Model output discussion pm 13/01/2016

[JeffC]

4 minutes ago, PerfectStorm said:

WHAT - is that...a...

Bartlett???

[Ali1977]

7 minutes ago, PerfectStorm said:

WHAT - is that...a...

I don't know, what is it?

[TSNWK]

2 minutes ago, JeffC said:

Bartlett???

Scandi high I Think...

[Rocheydub]

2 minutes ago, JeffC said:

Bartlett???

No, it's a Scandinavia High, with an undercut on the way. 

[Skullzrulerz]

8 minutes ago, PerfectStorm said:

WHAT - is that...a...

Would you like to explain what is going on for us please it's not helpful when we don't have a clue what this means???

[Snowman.]

3 minutes ago, Ali1977 said:

I don't know, what is it?

Possible another point of interest more negative tilt on the following low then it attempts an undercut.

 

Edited January 15, 2016 by SN0WM4N

[Snowman31]

I think he meant the shape of the isobars around London, unless I just have a dirty mind

Edited January 15, 2016 by Snowman31

[Eskimo]

Sorry folks, height rises across Scandinavia. Although looks like a sinker. Didn't actually notice the willy lol. 

Edited January 15, 2016 by PerfectStorm

[Banbury]

3 minutes ago, Snowman31 said:

I think he meant the shape of the isobars around London. You can see what it looks like, unless I just have a dirty mind

I can't believe people didnt get that , I must be similar to you lol

[Rocheydub]

1 minute ago, PerfectStorm said:

Sorry folks, height rises across Scandinavia. Although looks like a sinker. 

It does, but to be fair, it wouldn't take much adjustment for it to become a scandi HP. There was a good negative tilt to the low too. 

 

One to watch. 

[phil nw.]

Sensible discussions please guys.Ta.

[Eskimo]

Out of interest. What time does the ARPEGE 18z come out? 

[nick sussex]

The UKMO have gone with their own raw output in the fax charts which is surprising. I expect the last rites will be done tomorrow.

I can't see that UKMO output surviving past tomorrow morning, No support from any operational run and about 5 out of 50 ECM ensembles backed its view.

 

 

[Tim Bland]

I say it every year...99% of fax charts are a complete replica of the UKMO run. Makes me wonder why they bother with it to be honest. It is extremely rare for them not to follow the UKMO run

[feb1991blizzard]

2 minutes ago, nick sussex said:

The UKMO have gone with their own raw output in the fax charts which is surprising. I expect the last rites will be done tomorrow.

I can't see that UKMO output surviving past tomorrow morning, No support from any operational run and about 5 out of 50 ECM ensembles backed its view.

 

 

You are kidding me - please tell me that isn't true, they spend days contradicting the text forecast with their FAX and now the UKMO collapses, the BBC mention disruptive snow for midweek and they change their fax the other way!!!!

[ocean]

Have to say this week has been a fascinating watch and continues to be so.  Never seen such a rollercoaster of a week and continues to be so with model after model giving wildly variant outcomes. Great spectator sport

[shaky]

Just now, Tim Bland said:

I say it every year...99% of fax charts are a complete replica of the UKMO run. Makes me wonder why they bother with it to be honest. It is extremely rare for them not to follow the UKMO run

I was about to say the exact same thing mate!!!expect further changes in coming days!!!already the front that was meant to come in on monday doesnt make.it past wales on the 18z whereas this morning the 00z had it in the north sea!!

[Man With Beard]

41 minutes ago, Nick L said:

Ridiculous model disagreement going on at the moment. Even tomorrow night it's EC/Euro4 vs GFS with regards to where this snowfall is going. I've never seen anything like this.

This is utter chaos. The GFS, for all its faults, rarely chops and changes too much inside T60 but now the snow for Sunday morning is 150 miles further south than on the 12Z, the snow on Monday is 150 miles west, and the UKMO front for Wednesday magically appears with snow for Midlands north! The most surprising thing will be if the 00Z is anything like the same.

[PolarWarsaw]

I'd rather just have my snow fall tomorrow and Monday to be honest...let's hit reset, have a couple of milder days and go again. All we are doing by 'battling' this...is trying to milk awkward synoptics for snow fans which could or could not pay off - in the meantime, we have wasted another week to 10 days of 'meh' winter weather.

[nick sussex]

Just now, Tim Bland said:

I say it every year...99% of fax charts are a complete replica of the UKMO run. Makes me wonder why they bother with it to be honest. It is extremely rare for them not to follow the UKMO run

It depends I have sometimes seen them modify them but I think there was an office party this evening  at the UKMO and  the Duty Forecaster didn't want to miss out on the spin the bottle and just thought a quick replication of the raw output would suffice! lol

 

[feb1991blizzard]

Much better 18z in FI compared to 12z on the GFS, Warm Air Advection about to go into polar regions, could see a big Easterly come 384 but all for fun at this range of course.

12

18

[Chris K]

5 minutes ago, shaky said:

I was about to say the exact same thing mate!!!expect further changes in coming days!!!already the front that was meant to come in on monday doesnt make.it past wales on the 18z whereas this morning the 00z had it in the north sea!!

I'll be honest, I am struggling to understand it all at the moment. There has been huge uncertainty in the close time frames, but many of the model runs are still insisting of a milder spell of weather to return come mid week, with the High Pressure heading East into Europe and the Jet increasing in strength.

I get how in the short term fronts may back west etc and we may stay colder for longer but the end result is still the same, if delaying milder uppers to push in by a day or two. I am not saying it's certain to happen, but most outputs seem to be heading that way now...at least in my eyes.

Edited January 15, 2016 by Chris K

[lorenzo]

54 minutes ago, Spah1 said:

I keep seeing this posted and people getting excited by it. 

For the amateurs on here please can someone just give a basic explanation of what it is showing and how it may impact our weather. 

thanks

This is a plot of AAM or atmospheric angular momentum, will share some of my notes made through time.

That may sound pretty pretentious, but through time is about right really, it take around 5 years to watch and to get to grips with this mode! If you grasp it's nuances more quickly then credit to you, it is one of the dark arts I think left in our science. 

Do a search on the forum for our absolute legend at this mode @Glacier Point and look for his informative posts, these are supported by @Tamara to gain understanding. The GWO Global Wind Oscillation seeks to measure the the exchange of atmospheric angular momentum with the surface of the Earth.

A paper was published by Weickmann and Berry (2008/or 2009) about it, search AMS journals for it. The index that includes information about the MJO, but since it's a global integrated index of zonal wind anomalies over all levels of the atmosphere, they claim there are other modes of variability incorporated into this index, such as variability caused by mountain torque and extra-tropical variability. 

Each phase of the index represent a different state of the GWO. When you’re in Phases 2-3, you are in a low-AAM state. Typically during strong La Ninas, you'll spin around down here for most of the season. Phases 6+7 are high AAM states (El Nino's...). You often don't see big orbits in this index during NH Summer. 
 
The limit of predictability is about 7 days. Beyond that, the models cannot predict it and thus it's not very useful on most occasion of medium-range predictability. However it does have some seasonal implications but just if it's above the zero line (high aam), or below (low aam). 

AAM Timelines

•    higher AAMs trending north on the timeline probably would lead to higher confidence on northward displaced westerlies and perhaps a +AO for example. Or vice-versa.

Mountain torque changes AAM.

AAM stands for atmospheric angular momentum. It can be increased or decreased by mountain, friction or Coriolis torques. 

It can be fluxed by changes in the global wind patterns (which doesn't change the total values of AAM, but changes its spatial distribution). Since total angular momentum is conserved by definition, when AAM is higher than normal, the earth's rotation slows down and vice versa. 

The GWO plots AAM anomalies on the y-axis and d(AAM)/dt (i.e. AAM tendency) on the x-axis.

Frictional Torques and Mountain Torques

Any easterly surface wind (opposes Earth's spin) will act as a momentum source (since the Earth will have to exchange +AAM upwards with the air). 

Therefore, the Tropics/Easterlies are a source of momentum and the Mid-Latitude westerlies are a sink, where friction usually eats the excess +AAM. 

If anomalous low pressure develops west of a mountain chain, particularly one placed significantly along longitude lines, and anomalous high pressure develops east, then the mountain will oppose Earth's Rotation even more than it already would have.  Friction again will usually eat the excess +AAM (usually over oceans) produced by mountains.

When low-high positioning along mountains is enough to become a source ( the stronger the anomalies and easterly wind, the stronger the source). Overtime, westerly flow will increase in response to this "traffic-jam" as the Earth's Rotation transfers the +AAM upward.  Therefore, the Earth ends up slowing down as the Mid Latitude Jet ends up speeding up after the pressure perturbation
GWO or MJO

The reason the GWO is confusing is because there are many different forces that produce "power spectra signatures" of coherence in AAM. All of the processes I mentioned above can happen for many reasons on many different time scales. Larger looping GWOs are usually associated with intraseasonal oscillations (MJO) while quick loops are due to this internal "mountain-friction" cycle in the Mid Latitudes.

 

Theses are a bunch of notes from here there and everywhere

Make of them what you will those who are willing to read, investigate and learn more.

It is not a magic bulllet for forecasting at all but when in context and used correctly is highly informative.

You are lucky that this season is the best template one could wish for to display high AAM, conclusions of course are your own - and there within lies the trick of predicting the weather - it will only be and remains one element and one tool available.

 

[mulzy]

4 minutes ago, feb1991blizzard said:

Much better 18z in FI compared to 12z on the GFS, Warm Air Advection about to go into polar regions, could see a big Easterly come 384 but all for fun at this range of course.

12

18

A few 12z perturbations had some form of easterly in the medium term - the vagaries of NWP modelling or a growing trend? - time will tell I guess

[nick sussex]

8 minutes ago, feb1991blizzard said:

You are kidding me - please tell me that isn't true, they spend days contradicting the text forecast with their FAX and now the UKMO collapses, the BBC mention disruptive snow for midweek and they change their fax the other way!!!!

Blame the office party! lol Seriously though the UKMO output is an outlier not just for western Europe but over the ne USA and Arctic Canada.

Although the models have been all over the place if you put aside the differing views of placement of high pressure near Scandi they all have similar upstream and downstream patterns.

The detail might be a little sketchy but they're all singing from the same hymn sheet, the UKMO is singing in a different language.