Model output discussion - 5th December 2016 - Into Winter we go

[knocker]

1 minute ago, bluearmy said:

Assume ice means the Azores upper low will stop the mid Atlantic upper ridge from sinking south

what happens to the surface features is another matter !!

 

Yes I've edited my original post with my thinking on this because on it's own the Azores upper low certainly wouldn't stop it sinking as it would be the same scenario as the previous wave. I merely asked because IMHO there is quite bit posted on here that is just accepted without question and it shouldn't be.

 

[Dennis]

 

[Nick F]

10 hours ago, snowbunting said:

Wow. Woke this morning to a Greenie high, Nly flow and a block to the altlantic in early Jan with both the ECM and GFS agreeing for once at 240hrs. Cold core and wild cards indeed. Im not so good at teleconnections, stratospheric drivers etc but what has changed in the models direction last few days?

Good evening

I have posted in here a few times over the last few days, the models perhaps not handling well recently the pattern throughout the global tropics, with multiple competing modes of variability apparent, which could be creating noise to an active MJO and creating MJO plots in COD (Circle of death). A few days ago all models all of a sudden initialized the MJO in phase 6, despite forecasting it to stay in COD over previous days and also there is an increase in Pacific wave breaking forecast in next 7 days - hence IMO the change in direction of models in recent days.

Despite the MJO plots continuing in COD, apart from GEFS/GFS and JMA, the Homvoller, OLR and Vertical Velocity (CHI-200hPa) charts are suggesting an active MJO wave over the western Pacific. This enhanced convective / upper divergence signal shifting through this location shows well on from the velocity potential anomalies in this region. The GFS has persistently brought it out into phase 8 and/or 1 in early Jan and also JMA model.

A phase 6 brings the MJO over the western Pacific with enhanced upper divergence from the tropical convection here, well-illustrated by the development of a Typhoon Nock-Ten heading for the central Philippines. The wave propagation from this activity is likely why the models are showing a Pacific jet wave train and the enhancement north of a blocking high over far north Pacific / Gulf of Alaska - as per 330K PVU chart below >>>>

This amplification of the upper flow over N Pacific eventually working through across N America, with models dropping a lobe of the trop PV down across Canada and northern U.S. again - this amplifying a ridge downstream over N Atlantic and southern Greenland while at the same time the PV retracts from Greenland – sending the NAO negative in the means.

The neutral to –ve NAO N Atlantic ridge into southern Greenland is a bit of a wild card given models tend to be too keen to model it in the medium range then drop it short range. However, the empirical probability of a negative phase of the NAO is increased about ten days after the MJO is in phase 6, as per diagram below.

But with model initializing phase 6 at an amplitude of <1 and now in COD, is such as weak/negligible MJO signal going to have such an impact on teleconnections to bring this change to the upper patterns? Or maybe the models have been underestimating the strength of the MJO? This may be why the models are showing a temporary ridging over southern Greenland/Iceland and –NAO rather than a sustained block for now.

The forecast poleward N Pacific ridge well-advertised since early week and trop PV dropping south over N America – will help kick off a major anticyclonic wave break in the far north Atlantic that may eventually allow a Greenland ridge as advertised by the models, albeit it with the caveat it maybe transitory, during the first week of January. Something worth watching over the coming days... 

[knocker]

8 minutes ago, Iceberg said:

25w 30n on the 500 ecmwf.int chart

This has already been discussed and it's very unclear why this upper low would stop the HP sliding south east into Germany along the same track as the previous wave at T192

[weatherguy]

Regardless of specifics for our location (huge spread even at +240), the forecast disruption of the tropospheric vortex can only be a good thing when the it should be approaching its strongest at this time of the year.

ECM +24/240

GFS +0/240/384

[Methuselah]

12 minutes ago, Nick F said:

Good evening

I have posted in here a few times over the last few days, the models perhaps not handling well recently the pattern throughout the global tropics, with multiple competing modes of variability apparent, which could be creating noise to an active MJO and creating MJO plots in COD (Circle of death). A few days ago all models all of a sudden initialized the MJO in phase 6, despite forecasting it to stay in COD over previous days and also there is an increase in Pacific wave breaking forecast in next 7 days - hence IMO the change in direction of models in recent days.

Despite the MJO plots continuing in COD, apart from GEFS/GFS and JMA, the Homvoller, OLR and Vertical Velocity (CHI-200hPa) charts are suggesting an active MJO wave over the western Pacific. This enhanced convective / upper divergence signal shifting through this location shows well on from the velocity potential anomalies in this region. The GFS has persistently brought it out into phase 8 and/or 1 in early Jan and also JMA model.

A phase 6 brings the MJO over the western Pacific with enhanced upper divergence from the tropical convection here, well-illustrated by the development of a Typhoon Nock-Ten heading for the central Philippines. The wave propagation from this activity is likely why the models are showing a Pacific jet wave train and the enhancement north of a blocking high over far north Pacific / Gulf of Alaska - as per 330K PVU chart below >>>>

This amplification of the upper flow over N Pacific eventually working through across N America, with models dropping a lobe of the trop PV down across Canada and northern U.S. again - this amplifying a ridge downstream over N Atlantic and southern Greenland while at the same time the PV retracts from Greenland – sending the NAO negative in the means.

The neutral to –ve NAO N Atlantic ridge into southern Greenland is a bit of a wild card given models tend to be too keen to model it in the medium range then drop it short range. However, the empirical probability of a negative phase of the NAO is increased about ten days after the MJO is in phase 6, as per diagram below.

But with model initializing phase 6 at an amplitude of <1 and now in COD, is such as weak/negligible MJO signal going to have such an impact on teleconnections to bring this change to the upper patterns? Or maybe the models have been underestimating the strength of the MJO? This may be why the models are showing a temporary ridging over southern Greenland/Iceland and –NAO rather than a sustained block for now.

The forecast poleward N Pacific ridge well-advertised since early week and trop PV dropping south over N America – will help kick off a major anticyclonic wave break in the far north Atlantic that may eventually allow a Greenland ridge as advertised by the models, albeit it with the caveat it maybe transitory, during the first week of January. Something worth watching over the coming days... 

Thanks for the heads-up, Nick - though I'll never profess to fully understanding your posts, I do invariably read them...

One question that I have is: how is it that the models (not just the GFS) can show a Greeny High of circa 1050mb that then vanishes within the space 3 hours?

Anywho, tomorrow we might all be luck enough to wake-up to a 'Homvoller' of a run?

[Iceberg]

22 minutes ago, knocker said:

Yes I've edited my original post with my thinking on this because on it's own the Azores upper low certainly wouldn't stop it sinking as it would be the same scenario as the previous wave. I merely asked because IMHO there is quite bit posted on here that is just accepted without question and it shouldn't be.

 

Knocker I've gone back through the run using the 500 charts and can't see another example of such a strong upper low sat under the high and the high simply falling over it? I don't think it would  

can you post the chart your referring to ?

happy to learn

[Nick F]

7 minutes ago, Ed Stone said:

One question that I have is: how is it that the models (not just the GFS) can show a Greeny High of circa 1050mb that then vanishes within the space 3 hours?

Someone asked this question the other day re: why models show a strong surface high over Greenland only to quickly vanish, my reply back then is below which hopefully explains: 

On 12/19/2016 at 13:32, Nick F said:

Such strong Greenland highs are a common trait of NWP trying to model mslp at 3000m high on the Greenland plateau! So surface pressure maps over Greenland don't truly reflect the pressure over the plateau, rather they reflect the frigid cold air on the plateau. If the temperature changes on the plateau the pressure maybe a lot lower the next day. The 960mb seemingly so nearby is actually more accurately depicted as the low is over open ocean/ sea level.

In an ideal world, NWP should blank out the mslp lines around mountain ranges and plateaus such as Alps and Greenland respectively.

 

[Methuselah]

Thanks, Nick. That explains it perfectly!

[-uksnow-]

Even with 51 members, EC is going pedal to the metal with blocked Atlantic at 240 compared to the GFS.

 

 

[knocker]

27 minutes ago, Iceberg said:

Knocker I've gone back through the run using the 500 charts and can't see another example of such a strong upper low sat under the high and the high simply falling over it? I don't think it would  

can you post the chart your referring to ?

happy to learn

I'm afraid I can't post the charts I'm using but it goes like this. I grant that the previous wave and the HP dipping SE isn't precisely the same st the upper low is not so intense but moving forward. The revitalised upper low comes about when the Atlantic ridge deconstructs as the new HP wave gets under way and a lobe moves south as the ridge moves east and at T216 we reach this position (try to ignore the awful colours)

From here it continues to swivel and we end up here at T240 and as far as I can see there is nothing to stop it sliding SE unless the trough to the east phases in with the low to the SW which actually looks a possibility. Actually thinking some more about it you could well be partially correct if we take the combined efforts of the troughs helping to keep the HP centred to the south west of the UK but not ridging north.

 

 

Edited December 23, 2016 by knocker

[mulzy]

ECM control run is not that great tonight, but the extended eps look very decent.  Should be reflected in the De Bilt ensembles out shortly.

 

 

[Iceberg]

I've wrestled the laptop from my oldest, so can talk in a bit more detail re the high positioning.

I've put up the 500 anom chart as i think they are pretty good for these kinds of movements.

Always previously the high is well and truely linked across southern europe or down into the azores.

This time round the high is well and truely positioned mid atlantic, with the low below it we can safely say its not going south. If we look at the surface charts from 216 to 240 on the ecm we can see pressure falling 5-10mb in 24 hrs in France and Spain around the med, as the instability  from the colder air digger south drops heights. The natural movement of the high at 240 would then be to build west to NW due to WAA. We've not had a scenario such as the one shown at T240 on the ECM this winter yet. In many ways the high as the stability of a Omega high (although i admit it's not one).

The high at 240 does lose its greenland expansion due to the push of jet over the top, but not its real position.

Just imo.

[bluearmy]

Eps 10/15 days : mid Atlantic high, scrussian trough backing sw. Euro high anomolies become low anomolies. we sit in between. Mean uppers between -2/-5c, south to north. 

Not as flat as the gefs

be interesting  to see how many runs over de bilt are ne or even continental. looks like most will be onshore so not so cold. London should be a colder set later than the 00z suite. 

 

[Iceberg]

Just seen your reply Knocker and we are more in agreement i think

[knocker]

Having read Nick's excellent post earlier I was going to give the anomalies a miss but had a rethink and if nothing else keeps some continuity and perhaps they may be enlightening.

Strangely enough after today's  turmoil they aren't in bad agreement especially upstream. All have quite an intense Canadian vortex with a Siberian lobe and a positively tilted Aleutian ridge. Downstream, surprisingly perhaps, little amplification in  the Atlantic with a rather  amorphous zonal flow with varying degrees of positive anomalies, more so in the vacinity of the UK where there is some ridging  So as previously mentioned a westerly upper flow but quite slack over the south of the country where it probaly remain pretty dry Temps around average There's a glich with the ecm chart so no anomalies.

No total agreement in the 10-15 period although upstream isn't too bad with no significant changes although the EPS is still keen to promote the Russian vortex and the associated trough which is orientated SW and quite close to the UK. With NOAA and the EPS promoting quite postive anomalies and ridging to the west this scenario, IMO, continues to entertain some interesting possibilities The GEFS is not in agreement with this so in the pending file.

[Cleeve Hill]

https://mobile.twitter.com/BigJoeBastardi/status/812405629465882625/photo/1 

something for discussion. Happy Christmas all

[A Frayed Knot]

[Cleeve Hill]

RE the link don't think that is displaying properly. Basis Joe is saying big flip for Western Europe with Eurasia vortex setting up in Scandinavia in first week of January. Big chill coming. 

We shall see 

[Cleeve Hill]

3 minutes ago, A Frayed Knot said:

Thanks. Certainly did a better job copying across that I did. 

[knocker]

10 minutes ago, Cleeve Hill said:

https://mobile.twitter.com/BigJoeBastardi/status/812405629465882625/photo/1 

something for discussion. Happy Christmas all

Unless I'm having a senior moment both bluearmy and I have discussed it, albeit briefly.

[Methuselah]

As I've said before, there have been many winters in which cold northerly blasts have been interspersed with, often longer, periods during which milder Atlantic air has come around the northern side of Atlantic HPs...It's not always a strictly 'either-or' (frigid-ridiculously mild) scenario...The grey area in-between can be quite substantial?

[Cloud 10]

ECM ens. a lot more solid on the mid-Atlantic high than NAEFS at day 10,but at long last something to

keep an eye on.

 

ECM..NAEFS..

[Ali1977]

Hopefully GLOSEA and other METO models are still seeing this potential cold snap, I'm just hoping it can last till the 2nd week of Jan. 

[mountain shadow]

1 hour ago, -uksnow- said:

Even with 51 members, EC is going pedal to the metal with blocked Atlantic at 240 compared to the GFS.

 

 

Neither of these show a blocked Atlantic. If they did, the ridge would be away up onto Greenland.