I wasn't aware that the Met Office were still doing seasonal forecasts?

Gavs charts( UKMet) showing J J A certainly showed a cooler set up

Sorry but to say there is not doubt just isn't true

I'm not a weather expert in any shape or form, but we all know nothing is nailed on more than a few days out. Ever. 

I've been called worse!

Agreed and it been very long time since we had a decent warmth so we are well overdue for some warmth so I am banking ECM run. I never understand why northern blocking are being used and never have a wording like southern blocking and even so at southern blocking it still bring unsettled weather every now and then so same apply to northern blocking should bring some settled weather as well but in a cool side with sharp azure blue skies compare to hazy skies during southern blocking hot settled spells.  

After a fairly warm Saturday and Sunday for southern parts at least (though with some scattered showers possible), the exact details look crucial for Monday's weather. GFS (left) has the jet diving more sharply south, with cool air affecting most areas and a lot of cloud with that, keeping temperatures down in the low teens which is unusual for late May. Yet ECM (right) shows warmer air hanging on in the southwest, restricting the cool, cloudy conditions to the northeastern third of the UK (as a rough estimate).

Looking three days further on...

Both models show the Azores High having a greater influence again, this slowly gained during the preceding two days. The extent of it's influence has been upgraded a little over the past 24 hours, which is in keeping with the trends seen for Thursday-Sunday this week.

This tendency to underestimate the influence of the Azores High at the longer range may be down to Atlantic troughs being brought our way too quickly, as this over-progressive nature is one of the most common issues with numerical weather prediction beyond 4-5 days range. As the troughs are slowed down, the AH has a larger window during which to send a ridge our way.

The upshot is that we could see temperatures rise again for the middle part of next week. ECM's chart for Wednesday looks warm in the southwest with low 20's on the cards.

Beyond this point, we see the two models diverging markedly:

GFS (left) has slowed down the trough so much that it now makes it's drop south while just west of the UK. This then seems to set the stage for a blocking high to develop to our NE, this pattern of a trough to the west and blocking to the NE setting the theme for the rest of the run, airmasses often coming from warm sources but low pressure tending to produce a lot of cloud and rain - so mild nights and mediocre days.

ECM (right) still drops the trough to our NE, but then deals a wild card as cold air reaching the western North Atlantic via Canada triggers significant trough development between Greenland and Iceland, driving a classic westerly regime for the UK by day 10, most settled in the far south with temperatures on the rise, reaching average by day 10, edging above for day 11 I expect.

These two solutions are strikingly different, enough so that the speed of the trough later next week is unlikely to be the only major player in how things turn out - indeed the angle of the flow over Canada looks important because of the potential impact of that cold air I mentioned earlier.

Pivotal times as far as early June is concerned? Perhaps!

Superb analysis, James 

Agreed, one read and I'm up to date rather than wandering through some of the arguing previously.

HERE IS MY LATEST ANALYSIS USING DATA SUPPLIED BY THE NWP OUTPUT COVERING 5 OF THE WORLDS MOST POWERFUL WEATHER COMPUTERS ISSUED AT 08:00 ON THURSDAY MAY 21ST 2015.

THE CURRENT GENERAL SITUATION A ridge of High pressure across the UK will decline later as a front moves slowly SE across the UK tonight and tomorrow weakening as it does.

http://www.wetterzentrale.de/pics/Rtavn001.gif

MODELS-2 WEEK HEADLINE Slowly becoming drier and brighter especially towards the SW but still rather cool with a little rain at times towards the North and NE.

THE GFS JET STREAM FORECAST The GFS Jet Stream shows the flow currently well to the North of the UK before it diverts South across the UK later in the weekend. The flow then shows some desire to remain troughed across and near the UK but the strength of the flow is often weak and incoherent before settling to a point just to the North of the UK in a NE direction in two weeks time.

http://www.theweatheroutlook.com/twodata/datukgfshires.aspx?display=jetstream&model=gfs

GFS OPERATIONAL The GFS Operational today shows High pressure out to the SW of the UK with a ridge towards us at times the dominant player of the weather over the coming two weeks. Weak troughs are shown to round it's Northern flank and then move down over the UK at times offering a little rain but a lot of dry and benign weather overall. there is a period in the middle of the run when low pressure takes a more commanding influence across the Uk for a time with rain and showers for all before the Azores High builds strongly across the UK at the end of the run with sunny and warm conditions for all two weeks from now.

http://www.wetterzentrale.de/pics/Rtavn1441.gif

http://www.wetterzentrale.de/pics/Rtavn3841.gif

THE GFS CONTROL The GFS Control run also shows a lot of High pressure dominance this morning and makes less of the unsettled period mid run with only the North having any meaningful effect from this. This run too shows the chance of High pressure building across the UK later with temperatures becoming warm for all. A chance of a thundery shower in the extreme South is possible by the end day of the run.

THE GFS CLUSTERS The GFS Clusters today show total agreement on High pressure being the dominant weather pattern in two weeks time with various scenarios of positioning of the feature limiting differences in conditions to just varying degrees of warmth and sunshine.

http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cpre&HH=372&ZOOM=0&ARCHIV=0&RES=0&WMO=&PERIOD=

UKMO UKMO this morning shows a ridge of High pressure across the UK from a large High down to the SW of the UK lasting well into next week. The SW will see the best sunshine amounts and warmest conditions with a cool NW flow at times affecting the North and East but even here a lot of dry weather looks likely to ensue.

http://www.wetterzentrale.de/pics/Rukm1441.gif

THE FAX CHARTS The Fax Charts show a series of weak troughs moving SE across the UK on Friday and again on Sunday with the now outdated 20hr chart likely to be replaced tonight by more of a High pressure influence into next week as well.

http://www.weathercharts.org/ukmomslp.htm#t120.

GEM GEM this morning shows High pressure dominace too shifting it's centre more towards the NE late in the run. The weather will be best in the South and West in the first half of the run with cooler NW winds and a few showers affecting the East on occasion before all areas look like becoming dry and warmer late in the run as the NW flow becomes cut off.

http://www.wetterzentrale.de/pics/Rgem2401.gif

NAVGEM NAVGEM also shows the basic pattern of the rest of the output with High pressure down to the SW the dominant player. Dry and fine weather for many if not overly warm looks like the nain focus through next week with just a few showers at times towards the East.

http://www.wetterzentrale.de/pics/Rnvg1681.gif.

ECM ECM today also runs the theme of High pressure to the SW throwing a ridge towards the UK and maintaining light winds from the NW and keeping dry weather going for many apart from a little rain in the far North and East at times. There could often be a lot of cloud in the flow and a hiatus occurs later next week as Low pressure over the NE is expected to throw it's influence over all areas for a time with rain and showers before High pressure rebuilds strongly again across the South at the end of the run.

http://www.wetterzentrale.de/pics/Recm2401.gif

ECM 10 DAY MEAN The ECM 10 Day Mean Chart  from last night shows High pressure to the SW with a ridge close to Southern Britain while the North could be a little more changeable in a Westerly flow in occasional rain.

http://www.wetterzentrale.de/pics/Reem2401.gif

NOTABLE TREND CHANGES FROM PREVIOUS RUNS The pendulum has swung back to more High pressure domination across the UK through next week as the influence of lower pressure from the North is reduced this morning.

31 DAY HISTORICAL VERIFICATION STATS FOR GFS, UKMO & ECM The current verification statistics for the past 31 days shows ECM leading the way at 3 days with 96.6 pts followed by UKM at 95.8 pts and GFS at 95.1. At 5 days ECM  leads UKMO with 86.5 over UKMO's 83.4pts with GFS at 81.9. At 8 days ECM clocks in ahead of GFS at 52.2 over 51.9. Then at Day 10 ECM remains slightly ahead of GFS at 33.7pts to 32.9pts

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day3_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day5_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day8_PMSL_MSL_G2NHX.png

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/allmodel/daily/cor/cor_day10_PMSL_MSL_G2NHX.prig
 

MY THOUGHTS Well the pendulum continues to sway backwards and forwards between the risk of more unsettled and maintained cool weather to drier and fine weather with nearer to average temperatures through next week. The pendulum this morning has swung very much back in favour of OK conditions likely next week. Winds will still have a Northerly component to them so no particularly high temperatures look likely but in the strong late May/early June sunshine it will feel pleasantly warm and amounts of rain look like becoming particularly small for much of the two week period. The South and West look best situated to receive the very best conditions while the North and East are at risk of troughs trickling down the Eastern flank of the ridge across the UK with a few light outbreaks of rain or showers here and there but even here dry weather will dominate. There is then a chance mid term that Low pressure might give a brief unsettled period late next week and the weekend but in the output that's shown out to two weeks from now there looks like a good chance that High pressure could return and this time in a more favourable position to bring some proper warm sunny June weather. So all in all a good set of output this morning if it's dry and fine weather your after and while not record breakingly warm pleasant enough for many looks the order of the day. Then later after a brief breakdown renewed High pressure could see the UK more Summery in two weeks time.

Next update from 08:00 Friday May 22nd 2015

Seconded. Great and clear explanation of what's on offer. I would put my money on ECM being closer to the mark and a pretty decent beginning to June, if not a scorcher.

I know it's niimbyism but for those of us in the far south of the UK it has been a really good spring so far. No real heatwaves, but lots and lots of bright, sunny and useable weather.

It has indeed, Rob, and continues to look very decent. Not bad considering it's still spring. 

I'm noticing how the GFS appears to be going off the idea with the northern blocking type set up - and I think that is good news in forecasting terms as persistent northern blocking set ups doesn't do much as far as this end is concerned. The drawback is a continuation of the unsettled theme over the northern half of the UK while the southern half tend to have the best of the drier and brighter weather along with near-average temperatures . . . exactly how it should be as far as our climate is concerned.
  Okay, we're not quite seeing a 1976-esque set up just yet but the "default" mode can still provide some decent summer-like conditions for some of us anyway. 

I'll second that one Rob. Well said. Although its been cool quite a bit of the time - It's not been dark dank grey miserable and wet all the time.

Indeed some days have delivered nice cool dry and crisp sunny days.

Been a decent Spring here, sure you're in London and not Aberdeen?