Focussed Model Discussion

[IDO]

No surprise the ECM has flattened the pattern, it was the most progressive with the MJO led Pacific Ridge, that has now vanished from early February! It has gone to the extreme pattern after D8 that GEM was flagging when it followed GFS with the pattern change a day or so ago. I suspect ECM over progressive and yet another D8i-D10 run to the bin. It is an exasperating model at times!

The GFS op is also at the milder end of the envelope and likely a worst case scenario. It was always a bit of a push yesterday how it handled the trigger (now spoiler) low, splitting it, and the GEFS have downgraded this option. I suspect further runs today will upgrade the medium range, but again the NH pattern is not our friend and without the micro details favouring us we are not going to be as lucky with cold/snow after D8.

The mean from D8-D13 continues to highlight the draining of the Canadian vortex to the Pacific Trough, which as with previous runs means the slacking of the NW-SE flow. The Atlantic Ridge -v- Canadian PV flow dynamics change and the euro trough becomes less of a conduit for the energy:

This would be OK if we can get to a cold embedded upper cold by then but without the trigger lows and mini-ridges complying we are left in a rather underwhelming seasonal flow.

Let's see how the day plays out, hopefully, the op takes are improved on (should be unless a trend), for at least the medium term, then we can worry about the 5-7 day period where the Atlantic sector quietens. After that, the Pacific vortex lobe appears to move towards Siberia, so that could allow a more meridional downstream flow to the Americas?

[knocker]

The ecm is different this morning from quite early on. At T84 it develops a wave on the front at 30w of Cornwall/ It then deeps it rapidly and trackes it east over southern England on Tuesday with heavy rain and strong winds. Possibly some snow on the moors, It runs it up the Channel  After a very brief ridge heavy rain and gales arrive on Thursday as a major trough tracks east across the Atlantic bringing about a very unsettled end of the week

The Channel low next week develops this weekend on the front in the baroclinic zone off the north east coast of North America. It will be interesting to see if anyone else picks it up because Exeter certainly haven't

Edited January 25, 2019 by knocker

[knocker]

The ecm NH profile at day 10 is pretty much along the lines of last night's ext anomalies

Edited January 25, 2019 by knocker

[knocker]

The significant difference with the EPS mean at day 10 is no major trough in the Iceland area which creates doubts on the latter part of the det run

Edited January 25, 2019 by knocker

[mountain shadow]

30 minutes ago, knocker said:

The significant difference with the EPS mean at day 10 is no major trough in the Iceland area which creates doubts on the latter part of the det run

My feeling is though Knocker, is that the ECM det. run has been running the show of late with the ens. following.

I guess, more runs are needed.

[bluearmy]

23 minutes ago, mountain shadow said:

My feeling is though Knocker, is that the ECM det. run has been running the show of late with the ens. following.

I guess, more runs are needed.

Not at days 9/10 MS 

[stodge]

Morning all

I've not been in the Banter thread

2 hours ago, IDO said:

No surprise the ECM has flattened the pattern, it was the most progressive with the MJO led Pacific Ridge, that has now vanished from early February! It has gone to the extreme pattern after D8 that GEM was flagging when it followed GFS with the pattern change a day or so ago. I suspect ECM over progressive and yet another D8i-D10 run to the bin. It is an exasperating model at times!

The GFS op is also at the milder end of the envelope and likely a worst case scenario. It was always a bit of a push yesterday how it handled the trigger (now spoiler) low, splitting it, and the GEFS have downgraded this option. I suspect further runs today will upgrade the medium range, but again the NH pattern is not our friend and without the micro details favouring us we are not going to be as lucky with cold/snow after D8.

The mean from D8-D13 continues to highlight the draining of the Canadian vortex to the Pacific Trough, which as with previous runs means the slacking of the NW-SE flow. The Atlantic Ridge -v- Canadian PV flow dynamics change and the euro trough becomes less of a conduit for the energy:

This would be OK if we can get to a cold embedded upper cold by then but without the trigger lows and mini-ridges complying we are left in a rather underwhelming seasonal flow.

Let's see how the day plays out, hopefully, the op takes are improved on (should be unless a trend), for at least the medium term, then we can worry about the 5-7 day period where the Atlantic sector quietens. After that, the Pacific vortex lobe appears to move towards Siberia, so that could allow a more meridional downstream flow to the Americas?

This is an excellent analysis, my friend, and I've noticed some sign in furthest FI of the PV starting to shift but we need to see that come forward.

One or two of the models starting to sniff the slowing of the Atlantic juggernaut and seeing where we can get some heights.

Control at T+300:                                        Parallel at T+360:

I said last night the current pattern lent itself to snow rather than cold - the irony might be that come February we might be looking at cold and not snow if we can get HP setting up in the right places.

[Singularity]

I agree with the consensus on the ECM 00z being highly out of place past D6. I can't find sufficient reasoning in teleconnection science to justify what it does with the Atlantic trough and subtropical high, and the EPS remain much more as should (in theory!) be anticipated.

It remains to be seen whether the trough in the N. Atlantic will really prove such a difficult character; the GFS 06z offers a hint that it might not consolidate quite so well as the 00z runs were generally keen on.

A key positive development to watch out for is elongation along a NW-SE axis as that works in favour of the trough disrupting with smaller lows breaking away and sliding into the base of the trough already present E or NE of the UK.

At the other end of the scale is elongation on a SW-NE axis which would greatly interfere with the sliding into Europe process - something the ECM 00z took to the extreme even before the surprising subtropical ridge behaviour.

In the middle is no elongation at all... this can serve to build a ridge to the east of the system, but it looks unlikely that the zonal winds will drop out soon enough for such a ridge to avoid being 'toppled' across the UK, which while it could provide a decent easterly, probably wouldn't in this case as the Euro trough wouldn't receive the required reinforcements to sustain itself S of the UK at the surface level. It'd just most likely end up being cold and dry across the UK.

 

Past D8, there remains a distinct lack of clear and, above all, consistent indication for tropical-stratospheric co-operation despite the tropical guidance having improved markedly in recent days. Once I would have considered this to almost certainly be the models lagging in their adjustments to the changing forcing (which used to work very well for me!), but this winter has made me very wary of such assumptions. So I'm not sure where things really stand for Feb - a month during which increasingly exceptional weather patterns are needed to provide more than transient snowfall to the lowland south for example.

[knocker]

This is the area that the ecm developed the Channel low

[alexisj9]

12 minutes ago, knocker said:

This is the area that the ecm developed the Channel low

Not sure how much snow can be on that, unless the cold to the east is very potent, it'll be a very warm low.

[Man With Beard]

Morning all - Well there's a lot going on weather wise. From an IMBY point of view it's interesting to see some models playing with a snow event next Tuesday to Thursday that includes South of the M4 - but if that's going to be a complex forecast, then what follows looks even more. I've been following the ECM clusters for the turn of the month - a few days back there was an op vs ensembles standoff - the standoff appears over with a blend of previous options - no minor ridge approaching W Europe, but troughing stalled further west. The clusters make it look fairly straight forward... 

... but I'm far from convinced. The formation and positiining of the trough at T168 is dependent on a combination of low pressure heading east from Canada, and shortwave moving west between Norway and Iceland. That doesn't sound like a stable combination for a forecast. I give it at least 24 hours, maybe 48, before confidence can grow to sufficient levels. 

Further on, in the D11-D15 period, high pressure replaces low pressure as the dominant theme. Where that ends up remains questionable, but Scandi remains well placed in the options. But will the Canadian vortex relent, and is that being modelled correctly? 

[kold weather]

31 minutes ago, knocker said:

This is the area that the ecm developed the Channel low

I think I will need to bust out my tropical tracking models to see exactly what the models are forecasting down in that neck of the woods and see how realistic it looks, I've had quite a bit of experience in the summer looking how lows form within frontal boundaries down there.

Still enough uncertainty with the low and its behaviour to rule out anything for Wed-Thurs bigger low that comes down from Canada, the models are pretty keen on phasing it and strengthening at some point before it reaches the UK. I'd not say its a certainty, although the angle of approach probably means the south is going to have a hard time with anything other than maybe the briefest of transitionary snow unless the LP really does change its presentation.

Further north I think is where the games really are and I think personally the snow line is really a moveable feast to some extent. The double barrel nature of this low is going to cause the models all manner of problems and therefore away from the far south, I'd say its best to keep options open. Right now northern England and Scotland are on more firm ground for a snow event, but shifts of 100-200 miles at this range are pretty likely and that could make the world of practical difference.

After that, a good sign at least from the GEFS is the low moving eastwards, if it does get strong enough or remains strong enough it may help to drag back down colder air again which would basically reset us back to square one.

Beyond even that, and more than a few hints from the models of pressure rising to our north/north-east (right in time for my 5-10th Feb call) though it remains to be seen whether its actually going to be of any practical use for us.

[Drifter]

Hi all, a few days ago I read about the easterlies up in the stratosphere downwelling to the troposphere albeit slowly.

Has this happened yet / is it still on track to happen?

Thanks

[knocker]

A quick look at the next 36 hours. This evening and overnight much of Britain will remain under warm sector conditions so cloudy, mild and the patchy rain/drizzle on occasion, mainly in western areas. The exception to this is Scotland where rain is already into north western areas and this will continue through the evening and overnight and pep up considerable by the early hours, with some snow on the higher ground, as the triple point and cold front edge closer from the west.

The heavy rain will continue over northern Scotland through saturday morning whilst the aforementioned cold front with a belt of heavy rain tracks east from Ireland from 1000 onwards.The wind is now picking up and behind the front frequent squally showers which will be of snow over northern Scotland as by now the colder air is creeping south.

Through Saturday evening and overnight Sunday the wind now becomes a factor as it veers and strengthens as the low tracks east and in the colder air wintry showers become more prevalent and snow could reach low levels in the north and even a tad further south and blizzard condition could prevail on some higher ground in Scotland.

Edited January 25, 2019 by knocker

[bluearmy]

35 minutes ago, Drifter said:

Hi all, a few days ago I read about the easterlies up in the stratosphere downwelling to the troposphere albeit slowly.

Has this happened yet / is it still on track to happen?

Thanks

looking at the wording of the metoffice 15/30 dayer, i would say that they think its likely to happen by mid feb

[knocker]

The ecm this evening still develops the wave but tracks a weaker version from this morning south east into Biscay early Tuesday morning,. Not so the next one which develops in mid Atlantic, under the auspices of the main trough, by midday Wednesday. It then tracks east and deepens to be over Ireland 24 hours later Over the next 24 hours very wet and windy weather is the order of the day with a mixture of rain sleet and snow, with the latter more likely along the frond as it tracks north east but far too early to worry about the detail

[Drifter]

Just now, bluearmy said:

looking at the wording of the metoffice 15/30 dayer, i would say that they think its likely to happen by mid feb

Cheers - would that be unprecedented in terms of SSW and downwelling lag?  Seems like it's been a very long time.

[WhiteFox]

25 minutes ago, Drifter said:

Cheers - would that be unprecedented in terms of SSW and downwelling lag?  Seems like it's been a very long time.

It's an interesting question. If you look at this plot from earlier:

You can see that the reversal is forecast to reach the surface by end of January/start of February. The 12z GFS does show this, but it's in the wrong part of the Arctic to promote blocking in our region and serves to push lower heights to areas unfavourable to development to our north:

Of course, it would not be static and would move around (were the downwelling forecast to verify) so the positioning could change to a more favourable location.

A negative AO only tells us that the average heights over the Arctic are higher than the average heights around 37-45o North. 

It would seem that the Met Office are seeing something in their models which favours blocking towards our side, so it's something to watch. Obviously nothing really showing on the NWP models that we can see right now...

[knocker]

There has been a reasonably significant change with th EPS mean anomalies in our neck of the woods over last couple of days. A more concentrated Scandinavian ridge complimenting a weaker more negatively tilted European trough with a flat westerly upper flow across the Atlantic diverging in mid Atlantic around the ridge, Portending temps continuing below average, albeit not excessively so, leaving the det runs to sort a trick surface analysis

[Snowman.]

4 minutes ago, knocker said:

There has been a reasonably significant change with th EPS mean anomalies in our neck of the woods over last couple of days. A more concentrated Scandinavian ridge complimenting a weaker more negatively tilted European trough with a flat westerly upper flow across the Atlantic diverging in mid Atlantic around the ridge, Portending temps continuing below average, albeit not excessively so, leaving the det runs to sort a trick surface analysis

The connection of the aleutian low and Canadian lobe has to be of some significance? Wouldn't drain the lobe pulling it further west? 

[bluearmy]

14 minutes ago, knocker said:

There has been a reasonably significant change with th EPS mean anomalies in our neck of the woods over last couple of days. A more concentrated Scandinavian ridge complimenting a weaker more negatively tilted European trough with a flat westerly upper flow across the Atlantic diverging in mid Atlantic around the ridge, Portending temps continuing below average, albeit not excessively so, leaving the det runs to sort a trick surface analysis

More slidergate with the developing scandi ridging and the arctic high getting a little closer to influencing our side of the NH 

[Snowman.]

17 minutes ago, bluearmy said:

More slidergate with the developing scandi ridging and the arctic high getting a little closer to influencing our side of the NH 

Deep trough on the eastern flank of that high, what's your opinions on it?

[damianslaw]

2 hours ago, Drifter said:

Cheers - would that be unprecedented in terms of SSW and downwelling lag?  Seems like it's been a very long time.

2013 delivered a very long time lag, more than 2 months to have full effect, there was a quick initial response a week or so after the SSW in early Jan, it then became mild end Jan- early Feb, and then generally cold, but not exceptionally so rest of Feb, a milder blip early March, but with major northern blocking not taking hold until about 9-10th.. That was a very long time..

[knocker]

54 minutes ago, bluearmy said:

More slidergate with the developing scandi ridging and the arctic high getting a little closer to influencing our side of the NH 

Or if the ridge developed enough a surface high cell becoming the influential factor

[Man With Beard]

ECM clusters tonight. I think they show a. what a tight line it will be between a northerly and southerly flow for the UK in the D6-D10 and b. how difficult it will be to predict the phasing of incoming lows, not just once but maybe a few times:

In the D11-D15, ridging still looks set to take over all around us, but where it sets up, well, pin a tail on a Donkey probably easier :

Bear in mind that because of the curve on these charts, ridges far to the top right are actually more ENE than NE. 

Studying the individual ensembles, there indeed some whopping Highs by 8th Feb (1050mb or above), but plenty of the members also have the Highs slightly out of reach to have that much direct input into the UK. The fact that we have ensembles with Highs both to the NW and to the E is the reason for the mean NE ridge - i.e. the mid point (I think) but it doesn't tell the whole story. 

Edited January 25, 2019 by Man With Beard