hPa value for inland areas (not over the mountains) where the sun is shining to get an idea of the temperature down at ground level which we experience. As I said the other day this could (could, not will) mean we record temperatures in the 25C (77F) to 30C (86F) range in southern England.
If the warm up I’ve discussed does happen it probably won’t last for too long as there is good agreement between most of the computer model runs for the warmth to be pushed back east. The longer term outlook continues to be a changeable one, but currently lacking in the extremes we have often seen in recent summers. That’s probably because we’ve got the jet stream slightly further north than last summer and high pressure over the Azores building just enough to exert some influence over the weather in Britain. It’s a bit of a halfway house at the moment with neither washout or heatwave conditions taking hold. Sounds like a more typical British summer. At least for the moment!
Sat, 15 Jun 2013 18:08:46
80F in the south next week? – HEADS UP
As I mentioned in previous posts the big picture is for a changeable and unsettled outlook , but next week there will be some very warm air moving north from southern Europe. It looks as though the core of this plume will remain to the east of Britain, but we could be close enough to it for a decent warm up in southern and central regions for a time during the middle part of the week. The temperature forecast chart from the overnight GFS shows 27C (81F) in parts of the south next Wednesday and if we do catch the edge of the warm continental air I’d have thought this is realistic.
Nonetheless, the problem with being on the forecast edge of the warm air mass is that it won’t take much change for us to miss out on it completely, hence why I’ve put this as a ‘Heads Up’ rather than a confident prediction. There’s also a chance of it becoming thundery for a time in the south east before cooler and showery air returns from the west during Thursday or Friday.
Looking further ahead the outlook remains mixed with showers or longer spells of rain at times and some drier spells. If anything the balance has perhaps shifted slightly more towards drier weather in the latest computer model forecasts. If you’re heading to Glastonbury the current indications could be worse. It looks as though a blazing heatwave is unlikely, but so is a complete washout. Current indications in my view suggest the likelihood of some wet weather during the festival period, but also drier condition with sunny spells at times.
Fri, 14 Jun 2013 10:15:19
Unsettled weather with Glastonbury approaching
Yesterday I mentioned a possible glancing Spanish Plume, today it’s looking more likely to be a case of glance away and you’ll miss it, with the warmth probably staying to our east over the near continent. What that means for us is that changeable weather looks like continuing during the second half of June. There could well be some rain around for Glastonbury, although it’s still too early to forecast specifics. On a more positive note things still aren’t looking as bad as they were last June and there are likely to be some decent days!
In the next week it’s looking as though the heaviest and most persistent rain will probably be mostly in the north and west, although even the south east will see wet weather at times as this London GFS / GEFS plot from the overnight runs shows. The bottom half of the cart shows the rain forecast from each of the 21 GEFS runs and the 1 GFS run, with the thick white line showing the average.
One thing I have noticed in some of the computer output is for another area of low pressure to spin up to close to southern England during the last third of June. I’ll keep an eye on this because it’s the sort of thing which could bring heavy rain to the south, and possibly close to the time of the Glastonbury festival if it develops. That’s a big if at this range, and as I started off by saying, Glastonbury is still a long way off in weather terms.
In summary today the outlook continues to look changeable until the end of June. In the shorter term the heaviest rain is likely further north and west, but all of us will need an umbrella at times. In the longer term it’s worth closely watching how things develop to our south with the risk of low pressure spinning up. Warmer continental air will be close to Britain and even though the Spanish plume is looking less likely there’s still the chance of this lifting the temperatures and humidity in the south east at times.
Thu, 13 Jun 2013 10:39:47
Glancing Spanish Plume – HEADS UP
Yesterday I discussed the changeable outlook and mentioned the possibility of warmer air being pulled off the continent into the the south east at times. This looks increasingly more likely, but isn’t certain. The max temperature chart for Tuesday afternoon from the overnight GFS run shows very high temperatures in northern France as that plume of very warm air heads up from southern Europe. At this point the model run shows cloud and patchy rain across southern England which is why the temperatures are pegged back to much lower levels on the chart. Nonetheless we’re talking about 6 days ahead and that leaves a lot of time for the details to change for the better or worse depending on what you like.
Continuing forward another day and the GFS shows quite an impressive Spanish Plume pushing north across Britain, with the 15C 850hPa line across central parts. That’s the value at about 1500m, but what about ground level? As a rough approximation you can add 10C to 15C to that value inland areas (not over the mountains) where the sun is shining to get an idea of the temperature down at ground level which we experience. That means if everything comes together (low chance at the moment…read on) we could be recording temperatures in the 25C (77F) to 30C (86F) range.
Flies in the ointment? Yes. Firstly everything could be shunted further east with the plume staying over the continent. Secondly, the charts show low pressure in the mix, so cloudbursts and t-storms could break out quickly. Three fine days and a thunderstorm as George II said? Possibly, but at the moment it could well be a case of close but no cigar, with the core of the plume being pushed just a little too far east as is often the case.
Wed, 12 Jun 2013 08:37:07
Weather prospects continue to deteriorate
The next couple of weeks don’t look great with wet weather likely to affect all parts of the country at times, but I’m not expecting a complete washout. If you’re off to Glastonbury or one of the other festivals I’d suggest you keep a close eye on the weather forecast because it will probably remain changeable. The overnight plot from the overnight GFS/GEFS runs shows this quite well. The upper half of the plot shows 850hPa temperatures. These are the temperatures at about 1500m and are good for showing air masses because they far enough away from the ground not to be subject to day night variations. The temperature plots are mostly fairly flat, although some of the runs spike upwards at times. These show the possibility of warmer continental air being pulled into the south east. Unfortunately the bottom half of the chart which shows forecast rainfall indicates the ongoing risk of wet weather. The plot is for London and the south east, but the changeable outlook is applicable to all of the country.
In summary, my take is the outlook to the end of June is indifferent to poor at the moment. It could quickly change for the better of course, but the data available to me doesn’t offer too much encouragement. To end on a positive still, it’s still not looking like a June 2012 washout and some drier and warmer spells are still likely.
Tue, 11 Jun 2013 10:34:13
Changeable weather outlook
Views on the weekend just gone are going to vary widely depending on where you live. In my patch (the Chilterns) the weather was poor, and Saturday was very disappointing with the cloud refusing to clear and temperatures really struggling. Sunday was better for a while, but today it’s cloudy again and for the time of year it feels cold. Almost cold enough to switch the heating back on! Temperatures are being pegged back by the overcast skies and because we’ve got a north easterly air flow which is crossing the cold North Sea. Sea surface temperatures in the North Sea are widely below following the cold spring this year. On the other hand, in western parts and particularly Ireland I expect it has felt like summer, with temperatures of 21C (70F) or higher quite widely.
Will things warm up during the week ahead? The good news is we’re going to loose the north easterly flow. The bad news is the Atlantic is coming back in and that means more changeable weather with showers or longer spells of rain likely in most of the country as we head through the week. Pinning down where and when the heaviest rain will be is quite difficult with variation from one computer model run to the next. The north and west may well see the worst conditions, although even in parts of the south there could be some heavy bursts of rain mid-week. The Download and Isle of Wight festivals may see some rain, but a complete washout like last year isn’t looking probable .
As we head towards the weekend the Azores high pressure will probably build towards Britain, possibly giving a better day on Friday, especially in the south. However, it’s looking like a fairly weaker affair with cloud and rain returning for the weekend. The GFS 6z chart for Friday 14th June shows high pressure crossing Britain.
Looking further ahead the prospects remain mixed with more showers and longer spells of rain, but also drier conditions. Possibly not that far from the seasonal average and better than June 2012. At this stage it still feels as though the weather hasn’t really set out its stall for the summer and things could take a turn for the worse or better. The TWO summer forecast suggested things would go downhill as the summer progressed. I hope that’s wrong but at the moment it seems a reasonable call.
Mon, 10 Jun 2013 12:48:04
Ohh dear! It looks as though a couple of media organisations have taken a quote made by me in 2011 about the weather prospects for Glastonbury that year and are using it in their current editions. It’s difficult enough as it is to provide a view on the weather outlook in the UK without being badly misquoted like this. If you are interested in what I’ve said so far about Glastonbury 2013 scroll down and read my post ‘Isle of Wight, Download and Glasto weather ’ which I made on Wednesday 5th June. If you work for a media organisation and would like further information about the Glastonbury weather prospects for this year then please contact me directly. I’m usually happy to help and it’s a more reliable approach than using what could well be out of date quotes from other sources!
Sat, 08 Jun 2013 07:01:36