Model output discussion - 5th December 2016 - Into Winter we go

[Catacol]

3 minutes ago, fergieweather said:

As (post-00z) UKMO assessment stresses, little has really changed over last 24hrs in terms of resolving the ongoing uncertainty further into December. The marked ensemble spread into mid-month onwards is where confidence begins to quickly unravel, with - as UKMO describe it - "larger scale diagnostics favouring a more mobile pattern developing towards the end of December and early January, with the Christmas period falling in the tricky transitional period between that and the current, slow moving regime. As such, we are no clearer as to the Christmas forecast at this time." 

How long this impasse remains, in terms of very low forecast confidence, is anyone's guess.

Yes - thanks Ian - that feels a fair assessment. The extent to which a mobile or blocked pattern may evolve into early January seems to me to depend a great deal on finely balanced elements - propagation (or not) of stratospheric wind speeds to the trop, evolution (or not) of the GLAAM budget and strength of the MJO going forward. Day by day it is very difficult to pick a combination that looks coherent and, in that context, not surprising that the models are having a tough time. I note that none of the well regarded amateurs on here have made a stab yet at the first half of January. Even GP is quiet. I think this speaks volumes. Huge uncertainty. 

[daz_4]

Control run is interesting with HP pushing north.

Some GEFS ENS also trying.

[fergieweather]

13 minutes ago, Catacol said:

Yes - thanks Ian - that feels a fair assessment. The extent to which a mobile or blocked pattern may evolve into early January seems to me to depend a great deal on finely balanced elements - propagation (or not) of stratospheric wind speeds to the trop, evolution (or not) of the GLAAM budget and strength of the MJO going forward. Day by day it is very difficult to pick a combination that looks coherent and, in that context, not surprising that the models are having a tough time. I note that none of the well regarded amateurs on here have made a stab yet at the first half of January. Even GP is quiet. I think this speaks volumes. Huge uncertainty. 

Yup, a few days ago the GloSea signal for mobile/zonal period into turn of month was very marginally favoured, but has gathered some pace since then (albeit of course with low confidence). It'll be interesting to see if it receives any ECMWF Monthly support tomorrow. 

[bluearmy]

The vortex is modelled to be Canadian/e siberian as we head though week 2

that provides an awfully wide envelope for the ne Atlantic and nw europe

A more mobile pattern may not be a disaster for coldies if we see a continuation of a desire to amplify as the pattern crosses the Atlantic - the key remains removal of any high euro height anomolys, especially France to encourage the jet to split and send more energy into Iberia. 

[snow1975]

I'll class myself as an 'amateur'. The latest GFS 00z/06z hints at westerly mobility from about Xmas Eve onwards.

According to BigJoeBastardi SST anomalies in the Pacific are similar to Dec 1983. The so-called 'Polar Vortex' will make an appearance across the Midwest this week, similar to Dec 1983, but not quite as extreme.

Going forward, I'll take a punt that early January will be unsettled; mild in the south but colder at times in the North, with snow falling to increasingly lower levels. I hope it will turn out like Jan 1984 (nearly 2 feet of snow in my back garden).

[beng]

28 minutes ago, snow1975 said:

 

According to BigJoeBastardi SST anomalies in the Pacific are similar to Dec 1983. The so-called 'Polar Vortex' will make an appearance across the Midwest this week, similar to Dec 1983, but not quite as extreme.

Joe has hinted that he favours a more negative AO/NAO through Jan though which would be different to Jan 84.

https://mobile.twitter.com/BigJoeBastardi/status/807738199107862529

[IDO]

The GEFS are singing from the same song sheet if you look at the 06z GEFS clusters: http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cslp&HH=300&ZOOM=0&ARCHIV=0&RES=0&WMO=03503&PERIOD=

T300 95% support for a Euro high, just where the core heights will be placed the differentiating factor. After that the members show a larger range of options, though saying that the overall theme is maintained by the majority.

Possible mobile pattern establishing late December may be due to the recovery of the strat. PV; not sure of the propagation timescale to the trop. to be sure of that ?

 

[Scandinavian High.]

Well looking at  this it looks like a cold Christmas with frosts wind coming from south east no mild south westerly there.

Edited December 11, 2016 by abbie123

[SMU]

18 minutes ago, IDO said:

The GEFS are singing from the same song sheet if you look at the 06z GEFS clusters: http://www.weatheronline.co.uk/cgi-bin/expertcharts?LANG=en&MENU=0000000000&CONT=euro&MODELL=gefs&MODELLTYP=2&BASE=-&VAR=cslp&HH=300&ZOOM=0&ARCHIV=0&RES=0&WMO=03503&PERIOD=

T300 95% support for a Euro high, just where the core heights will be placed the differentiating factor. After that the members show a larger range of options, though saying that the overall theme is maintained by the majority.

Possible mobile pattern establishing late December may be due to the recovery of the strat. PV; not sure of the propagation timescale to the trop. to be sure of that ?

 

To be fair if theres one thing ive been saying for the last 8-10 days its a summary of the above- ie the strat vortex was on the significant rise & that it would overwhelm any tropospheric signal !

@Catacol

week 1-2 jan is the way downwards ( expected ) for the strat zonal + 10 days propergation -so background signal is +AO  until then ( neutral at best ) 

within that some MLB availability which could locate favourably for the UK

Glosea + EC also late to the party in terms of picking up the signal...

 

[Summer Sun]

It does look like temperatures will drop into lower single figures over time

The chances of snow are very low even for Inverness

[snowwman]

16 minutes ago, Steve Murr said:

To be fair if theres one thing ive been saying for the last 8-10 days its a summary of the above- ie the strat vortex was on the significant rise & that it would overwhelm any tropospheric signal !

@Catacol

week 1-2 jan is the way downwards ( expected ) for the strat zonal + 10 days propergation -so background signal is +AO  until then ( neutral at best ) 

within that some MLB availability which could locate favourably for the UK

Glosea + EC also late to the party in terms of picking up the signal...

 

I did some work a few years ago, chosing winters with negative CET months and concluded that there were no SWW or any which occurred in time to explain the cold, and that a split vortex was absent in all or almost all these winters. Also, examining the historical data, as per here:

http://ozonewatch.gsfc.nasa.gov/meteorology/wind_1985_MERRA2_NH.html

shows that there's not a lot of evidence supporting worrying what winds at 10hPa are doing, let alone worrying about forecasts for this far up in the stratosphere.

 

 

Edited December 11, 2016 by snowwman

[blizzard81]

4 minutes ago, snowwman said:

I did some work a few years ago, chosing winters with negative CET months and concluded that there were no SWW or any which occurred in time to explain the cold, and that a split vortex was absent in all or almost all these winters. Also, examining the historical data, as per here:

http://ozonewatch.gsfc.nasa.gov/meteorology/wind_1985_MERRA2_NH.html

shows that there's not a lot of evidence supporting worrying what winds at 10hPa are doing.

 

 

Post of the day if that is true.

[Methuselah]

4 minutes ago, snowwman said:

I did some work a few years ago, chosing winters with negative CET months and concluded that there were no SWW or any which occurred in time to explain the cold, and that a split vortex was absent in all or almost all these winters. Also, examining the historical data, as per here:

http://ozonewatch.gsfc.nasa.gov/meteorology/wind_1985_MERRA2_NH.html

shows that there's not a lot of evidence supporting worrying what winds at 10hPa are doing.

 

 

Well said. Of course SSWs and split PVs can increase the likelihood of a cold outbreak, but neither is strictly necessary, IMO...So, I'll no' be writing January off just yet. I just hope that this afternoon's GFS 12Z is a wee bit better than was the 06!

[snowwman]

2 minutes ago, blizzard81 said:

Post of the day if that is true.

There's a lot of data on SSW events, some contradicting others, from what I've found, it seems. I think I worked with some on Martineau's data, I seem to recall. Perhaps someone with more access to the research could run an analysis to try to confirm my findings.

[SMU]

26 minutes ago, snowwman said:

I did some work a few years ago, chosing winters with negative CET months and concluded that there were no SWW or any which occurred in time to explain the cold, and that a split vortex was absent in all or almost all these winters. Also, examining the historical data, as per here:

http://ozonewatch.gsfc.nasa.gov/meteorology/wind_1985_MERRA2_NH.html

shows that there's not a lot of evidence supporting worrying what winds at 10hPa are doing.

 

 

Good link

The Merra reanalysis will be very similar to the ERA interim reanalysis

it does surprise me around the negative CETS- did you consider the 2 week propergation window?

next level of analysis is whats the best case scenario with no SSW...

PS

just adding to that - The SSW correlations are more concentrated towards the -AO not UK CET

so a SSW enhances the probability of a cold outbreak in the UK-

I did some personal research on 62/63 & 100% the SSW caused that opening outbreak of cold

anyone want any proof? Look at the 10hpa warming on 12-13 Dec 1962- same as 2009

S

Edited December 11, 2016 by Steve Murr

[snowwman]

3 minutes ago, Ed Stone said:

Well said. Of course SSWs and split PVs can increase the likelihood of a cold outbreak, but neither is strictly necessary, IMO...So, I'll no' be writing January off just yet. I just hope that this afternoon's GFS 12Z is a wee bit better than was the 06!

I'd like to re run my analysis, but I concluded the last time that a split strat is positively harmful for our chances of cold.

[Frosty.]

The extended GEFS 6z mean is all about anticyclonic conditions with high pressure to the east and low pressure stuck out in the atlantic with the uk largely settled with variable cloud / sunny spells with night frosts and fog where skies clear..so, a chilly christmas for a change!

Edited December 11, 2016 by Frosty.

[snowwman]

3 minutes ago, Steve Murr said:

Good link

The Merra reanalysis will be very similar to the ERA interim reanalysis

it does surprise me around the negative CETS- did you consider the 2 week propergation window?

next level of analysis is whats the best case scenario with no SSW...

As I recall, I factored that in, and even went to 4 weeks.

[feb1991blizzard]

30 minutes ago, Ed Stone said:

Well said. Of course SSWs and split PVs can increase the likelihood of a cold outbreak, but neither is strictly necessary, IMO...So, I'll no' be writing January off just yet. I just hope that this afternoon's GFS 12Z is a wee bit better than was the 06!

In the current situation I disagree with that, if the Strat vortex ramps up above Normal by late December and these zonal westerly tropospheric model runs with a rampant PV verify. the only cold spell that could occur are topplers or PM incursions, in fact there's an argument to suggest not only do we need an SSW even more as we have even less time of winter left after the usual period of VI, because the PV and strat zonal winds have ramped up later, its like we are starting from the beginning in terms of trying to split the PV so the chances of any SSW in time to deliver anything before the end of winter is actually lower, To people saying we want rid of the high and a reset now, I suggest any prolonged Russian blocking in January is our only chance now (a likely  precursor pattern to an SSW).

Edited December 11, 2016 by feb1991blizzard

[feb1991blizzard]

5 minutes ago, Steve Murr said:

Good link

The Merra reanalysis will be very similar to the ERA interim reanalysis

it does surprise me around the negative CETS- did you consider the 2 week propergation window?

next level of analysis is whats the best case scenario with no SSW...

PS

just adding to that - The SSW correlations are more concentrated towards the -AO not UK CET

so a SSW enhances the probability of a could outbreak in the UK-

I did some personal research on 62/63 & 100% the SSW caused that opening outbreak of cold

anyone want any proof? Look at the 10hpa warming on 12-13 Dec 1962- same as 2009

S

Feb 09 and 91 just 2 more I can think of off the top of my head but there are many more.

[SMU]

When you say negative CETs do you mean sub ave or sub zero?

[Nick L]

This is not the thread for discussing "who works where". Thanks.

[SMU]

You also have to differentiate between w1 warmings & w2 warmings

[blizzard81]

I wouldn't be surprised to see a strengthening of the scandi block in the 4 to 5 day time frame on the 12z runs. It is well known that these little beasts are very hard to model, even at short range. Catacol mentioned earlier the possibility of the scandi block being a little further west and north. This is in line with my thoughts but more importantly it is what GP referred to a week ago - a build of pressure over the Kara Sea area due to low ice build feedbacks. This would then force the atlantic fronts on a more nw/se trajectory. If this trend comes about, the models will look very different at plus 6 days out to what they presently show. The azores high will not be able to ridge north east towards north west Europe and northern Europe will be in an easterly flow

[snowwman]

12 minutes ago, Steve Murr said:

Good link

The Merra reanalysis will be very similar to the ERA interim reanalysis

it does surprise me around the negative CETS- did you consider the 2 week propergation window?

next level of analysis is whats the best case scenario with no SSW...

PS

just adding to that - The SSW correlations are more concentrated towards the -AO not UK CET

so a SSW enhances the probability of a could outbreak in the UK-

I did some personal research on 62/63 & 100% the SSW caused that opening outbreak of cold

anyone want any proof? Look at the 10hpa warming on 12-13 Dec 1962- same as 2009

S

As I recall, the SWW in 1962 happened way after the cold set in on in late December. I'll try to recover some of the data and get back to you.