stodge

Evening all Glancing at the charts as we move past the middle of the month and a comment I made partly in jest about the northward movement of pressure systems keeps nagging at the back of my mind. It looks to me as though the Azores HP is pitching further north than usual and becoming more of a mid-Atlantic feature which in turn seems to re-enforce blocking to the north and east and leaves the trough over the British Isles and NW Europe or perhaps further south over Iberia . It certainly seems an extension of the post-SSW post-winter pattern - whether this is in any way connected to events elsewhere is above my pay grade. The one thing I'm still not seeing is an active Atlantic.

Evening all My only observation on the 12Z output is the degrading of the influence of Scandinavian heights in favour of a broad but shallow trough from the Atlantic by T+240. This would keep the weather unsettled to a point with showers and perhaps storms but nothing desperately cold or warm. Day time heating would trigger shower development and some could be heavy and prolonged with little or no wind. April Showers in May? It's happened before and it'll happen again. Much further into FI and some hints of the Azores HP becoming influential (or trying to) as we approach mid-May. There's quite a deep LP over North Africa and that keeps the Azores HP either out to the West or its ridging is less extensive. It has been argued the changes in weather patterns associated with a warming world would include the northward shift of equatorial or tropical pressure systems. That would, it seems to me, bring the unstable tropical LP further north perhaps into North Africa or even southern Iberia re-enforcing the traditional "heat low" as the temperatures rise. A sitting LP over south west Europe is going to have an impact on the summer weather pattern further north.

Yes, though we do occasionally get a final N'ly burst in early May (the Buchan cold spell anyone?) The wedge of heights moving SE from Greenland to Scandinavia - reverse retrogression if you like - initiates an E'ly flow over the British Isles. Some disparity as to whether we get a more ESE'ly flow or as ECM suggests quite a cool ENE'ly (Scotland stays under negative 850s). From there, nothing certain - GFS, as it tends to, wants to return to "normal" service so we see a return of the Azores HP and lower heights along with a more active Atlantic though even then the tendency for heights to stay to the north and push a still weak jet south is in evidence. As @damianslaw suggests, nothing too dramatic, probably not that brilliant in the east especially if ECM is right with the west and to an extent the north west the best places for warmth. An increasing possibility of more unsettled conditions coming into the south west as the Atlantic trough finally gets a bit closer but that's for after the Coronation I suspect.

Evening all Not a lot to add tonight. 12Z ECM OP goes in a different direction with the return of an Atlantic influence but otherwise it's northern or north eastern blocking into the middle term with E'ly winds across the British Isles. How does this change further into May? Hints perhaps from GFS of the Greenland heights finally starting to break down but the Atlantic remains slack to say the least and all we get are shallow troughs meandering east on a broadly southerly jet so showery and unsettled albeit warmer than now (which wouldn't be difficult) as we head into the new month would be my call especially from after Coronation weekend (which at least looks respectable currently).

Evening all Well, contrary to some, I've not minded the weather over the past few weeks. Anyway, this is about the models and I have to say GFS 12Z OP is a treat if you enjoy cool, anticyclonic weather but it looks like an outlier and smells like an outlier so probably is. The propensity for northern blocking continues and it's not just GFS which keeps that signal - the Atlantic is moribund and it may be we'll see lower heights over Europe become more influential as we move through May which again won't suit many. I do think we'll move to a more SE'ly component particularly if the Atlantic trough can get a little closer but at this time a lot of options are on the table albeit with nothing happening very quickly.

As the wind has risen, the clouds have dispersed and it's now fine, clear but chilly here in downtown East London. We often see this with easterlies, an initial cloudier spell and then the drier, clearer air moves in.

Evening all A classic mid-spring easterly spell setting up with a retrogressive HP this week ambling west to the north of the British Isles. Oddly enough, it’s the attempt to build heights from the south west which prolongs the cool spell as it prevents a west-based NAO developing and the developing trough takes over Scandinavia and drags down an unseasonal NNE flow. Ground frosts in sheltered areas and snow over Scottish mountains along with cricketers wearing snoods - the tell tale signs of spring. Further on and persistent heights to the north and a moribund Atlantic keep an Easterly component - we have to hope the Atlantic trough gets close enough to introduce more of a SE’ly in time. Worth repeating if you had to put your mortgage on one time in the year when an E’ly was most likely, this would be pretty close. It will warm up - of course - and perhaps we’ve been spoiled by some warm Aprils in recent years but the synoptic evolution is keeping us on the cold side of the street for now.

Evening all Quite unsettled for much of the week with LP very much in charge especially Wednesday and Friday. Signs then of a pattern change with heights rising to the east and the Atlantic influence withdrawing and the long-modelled anti cyclonic E’ly setting up. Good to see such wide cross model agreement at this stage but the Atlantic has proved more resilient than I expected a few weeks back. Longer term, we may see another attempt as we often do in April to build blocking to the north but that’s a long way off.

Evening all GEM does sit a little on its own this evening with the ridging coming from the south. Much of the other output builds heights over southern Scandinavia - it’s not a classic winter “Scandy High” by any means but the lack of zonal wind and a moribund Atlantic enables a broad build of heights to the east. For the British Isles, it will be best in the north and west with warmth and sunshine and it’s hardly going to be winter further south and east but the fact is the cooler North Sea would promote duller, cooler conditions. If we can get a more SE’ly tilt that would bring widespread warmth but raise the chances of rain or showers to the south and west. Nothing unusual, it has to be said, for April.

Evening all Once again we see evidence tonight of the pattern change to the south as the heights which have dominated the winter over Iberia are replaced by the trough extending north from Africa. This pushes heights to the north over the British Isles and promotes east or southeasterly flows. Not unusual for spring in response to a slow Atlantic. It often leads to another chilly spell in mid April as we can get a north easterly which while not wintry would take the edge off the spring.

Evening all My eyes are drawn to the trough and LP developing over Iberia. It’s this rather than Greenland blocking which opens the door to an E’ly. It’s something we see in late spring and brings unsettled weather with showers and storms to southern Britain while the north and especially north west Scotland does well. The trough develops over the Western Sahara and Canaries and moves north - a broad but shallow feature on 12Z GEM but deeper and more defined with time on 12z GFS. Let’s see if ECM develops a similar idea.

Ah yes, but well worth the wait...

Alone of the models UKM doesn't show a shortwave around Iceland at about T+90 - that holds back the heights ridging south from Greenland and allows heights to sink south into Europe which in turn tilts the Atlantic trough back positive and brings back the southwesterlies. Without this shortwave, heights develop as we see at T+144 and push south holding the Atlantic back and maintaining a NE'ly flow across much of the British Isles.

Evening all Not too much to add this evening - the clash of airmasses across North America seems set to generate LP systems which trundle out into the Atlantic and toward us. No all-powerful jet stream or PV at work but the north vs south battle we often see across North America at this time allows for cyclogenesis where the air masses meet and, as we know, at this time there's plenty of risk of severe weather including tornadoes. The Greenland HP continues to wax and wane and we're now seeing a signal for renewed heights from the south which is usually the signal for something warmer, drier and more settled and I'm beginning to think we could soon see a better spell (perhaps around the turn of the month) as HP builds in from the southwest but that's a very long way off. The signal for Greenland ridging south east seems to have faded for now but it's hard to believe we won't see any northern blocking as we move into April.

And for those following the 18Z OP, it gets there without the spoiler LP.

To be fair, it's the same old story. The ECM 12Z OP evolution was perfect for the NNE'ly flow with the Greenland HP and a strong ridge to the south east. GFS 12Z OP develops a shortwave near Iceland otherwise it might have been very similar. Oddly enough, both GEM and JMA on their 12Z OP runs also develop a shallow LP near Iceland so there's obviously a signal for the Greenland HP to re-assert though to be fair this has been evident for a while but what we've not seen is complete trough disruption allowing mid-Atlantic ridging in the way ECM shows tonight. As we know and I accept my earlier was a bit lazy, -8 850s in late March can still pack a punch and if we can go to -12s over the far north, we can expect lying snow to high ground and perhaps transient lying snow to lower ground in heavier wintry showers (less likely further south but you'd certainly think any showers over the Pennines and Snowdonia would be snow in a set up with -8 850s). As said earlier, not an unusual set up in and of itself given either an SSW or an early final warming weakening the PV and reducing zonal wind speeds.

Heights to the north and/or east in April and May are far from unusual and can be result of a normal final warming let alone an SSW. I'd be surprised if we went through April and May without a spell of Easterly winds though whether north-easterlies, south-easterlies or straight-line easterlies depends on the orientation of the pressure systems and that's a tough one to call at this time. The Atlantic, as we're seeing now, goes quiet with decreased zonal winds - what can of course happen is heights to the north east lead to a general trough over Europe which can pulse north bringing showers or thundery rain to southern areas - it's not just about the anomalies but the wider synoptics.

Evening all Spring is, as we know, a time of conflict between contrasting air masses and we see that in tonight's output. The atlantic isn't pushing through in full-on zonal mode by any stretch and there are hints aplenty of trough disruption with the Greenland HP occasionally flexing south pushing the jet south with it. Occasional short-lived bursts of PM air notwithstanding there's nothing spectacularly cold in tonight's output nor, conversely, is there anything offering dry, settled and warmer conditions apart from a transient ridge.

Evening all Last night's theme of an elongated and shallow trough between heights to the north and south continues and it's quite an unsettled picture with plenty of rain over the next few days as we move more W'ly than SW'ly as the jet is squeezed down towards us. One or two models showing what might happen if the trough is split and heights rise but no clear signal as yet for a Scandinavian or Greenland heights rise to be sustained to the point it takes over from the Atlantic. In truth, nothing remarkable - interesting but no more. No sign, it must be said, of any prolonged warmer and drier weather before month end.

Evening all My rather simple take (compared with some of the quality posts on here) is that between residual Greenland heights and slack heights over the Azores, an elongated but shallow trough covers the Atlantic and periodically extends across the British Isles. We're not talking LP of 950 MB or anything like that - little or no cyclogenesis, indeed the LP approaching begin to fill and weaken as they arrive on a jet which is increasingly moving to the south. JMA shows what could happen if we caught a break between LP systems but other models don;t allow for that and instead maintain a broadly unsettled theme with neither the heights to the north nor those to the south able to break through the trough in th short term. Some indication toward the end of the month of another attempt at heights over Scandinavia but that's a long way off.

Evening all More signs this evening of the traditional late winter/early spring northern blocking heaving into view. As the LP next week, as it slows and disrupts in mid-Atlantic, heights can build from the north (or possibly the south, as JMA suggests). As the HP moves into Scandinavia, the Baltic trough heads south west and the NE flow re-establishes over the British Isles (even though its; the second half of March, plenty of -12 850 air embedded). Tonight's GEM 12Z OP is a gem (sorry) for cold fans with the Scandinavian heights and LP heading ESE crating a nice battleground through central Britain. The battle between colder and warmer airmasses is what spring is all about - we know the warmer air mass will win out at some point. The margins are very fine - it doesn't take much to shift the pattern between cold and warm at this time of year so we often see quite wild fluctuations in synoptics and in surface conditions so it can be 5c one day and 15c and a couple of days later and then back to 5c again.

Evening all GEM first proposed the notion of the Atlantic LP disrupting in situ middle to end of next week allowing heights to build from the north a couple of days ago. It's now showing up on a lot of the 12Z output - not perhaps a full disruption but the LP fills and eases ESE as heights build down and from then an E'ly is on the cards as we move into the final third of the month. It may be Northern Scotland never really loses the cold and snow tornadoes while further south the milder interludes get briefer and the colder spells get more pronounced - nothing desperte in all fairness (-8 850s at best, the hint of an occasional -12 but certainly a long way short of spring.

Evening all MY weather day started with a 5.30am start to see some big flakes of snow falling. A typical marginal "wet snow" event. By 8am there was a general covering on surfaces but no more than 1-2cm. By mid morning most of that had melted and a spell of rain at lunchtime finished off what was left. A typical transient snow fall for east London - nothing like what we got in mid December but a decent end to what has been a fair winter. I'm not expecting any more snow in my neck of the woods though I appreciate those further north and with altitude may still have hopes for tomorrow's LP.

Evening all As ever, I expect little or no snow in lowland East London but the evolution through the end of the week into the weekend continues to confuse. The colder airmass is proving difficult to shift and returning shots of PM air continue to affect the British Isles into next week. The EC46 suggests a return of northern blocking later in the month - to be fair, northern blocking at the end of March isn't unusual nor are E'lies in early April if I'm being honest.

Evening all Not wishing to sound like I'm stuck in a temporal loop but 24 hours and 14 pages on and my confusion remains undiminished.. I thought GEM was superb for cold fans but the inevitability of a messy breakdown from Thursday seems inescapable at this late hour. It does look as though it won't be a straight line to spring by any stretch with another PM cold shot likely through the weekend. Beyond that, who knows?