snowking

Might be a good idea just to do a quick illustration to clear this one up (I do understand it is confusing with the difference between heights and SLP - getting your head around the different pressure layers of the troposphere is one of the most tricky things to do, but its essential for more expansive forecasting) So, heres a couple of basics, the sort of things that I used to take a look at when I only had a chance to glance quickly at the models. I have made some markings on the below image - the latest height anomaly projection from the ECMWF As John has said, ignore the colours for now - follow the lines! (Again its tricky to get your head around, but don't automatically assume that the higher heights (reds) will always lead to high pressure, and vice versa with blues). By the lines, we are talking about the "horizontal" black lines, which are indicated by the green arrows drawn. If anyone can think back to GCSE Maths (or possibly even physics), think of these in terms of a Sine wave. When they point up, they are a peak (or in meteorological terms, a ridge) and when they point down, they are a trough. You might have heard that term trough used a fair bit on here - ridges and troughs are what make up the Longwave Pattern across the Northern (and Southern - though we rarely focus on this) hemisphere. By this, we mean that the weather all around the globe follows a series of ridges (areas of high pressure) and troughs (areas of low pressure). We can identify such areas on the annotated chart above. I have shown a ridge (in the blue box) forecast across the UK - taken in current context, in around 8-10 days time, the current ECMWF suggestion is of ridging across the UK. How can we tell it is a ridge? Because those black bars are pointing towards the north pole. I have also identified a trough (in the yellow box), which would indicate an area of 'troughing' - essentially, an area (or collection) of low pressure. We can tell its a trough because the black lines are facing towards the equator. So, its a case of looking for ridges (black lines facing poleward) for the chance of more settled conditions, and troughs (black lines facing equator-ward) for unsettled conditions. It gets a lot more complex than that - we can start looking for closed ridges/troughs, and in the winter, we also look at certain colours of the black lines indicating where the 528DAM line (considered a good measure of the 'snow line' under most circumstances) is. But we'll worry about that another day. In the meantime, when looking at height anomaly charts, look for ridges for potential settled spells, and troughs for potential unsettled spells, in the vicinity of the UK SK

Absolutely - 10-20th looked to be the period to me, though with a trip planned next weekend i'm hopeful it may be just a touch sooner! MJO enters phase 3 in around 12 days time if its current projection is correct - and thats also fairly consistent with the EC32 day MJO projection. In the meantime, phase 2 offers this for July: A bit of no-mans land really, with a slight troughing structure just about evident. So it looks likely to be a slow process to get to something more extensively settled. GWO phase 3, which offers an azores ridge and above average T2m values also happens to coincide in current forecasts with MJO phase 3. So all the signs there, which is why I suspect the FI outputs are offering the eye candy. Its now just a case of whether it will deliver! SK

I can only be brief, but ECM today looks more realistic time-wise in the longwave pattern - might take a few days longer, but MJO phases 2/3 show a gradual increase in heights across NW Europe (not the sudden switch shown in recent days) We will likely see next weekend as the transitionary phase - the following week likely to be fairly settled so long as GWO/MJO signals are correct SK

Medium range NWP continuing to match up nicely with the MJO and GWO signals (phase 8-1-2-3 progressions): http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ALL_emean_phase_full.gif Though, as ever, the poor old GEFS a little slow to wake up and smell the coffee. ECMWF has been very good with its MJO projection so far this summer. My own summer forecast had anticipated a decent spell of weather during the middle third of July, so at present things looks to be progressing just a little quicker than I had anticipated. The medium range outlook pretty easy to sum up really then - North/South split developing into the weekend, turning more unsettled for most of the country into the start of the new week, before things settling down again towards next weekend. SK

MJO signal really leading the medium range output at the moment. More time spent in phase 8 than expected to finish June, and so much of this week should be fairly pleasant - still not overly optimistic at present for next weekend, and I suspect we may see subsequent runs pushing towards a more North-South split, particularly given the current low AAM leading us towards GWO phases 1-2-3 Ensemble means out to day 10 show a general lowering of heights (and subsequent lowering of SLP), consistent with the transition towards MJO phase 1 as we head into early July. The signal then still remains for the middle third of July to be rather more settled, dry and warm, with both GWO and MJO composites (MJO likely to move into phases 2-3, with gradually more settled conditions developing, with GWO phase 3 suggesting above average 2m temps.) favouring such an outcome. So from my perspective, a bonus week of decent weather coming up, still likely to see a transition to something less settled again as we head into July, before the return of some decent weather towards the middle third of July. SK

Quick one from me Outlooks largely the same as suggested a few days ago - likelihood of transient ridging towards the final days of June, should bring a good few days of dry weather away from the far North. Question-marks remain, as pointed out by Rob, over cloud amounts. Beyond that, hints of something more unsettled once again for the start of July. Summer forecast had a strong signal for a decent spell around the middle third of July, so it will be interesting to see whether this pans out as the outputs begin to move into this period over the coming days. Incidentally, whilst there has been the expected split in the conditions for June thus far, with the first half more settled than the second overall, it has panned out a better month overall than I expected - the 'plume' (if you wish to call it that) this week has helped the CET somewhat, though given the temperature projections over the next 3-5 days, we will likely end up very close to average overall. Lets hope next weeks settled spell finally brings some more widespread sunshine - I fear this will not be the case given the flow off the Atlantic SK

Interesting juncture coming up in the 10-15 day period MJO forecasts still undecided as to whether to head into phase 8 or phase 1. On the face of things, the GFS seems pretty steadfast on phase 8: Where as the ECMWF moves briefly through phase 8, and then onwards to phase 1 fairly rapidly: In terms of where each phase leaves us heading towards July, phase 8 gives us something more settled: Where as phase 1 leaves lower heights slap bang over the UK: So you may think thats it then, a simple ECM/GFS split. However, if we take a look at the bias corrected GEFS MJO projection: We see a progression more akin to that suggested by the ECMWF - that is temporary phase 8, before heading towards phase 1. Which would suggest to me a temporary ridging structure in around 12-15 days time (final days of June/July) - reanalysis of the composite years used for the summer forecast offers around 75% correlation with such a notion, though based more around the first few days of July, as opposed to the final days of June. With the recent (and forecast continued) fall in AAM, the GWO looks likely to oscillate around phases 1-4. Composites for such a progression are mixed, but the likely transition from phases 1-2 during the final days of the month also offer the chance of a temporary ridge, so the chance of a few more settled days later this month. However, all of the suggestion beyond this and into the start of July, at present, suggests a rather unsettled picture - the GEFS, for now, should perhaps be disregarded beyond day 10 given the discrepancies between teleconnection forecasts and its own raw un-corrected output. So the general idea into the 10-15 day period is perhaps a temporary ridge, before things go downhill once again into early July SK

Quick update from me ECM op and control nowhere near as high as the temperature projection from GFS for Wednesday - current mean consensus would suggest around 25c at present. Wouldn't entirely rule out 30c being hit, but I would suggest its <10% risk. Its a similar story too from the ensemble means, with max values around 21-25c from both the ECM and the GFS as of 0z. ECM ensemble mean, pictured for 1800 Wednesday, currently offers the best estimate: Currently actually the biggest story from this spell for me would be the huge thunderstorm potential. The highest resolution modelling I have access to is just beginning to come within range, and below is the projected CAPE out to 10am Wednesday: Combined with LI values around -9k and K-Index of around 34-40, some very impressive storms could well come to pass if current projections prove accurate....and if you're really looking for some action, the values on the continent are off the scale, giving a significant risk currently of supercell activity. SK EDIT: Writing after a night of drinking seems to make the word "currently" appear a needless number of times. Edited!

Yep I certainly do, although I have found it is only useful when we see it appear close to the overall ensemble mean. Its not too far away from the mean today, though a pretty notable anomaly towards the middle of the run: The overall idea from the ECM control for the mentioned period is a mid-atlantic ridge development influencing the UK for a time too SK

Back towards something summer related This tweet from Matt Hugo has taken my notice: That would very much fit in with the expectation from my summer research - we are looking largely unsettled up until the period of around July 10th (given or take a few days). But the middle third of July is looking more settled once again. Its a very similar signal to the one which projected the settled spell for the start of June, around 7-10 days in duration, and whilst unlikely to give anything sweltering, it would certainly promote a more seasonal feel SK

Whilst confusion and head scratching reigns (as ever) between the individual operational runs, the ensemble means actually paint a relatively straight forward picture in terms of SLP: Almost all of the UK is under the influence of low pressure for the remainder of this week, with a predominant westerly flow offering cooler temperatures than of late, and more unsettled conditions. And out to day 10: We see a trough structure in place across the UK - once again likely symbolising lower SLP, and with a continuation of a mean westerly flow. Some finer details to sort out in between, and yes the chance of one or two collapsable ridges here and there, much as we saw for the majority of the UK during May, but unfortunately nothing anywhere near as settled as the recent spell is really on the horizon from the current outputs into the day 10 timeframe. A more pronounced push for the MJO into phases 4 and 5 once again doesn't promote anything particularly settled. Still plenty of time for change yet, but if face value model output is your thing, its a predominantly unsettled picture through the middle third of June SK

Here you go mushy: http://www.americanwx.com/raleighwx/MJO/MJO.html SK

I've just had a chance to catch up with the models and its still largely the same picture as painted in runs from earlier in the week - i.e. gradually less settled. First of all just a word of warning - in times of uncertainty, stick to your ensemble means beyond a few days. Its something GP always used to caution and the volatility in the medium range operationals in the past week (not to mention of course through the winter months) has been nothing short of laughable, as can only really be expected from models which not only traditionally struggle with confrontation between HP and Atlantic LP's, but are trying to project something as chaotic in nature as the weather! The ensemble means have been painting the same overall picture into next week for some time now, LP anchored just to the NW of the UK, not necessarily introducing endless rain, more an unsettled sunshine and showers type scenario predominantly. And indeed this is still the direction the ensemble means are headed in for next week: (ECMWF still 0z at the time of writing) I think thereafter, and it's something that AWD as alluded to rather well above, some may be getting a little confused between the heights, and what particular heights will lead to in terms of surface conditions at different times of the year. Heres just a quick example of it i've picked out from July last year: Such a setup may not appear too bad on the face of things for Southern areas, particularly if people are still in the winter mode of model viewing, however in practice it lead to a rather unsettled picture nationwide, not just for Northern areas. The 0z ECM ensemble mean paints an almost identical picture towards days 9/10 at present: As stated previously, my own LRF didn't expect a sudden influx of Atlantic lows bringing days of endless rain, more a return to the kind of conditions experienced in May - i.e. showery. Of course we should also bear in mind that we had a few settled weekends during May as we saw temporary ridges develop particularly across Southern parts. However, the predominant story was a case of nothing to write home about. MJO headed for phases 3-5 according to the ECM at least, which doesn't bode particularly well for anything dry and settled for too long for the UK either: http://www.americanwx.com/raleighwx/MJO/MJO/JunePhase3500mb.gif http://www.americanwx.com/raleighwx/MJO/MJO/JunePhase4.gif http://www.americanwx.com/raleighwx/MJO/MJO/JunePhase5500mb.gif So all in all its the case of the headline summary from my summer LRF - better than 2012, but still not ideal. Finally given the projected direction of flow for the medium range, the CET might take a bit of a hit during the second half of the month too. SK

Some subtle differences in this mornings Ensemble means, but largely a similar picture as we move through next week, with lowering heights and lowering pressure likely to turn things rather more unsettled, with conditions that look conducive of a sunshine and showers type setup: Perhaps the risk much later on of low pressure rolling in off the Atlantic: Though as you can see, still differences in the overall suggestion towards day 10 even from the ensemble means So a slight downhill turn likely next week SK

I'm not entirely sure where the notion of the 'total breakdown' has come from (though I have been a bit busy for the past couple of days so perhaps i've missed something) As far as I can see its a largely similar story to the ensemble mean picture painted a few days back - trough anchored just to the NW of the UK next week, just close enough to promote a sufficient lowering of heights to leave the UK just the wrong side of settled, so a largely sunshine and showers type scenario, and thats very much where we look placed this evening so far (obviously with the caveat that we await the 12z ECM EPS suite). We can see this general lowering of heights on the GEFS suite: Today - 7 Days time: We see a similar(ish) scenario from the ECM det.: The rest of the ECM det. does actually show a slight rebuild of pressure once again, but given the recent volatility in operational NWP modelling, it might be best to hold fire until we have seen the ensemble mean consensus, and the strongest recommendation I could make at the moment is to stick to the ensemble means. So the story really remains the same as it has done for some days now (and I am sure John will confirm similar from the mean height anomalies) - increasingly less settled. In terms of the potential temperatures into next week there really is very little point speculating at present - very subtle changes in the flow, set against the background of the anomalously cool SST's at present, will make a huge difference from seeing value in the mid-high teens, to seeing temperatures soar into the mid 20's. Until we can get some sort of definitive picture on the surface flow, we are unlikely to be much the wiser. So as has been said previously really, we are not looking anywhere near as bad as last year, just unfortunately those hoping for the almost completely dry weather of this week to continue may be left a little disappointed. SK

Unfortunately another snippet from the summer forecast has already begun to ring true, and I fear theres plenty more on the way through the course of the summer http://www.bbc.co.uk/news/world-europe-22752544 The projected May rainfall anomaly: http://www.ukweatherforecast.co.uk/wp-content/uploads/2013/04/EuroRainMay.png The June anomaly: http://www.ukweatherforecast.co.uk/wp-content/uploads/2013/04/EuroRainJune.png And unfortunately, the July and August composites offer a similar prospect again. It could be a similar summer for the near continent to that of 2012 in the UK SK

^^ what AWD said ECM op follows the ensemble mean from this morning, with low pressure being anchored just to the North West of the UK. To answer Backtrack's query from earlier - we could end up with a NW/SE split yes, though it is likely to turn more generally unsettled for the UK as a whole (versus what we will see this week), the best chance of staying dry being further East, though even here I would expect some shower formation given the time of year and the type of flow suggested in current medium range NWP. Not a washout by any means, more just a general sunshine and showers type setup - thats the kind of base state I think we are looking at for the summer as a whole, though the expectation is for the centre of the toughing to migrate Eastwards over time SK

Beat me to it Phil, The GFS and ECM ensemble means looking remarkably similar to one another today at day 10: We can also view them as height anomalies here: As Phil says, you would describe such an upper pattern as more 'unsettled' or showery as opposed to full on cyclogenesis. The 11-15 day GEFS mean offers a continuation of this setup: Bearing in mind this is of course a height anomaly chart, whilst the significant feature initially looks to be the positive anomaly to the North-East, the real story for me is the lowering of heights through the Eastern Atlantic, meaning that lower pressure will never be too far away from the North-West of the UK, and is likely to see a continuation of the showery type setup. Though it should be noted we are still seeing a fairly considerable swing between even ensemble means on the final position of the longwave pattern at present. It's good to see a little continuity between suites this morning, and hopefully we can carry this forward and start to get a more stable outlook from medium range NWP. SK

(Sorry to be a little off topic with the first post Phil - just a few answers to some of the queries from the previous thread!) Hi Barry, No offence taken, this is a discussion forum and this is what it's all about. I think Tamara covered it pretty well above really. The only addition to make is that signal for the upcoming settled spell was there all the way back in late March when I first began compiling the preliminary summer forecast for another website, and indeed this was mentioned within that forecast too. So for me, this upcoming spell is the first major piece of verification for the forecast, aside from the overall cooler and unsettled theme projected for May. This is beginning to suggest to me that the analogue QBO and ENSO years selected are currently providing us with helpful hints towards the broad-scale (longwave) setup well in advance, and hopefully this helps to answer why I am now offering (with slightly more confidence) insights into the other strong signals derived from the forecast. The next such strong signal for a decent settled spell (i.e. more than 2-3 days in duration) is during mid July. The insight into the potential for a decent October, again as Tamara alludes to, should of course be taken with a pinch of salt being so far away. The technique I have used will have to be re-visited in a couple of months time to see whether my projections for the QBO and ENSO indexes are still following the same pattern as this summer - if they are, then the projection for October will have higher confidence. If not, then I will need to re-visit the analogue years to produce new composites for the autumn. I completely understand, given the track record of previous such forecasts from various organisations, that there is, and will likely remain, a lot of skepticism surrounding LRF's - i'm in the same boat, I was sceptical even of my own forecast, and remain so until I see further verification. However, hopefully the initial hit with the upcoming settled spell helps to add a little confidence to the forecast. And if I end up being incorrect, well then let's all hope its for the right reasons - i.e. unbroken sunshine all summer long! Also, just to answer 049balt's question quickly - i'm not expecting anywhere near the rainfall totals seen last year in the UK, with values likely to finish around the seasonal average. By way of comparison, here is the rainfall anomaly from last summer: And here is the projection for this summer based upon the composite years: Anyway, I had best get back on topic before I get myself in trouble! Just as a quick update - the 0z Glasgow ensembles, rather similar to yesterdays 12z in terms of the increasing precip. signal beyond the 10th: So unfortunately the medium range signal continues to be a less settled and slightly cooler one once again, much in line with the most recent ECM32 run with a cooler outlook beyond the first 10 days of June: SK

Thank you for your kind words Believe me I very much hope I am wrong too! I can deal with cold but it's the constant rain during the previous few summers that irritates me. We should end up better overall than the previous summers, with the next lengthy settled spell likely in mid July. Looking a little further ahead, the best month of the year could end up being October. But overall we may get off lightly rainfall wise - the near continent looks to have well above average rainfall, and we could see some issues here with flooding as the summer goes on, so anyone with a holiday planned, I wouldn't expect too much weather wise SK

Hi John, Completely agree. I was using it more as an easy demonstration of where we were headed as opposed to using it as an actual forecast tool SK

Yep and unfortunately this looks a very plausible route to me and is exactly in line with the summer expectations, with a changeover date of circa 10th June. We see strong signs of lowering heights and an overall Sceuro trough type development once more from the GFS at day 10 today: We can see signs of life from this sort of pattern on this mornings operational ECM too: The 12z Glasgow ensembles depict the transition rather well: And indeed the tendency shown by the MJO to move into phase 2: Corresponds to a similar pattern: But perhaps what best illustrates the likelihood of a return to below average temperatures and unsettled conditions is this: So from current medium range output the likelihood is of increasingly unsettled conditions by around the 10th of June. Of course before all that, we have some very pleasant days to look forward to - I would expect to see a 24c, perhaps even a 25c before the week is out where the sun stays out all day, and really we couldn't ask for a better start to summer. SK

Just to quantify my own preliminary summer thoughts, here was the temperature anomaly projection for May based upon the strongest match QBO/ENSO years: http://www.ukweatherforecast.co.uk/wp-content/uploads/2013/04/EuroTempsMay.png So in terms of the CET measurement area, its a prediction of between -0.3c and -0.6c. The current Net-Weather tracker - http://www.netweather.tv/index.cgi?action=cet;sess= - has us running at 10.8c, so -0.5c as an anomaly. So I am fairly pleased with that as a whole. The next stage is to see how the upcoming settled spell plays out, with the expectation that it would last around 10 days in duration, and that certainly by mid month we will be back into the unsettled and cooler regime. I will paste below the summary from the final summer forecast, issued on Monday, and the link to the full forecast is also below. SK

Just a quick note re: the potential area of lower thicknesses - this is one of those situations where you need to take a look at the individual GFS members to pick up on it, as opposed to just following ensemble means. All but three of the 0z GFS members have this area tracking towards the East of the UK, its just that there is such variation in both the track and the exact thickness that by the time you produce a mean output, it is 'washed out'. In the longer term, some wise words (as always!) from Tamara. If we take a look at the 6-10 day GEFS mean height anomalies: Note the negative anomaly just to the South of the UK - it really doesn't take much of a shift North for that to start to affect Southern parts of the UK with something slightly more cyclonic. The signal I picked up back in April from the preliminary summer thoughts for this settled spell was around 9-12 days in duration, so I would personally punt at this moment in time for some fine weather through until at least the 10th June once this spell sets in, with a return to the cooler, showery theme of May so far sometime between the 10th and the 15th of June. SK

Yep and, crucially, good agreement between the GFS and ECM suites: There could finally be some good news on the horizon this evening SK