stodge

Evening all The T+240 view tonight from the main models: Respectively - GEM, ECM, GFS Op, GFS Control You pays your money - well, you know the rest. As always, huge differences depending on where heights are located - strong heights to the NW and the threat of that colder incursion from Scandinavia remains but nothing so stark from ECM which keeps the core of heights over or just to the NE and GFS OP which aligns the heights nearer to the British Isles so it's an E'ly but nothing very dramatic although the European trough is close. JMA continues to keep very strong heights over Greenland and to the north so it's a robust E'ly - it looks like another of those "if it were only January" runs.

I couldn't resist this: 12Z JMA at T+180. How often do we see a 1075MB Greenland HP any time and certainly in winter?

Evening All The 12Z output is still coming but the E'ly or SE'ly continues to firm up. That's the T+144 from UKMO, GEM, GFS Control and GFS OP. Some differences in HP positioning and the Atlantic profiles as you'd expect at this range but the net effect is the same with an airflow from the east or south east across the British Isles. Nothing too dramatic to be honest. Moving toward the end of the month both OP and Control keep northern blocking but the OP brings the trough much closer from the south. This broad but shallow feature would bring disorganised bands of rain and showers to southern parts but keep it on the warm side and even humid. The 12Z Mean at T+240 hasn't changed that much: I don't think there's much chance of a NE'ly blast from Scandinavia at this time though whatever happens the best of the weather look to be points north and west. The key is how close the trough gets to southern parts as we approach the end of the month.

Afternoon all ECM swung dramatically toward GFS overnight and this morning's GEM plays a very similar tune. While we might get a true E'ly, there are two other thoughts which are cropping up in the Ensembles across the board: 1) IF the northern blocking is too far north the south gets closer to the European trough and we'll import rain or showers from the Continent leaving the fine weather for the far north. The response to strengthening heights to the north is a broad but shallow trough from the Atlantic through Europe. IF the heights across Scandinavia are robust enough the British Isles is in the E'ly flow with the continental influence felt only in the Channel Islands and along the south coast as a strong wind - if not, pressure falls to the south and the instability manifests in the form of areas of rain or showers. 2) What often happens is the heights drop out of Scandinavia and retrogress to Greenland so we get a new LP developing to the north of Iceland which swings SE and introduces a cool/cold NNW'ly airflow so the flow is E then NW then N as the HP re-consolidates over Greenland/Iceland which is effectively what 06Z Control shows. The 06Z Mean tells you all you need to know:

Singularity makes his usual interesting points - a late April E'ly is hardly unusual and neither is a cold spell in early May - both are usually related to the final warming, the weakening of the PV, amplification in the Atlantic and warmer 850s finally making it to Greenland and Iceland from either the south via a mid-Atlantic HP or from the ESE via retrogression from Scandinavia. I've put the ECM, GEM< GFS Control and GFS OP charts together - 12Z Output for T+240. The GFS OP looks the outlier as mb018538 has argued yet when you see the GFS OP consistently as an outlier it can mean it's seen a signal for a trend so I don't dismiss it that easily. The Control is much nearer the Mean while ECM and GEM play the spoiler LP game. It's not surprising as it happens so often whereas GFS OP has a cleaner (perhaps too clean) evolution. The GFS Mean still suggests an E'ly of some sort in the medium term and beyond so I think that's still the form horse and it's going to be a question of timing. Again, northern blocking late April-early May is nothing unusual. It can drop favourably for the UK and early May is often the best time to visit the NW Highlands and Hebrides which can benefit from the E or SE'ly set up.

As we await the 12Z Output, growing signs for an E'ly spell later in the month: The 06Z GFS Mean tells the story: Nothing too dramatic on the 850s at this time - the question is whether the air source is going to be more south than north of east. GEM 00Z OP in a similar place: ECM not quite there but being dragged toward the E'ly evolution. Nothing unusual about an E'ly in late April - we often see one as the PV finally fades - and this can transit into a colder interlude in early May. The GFS 06Z OP retrogresses in far FI with a much colder NE'ly airflow setting up.

Looking at the main 12Z OP runs at T+240: GFS: GEM: ECM:

Evening all The possibility of northern blocking later in the month remains very much on the table after some of the 12Z output. There are two scenarios I would argue - the first is we keep heights close to the British Isles, perhaps more over Scandinavia, and that draws up a warm ESE or SE flow. Dry for most, dull and misty along eastern coasts and the threat of some more unsettled conditions to the SW depending on how organised the trough becomes. The second scenario is the heights are too far north and the trough fills the gap - this is again not unusual for an early summer option. The trough sets up either over or close to the British isles but with little in the way of a jet the pattern stagnates - that either means rain or showers (or both) depending on how the trough is organised. ECM remains less than convinced for now and that's worth noting but I'll be interested to see if we start seeing some hints of an E'ly evolution in the modelling before long.

Afternoon all Hope all are keeping well. Both the GFS 06Z OP and Control get to an E'ly in FI and indeed hot for the first time the OP is quite keen on the E'ly setting in rather sooner. As the next HP cell weakens east, the trough to the south fills the gap by the end of next week with quite a thundery evolution I would think before the HP returns to the north and NE and the E'ly sets up. Control gets there by a slightly different route and would end rather colder but as you'd expect at this time of year the journey past mid month has both its warmer and colder alternatives. Coldies can salivate over P18 while P11 looks on the warm side of decent in a fortnight. ECM certainly wasn't interested in any kind of E'ly this morning but GEM had developed a warm but unstable SE'ly by T+240 in its 00Z OP. Also worth noting the final warming which Singularity referenced the other day and now shows up strongly in 06Z FI. It's this which often provokes the rapid tropospheric response which produces a sharp colder outlook in early May (the Buchan cold spell which is often a potent N'ly supported by strong heights over Greenland). I still think we will see, quite apart from the coming Sunday/Monday, another sharp colder interlude though whether that's later this month or early May remains to be seen.

The 850s are unremarkable after Monday so quite a diurnal range I'd venture with ground frost. ECM GEM and GFS all in slightly different places after midweek. The signal to build in HP is there but does it settle over us, to the north or to the north west?

Afternoon all An early glance at the 12Z output suggests we are looking at synoptic evolutions that we often see at this time of year as the winter PV weakens. HP is able to build north as pressure drops over Iberia and the Med basin - something we often see in late spring/early summer. GFS keeps the HP close to the British Isles despite an attempt at retrogression in far FI. The question will be how the European trough develops from mid month as to whether it influences the weather in the far south but with HP centred over to just to the north, it will be fine for many away from southern and eastern parts and as we often see in such a set up it can become quite warm in the far NW - often, late April/early May is the best weather of the year in the NW Highlands and Hebrides. GFS 12Z Control shows what can happen if we do get retrogression, the trough drops into Scandinavia and we get a potent N'ly - again, not unusual for a final burst of cold at this time and this is a recognised Buchan cold spell and it's a classic set up with -4 to -8 850s coming down from the north and north east. Would that be enough for snow for the mountains ? I think so.

Evening all In truth, we knew the N'ly was finished when it became clear the zonal winds were heading back well above average after the warming. The resumed deceleration is all well and good but the base wind speed remains well above the normal so the Atlantic very much in charge and plenty of chance for some early warmth with the winter nightmare synoptics and a long fetch SW'ly. GFS FI suggesting something more interesting heading toward mid month as the effect of the slowing zonal winds leads to a weakening and more amplified Atlantic with the jet heading a long way south. Nothing unusual - it often happens late April we see the Atlantic amplify and a build of pressure to the NW allowing for a late and often potent N'ly in early to mid May as identified by Buchan.

I think this tells us all we need to know about the evolution going forward. The current strong warming has only taken the zonal winds back to where they should be from the record-breaking levels we saw earlier this month. I thought (or hoped) the warming might have been enough to initiate the final breakdown of the PV but that was unrealistic given how strong the PV has been all season and as we know most warmings, after the initial dislocation, are followed by a re-strengthening of the vortex and this is going to happen this time so from zonal wins speeds of about average we'll see a new strengthening to the mid 30s by the end of the month. This will scupper both an E'ly after this weekend and a N'ly and allow the Atlantic to fire up for early April. The re-strengthening of the vortex at this time of year is in the nature of a dead cat bounce and it begins another sharp fall away in April but remains still well above average with reversal unlikely before mid month and more likely in the last week of the month (though some members keep positive wind speeds into May). It's a sharper decline than usual which may have some impacts - we often see northern blocking in early May along with the famous Buchan cold spell. I'm also noting the reversal may be stronger than average which may or may not be significant - I don't know. I suspect those hoping for a N'ly or E'ly in April are going to be disappointed with a more Atlantic profile than seemed likely a few days ago but early May may yet produce a late chill, we'll see.

Evening all An interesting set of 12Z outputs with sliders and shortwaves aplenty to keep us all guessing, I've ended up dazed and confused so a summary of sorts: UKMO: dry but increasingly chilly with -8 850s into early next week. IF we get some clearer air overnight frosts (and quite sharp frosts) look certain but so much depends on the cloud in the circulation of the HP. GEM: Not quite as good for the cold fraternity as you might expect from the 500HPA synoptics. The retrogression is clean enough but instead of a straight line N'ly, we get the trough coming in from Europe so a lot of cold rain with -4 850s. GFS Control and OP: Curious runs to this observer. Retrogression is thwarted by shortwaves but northern blocking sets up and the Atlantic in far FI tries to come back on a delayed by a deep LP which forms to the east of Greenland and moves east rather than SE so the N'ly is transient and as usual back comes the PV and the Atlantic in far FI but with the jet displaced to the south of the British Isles. ECM: Again, no real retrogression but the Scandinavian trough becomes the main influence and LP becomes negatively aligned pushing SE against some very cold air in situ. To be honest, I look at ECM and think higher elevations might well see some snow from the T+240 set up - frontal rain pushing into -8 850s could mean snow for the Pennines and Peaks perhaps (all very alliterative, I know). My conclusion is there's a lot of confusion post T+144. There's plenty of options around the fate of the large HP to the NW - will it retrogress, decline SW or decline over the British Isles? I'm none the wiser.

Evening all A couple of observations - UKMO has the HP much closer than some of the other models so we'll see. Second, the 12Z ECM T+240 is a notch colder than the 00Z version but the journey to the N'ly is somewhat different - GEM is a million miles away and while both GFS OP and Control show some form of NW'ly, it's a fleeting effort unlike the ECM which looks a serious early spring chill. Early April far from clear at this time.

I suspect not - UKMO has the SE at 1040 MB - GFS at 1025 MB - so any precipitation is going to be very light. GEM follows the trend though the Atlantic HP is being flattened at T+144 and is ridging east across Northern Britain - still a chilly air mass with -8 850s for most.

Afternoon all The UKM 12Z has raised some eyebrows: With 850s of -8 to -12 it will certainly be very chilly especially the further south and east. GFS 12Z OP at the same time: Both following the ECM 00Z OP this morning. Interestingly, the ECM kept heights to the west and north west even as the HP itself declined while the GFS migrates the heights more due north of the British Isles keeping a chilly but dry ESE'ly flow in place.

The question for me is whether the duration and strength of the PV this year has made them more rather than less likely. The current warming is substantial and that may be what is weakening the PV to allow blocking to occur.

Evening All Fascinating to see tonight's ECM 12Z OP follow last night's GEM 12Z setting up a large HP between Iceland and Greenland and sending a very chilly NE'ly flow across the British Isles. JMA also supportive of the evolution. GFS still struggling with this more unusual evolution - the mid Atlantic HP goes NE and to the north of the British Isles but the E'ly flow is maintained by the trough over Europe with LP close to southern parts. There's a breakdown of sorts in far Fi. In the shorter term the OP looks to have plenty of support in the Ensemble as the Mean suggests: It looks fine but chilly to the north and west and thoroughly unpleasant to the south and east - -12 850s approaching next Monday suggesting below average temperatures in contrast to this time last year..

Evening All Not a lot of clarity in the medium term this evening. The question is what happens with the second push of HP at the end of next week and there are four scenarios out there currently: 1) ECM 12Z OP: The HP tries to ridge north but fails and withdraws back SW though still as a strong anticyclonic feature. With heights to the SW and NE unable to assert the gap is filled by the trough and by T+240 clear signs of the trough becoming negatively aligned through the British Isles. 2) GFS 12Z OP: The HP builds NE and then transits to the east well to the north of the British Isles before collapsing SE into western Russia. There's a brief spell of E'ly winds before the Atlantic re-asserts. 3) GFS 12Z Control: The HP builds NE and sets up shop to the north of the British Isles instigating a pattern change to more northern blocking and a slack E'ly flow over the British Isles. 4) GEM 12Z: The HP builds NE and sets up to the NW of the British Isles as an intense HP in response to which the Scandinavian trough tilts SSW into Europe leaving the British Isles in a strong and cold NE'ly airflow. I'd argue looking at the GEFS at T+288 the OP is an outlier with the ensemble members strongly supportive of northern-based blocking though with varying permutations in position and orientation.

Evening all As we often see at this time of year some curious synoptics as the perennial battle between warm and cold air masses gets going. ECM 12Z OP ends with HP building to the north and north east: GFS 12Z OP looks very different: Control looks very different again: GEM closer to ECM as is often the case: The GFS 12Z Mean tells the story - a number of the GEFS are toying with rising heights to the NW as the PV shifts from its usual position further west or across the Pole to Siberia. The question is whether with heights to both NW and NE we will see the trough sit over or just to the north of the British Isles keeping us in a cool and unsettled NW'ly flow.

Evening all What strikes me from GFS and ECM in particular is the pattern change we are seeing in the medium term as, after months of relative heights over Europe, the continent sees a broad but shallow trough take over later in the month. Indeed, some of the charts look more like May than March in that regard with heights developing over Scandinavia and further NE. It doesn't look as though we will get an E'ly from an Scandinavian HP but from a European LP with the British Isles close to the trough.

Morning all It looks as though there will be too much residual energy in the jet to hold a Scandinavian HP in position so it sinks south to become a mid latitude feature. A continued lack of clarity going forward toward the end of the month. The PV at the 10 HPA continues to look very distressed at month end so a resurgence of northern blocking during April looks possible - again, nothing unusual in that. A bleak start to April from the 06Z GFS OP:

It looks as though the first attempt by HP to push NE into Scandinavia doesn't,work as there is still too much energy in the northern arm of the jet but the second attempt is more successful (Control says the third attempt). 10 HPA by the end of the month:

Nearly afternoon all Extraordinary weakening of the vortex as we approach month end but a long way off still.