In Depth Model Discussion, Analysis and Summaries

[knocker]

That's odd, comes up okay with me.

[johnholmes]

That's odd, comes up okay with me.

yes, it is, just tried again and got the same

no difference when I play about with various security settings either?

Edited October 23, 2010 by johnholmes

[Met4Cast]

I've been reading through and I think I may be getting and hang of this more technical stuff now. Can anyone tell me if what I'm saying would be correct?

The MJO has moved into Phase 5 and the composites for that for November suggest a weak high pressure to our East, with a major trough in the Atlantic.

The MJO is forecasted to move back into Phase 6 later on

The composites for that suggest High Pressure to our North, but largely over the United Kingdom

The NAO and AO are forecast to move to a more neutral/weak positive, before returning negative again in the next 10 days. So does this mean we can expect to see a temporary return to Atlantic weather systems, with the wettest and windiest weather towards the North and West, before a return to a cooler, more blocked type weather system into the second week of November?

I'm still learning, so If i've said something wrong, could you help? Thanks.

Edited October 24, 2010 by Daniel AKA WMD

[chionomaniac]

I think that you are getting to grips with it, Daniel.

One has to be aware though that the strong La Nina may somewhat override the MJO signal if it remains weak. Also, there is no consensus on the MJO forecast presently - other forecasts found here - http://www.cpc.ncep.noaa.gov/products/people/wd52qz/mjoindex/MJO_INDEX.html

Keep up, the more enthusiasts getting to grips with this, the better!

Edited October 24, 2010 by chionomaniac

[Cheese Rice]

Despite the GFS showing an unsettled outlook for much of the run, I can't see this been the dominant pattern for the rest of October/Start of November. Tentative signs have been in-place for much of the summer for high pressure and a suppressed jet for the second half of Autumn. I expect some sort of new pattern to emerge in the coming runs with the unsettled spell transient in the bigger picture. 

Edit: Whoops wrong thread 

Edited October 24, 2010 by 10123

[MR EXTREMES]

Hmmm, just like the ECM 12z shows. The model to watch

BFTP

funny you mention ecm model output thread noaa they are keen on this model aswell.

[Isolated Frost]

AO index - extremely negative

NAO index - negative

Very interesting to see what's happening with these currently, both positive during early October (warm spell in the UK).

Also interesting.

So, do you think the AO & NAO will remain negative throughout this winter?

[johnholmes]

Forecasts do go wrong!

With the best attempts and with the teleconnections seeming to suggest a definite forecast it can go wrong.

As the excerpt from one of my lrf’s shows well enough.

Issued 15 October

The QBO and MJO both suggest that events away from the tropics are suggesting blocking as the most likely option. Some indication with data about ENSO that mainly supports this.

So in summary-mainly blocked and with the major upper trough spending more time over/east of the UK than west of it. This would suggest temperatures below normal for the whole country.

The only proviso on the above were these two comments

As we get closer in the time scale then AO, NAO and PNA are not quite in sync especially in the later stages of their predicts. Maybe that is just one of the blips I suggest a couple of sentences on?

And

However there are indications that at least for some of the time that the surface high will have its centre of gravity south of 50N with depressions in that period running along their preferred track between Iceland and Scotland thus giving more unsettled spells of weather especially further north.

So do remember that forecasts can and do go wrong no matter how experienced an amateur may be nor indeed from one of the professional centres.

As I rather often say, no one amateur or professional has yet got forecasting totally tied down, be it in the shorter time scale, 24-120 hours or in the 10-30 days ahead let alone the following season.

Its fascinating trying to collate all the connections but even when the great majority suggest one outcome its by no means certain.

For those on this forum in 2009 remember back to mid winter when everything from the 30mb temperature right down to synoptic charts from GFS and ECMWF predicting a continuation of the cold-it did not happen.

So what is the updated outlook for the weather into early November?

Pretty well all the data we can find on the web now suggests that air is going to be drawn from a southerly direction for much of the time. Just temporary incursions of Pm or rPm air. Pretty unsettled with rain or showers and some heavy rainfall in parts of the west as depressions run along their preferred track between northern Scotland and Iceland. Very windy in the west and north west at times possibly up to severe gale force close to one or more of the depressions. Less windy and wet the further south east one lives. Snow or frost is going to feature with below average frequency into early November.

There are a few indicators that the overall mild spell MIGHT change after about the first week in November but its too far ahead to have a lot of confidence in that outcome.

I found during 3 years of lrf work that forecasts in the 10-18 day period were ‘right’ on about 70%+ of the time. This decreased to about 60%+ by the 18-30 day period, but a touch lower by 30 days, say 55-60%.

This is still well above persistence forecasting or pattern matching.

[Nick F]

Hi John, I think those who have a go at LRFs and admit that their forecast hasn’t perhaps followed accordingly should be admired the most, as occasionally I feel there is some trumpet blowing from LRFers when they’re right but a telling absence or no reflection when their forecast hasn’t gone to plan. I certainly wouldn't like to give too much confidence in a forecast beyond the medium range anyway!

I haven’t really delved into producing my own LRF’s, as I am more interested in short-range forecasts, but I still like to try and interpret what is likely to happen in the medium range by having a look at what’s occurring upstream. There were warning signals for perhaps a protracted unsettled Atlantic driven westerly type pattern that we are entering tomorrow, given the jet powering up over the E Pacific which has resulted in a rather strong zonal, though split, flow across N America – with little signs of any arctic incursions there and the same pattern looks to manifest downstream across the N Atlantic sector. But also as some have mentioned, background teleconnection signals that pointed to a more blocked pattern. But like you have said John, a change may and more likely to occur now after the first week of November, though I would be interested to hear of any pointers to what may be the precursor to a pattern change into November.

[Harry]

Please, no more -NAO....bring back the +NAO of my youth

Edited October 25, 2010 by Harry

[Glacier Point]

The angular momentum budgets show nicely the current situation and perhaps the most probable outcomes going foward in what is a highly complex situation outside of the tropics.

Total and relative angular momentum is continuing to fall as the westerly wind introduced from the MJO in early October is removed from the atmosphere.

http://www.esrl.noaa...m.sig.90day.gif

However, poleward fluxing of westerlies has strengthend the westerly flow across 40N - 50N:

http://www.esrl.noaa...p.sig.90day.gif

This is the thing that is driving our current pattern.

Moving forward, further falls in angular momentum are very likely given the depths of La Nina which we are now plumbing and the westerly winds in the extratropics are removed through frictional and mountan torques.

Where this takes us in terms of the GWO is firmly towards a phase 1 - 2 orbit.

Composites for these two phases have been a bit problematic to interpret, but I think I'm now happy with the two current solutions below as being the most likely representation of the hemispheric picture although not perfect if you look at the Pacific and Siberian sectors.

Basically a signal for unsettled conditions to persist for some time yet and going against a height rise over Scandinavia as per some GFS runs.

I'm still thinking as La Nina strengthens here grip we should see a stronger ridge developing over the Aluetians and eastern US / Canada with the latter steadily migrating eastwards to take up residence in the mid Atlantic.

Edited October 28, 2010 by Glacier Point

[Glacier Point]

Following on from last posting, long range modelling is starting to go with the idea of the Pacific sector developing a ridge and blocking structure setting up between Newfoundland and Hudson Bay, perhaps indicative of the atmosphere really starting to show up a distinctive Nina pattern going into the winter.

A renewed trade wind surge across the equatorial Pacific is underway and this should continue to upwell anomalously cold sub-surface waters taking us into strong Nina category. There are also substantive eastely zonal wind anomalies across large parts of the tropics which is taking total and relative angular momentum below average. At the same time, we continue to see anomalous westerly flow in the northern hemisphere across 40N - 50N which is driving a stronger than normal polar jet.

The Global Wind Oscillation is responding with orbits in phase space around the La Nina base states 0-1-2-3. This looks to continue as we see further coupling between the ocean and atmosphere until late November and early December when things could get really interesting with a possible high amplitude MJO event triggering a major amplification in the longwave pattern. Composites for these phases seem to suggest a continuation of the mean trough over NW Europe, a ridge in the middle North Pacific and blocking over NE Canada / NW Atlantic supported by an upper weakness over the SE Atlantic.

Temperatures over the Arctic are falling rapidly. The rate of descent here is very steep and no surprise that low pressure is prelevant at the surface and the AO firmly positive.

Notice however that the rate of cooling moderates according to climatology in the next few weeks. I suspect that we will continue to fall below average and probably over-shoot seasonal normal a little (just a hunch) which would tend to favour a continuation of the anomalous westerly winds at the mid latitudes, and therefore trough solution for much of NW Europe.

Going back to the composites, what takes my eye is the development of a very Nina-ish pattern (remember ridges in the Pacific and NE Canada to start). Both ECM and GFS ensemble mean height anomalies are depicting a similar pattern. Picture here is the ECM 12z 03/11/10:

For Novembers which featured +ve height anomalies in the region from Newfoundland to Hudson Bay, a large number (probably significant proportion) were La Nina years. Comoposite years for November pattern as projected by long range models:

If we roll these forward into December:

These lend weight to the idea that blocking will feature over large parts of the North Atlantic to start the winter, probably not as much over Scandinavia as hinted at here as I suspect the tendency for pressure to be higher to the north and north west of the UK.

So, going forward, a continuation of the unsettled conditions but noticeably below average (but not excessively so) as the jet flow is negatively tilted c/o the blocking over the NE Canadian sector. Into December, and we're looking at the sort of switch around that happend last year and the year before with drier and colder conditions taking hold and -NAO pattern.

Edited November 3, 2010 by Glacier Point

[La Bise]

Mods delete this at your ease but I just want to say "I love you" to GP...

[ZONE 51]

Excellent GP thanks.

[Iceberg]

There are definately changes afoot in the middle timeframe.

Zone's 1,2 and 3 have experienced a marked uplift in ENSO temperatures in the last week along with a subtle shift in the tropics.

It's too early to see whether this is a longer term 3 month change but will need watching over the next few weeks. What we have also seen is the SOI 90day avg hitting 20+ and the 30day avg hitting 25+

In the last decade whenever the 90day avg has gone above 20 it has always been followed by a sharp fall to at least 10, it looks like some almost in built mechanism.

My prediction is that October will be a month of variability and shifting in the longer range predictors.

The SOI is continuing to fall the 30 day avg has gone from 25.8 for Sept, to 19.7 for Oct and now 17.9 for the last 30 days.

The 90 day avg will really fall when the very strong +40 figures recorded in Sept start to fall off.

The Enso zone (3.4) has fallen to -1.4 for a weekly figure which is the highest since august.

Zones 1,2 and 3 are all still very variable.

The predictions generally have OND as the peak for this La Nina, considering we are now in the middle month, it would not be a great surprise to see La Nina leveling off and even declining a little.

The SOI tends to lead ENSO a little and with a still substantial cold water pool it might yet come back to the surface, or it might start to sink and mix out.

Regardless, in my eyes the later half of the winter is looking a little more promising than it did.

Very good summery GP.

[Gavin P]

Great summary from GP. Really good.

Looking at his December composties I think I might stock up on some De-Icer when I'm in the supermarket tomorrow.

[BLAST FROM THE PAST]

The SOI is continuing to fall the 30 day avg has gone from 25.8 for Sept, to 19.7 for Oct and now 17.9 for the last 30 days.

The 90 day avg will really fall when the very strong +40 figures recorded in Sept start to fall off.

The Enso zone (3.4) has fallen to -1.4 for a weekly figure which is the highest since august.

Zones 1,2 and 3 are all still very variable.

The predictions generally have OND as the peak for this La Nina, considering we are now in the middle month, it would not be a great surprise to see La Nina leveling off and even declining a little.

The SOI tends to lead ENSO a little and with a still substantial cold water pool it might yet come back to the surface, or it might start to sink and mix out.

Regardless, in my eyes the later half of the winter is looking a little more promising than it did.

Very good summery GP.

Also a nice update there too Ice. Also I agree with the in bold sentence, I think we could be in for one heck of February.

BFTP

[Gavin P]

Thats interesting Blast, cause the general consensus has been for a cold start to winter followed by an early spring. However, my personal view is that a lot of the teleconnections, (ENSO, PDO, AMO, etc...) are in rather a 1950's state at the moment and that of course keeps February 1956 at the back of my mind.

Edited November 4, 2010 by Gavin P

[Glacier Point]

Ensemble mean products are continuing to advertise a blocking structure to develop over the Canadian Arctic as the jet bifurcates and sets up something of an Omega block between Newfoundland and Hudson Bay steadily migrating eastwards towards southern Greenland and the North Atlantic (very Nina-like). Note also how the upstream pattern in the Pacific is dominated by that Aluetian / NE PAC ridge and troughing persistent over NW Europe.

ECM 00z @ t168 and day 6-10:

http://raleighwx.easternuswx.com/models/ecmwfens/00zECMWFENS500mbHeightAnomalyNH168.gif

http://raleighwx.easternuswx.com/models/ecmwfens/00zECMWFENS6-10day500mbHeightAnomalyNH.gif

GFS 06Z @ t168 and day 6-10:

http://raleighwx.easternuswx.com/models/gfsensemble/06zGFSEnsembles500mbHeightAnomalyNH168.gif

http://raleighwx.easternuswx.com/models/gfsensemble/06zENS6-10day500mbHeightAnomalyNH.gif

[BLAST FROM THE PAST]

Thats interesting Blast, cause the general consensus has been for a cold start to winter followed by an early spring. However, my personal view is that a lot of the teleconnections, (ENSO, PDO, AMO, etc...) are in rather a 1950's state at the moment and that of course keeps February 1956 at the back of my mind.

RJS and I have consulted and we have a draft which we are finalising. Retrograde of Siberian HP seems the order of the day late on.

GP, it is developing nicely and I think Nov is showing signs of going the way I like to see. It is currently strengthening my already strong view of a significantly cold December.

BFTP

Edited November 4, 2010 by BLAST FROM THE PAST

[Glacier Point]

The predictions generally have OND as the peak for this La Nina, considering we are now in the middle month, it would not be a great surprise to see La Nina leveling off and even declining a little.

The SOI tends to lead ENSO a little and with a still substantial cold water pool it might yet come back to the surface, or it might start to sink and mix out.

I think when we're assessing the potential magnitude of this Nina event , we need to consider the size of the cold reservoir beneath the equatorial Pacific and the existing ocean-atmosphere coupling that is already in place.

In terms of the reservoir, the fuel in the tank, we have -6C anomalies extending to depth. Upper ocean heat content for October was -1.94. That places us in third behind 1998 and 1988.

Globally Integrated Angular Momentum is around -1 SD. This rules out 1998 (high angular momentum) and leaves us with 1988 as the only near comparison for both indices since heat content was recorded in 1979. With the -PDO overall hemispheric SSTA, this is going to continue to drive net imbalance of easterly motion in the atmosphere which should constructively interfere with La Nina coupling the ocean and atmosphere. These should allow trade winds to continue and for upwelling of the cold water anomalies. During December and particularly January and February, there is a strong signal for angular momentum to crash which will give every opportunity for upwelling and a possible spike in cooling over ENSO regions, particularly 3.4 and 4. Therefore, if the cold sub-surface water's still in place, strong Nina conditions will continue I think.

[Gavin P]

GP, do you think we're in with a shout of a record Nina (since 1950 anyway) in region 3.4?

BFTP, its great to hear that you and RJS are collaborating again.

[Glacier Point]

Yes, and also in terms of how the atmsphere repsonds in terms of Angular Momentum.

[Gavin P]

Cheers.

[BLAST FROM THE PAST]

GP, do you think we're in with a shout of a record Nina (since 1950 anyway) in region 3.4?

BFTP, its great to hear that you and RJS are collaborating again.

Thanks Gav, as you know I hold Roger in high regard. We were pleased with last year so fingers crossed. Stew, do you think we could see some extreme hemispheric anomalous patterns emerge?

BFTP