In Depth Model Discussion, Analysis and Summaries

[oldsnowywizard]

Not taking anything away from gp I await his updates as much as the rest I was referring to the post after by chio which implies anyone with a different opinion or using different methods (Which could have different potential outcomes) is foolish

[lorenzo]

Quality updated GP, almost like reset to default then. Moving into spring and MJO being dormant is it likely to kick off convection again or is it in a 90 day lull.

The QBO and La Nina combination really have been the death of this winter at least as far as I can see. Looking back I wonder if all the monster blocking activity and anomalies in Nov/Dec ( Black Holes on Naefs) were a historic pre cursor to that coupling.

[Alex]

Gp any thoughts going forward, I.e beyond March into April, May and even June?

[chionomaniac]

Not taking anything away from gp I await his updates as much as the rest I was referring to the post after by chio which implies anyone with a different opinion or using different methods (Which could have different potential outcomes) is foolish

Perhaps I was being a little harsh in using the word foolish but I wasn't criticising any different method use. However I still stick to the MJO forecast (like GP) that suggests that the GFS may be over-emphasising the amplification of any ridge. The MJO forecasts are not suggesting a phase 8 outcome and this indicates that anything other than mid latitude ridging (probably centred towards the UK) that is likely to affect us in the 8-10 day range.

There is a big difference between the GFS and ECM here but no doubt we will see a solution in between

http://www.meteo.psu.edu/~gadomski/ECMWF_12z/hgtcomp.html

I cannot believe that the GFS will not modify itself to a less cold scenario in time.

Edit - like the latest 18Z!!

[cooling climate]

It will take a brave person to bet against this Stewart. Or foolish. The exceptionally cold stratosphere in control for a while yet.

The posters that forcast the failed easterly were nearer to the synoptics pattern

than what GP had forecast for that period.

The MJO looks to be firing up again and I would not be surprised at all to see

a more amplified pattern than what GP suggests.

GP is very good at times but this love in with him is getting silly to say the least.

Edited February 26, 2011 by Osbourne One-Nil
No need.

[La Bise]

To my untrained eye, february did not pan out as I thought it would based on GP's thoughts, it certainly felt rather more damp than I thought it would be. Maybe a misunderstanding on my part or I'm being guilty of a NW bias...

[Jack Wales]

The posters that forcast the failed easterly were nearer to the synoptics pattern

than what GP had forecast for that period.

The MJO looks to be firing up again and I would not be surprised at all to see

a more amplified pattern than what GP suggests.

GP is very good at times but this love in with him is getting silly to say the least.

To suggest that there is a love-in with GP is a ridiculous, Stewart is merely getting some recognition for an accurate winter forecast. In addition to that he is probably one of the most dignified members of this forum who has always contributed an enormous amount of time, knowledge and research into his forecasts, which I think other members appreciate. The notion that people who forecast the “failed†easterly as nearer to being correct is something of an oxymoron. GP’s analogues actually played out well for the first part of the month with the pattern shifting to a more zonal theme in the second half, probably aligned to a more amplified cooling and downwelling of the stratospheric temp anomalies. I too expect to see a slightly more zonal flow after mid March, as with the PV & Jet buidling up steam heights could eventually become displaced to the south.

[Iceberg]

Thought I would post this here.

I've been playing with the AO figures since 1950 (looking at relationships with other variables, but specifically arctic ice and ENSO).

This is a rather nice little graph that shows day and the figures where the AO is greater than -4.

What is shows nicely is are the rends around recent years of highly negative AO.

e.g 2009/2010 and 1976 and 1977 and the 68/69. Also how rare they have been 1980 and 1995.

The Trigger for a guaranteed really cold spell of weather seems to be around -5.

[damianslaw]

This thread seems to have died of death in recent weeks - its a pity as it was one of the best threads earlier in the winter with GP's and chinos and others contributions about upstream pattern signals etc - based on state of stratosphere and polar vortex. With GP saying he will no longer be posting until May, I doubt there will be much further action in this thread for quite some time.

The model discussion thread has also degenerated and the stratosphere watch seems equally dead. I'd like to hear some people's views on the state of teleconnections and upstream pattern signals and likely placement and strength of the polar vortex which has been the killer since late dec in terms of any decent heights rises to our north. Surely it is only a matter of time it begins to weaken it traditionally does as we enter spring.

I'm interested in knowing these thoughts as I hold onto the hope that we will see at least one decent northerly with potential for snow before easter - it seems everything has been against even a one day northerly all year - what is causing this to happen, even in strong zonal winters northerlies often pop up as we head into spring - and we were on course to see one this weekend but it all went **** up with the current low development appearing out of nowhere deflecting the chance of any northerly.

[summer blizzard]

The stratosphere is continuing to run well below average which to me indicates a continuation of our current mid-lattitude blocking until early April.

[jethro]

Given the magnitude of the earthquake in the Pacific off the coast of Japan and the following Tsunami which crossed the ocean all the way to the Western shores of the USA, does this have the potential to alter the temperature profile of the La Nina and thus impact upon weather?

[The PIT]

Any more thoughts at all GP or have you quit now it's spring ???

[SnowAngel]

Any more thoughts at all GP or have you quit now it's spring ???

I think people have thrown in the towel and accepted spring is well and truly here...though in the past, this time of the year used to throw many surprises. Mornings hot enough for sunbathing in April with two foot of snow by the afternoon. The spectacular start to winter has been followed by months of meh...I guess us snow lovers wanted just one more sight of the white stuff. Down here in the south, the soil is dry as a bone already...we actually only had one night of heavy snow...it remained so long because of the extreme cold and very little rain since...already talk of a drought

Edited March 23, 2011 by SnowAngel

[The PIT]

However it would still be nice to have GP's thoughts for spring then later summer.

[Glacier Point]

....still around Pit.

Right now the key thing for me is the longer the polar vortex extends its existence well beyond its normal sell by date, the increasing pressure for a jet that is tilted SW-NE across Europe leading to some anomalously warm temperatures across western Europe. The persistence of La Nina in the atmosphere / west QBO is remarkable and should ensure a very much above normal start to April. Rainfall amounts as of the mid part April look seriously below average for the southern UK where high pressure over continental Europe is going to be the problem.

It has been well documented now how the atmosphere is still solidly La Nina like despite fading cold anomalies over the Pacific. The dry, settled weather over the mid latitudes is very consistent with this - think 2007 and 2009. Most assumptions are for the atmospheric Nina to fade into May which would allow for a more normal late spring pattern Not so sure here (but this is still gut feeling and a fulll summer forecast is some way off). The very delayed break up of the polar vortex is probably going to lead to a switch between very warm and very cold conditions, 1995 being a possible analogue here.

[Anti Boring Weather]

so GP does that mean it will be a dry warm spring and a cool wet summer esp August that has happened for about the past 5 years typical

[chionomaniac]

....still around Pit.

Right now the key thing for me is the longer the polar vortex extends its existence well beyond its normal sell by date, the increasing pressure for a jet that is tilted SW-NE across Europe leading to some anomalously warm temperatures across western Europe. The persistence of La Nina in the atmosphere / west QBO is remarkable and should ensure a very much above normal start to April. Rainfall amounts as of the mid part April look seriously below average for the southern UK where high pressure over continental Europe is going to be the problem.

It has been well documented now how the atmosphere is still solidly La Nina like despite fading cold anomalies over the Pacific. The dry, settled weather over the mid latitudes is very consistent with this - think 2007 and 2009. Most assumptions are for the atmospheric Nina to fade into May which would allow for a more normal late spring pattern Not so sure here (but this is still gut feeling and a fulll summer forecast is some way off). The very delayed break up of the polar vortex is probably going to lead to a switch between very warm and very cold conditions, 1995 being a possible analogue here.

There are signs Stewart that the vortex is going to break up early to mid April with a stratospheric Final Warming probably occurring around then, so I would suggest a switch to colder conditions would occur then.

Both the GFS and ECM are suggesting warming at the 10hPa level (which could potentially coincide with the MJO in phase 8 ).

With this warming we are already seeing forecast signs of a dramatic reduction in the mean westerly winds. Once these change to easterly I think they will remain there until the start of the next stratospheric winter.

I think as this changes filters through to the troposphere during April we will see the strong vortex that has prevented northern blocking give way leading to significant changes. If I was a betting man I would say that the CET for the second half of April will be lower than the first half.

c

Edited March 25, 2011 by chionomaniac

[Glacier Point]

Interesting thoughts there Ed, and if the MJO manages to gain some high amplitude in phases 7 and 8, we could break the cycle that we are currently locked in.

However, I suspect that the tropospheric drivers (low angular momentum - Nina like), will tend to oppose this and maintain low heights to the north but with an increasing longwave trough edging in from the west. I'm very much in the above average camp for April.

Relative angular momentum in the middle and lower parts of the atmosphere is extremely low, some -2SD despite cold surface temperatures over ENSO Regions rising to weak to moderate Nina status.

Much of this is due to strong easterly winds across the tropics following on from a weak MJO event in February.

The GWO is responding through orbits in phases 1-2-3, the low angular momentum base state.

The MJO is showing some amplitude through phase 3 (therefore coupled with the GWO at present) and forecast by most global models to reach phase 6 in the next 15 days.

If we think as the MJO as the engine of future rises in angular momentum, the lack of any real strong MJO signal means that we are probably operating on the premise of low angular momentum conditions persisting in the atmosphere for some time into April, and the GWO therefore locked in around phase 1-2-3 type orbits, trending more towards phase 3 from mid April onwards as the impacts of this MJO event work their way through the system.

Composites for phases 1-2-3 give us an idea of the likely evolution in the longwave pattern:

==> ==>

Points to note the development of an Atlantic trough and above normal heights (ridge) over Europe driving a very mild pattern to start. As we progress however, the trough looks to edge eastwards towards the UK but I suspect these composites are over-doing the strength of the trough, especially given that the Arctic Oscillation is looking positive although more unsettled as time progresses in April looks a reasonable call. The continued existence of an upper Icelandic low looks another sustained feature.

Weatherwise, a very much above average start to April and split between a more unsettled north and settled south. From mid month, the signal is for more unsettled conditions to become more widespread although still probably above average temperatures for southern UK. It's probably not until the final third of April where things might become a little cooler and showery for all as the trough is pushed through.

Edited March 25, 2011 by Glacier Point

[The PIT]

Very Interesting reading folks so a split month possibly coming up.

[Glacier Point]

Perhaps somewhat unexpected this, but deep tropical convection totals are mounting up in the Indian and far western Pacific Oceans associated with an MJO wave passing through the region. This has initiated a strong mountain torque event over the Himalayas and other parts of Asia. The combination of the burst of westerly winds tied into the MJO and mountain torque have substantively increased westerly winds to the global circulation to such an extent that tendency in relative angular momentum is the highest it's been all year.

http://cawcr.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR/m.3d.html

http://cawcr.gov.au/...Last90days.html

http://www.esrl.noaa...ltaum.90day.gif

Analysis of the last peak in tendency in relative angular momentum which occured in mid January suggests that this will have weather ramifications over the next 30 days. Notice how the westerly burst of winds associated with the MJO (tropical convection) propagated poleward over time and reduced the subsequent low points of relative angular momentum in February.

What this suggests is that the Global Wind Oscillation will be tilted more towards phase 4 which is the signal for anomalous mid latitude ridges. Couple that with the continued very positive Arctic Oscillation, and you begin to set out the table for a solidly above average April with high pressure setting up shop just to the south of the UK. That means the trough solution scheduled for the final third might be in jeopardy, and with it any hope of getting some decent rainfall totals.

Also of interest here, the MJO has now shown some 'willing' to develop two fairly strong waves in the last 90 days with one much weaker wave in February. If this were to continue, we would be looking at the next wave in April being a fairly weak affair leading to angular momentum falling back a touch in May (mid Atlantic ridge set to return) and then the next strong MJO event triggering a surge in angular momentum in June. That would be interesting in terms of setting up further areas of high pressure within the mid latitudes if the Arctic Oscillation were to remain positive.Maybe not flamming June, but high pressure wouldn't be far away and certainly not the washout that PWS are trailing.

Edited March 29, 2011 by Glacier Point

[chionomaniac]

It looks like the strong Asian MT event is causing the wave breaking event that is setting off the forecast warming in the stratosphere. This looks like setting off a strong reversal of zonal mean winds in the upper levels of the stratosphere which is bound to have a knock on effect to the tropospheric polar vortex below.

Looking at the 10 hPa level, this certainly looks significant and probably the final warming.

The question remains I think as to how much this can effect the strength of any mid latitude ridging that is likely to be the form horse in April?

Oh and GP can you not get your thoughts splashed all over the papers like PWS?

Edited March 30, 2011 by chionomaniac

[Glacier Point]

Yes Ed, once again we're discussing a sudden increase in stratospheric temperatures with another big MT 'in town'. The updated dynamical model MJO forecasts are suggesting a phase 7-8 event which should assist in helping to disrupt the tropospheric vortex and the timing is about right for the downwelling west QBO wave which started in mid January to fade out.

All of this should change the pattern although the strength of the forcing from the autumn w/r/t polar vortex / low angular momentum regime gnaw away at me and I wouldn't be suprisied to see the vortex actually re-form or low level westerlies and low heights remain in place during the late spring.

[Alex]

With the QBO wave possibly fading, I assume this is bad news for July and august I'n terms of settled conditions GP?

[SteveB]

Could we be looking at another extended period of dry weather for April/May/June. I would certainly enjoy a dry warm Spring early Summer, but would be very concerned if it turned out to be very dry.

[Glacier Point]

With the QBO wave possibly fading, I assume this is bad news for July and august I'n terms of settled conditions GP?

It won't hinder the prospects although ultimatley this period will be most influenced by the tropics. If we start to see the atmsopheric indicators signalling a shift away from the low angular momentum base state, perhaps another bout of tropical convection in late April, that would encourage me that prospects for this summer would be at least reasonable.