Model output discussion - mid January

[Chesil View]

Just for fun but there are more than enough cold/verycold/snowy outcomes in the gfs perturbations longer term to keep ones interest maintained as we head towards february. Despite talk of higher sun and longer days in Feb.The deepest snow and biggest drifts I ever saw (20 feet) down here in Dorset occured in the second half of February and was still hanging around in April.

[Cleeve Hill]

For those that follow joe bastardi on twitter, he is pretty bullish about a v cold feb somewhere in the N hemisphere. He’s talking about MJO groing into 8,1,2,3 during February. Also M Ventrice showing GEFS going strongly negative NAO into Feb, although ECM not supporting this. 

[A.J]

* has a look at the thread title *

* looks at post content for the past few hours *

* leaves said thread with a slightly puzzled look on the face *

talking of which, considering the so so output for coldies the past few days, I quite like the 06z GFS, the building in of high pressure from the Azores eventually forming a mighty block....The atlantic sure won't be piling in if that verifies, and as it enters FI, there has been in recent outputs, a trend for retrogression which open the floodgates to some much colder air from the east/north east

Edited January 20, 2018 by ajpoolshark

[The PIT]

21 minutes ago, Cleeve Hill said:

For those that follow joe bastardi on twitter, he is pretty bullish about a v cold feb somewhere in the N hemisphere. He’s talking about MJO groing into 8,1,2,3 during February. Also M Ventrice showing GEFS going strongly negative NAO into Feb, although ECM not supporting this. 

That means a record warm Feb then. Don't take any notice of him he always says cold without fail every winter which generally ends up being a huge fail of a forecast.

[Polar Maritime]

Some posts have had to go, Only Model Ouput discusson please in here, There is the Winter thread or regionals for anything other.

Thanks please continue.

Edited January 20, 2018 by Polar Maritime

[feb1991blizzard]

1 hour ago, Dancerwithwings said:

The HIRLAM 0.1, AROME and the ICON was on town with APERGE then.........................Or are they on to something

There's an old saying at the Met Office, when the Hirlam, Icon and Arpege are all in agreement over frontal snow then they are almost certain to verify.

[Tim Bland]

GfS has shifted south a bit with snow tommorow as well

 

[Tamara]

A further illustration from me to show how the various trends in atmospheric angular momentum impact the tropospheric patterns as modelled by NWP

Here is the current year AAM plot which straddles the rolling year starting Jan 2017 to date Jan 2018. I think using a long term trend period of the atmospheric circulation that is representative of how the global wind-flows have ebbed and flowed within that time, focusses particularly well on NWP output and the key synoptic changes and 'weather events' that occurred as a result of those (often) sudden changes in AAM.

 

Some folk may be trying to remember the last attempted cold air advection Scandinavian ridge - though many will remember. It evolved during the opening 10 days of February 2017 - and look how it precisely coincided with the spike in AAM - which corresponded with an (albeit rather transitory) orbit of the GWO through Phase 4. Which has been a constant theme of discussion to look out for during this winter - and thus far elusive due to the strong easterly trades c/o the grip that La Nina has on the atmospheric circulation.

As reflection of the brief GWO orbit to Phase 4, note the brief if prominent spike of AAM tendency that produced it. The associated amplification flux in the troposphere that was responsible for its creation, and following a very brief weakening of the polar vortex, was rapidly scrubbed out by the MJO returning to a Nina atmospheric signal and the higher latitude ridge was unable to retrogress as it would have done under more sustained +AAM anomalies

Take a look again at the above AAM plot and see how momentum collapsed again properly during the summer - and, again no coincidence, mirrored synoptically by the poor weather seen especially after mid July, lasting through much of September after a reasonable start to the summer (but more so for southern parts)

.

Finally, see how an October rally in tropical forcing led a recovery of relative angular momentum into the early part of the winter - again coinciding with the repeated amplified patterns seen through that period, leading to the series of cold incursions that at least allowed glimpses of wintriness further south

Charts will be more recent and relevant in people's minds so space saved by no need to post them

That leads us more or less up to date with the further collapse in AAM heading into January, this time even more pronounced, and the consequent failure of the early winter pattern to re-amplify once more.

As the AAM plot above shows, the latest downward tide-mark has just about eclipsed the early autumn minimum.

So plenty of intra seasonal evidence just packed into a 12 month period to illustrate why rising AAM tendency propagating from the tropical to extra tropical circulation can build downstream amplified ridges that can assist cold weather in winter, and also, (because of the natural changes of wavelength that tends to migrate the ITCZ further northwards under higher angular momentum states in summer) warm spells at this time of year.

For many, the two most popular types of weather to chase between seasons on this MOD thread.

A year on from last Jan/Feb another Scandinavian high pressure is being chased. Also, a year on we are look again at a similar scenario in many ways in terms of waiting for tropical forcing to propagate into the Western Pacific and set up another significant rally in angular momentum tendency to usher the GWO (representing tropical and extra tropical wind-flows) away from the Nina dominated Phases 1,2 and 3 into Phase 4.

That just happens to lead us towards a focal point of anticipated hope that is similar time-period to 2017

Recent summaries have outlined the odds stacked against. Not insurmountable, but to give full credence to this methodology and how it works, the risk outcomes must be stressed fully to encompass the total range of probability of solutions that NWP might pursue over this last third of January.

The commonly referenced GEFS product forecast needs the usual caution caveat applied to it in terms of interpretation. Its often Nina biased, but this is one of those occasions where its focus of tropical bias might lead its modelling trends to actually under emphasise the atmospheric circulation in the extra tropics which will be swamped with easterly inertia c/o the La Nina forcing.

This has to be meaningfully overcome before rising AAM tendency can be seen to lift total atmospheric angular momentum to an equilibrium that enables the more amplified Phase 4 pattern taking heights further north and east to become more than phantom suggestions that come and go in some extended NWP ensemble sets.

This essentially re-emphasises yet again the main point of the last watching brief earlier this week, and posts prior to that. As others have posted, there are tentative signs of changes to perhaps impact patterns in the extended period that relates to beyond the turn of the month.

This can happen - a lot of data sets with new information are going to come and go over the next 10 days to a fortnight. However, with that in mind, subsequent AAM budgets really need to show that tropical signalling c/o the eastward propagating MJO are overcoming the considerable lag of easterly trade winds dumped into the extra tropical circulation.

In that sense its not at all just about the MJO - its about the consolidated La Nina feedbacks within the global circulation which have continued to cancel out attempts from the tropics to shift patterns.

That annual AAM trend tells us that we approach Feb 2018 with angular momentum required to recover from a lower base than 2017. That is a measure of the la Nina feedback in the extra tropics that has to be overturned in order to amplify the tropospheric pattern. It also puts some perspective on the stratospheric angle in terms of how tropospheric wave flux through frictional torque can propagate from the tropics c/o the MJO into the extra tropics and activate mountain torque induced perturbing of the vortex boundary layers 

Anyone continuing to debunk the concept of poleward tropical>extra tropical forcing and thinking that a La Nina tropospheric circulation has no bearing on mitigating the process of poleward +AAM disturbance within the polar field really needs to think again and adapt a wider acceptance more open minded perspective in my opinion. 

 

 

Edited January 20, 2018 by Tamara

[Man With Beard]

Perhaps a nuclear explosion forecast over Russia by UKMO?

[bobbydog]

1 minute ago, Man With Beard said:

Perhaps a nuclear explosion forecast over Russia by UKMO?

strange... 'stairway to heaven' maybe?

[steveinsussex]

Thanks for the in depth post @Tamara but could you please explain in simple terms what it means?

[BLAST FROM THE PAST]

GFS now showing signs of the HP control being the potential wrong direction.  UKMO showing further squeeze south.  So what I look for is deep depression / displaced PV coming in from Atlantic on fair south trajectory crossing the UK as we go through last week of the month and into Feb.  I am encouraged by what may be developing on the models.

I was interested yesterday on the Beeb forecast when they said Sat had gone backwards due to the failure of the front to push through NE.  Made think...is this the start of the adjustments 

BFTP

[summer blizzard]

2 hours ago, Cleeve Hill said:

For those that follow joe bastardi on twitter, he is pretty bullish about a v cold feb somewhere in the N hemisphere. He’s talking about MJO groing into 8,1,2,3 during February. Also M Ventrice showing GEFS going strongly negative NAO into Feb, although ECM not supporting this. 

The last two MJO waves have not really done much in phases 8 and 1 due to the La Nina so i doubt he'll be correct. 

[ICE COLD]

Is this not quite a significant warming showing ? And it's not to far out out in la la land . And wouldn't this have an effect ? 

[summer blizzard]

2 minutes ago, ICE COLD said:

Is this not quite a significant warming showing ? And it's not to far out out in la la land . And wouldn't this have an effect ? 

It may slow down mean zonal winds (amplify the pattern) but we really need a wave 2 event to cripple the vortex. 

[jvenge]

57 minutes ago, steveinsussex said:

Thanks for the in depth post @Tamara but could you please explain in simple terms what it means?

It means be cautious with MJO ramp posts and tweets, because although it may be more "interesting' than 5 or so days ago, it still has a lot to overcome. Not impossible for what is now after the first week of Feb, it is not majority favoured solution.

[SLEETY]

We just  CANNOT get sustained northern blocking in the model output, during the winter months any more,thats  why only really Scotland are having a cold winter ,because their location is far enough north to benefit from colder maritime polar air than further south.

Further south you need maritime Arctic air or  continental polar/artic air to bring cold and snow further snow,because of the shorter sea track

thats the simple explanation,of the differences and still NO sign of blocking setting up in the correct location from ANY model to bring a decent cold spell for all the country.

[bobbydog]

5 minutes ago, SLEETY said:

We just  CANNOT get sustained northern blocking in the model output, during the winter months any more,thats  why only really Scotland are having a cold winter ,because their location is far enough north to benefit from colder maritime polar air than further south.

Further south you need maritime Arctic air or  continental polar/artic air to bring cold and snow further snow,because of the shorter sea track

thats the simple explanation,of the differences and still NO sign of blocking setting up in the correct location from ANY model to bring a decent cold spell for all the country.

yet....

[Thunderywintrysnow]

14 minutes ago, SLEETY said:

We just  CANNOT get sustained northern blocking in the model output, during the winter months any more,thats  why only really Scotland are having a cold winter ,because their location is far enough north to benefit from colder maritime polar air than further south.

Further south you need maritime Arctic air or  continental polar/artic air to bring cold and snow further snow,because of the shorter sea track

thats the simple explanation,of the differences and still NO sign of blocking setting up in the correct location from ANY model to bring a decent cold spell for all the country.

Only Scotland?

[jvenge]

17 minutes ago, SLEETY said:

We just  CANNOT get sustained northern blocking in the model output, during the winter months any more,thats  why only really Scotland are having a cold winter ,because their location is far enough north to benefit from colder maritime polar air than further south.

Further south you need maritime Arctic air or  continental polar/artic air to bring cold and snow further snow,because of the shorter sea track

thats the simple explanation,of the differences and still NO sign of blocking setting up in the correct location from ANY model to bring a decent cold spell for all the country.

Liquified nonsense. La Nina. Read. Then read GWO in reference to suppressing La Nina impacts. Such magic...

 

[feb1991blizzard]

Reasonably decent 240 ECM.

[Froze were the Days]

wow!...hardly a mention about the ecm 12z run (must say it all). We're still on the same page from 4 hours ago.

The wheels have really fallen off...that's decent!?!

Edited January 20, 2018 by Froze were the Days

[mulzy]

GFS seems to be overplaying the High over the UK in the medium range - other models are much flatter.  The problem for us coldies is the lack of upstream amplification.

Edited January 20, 2018 by mulzy

[karlos1983]

Is it just me or does the 216-240 transition look very odd!

[Froze were the Days]

It's you  yes to a degree...the low heights seem to move south over Scotland on a west to east weak jet, won't make any difference to the overall theme.

Edited January 20, 2018 by Froze were the Days