Model Output Discussion - The Start Of Winter

[OldMetMan]

I do hope your instincts are correct on this but the GEM is the king of the amplifiers and has seemingly performed quite

badly recently. What better time though to thoroughly redeem itself

Indeed yes it would be! It was the only run that "looked right", according to my unscientific appraisal! If the GEM model is the amplifier, then I guess the GFS is the opposite, so maybe the actual outcome will be somewhere in between. We'll see!

[blizzard81]

Have done a synoptic analysis for the coming 10 days or so - including the weather 'bomb' tomorrow and the wintry spell following for northern areas, then the pattern next week/beyond:

 

http://www.netweather.tv/index.cgi?action=news;storyid=6340;sess=

 

Not a strong heavy snow signal from 18z GFS early Friday as that wave and associated fronts move through, with precip likely to turn to snow quite light and heavier precip further south in the milder air. But could change - so one to keep a close eye on.

 

18z seems to have flattened out the flow mid-week next week too to more in line with ECM, 12z op was more amplified.

Hi Nick, should we not be paying more attention to the GFS Parallel runs though? Are these not the upgraded version of GFS?

[blizzard81]

Indeed yes it would be! It was the only run that "looked right", according to my unscientific appraisal! If the GEM model is the amplifier, then I guess the GFS is the opposite, so maybe the actual outcome will be somewhere in between. We'll see!

 

Yes, 9 times out of 10 will be a middle ground.

[blizzard81]

Could anyone tell me if the 18z GFS has more credence these days? I hope not as both the (old) GFS and GFS P for the 18Z

have followed the ECM 12z with the propensity to build heights over south west Europe. Please someone tell me that the 18z

is still a drunkard lol - and even the pretender to the throne - parallel.

[Jason M]

Hi Nick, should we not be paying more attention to the GFS Parallel runs though? Are these not the upgraded version of GFS?

I'd guess yes, but tbh its just as grim and very similar the existing GFS.

[Vorticity0123]

With western Europe now being entrenched in a quite strong westerly flow, the weather looks to be unsettled over the UK over the next couple of days. How will the general surface pressure and 500 hPa pressure patterns evolve over the next few days, and are there any indications for changes in the large-scale pattern? A broad insight in the weather pattern (focussing mainly on the tropics on the long term) will be given in order to answer these questions. N.B. No direct translation of the synoptics to surface conditons in the UK will be given.

 

Current situation

 

For the description of the near-term weather, the GFS 18Z run of 9-12-2014 will be used.

 

First, the current synoptic weather map looks as follows:

 

GFS surface level pressure + 500 hPa heights (colours) 18Z run, T0.

 

What can be seen is that there is a large 500 hPa trough (purple colours) near Iceland. This trough has been influencing our weather over the past few days, and currently a very deep surface low pressure area (sub 950 hPa low) is located near Iceland as well. This low will bring gales to the UK tomorrow, as discussed by others before.

 

Furthermore, the Azores high (at the surface as well at is also quite strong, located over sea to the west of Spain. This is helping to create a very sharp gradient in pressure (read: strong wind field) south of the low pressure area over Iceland.

 

The Russian high pressure is located in the far east, too far away to exert any influence on the weather near the UK. The same accounts for the cut-off 500 hPa low (green colours) over the central Mediterranean.

 

Mid-term outlook

 

If one looks 48 hours away from today 18Z, the pattern seems to become more amplified, as can be seen in the link below.

 

http://www.wetterzentrale.de/pics/Rtavn481.gif

 

High pressure appears to be edging toward Greenland from the Azores high (both at 500 hPa and the surface),  and the trough over Iceland has become elongated in a North-South direction.

 

However, 2 days later (so 4 days later from now), the pattern has returned to a more zonal flow:

 

http://www.wetterzentrale.de/pics/Rtavn961.gif

 

The high pressure area toward Greenland has weakened, and a new low pressure area has developed near Iceland (at the surface), causing the flow over the UK to reorient more in an East-West direction.

 

Thereafter, the pattern is forecast to stay mainly zonal (being weakly wavy, or in other words the flow is not completely straight but modestly amplified). The NOAA 6-10 day forecasted heights and anomalies (as suggested by John Holmes) show this:

 

http://www.cpc.ncep.noaa.gov/products/predictions/610day/610day.03.gif

 

Note that the green contour lines are very close together over the Atlantic between the UK and Canada, indicating a strong pressure gradient. Furthermore, there is also a very dominant trough at 500 hPa near Iceland, as indicated by the below-average heights (which tend to be low at this time of the year on average as well).

 

Long-term analysis and trends

 

The 8-14 day 500 hPa heights and anomalies from NOAA suggests that the westerly flow is going to continue, with a deep 500 hPa trough over Iceland and a dominant Azores high just to the west of Spain:

 

http://www.cpc.ncep.noaa.gov/products/predictions/814day/814day.03.gif

 

This signature is also indicative of a positive NAO (North Atlantic Oscillation).

 

Tropical-extratropical interactions

 

The interesting part comes when one checks the MJO forecasts, or more physical, the evolution of the tropical convection anomalies. These anomalies (which are partly explained by the MJO) tend to influence the weather in the midlatitudes (e.g. the UK). Note that this relationship is in both directions (i.e. the tropical convection anomalies influence the extratropical synoptics, but also vice versa). A good read about this can be found in the link below:

 

http://www.atmos.albany.edu/facstaff/roundy/convection/Walich14.pdf (scientific article about the interaction between the pressure pattern in the extratropics and the tropical convection anomalies).

 

From the weekly discussion from the Climate Prediction Center (from the NOAA, given in the link below), it appears that the uncertainty in the weather pattern is very high in the tropics:

 

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/

 

I will try to give a short summary, using quotes from the discussion in the link given above. 

 

Lack of Atmospheric El Niño response

 

The first thing that comes to mind is the lack of coupling of atmospheric conditions with the El-Niño like conditions in the ocean. Usually, an El Niño event tends to influence the general weather pattern quite a bit, but this does not seem to be the case at the moment. From the discussion:

 

 

 

There is a complicated situation evolving across the global Tropics during the next couple of weeks. We continue to see above average SST's in the central and eastern Pacific consistent with El Nino like conditions. Enhanced convection in these areas, however, remains quite marginal and in fact suppressed convection has been observed near the Date Line more often than not over the last several weeks. 

 

A link to very brief information of what the influence of an El Niño event on the weather patterns in the midlatitudes can be found in the link below:

 

http://www.wmo.int/pages/themes/climate/significant_natural_climate_fluctuations.php

 

MJO evolution uncertainty

 

The next thing that is notable is the uncertainty regarding the evolution of the MJO (madden-julian oscillation). A few days ago, it seemed that the MJO could move into phase 7 or 8. Without going into too much detail, this phase tends to coincide with positive anomalies (higher than average 500 hPa pressure, or in other words, a ridge) near Scandinavia. A whole set of composites can be found in the link below:

 

http://www.americanwx.com/raleighwx/MJO/MJO.html

 

However, for now, some models are forecasting the MJO to weaken (i.e. decrease in amplitude), which would result in its influence being negligible over the weather over the midlatitudes. It has to be stressed, though, that uncertainty associated with this forecast is very high. This is also noted in the discussion of the Climate Prediction Center:

 

 

 

Moving forward, the majority of the dynamical model RMM forecasts of the MJO indicate a weakening of the MJO signal later during Week-1. It is unclear how much, if any, interference from the ERW is playing in disrupting the MJO signal in these forecasts. It is too early to favor an end to the current MJO activity given this and the fact that above average SSTs in the central Pacific would be very conducive for eastward propagation of enhanced convection into these areas. 

 

Long-term summary

 

Given the all above, it appears that uncertainty is very high regarding the weather in the tropics. This could have implications on the predictability (read: a decrease in predictability) of the weather in the extratropics. This is nicely summarised by the CPC:

 

 

 

It is quite difficult to ascertain impacts to the U.S. from the ongoing subseasonal tropical varaiability during the next few weeks given the uncertainty in whether the convective signature of the MJO continues eastward to the central Pacific or decays. The strongly positive NAO and El Nino like conditions appear to be dominating the current and forecast mid-latitude circulation anomalies.

 

Overall summary

 

At first glance, the forecast for the next few days looks pretty straightforward, with slightly amplified (wavy) zonality continuing for the next several days. Thereafter, there are signs that the weather will not change (e.g. the 8-14 day anomalies from the CPC), but given the large uncertainty in the tropical weather, the predictability of the weather in the extratropics after about 7 days could be very uncertain, regardless of what the models are showing. And then the stratosphere, and the other hints mentioned by other members are not even considered in this post  . So I would suggest an exciting period lies ahead in terms of model watching, which I will followed with interest!

 

Of a final cautionary note: the uncertainty mentioned in the tropics does in no way gurantee any pattern change in the extratropics, it only shows that a pattern change is possible in the midlatitudes.

 

Sources:

http://www.americanwx.com/raleighwx/MJO/MJO.html

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/
http://www.cpc.ncep.noaa.gov/products/predictions/814day/500mb.php

http://www.wmo.int/pages/themes/climate/significant_natural_climate_fluctuations.php

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf

http://www.wetterzentrale.de/topkarten/fsfaxsem.html

Edited December 9, 2014 by Vorticity0123

[Weather of Mass Disruption]

Big differences tonight in the models for just 48  -60 hrs.

Latest GFS (above) shows the secondary coming straight across the Midlands with a period of back-edge snow.

BBC (UKMO) has temps of 9C for the Midlands at  the same time with Severe gales and the secondary crossing central Scotland.

 

Who will be correct?

 

MIA

 

.

Given that the local Meto (for BBC East Midlands ) were forecasting snow for yesterday IMBY (it didn't even rain!) I would be inclined to go with the GFS      

[shaky]

The thing is both the gfs and parallel run have the low at 60 hours virtually in the same place so can they both be wrong?

[Mark Neal.]

The thing is both the gfs and parallel run have the low at 60 hours virtually in the same place so can they both be wrong?

Yes they can, even at that timeframe there is the chance that are both are somewhat off. Just keep watching developments on future runs, generally as we get closer models "usually" gets model agreement. Short range models handy like the Euro 4 as we get closer (goes out to 48hrs?)

Edited December 9, 2014 by Mark N

[shaky]

Yes they can, even at that timeframe there is the chance that are both are somewhat off. Just keep watching developments on future runs, generally as we get closer models "usually" gets model agreement. Short range models handy like the Euro 4 as we get closer (goes out to 48hrs?)

18z euro4 should be coming out now!! I understand if one of the gfs runs were showing the low further south and the other run showing it to be further north but with both of them showing it in a similar position i wouldn't think they'd be that far off!!

[shaky]

Just seen the pressure chart on the euro4 and its pretty much the same as the 18z gfs so maybe its onto something! ! Ian Ferguson could maybe give us a bit more information on the potential!

[80sWeather]

Morning all, have just read post #1339 from Vorticity0123 and would just like to say what a wonderfully explained post it is.

Even I could understand it. :-)

[Captain Shortwave]

Day 6 charts

ECM

Similar to yesterday, the Azores high move into southern Europe for week 2

UKMO

The Azores high is in a similar position to the others this morning.

GFS

Aga

The GFS shows something more promising with a chance of a colder shot once again at days 7/8

Parallel

Makes less of the cooler shot than the GFS

GEM

Whist not visible here, the GEM soon becomes the odd one out with significant Atlantic ridging. Given it's the GEM it's probably not worth paying too much attention to it. For me the outlook looks likely to be a westerly dominated pattern with rain and strong winds at times. If anything there is a trend for temperatures to climb back to average or even a little above later on if the Azores high shifts into southern Europe.

Edited December 10, 2014 by Captain shortwave

[bluearmy]

ECM op develops a pretty big scandi trough in week 2 but even that becomes negatively tilted in the face of the Siberian ridge. Looks like the jet aligning more nw/se which is a predictable response. this follows on from ed's post yesterday re this possible evolution.

[MattH]

Day 6 charts

ECM

Similar to yesterday, the Azores high move into southern Europe for week 2

UKMO

The Azores high is in a similar position to the others this morning.

GFS

Aga

The GFS shows something more promising with a chance of a colder shot once again at days 7/8

Parallel

Makes less of the cooler shot than the GFS

GEM

Whist not visible here, the GEM soon becomes the odd one out with significant Atlantic ridging. Given it's the GEM it's probably not worth paying too much attention to it. For me the outlook looks likely to be a westerly dominated pattern with rain and strong winds at times. If anything there is a trend for temperatures to climb back to average or even a little above later on if the Azores high shifts into southern Europe.

 

Morning,

 

Not that I often post in here, but I think the above post sums up the situation well and just wanted to relay my own thoughts, as a one off. Starting with the stratospheric events and clearly that will have little impact on present day so despite that being a positive development towards the end of December, any influences from that will not be felt until January, so anyone thinking that will have an impact in the short and medium term will, unfortunately, be let down. The developments at the moment continue to point towards an area of the polar vortex remaining in place over Greenland and surrounding areas, perhaps wandering a little, but overall it remains in place. The other feature which seems to be developing, as mentioned in the post above, is there is growing ENS support for the Azores high to build into SW Europe rather than remain well to the W and SW of the UK and hence allow for these NW'ly outbreaks. This, as a result, does look as though it'll lead to more of a tropical maritime air mass at times and again this will lead to a rise in temperatures. 

 

Whilst day-to-day variations could change, it would seem that the broader pattern is now almost 'locked in' for the next 2 weeks at least, which takes us towards Christmas. The MJO has failed to make any impact and is about to head into the 'circle of death' as it is so-called named. Clearly Christmas is just around the corner and whilst a temporary NW'ly may occur for Christmas (pot luck setup as per usual in the UK), the weather does look like being mild and unsettled at the moment as the most favoured outcome. The potential for a 2nd half of the month pattern change is now becoming increasingly unlikely, perhaps with the exception of the final week of the month and more potentially into the New Year, but the persistence of the +NAO pattern looks set to continue and I, personally, cannot see any significant pattern change to bring 'true' winter synoptics across the N Atlantic until the end of December at the earliest now.

 

Regards, Matt.

[terrier]

Looking very likely now that next week we will be heading to a westerly regime with rain and plenty of wind. Plus if the Azores high ridges into Southern Europe we could be looking at temps above average. So think after these pm hits this week. Think into next week if the gfs is correct we willbe seeing temps recover.

[TEITS]

Very disappointing output. It looks as though another brief NW,ly cold outbreak may occur around the 18th Dec but thereafter a mild/very mild SW,ly will spread across the UK. This can be seen on the ensembles but also this would follow on from the ECM +240 chart.

 

https://max.nwstatic.co.uk/ensimages/ens.20141210/00/t850Cambridgeshire.png

Edited December 10, 2014 by Polar Maritime
To remove LRF comments.

[SMU]

Morning All

Nice to see matt posting in here, although probably not what most fancied reading.

On a model update looks like UKMO is back up & running - 72 on meteociel

As for the models an update today around 10 which should be a little more positive ......

 

S

Edited December 10, 2014 by Polar Maritime
To remove LRF comments.

[Polar Maritime]

Models Discussion please, There are other threads for LRF's.

 

Just for a little perspective this morning, We are currently only 10 days into Winter..

 

Thanks, PM

[IDO]

Yes previous posters have summed it up. The D16 GEFS mean:  

 

Though I could have used anyone from the last 6-7 days and it would be the same. Very consistent GEFS along with JMA and EC32. No shock really, it was always going to be a medium term problem, Novembers amplified pattern, as it just delayed the inevitable 2-3+ weeks of Atlantic driven weather. However November's pattern kept the PV disorganised and at the moment there is no sign of imminent recovery; so for the last half of Winter we may benefit. CFS run after run is consistent for winter in Feb-April with the Greenland negative anomalies gone:

 

 

 

It has however not been keen on a blocked setup in January.

 

The ECM showed the odd outlier suit where blocking fleetingly visited, the GEFS did yesterday (12z) but we need these to run consistently for several days before we can draw conclusions. The GEFS are not doing that.

 

GEM is notorious for over amplification on its op but looking at last night's mean is it in line with the other models:

 

 

ECM again at D10 offers some amplification downstream but that is it's will and will be gone tonight: 

 

I am not confident that the trop can develop a more blocked pattern without an SSW so its a matter of waiting till mid-Jan for a significant pattern change. We may get variations on the theme, from a NW-SE jet, to a flatter jet, but nothing that is likely to herald a cold wintry period. The trend for temps in the south remains for average to above in FI:

 

Edited December 10, 2014 by i'm dreaming of...

[mountain shadow]

Thanks Matt, your comments confirm my thoughts from yesterday.

Certainly no tropospheric positives in the model output at the moment.

[Severe Siberian icy blast]

Morning,

 

Not that I often post in here, but I think the above post sums up the situation well and just wanted to relay my own thoughts, as a one off. Starting with the stratospheric events and clearly that will have little impact on present day so despite that being a positive development towards the end of December, any influences from that will not be felt until January, so anyone thinking that will have an impact in the short and medium term will, unfortunately, be let down. The developments at the moment continue to point towards an area of the polar vortex remaining in place over Greenland and surrounding areas, perhaps wandering a little, but overall it remains in place. The other feature which seems to be developing, as mentioned in the post above, is there is growing ENS support for the Azores high to build into SW Europe rather than remain well to the W and SW of the UK and hence allow for these NW'ly outbreaks. This, as a result, does look as though it'll lead to more of a tropical maritime air mass at times and again this will lead to a rise in temperatures. 

 

Whilst day-to-day variations could change, it would seem that the broader pattern is now almost 'locked in' for the next 2 weeks at least, which takes us towards Christmas. The MJO has failed to make any impact and is about to head into the 'circle of death' as it is so-called named. Clearly Christmas is just around the corner and whilst a temporary NW'ly may occur for Christmas (pot luck setup as per usual in the UK), the weather does look like being mild and unsettled at the moment as the most favoured outcome. The potential for a 2nd half of the month pattern change is now becoming increasingly unlikely, perhaps with the exception of the final week of the month and more potentially into the New Year, but the persistence of the +NAO pattern looks set to continue and I, personally, cannot see any significant pattern change to bring 'true' winter synoptics across the N Atlantic until the end of December at the earliest now.

 

Regards, Matt.

Wise words , which although hasn't occured yet , it just reminds me of the unpredictability of the weather , whilst the strat warming gives us hope , it's also a reminder to me that even with other factors on our side this year , for example the massive SSI we saw in October , the weather in the main has its own ideas , because at the turn of the month the massive russian high was replaced by a massive Russian low ! Which really holted the progression of the feedback process , infact it was indicative of a low snow advancement index , which really gives question marks on the reliability of it . Of course that's now reverted back to the expected pattern of high pressure over there, Sure a "a cold hearted winter" may well happen , let's all hope so , but a SSW doesn't guarentee a thing in itself , just increases our chances . Time will tell I suppose .

I for one hope for a flip in the models ASAP and know how quick models can change , just hope the high doesn't get into South europe cause that can be one disgusting pattern.

Edited December 10, 2014 by Polar Maritime
To remove reverences to LRF's.

[terrier]

So looks like average to above on the charts this morning. Not great output if it's cold and snow your after. Especially with the Azores moving into Southern Europe. This could move the temps into the above average category. Think until we see the ssw take effect we will just have to grin and bear it. In the words of frosty mild mush is making a comeback I'm afraid.

[Frosty.]

I don't get all this we will be returning to a westerly regime next week business..we are already in a westerly regime are we not? As for it turning generally milder, when the met office stop saying cold incursions then I will accept it but for now, there has been no downgrade..I mean, what is there to downgrade from? the south has had diddly squat cold weather as it is..so what's new?

[Frosty.]

 

 

Thanks, PM

Indeed, with lots more pm to come, especially oooop north