stodge

We may well get an initial warmer phase as the HP moves in but if it migrates to Scandinavia in the medium to longer term it will turn colder.

Afternoon all The question seems to be whether we will see the Azores or Atlantic HP migrate through the British isles into Scandinavia or stay to the south west or just sit over us as a mid-latitude feature. All three options seem to be on the table at present - GEM 00Z OP and GFS 06Z OP and Control look to be heading to the Scandinavian HP route while ECM 00Z OP doesn't suggest that. I do think some form of HP or blocking is going to come into play after mid month but positioning and orientation (which are so important) far from resolved as you would expect. As many have said, relief for those areas with flooding issues but perhaps some overnight frosts and considerable diurnal range though IF we get a Scandinavian HP there's plenty of cold air to tap into and I would imagine -12 850s even at the end of March will have a bit of a kick.

Yes, Steve, so much depends on the positioning and orientation of the Scandinavian HP. If we get it right, there's plenty of cold air to call on but it's equally possible we'll see more of a mid latitude feature drawing in warmer air. The signal for a break in the Atlantic dominated mobile westerlies becoming more apparent from next week onward.

Evening All A stronger strat profile with colder 10 HPA values on the GFS 12Z OP tonight but a strong and prolonged warming throughout FI. Not as pronounced as yesterday but this warming cis in progress for a week and batters the PV back.

Tonight's GFS 12Z OP in far FI: Knocker has already posted the big change in the strat and the forecast for a rapid decrease in zonal winds by the end of the month albeit to still above average levels. The Mean tells a different story at this time:

Afternoon all Clearly "something" is going on - the 06Z GFS OP showed a very sick PV with a strong warming from the Canadian side through Greenland - quite unlike the usual warmings which emanate from Eurasia and push the PV back over to the Canadian side. The PV retreats further west which might explain the increasing signal for heights over Scandinavia though the 06Z Control threatens full retrogression at the end of FI. It looks as though we could see a lot of northern blocking through late March and into April - not unusual it has to be said

Evening all I'm sure I'm missing something but this looks like a split or splitting vortex to this observer: Obviously only one run but it's the GFS 12Z OP so some credibility. Is there anything at all in the strat forecasts to suggest a split two weeks down the line?

Evening All ECM 12Z OP continues the familiar theme for vigorous LP systems crossing over or close to the British Isles in the coming 7-10 days. Brief milder incursions mainly for the south but plenty of rain to come. GFS 12Z OP has another go at displacing the PV in FI and that allows height rises over Scandinavia but we'll see. The GEFS are a complete mix but with a tendency for more anticyclonic options as we move past mid month though the positioning and orientation of the HP vary considerably as you would expect.

I'll raise you P14:

Morning all As I've remarked on the strat thread the GFS is again showing a signal for change with the PV finally weakening and the Atlantic slowing. We've been here before of course but there has been a signal for this change to occur after mid month for a while (muted at times admittedly). The 00Z Ensembles (as with the ECM) showing no clear trend as we go past mid month and especially toward the end of the week after next.

Morning all Forgive me for being a little confused but as I look at the 10 HPA profile on the GFS into FI, I have the sense the Sun is starting to have an effect and the strat is warming. That doesn't look like a PV in its prime and for the second OP run in a row GFS is starting to break the pattern with the PV splitting away into Siberia and allowing warmer upper level temperatures into Greenland and encouraging strong northern blocking on the back of a slowing Atlantic.

Both the OP and the Control seem keen to displace the PV either over the Pole or to Siberia. This seems related to HP building in the central or western Atlantic. To be honest, the GFS went off on one yesterday in far FI but that happens with the modelling so far ahead. Until it comes to within the modelling range of ECM and GEM we can quite rightly be sceptical.

GFS and ECM look poles apart to this observer tonight. GFS 12Z OP at T+192: ECM 12Z OP at the same time: GEM 12Z OP at the same time: Nearer ECM than GFS as far as I can see. ECM screams no change to this observer with a continuation of the flat pattern into next week. A couple of better days with transient ridges but mostly unsettled with further rain for many areas.

GFS and ECM look poles apart to this observer tonight. GFS 12Z OP at T+192: ECM 12Z OP at the same time: GEM 12Z OP at the same time: Nearer ECM than GFS as far as I can see. ECM screams no change to this observer with a continuation of the flat pattern into next week. A couple of better days with transient ridges but mostly unsettled with further rain for many areas.

Evening all Well, after a week of unrelenting similarity, the models are starting to sniff change in the air (or something else, in my part of London you never can tell). The attempt to build a wedge of heights fails on the OP but doesn't on the Control leading to trough disruption and a warm SE'ly. The CFS 06Z monthly is eye candy for cold weather fans (the T+534 chart is a thing of beauty especially for the SE). I can't quite see why the 12Z GFS OP does what it does - the PV still seems very strong over NW Greenland while the Control takes the bulk of the PV energy over the Pole to Siberia. The 10 HPA on the 12Z OP looks interesting as the coldest strat profile seems to transfer back from Siberia to Canada in far FI - all very curious. GEM keeps the zonal train on the rails to T+240 while ECM 12Z is still rolling and we'll see. Is this a GFS curiousity or is there a new signal in town?

Whatever any of us "hope" is of course entirely immaterial. GEM isn't interested in settling the weather up to T+240 and looking through the 12Z GEFS it's certainly strongly anticyclonic on the OP but Control is different and the Ensembles are all over the place with some cold options for those who like that sort of thing. ECM 12Z isn't interested in HP building in as you say and the signal for that pressure build next weekend doesn't look as strong tonight as it did last evening. I can see nothing in the stratosphere to help us though the CFS once again posits the PV relocating to Siberia later next month and heights building into Greenland. For now, it seems "as you were" with a week of unsettled mobile westerlies with some potent secondary LP systems for the south and none too warm with 850s mostly below zero for much of the week.

NO, what you need is a tweak SE from the incoming LP. More of a slider which would allow the HP time to build - it' s stronger than on the ECM this morning but the net effect so far is the same.

(Snipped for ease). I'm also sceptical of the GFS FI "reset" or "Azores Ridge building in" options. The 00Z Ensembles in FI were even more all over the shop than usual with both very cold and warmer options. The question is whether residual strength in the northern arm of the jet will keep blocking to kid-latitude with HP centred over or close to the British Isles. I see no prospect of a Greenland HP but Scandinavia is different and it's possible to argue as the PV weakens (naturally) the opportunity for it to become dislodged a fraction further west to enable ridging into Scandinavia as the Atlantic amplifies will exist. I think you've called it pretty well - the crucial time frame for now seems to be the weekend of 7th-8th in terms of establishing a variation to the current pattern.

Morning all It certainly seems as though the mobile unsettled pattern is to be with us as we go in to the first week of March with any number of secondary LP systems heading across the south exacerbating rainfall issues. Moving to the end of next week, I've picked up a few charts for Saturday March 7th (T+216 on the 00Z suite): ECM: A NE'ly for the SE? Well, a faint one perhaps. GEM: A ridge across much of the British Isles settling the weather. GFS OP (00Z):: A stronger ridge as cells of HP from the Azores ridge NE. GFS Control (00Z): Very different with the unsettled theme very much in charge. I see no warming of any kind in the stratosphere to promote amplification so the best it will be is a transient tropospheric response and while the OP evolution into FI on the 00Z hints at spring we've been here before with the GFS which seems to "default" back to a zonal pattern in the OP. There's huge variety in the Ensembles including many much colder options. The monthly CFS 00Z run hints at a vortex displacement to Siberia in mid March but I struggle to see why this should happen. The form horse looks to be a continuation of the unsettled mobile westerly theme as IDO suggests but the bigger question for me is whether the near-record zonal wind speeds will fade away gradually or less gradually. The former would suggest the pattern continuing for a while but with the jet slowly easing back north as spring proceeds. The latter, a collapse in zonal wind speeds possibly via a strong final warming, offers the possibility for amplification and strong northern blocking - again, not unusual in April and May as we've seen in years past. What I suspect may happen is we will see pulses of weakening and re-strengthening during March and April. During the weaker periods, warmer air will get into the higher latitudes and colder air will escape south but that will in turn trigger a feedback response so the colder air re-asserts but in a weaker form. Eventually, by early May, as we know, the PV is pretty much dissipated for the season but the manner of its departure can have consequences for the northern hemisphere summer.

Morning all The "wintry mix" has reached lowland East London so it's good to be able to report I've seen falling snow in the 2019-20 winter season. It's not going to settle - the surfaces are too warm - but it's nice to see and it looks as though we have a bit more of this rain/sleet/snow mix to come though amounts not large.

Cohen does suggest normal to below normal temperatures for the UK over the next couple of weeks. I'd also suggest while he doesn't see the IOD as a reason for the mild winter, he hasn't got a better (or rather another) reason at this time. Finally, the question needs to be asked what happened this winter that the PV became so strong and the AO so positive. I do believe that the extreme positive AO was in large part related to the strong PV. But what caused the strong PV? I know the direct answer to this question. The large-scale circulation pattern in the NH was hostile to disrupting the PV for all three winter months of December, January and February. The pattern most favourable for disrupting the PV is ridging/high pressure across Scandinavia and the Urals with troughing/low pressure in East Asia the northern North Pacific. This pattern existed in November, when we observed the only disruption to the PV this fall and winter, but the opposite pattern has persisted non-stop for three straight months (see Figure iv). Weather patterns typically change every week or so what caused the same weather pattern to persist for three months? I have no idea and I don’t think there are any easy answers. For much of the winter as I have discussed previously, I do believe that Arctic sea anomalies were not favourable for disrupting the PV but I fail to see how that is really the answer. The Madden Julian Oscillation (MJO) did behave strangely this winter but it did vary and the MJO were in the phases considered most favourable for disrupting the PV (Garfinkel et al. 2012). People have mentioned the Indian Ocean Dipole (IOD) being in the positive phase but I just checked and the period when the PV was the least susceptible to weakening and the AO was its most positive, the late 1980’s early 1990’s, the IOD was predominantly negative. So, for now I believe any easy answers will remain elusive. So the question remains - why, once the pattern changed in December did or has it remained so persistent?

Afternoon all The GFS 06Z OP has picked up plenty of interest - Control goes in a completely different direction which makes me think the medium to longer term evolution is far from resolved. It's almost expected that in the absence of a clear signal GFS FI will default to a zonal Atlantic scenario and so it proves. Yet both OP and Control have support in the Ensembles so it's heads I win, tails you lose at the moment as to whether a tropospheric led change is likely in the second week of next month. The other change is the growing signal for a new warming at the very edge of FI - we've been here before but it's in the OP rather than being led by Control so I give it more credence. It also appears to be originating from the Canadian side which would support a vortex push into Siberia and perhaps some opportunities in mid to late March for us if the dice fall right. I'm also pleased to see Control following along however.

I also like the developing heights over Scandinavia at T=216 and T+240 which keep the trough negatively aligned.

Afternoon all Not much to add to what has already been said. The morning ECM 00Z OP certainly looked a chilly run especially for the north with milder incursions further south so not a huge change from what we've seen. The GFS 06Z OP certainly was a chilly offering - the jet heading south putting us on the cold side of the trough so secondary LP systems crossing the south means more rain and snow to northern hills and especially Scottish mountains. FI goes off on a bit of a tangent so we'll see. Control, it has to be said, keeps the jet that bit further north - the key, as I said yesterday, is the extent to which the Azores HP ridges into Europe. If said HP is held back in the Atlantic and the LP can move ESE into Europe supported by a build of pressure into Eurasia the trough becomes negatively aligned and we stay on the colder side. If the HP heads into Europe, the alignment goes positive and TM air spreads across the British Isles and into Europe. It looks a chilly and unsettled week to come though rain amounts don't look that great which I find surprising given the synoptics.

Indeed, not a hint of Wave 1 warming in the next two weeks.. The PV cannot continue at such levels ad infinitum - the question is whether the decline will be gradual well into April or even May or whether we will see a sudden and intense Final Warming which might not only open the door for some late cold but set up strong northern blocking for late spring and early summer.