Early run up to Winter 2020/2021 discussion

[Blessed Weather]

On 23/11/2020 at 13:14, jules216 said:

You need to read the whole GSDM synoptical conundrum. As a general rule to get cold weather in to Europe in winter from AAM perspective we need a robust MJO convection to travel eastwards from Indian Ocean to Maritime continent and Western/Eastern Pacific - phases 4-8. Initially there is a rise of frictional torque followed by mountain torque events that slow that general westerlies in mid latitudes. The Rossby wave train associated with strong MJO pulses initially effect the Pacific jet stream and initially force a equatorward momentum flow at 35N which help promoting ridges to the north. It is a very complex diagnostics very much dependant on the base state of the atmosphere plus seasonal wave lengths. So AAM response in winter may be different to the summer one. We have some experts here in the forum like @Tamara or @Blessed Weather who can explain this in greater detail then me for sure

A Synoptic–Dynamic Model of Subseasonal Atmospheric Variability | Monthly Weather Review | American Meteorological Society

JOURNALS.AMETSOC.ORG

 

Sorry for only just getting around to responding. Thank you for your comment Jules. My knowledge is nowhere near that of our resident expert, @Tamara, and it’s an appropriate time for me to publicly thank her for her time and patience helping me get to grips with the GSDM. We are fortunate to have her sharing her expertise with us here on Netweather.

It would take pages to try and fully describe the model and do it justice, so I’ll just expand a little on your overview of the process (above) with a focus on the current situation (La Nina and the MJO) but mainly point people in the direction of further learning. (As requested by @BREZEEK )

The first thing to understand is the total envelope that is ‘the GSDM’. This is best summarised by use of a few slides used in a 2018 presentation to the American Meteorology Society by Ed Berry, who with fellow scientist Dr Klaus Weickmann jointly developed their model while they were working at NOAA in the late 1990s.

If you wish to watch the full presentation it’s here.

It can be seen that the model embraces many of the individual teleconnections that we are all familiar with and places them within an overall framework to better understand the interactions and how they impact NWP output.

My take on where we are at the moment? The east based La Nina - currently not overly strong - is demonstrating a typical base state influence, with the easterly trade winds in the tropics underpinning mid-latitude ridges, in our case the Azores high ridging into the Atlantic with troughs (and brief incursions of colder air) impacting the UK or just further east into Europe. In GSDM terms, the excess easterly wind in the global jet flows has lowered angular momentum and resulted in negative frictional torque at the surface creating a series of ridges in the mid-latitudes.

So what could help trigger a favourable pattern change for UK/NW Europe (assuming blocking and cold your thing)? Events in the tropics is the place to look with MJO a key teleconnection in altering the propagation of global wind-flows by adding westerly momentum across the tropics as the convection wave heads eastwards and creates additional amplification of the mid latitude ridges (under La Nina) further downstream.

La Nina (the easterly trades) has been destructively interfering with the MJO in recent weeks, but there are hints from some models that tropical convection will in the near term make it eastward over the Indian Ocean and the MJO will emerge into Phase 5 or 6. The unknown at the moment is how far east the westerly wind bursts associated with the tropical convection proceed and generate the rossby wave eddies that increase wind-flows across the tropics and set in process the ripple effect of these wind-flows into the extra tropics.

I described this process in more detail in a post here that I made last year.

Depending how far east and how strong the rossby wave train is, this can, within the GSDM framework, eventually trigger an increase in mountain torque to perturb the stratosphere. It’s worth noting that there is typically a lag of 10 days before MJO phases impact the North Atlantic/European region. And a word of caution that research shows that with MJO events during La Nina, you are looking to Phase 8 to drive a negative NAO (although other phases can still impact the stratosphere). Again, more in another post here that I made last year.

In summary, within the GSDM framework the Global Wind Oscillation (GWO) is effectively a measure of the global wind flows and exchange of momentum between the tropics and extra-tropics at any given time, expressed as phases. From this, you get an idea that by following the phase orbit of the GWO you are getting an idea of where the Jetstream is amplifying most (west or eastern hemisphere) and also, based on the associated AAM plots, where the associated 'torques' are occurring.

Jules - you have already posted the latest GWO phase plot published by meteorology professor Dr. Victor Gensini of North Illinois University (and who you will see in the YouTube video referred to above). For interest, here’s the GWO Phase correlations with DJF 500-hPa Geopotential Height Anomalies developed by Nicholas Schiraldi from the Dept of Atmospheric Sciences at Albany University.

There’s lots more that could be discussed, including the impact of Arctic Amplification and also the impact of the current Kara Sea low sea ice which has been found to drive large scale NH circulation anomalies including a negative NAO (more on that here). But I’ll stop at this point and end by providing some links to lots more reading material available in the Learning and Research area, specifically:

Global Synoptic Dynamic Model (GSDM)
Atmospheric Angular Momentum (AAM)
Global Wind Oscillation (GWO)
Frictional Torque (FT)
Mountain Torque (MT)

 

Edited November 26, 2020 by Blessed Weather
Note to Brezeek added.

[summer blizzard]

With all the (over) excitement at the moment and level 2 ramping (cold since comments) I took a look back at our fair decade and just to be coldest since 2010 we still need to beat 3.8C in 2017 and 2.9C in 2012 for the first half.

[SqueakheartLW]

MY FULL DETAILED CFS MODEL BASED DECEMBER UPDATE AND FORECAST

After general updates for December 2020 based on the CFS monthly 500mb and 850mb anomaly charts on weather outlook I shall now add my much more detailed analysis from Meteociel and the CFS 9 monthly runs to my December 2020 analysis and will now produce my forecast for December 2020 based on all of this combined

General Monthly Analysis

First I will remind all of you what figures I got for the general monthly charts based on runs from 06/07/2020 to 30/11/2020 when I had my last monthly run update
                   (06/07/20 -        (23/09/20 -      (07/10/20 -          (21/10/20 -         (04/11/20 -
                    22/09/20)          06/10/20)        20/10/20)            03/11/20            17/11/20)
Temps            Dec                    Dec                   Dec                      Dec                     Dec
V Mild               1                         0                        0                          0                         0
Mild                 16                        1                        0                          0                         0
Average           24                       8                       11                         9                         8
Cold                 38                       5                        3                          5                         6
V Cold               0                        0                        0                          0                         0

                   (06/07/20 -        (23/09/20 -      (07/10/20 -          (21/10/20 -         (04/11/20 -
                    22/09/20)          06/10/20)        20/10/20)            03/11/20            17/11/20)
Precip            Dec                    Dec                   Dec                      Dec                      Dec
V Dry                0                         1                        1                          2                           0
Dry                  37                        8                        7                          7                           3
Average          24                        2                        4                          5                           8
Wet                 18                        3                         2                          0                           2
V Wet               0                         0                         0                          0                           1

CET        -0.25C Colder    -0.29C Colder    -0.21C Colder    -0.36C Colder    -0.43C Colder
Precip    87.97% of Av    75.00% of Av    75.00% of Av    60.71% of Av    103.57% of Av

Now combining the above figures into overall totals we end up with the following:

December 2020 Temps    V Mild    Mild    Average    Cold    V Cold
                                                  1          17           60           57          0        

December 2020 Precip     V Dry      Dry     Average     Wet    V Wet
                                                  4          62           43           25          1

CET - The overall totals show a below average CET is expected with an anomaly of -0.28C Colder on average
Precip - The overall precipitation signal is drier than average at 84.07% of precipitation predicted

NOW HERE IS THE BIG PART

Time to add my detailed CFS 9 monthly run analysis into the mix. A total of 30 days worth of runs from the whole of November with 4 runs per day equalling 3600 500mb daily charts in all and 3600 850mb charts too. A lot of data has been gathered here and the final figures are below for these runs

TEMPS        00Z             06Z            12Z            18Z     TOTALS       Days
V MILD          3                1                  1                0             5              0.04
MILD            93               69               60              60          282           2.35
AVERAGE    412             390            330            429        1561         13.01
COLD          357             400             442            362        1561         13.01
V COLD        65               70               97              79           311           2.59

PRECIP        00Z             06Z            12Z            18Z      TOTALS       Days
V DRY            9                 1                 1                6             17             0.14
DRY             240             226            248            272          986            8.22
AVERAGE    472             517            461            445         1895          15.79
WET             208             184            215            207          814           6.78
V WET            1                 2                 5                0              8              0.07

CET           -0.43C        -0.52C        -0.64C       -0.51C      -0.53C
PRECIP    100.67%    101.11%    101.94%    99.06%    100.69%

Overall CET - After such detailed analysis overall the signal came out colder than average overall for December 2020 with a predicted CET Anomaly of -0.53C Colder than average
00Z CET - The 00Z run came out with -0.43C Colder than average and was overall the least cold run of the 4 of them
06Z CET - The 06Z was a very close 2nd coldest of the runs with a decent -0.52C Colder than average signal
12Z CET - The 12Z has been the coldest run throughout the whole month and ended up with a nice -0.64C colder than average signal
18Z CET - The 18Z has been in a close battle with the 06Z for 2nd position but fell just short in 3rd with -0.51C colder than average signal in the end

Overal Precip - After the detailed analysis overall the signal came out around average overall for December 2020 with predicted precipitation at 100.69% of average
00Z Precip - The 00Z was the most average of all the runs with closest to 100% at 100.67% of average precipitation signal
06Z Precip - The 06Z was a tiny margin wetter than the 00Z in the end at 101.11% of average precipitation signal
12Z Precip - The 12Z was the wettest run overall at 101.94% of average precipitation signal
18Z Precip - The 18Z was the driest run overall at 99.06% of average precipitation signal

You may have noticed the days column in the data. This is the predicted number of days of December that that outcome is likely to happen based on the overall data if this came off

A NEW FEATURE

I have added a new feature here for this December forecast and this is the trend showing what the overall CET anomaly prediction and precipitation prediction was after each days worth of runs

1      -0.58    Colder        91.25    Precip        16    -0.46    Colder        98.91    Precip
2      -0.43    Colder        93.75    Precip        17    -0.45    Colder        99.04    Precip
3      -0.37    Colder        96.25    Precip        18    -0.45    Colder        99.40    Precip
4      -0.39    Colder        96.56    Precip        19    -0.46    Colder        99.45    Precip
5      -0.39    Colder        96.83    Precip        20    -0.45    Colder        99.73    Precip
6      -0.38    Colder        96.74    Precip        21    -0.46    Colder        99.84    Precip
7      -0.37    Colder        96.25    Precip        22    -0.47    Colder        99.28    Precip
8      -0.39    Colder        97.66    Precip        23    -0.48    Colder        99.31    Precip
9      -0.39    Colder        96.62    Precip        24    -0.48    Colder        99.44    Precip
10    -0.39    Colder        95.83    Precip        25    -0.49    Colder        99.50     Precip
11    -0.41    Colder        96.93    Precip        26    -0.50     Colder       99.86    Precip
12    -0.43    Colder        97.95    Precip        27    -0.51    Colder        99.54    Precip
13    -0.44    Colder        98.46    Precip        28    -0.52    Colder        100.12    Precip
14    -0.45    Colder        98.72    Precip        29    -0.52    Colder        100.30     Precip
15    -0.47    Colder        98.47    Precip        30    -0.53    Colder        100.69    Precip

As you may have noticed I got off to a pretty decent start in terms of cold and overall never did get back to -0.58C colder but it wasn't for the less cold runs in the early part of the month we could have ended up with a more decent overall anomaly in the end. In general we trended wetter and wetter as the month went on

PUTTING EVERYTHING TOGETHER

Predicted CET Anomaly

Based on all of the above analysis both from the detailed runs as well as the general monthly runs we can conclude the following for the CET Anomaly

Using individual blocks of CFS analysis as follows:
Monthly Analysis Summer            -0.25C Colder
Monthly Analysis Autumn 1          -0.29C Colder
Monthly Analysis Autumn 2           -0.21C Colder
Monthly Analysis Autumn 3           -0.36C Colder
Monthly Analysis Autumn 4            -0.43C Colder
Detailed Analysis November 00Z    -0.43C Colder
Detailed Analysis November 06Z    -0.52C Colder
Detailed Analysis November 12Z    -0.64C Colder
Detailed Analysis November 18Z    -0.51C Colder
OVERALL ANALYSIS AVERAGE       -0.40C Colder

December 2020 CET Anomaly Forecast
Based on the overall analysis a colder than average December 2020 is predicted with an overall average CET anomaly of -0.40C Colder than the 81-10 mean. This is only the average and there is a wide range of values within the individual analysis so the margin of error could be anything from slightly below average CET anomaly of -0.21C Colder to the coldest end of the margin of error at -0.64C Colder than average. Since we have a general scatter between the less cold and the colder values then we could really finish up anywhere between the lower and higher values in the end assuming the CFS has got December right that is as it has done a big flop for November 2020

Predicted Precipitation Levels

Based on all of the above analysis both from the detailed runs as well as the general monthly runs we can conclude the following for the Precipitation levels

Using individual blocks of CFS analysis as follows:
Monthly Analysis Summer             87.97% Precip
Monthly Analysis Autumn 1           75.00% Precip
Monthly Analysis Autumn 2           75.00% Precip
Monthly Analysis Autumn 3            60.71% Precip
Monthly Analysis Autumn 4            103.57% Precip
Detailed Analysis November 00Z    100.67% Precip
Detailed Analysis November 06Z    101.11% Precip
Detailed Analysis November 12Z    101.94% Precip
Detailed Analysis November 18Z    99.06% Precip
OVERALL ANALYSIS AVERAGE       89.45% Precip

December 2020 Precipitation Forecast
Based on the overall analysis a drier than average December 2020 is predicted with an overall average precipitation level of 89.45% of the December average. There is a large margin of error however with the least dry value at 103.57% of December average and the driest value at 60.71% of average. However the more recent values have been around average so there is a high likelihood that December 2020 will finish with more that 89.45% of precipitation in the end and with the colder signal this could present the chance of snow events at times during the month

[Don]

What are people's thoughts about the recent uptick in solar activity and the potential ramifications it may have on winter?

[Methuselah]

1 minute ago, Don said:

What are people's thoughts about the recent uptick in solar activity and the potential ramifications it may have on winter?

None whatsoever, Don!

[feb1991blizzard]

12 minutes ago, Don said:

What are people's thoughts about the recent uptick in solar activity and the potential ramifications it may have on winter?

May well reduce the chances of cold spell soon, as long as it isn't sustained or only in line with other solar mins, can't see it ruling out a cold spell for whole winter.

[Don]

53 minutes ago, feb1991blizzard said:

May well reduce the chances of cold spell soon, as long as it isn't sustained or only in line with other solar mins, can't see it ruling out a cold spell for whole winter.

It seems at this stage to be picking up quicker than SC24, but I don't think it's out of place with other solar cycles, although someone else could probably confirm that?

[Weather-history]

 

2 hours ago, Don said:

What are people's thoughts about the recent uptick in solar activity and the potential ramifications it may have on winter?

Solar activity didn't prevent those winters of 1916-17, 1928-29, 1946-47 and 1978-79 being notable.

Whilst the deep minimum of 1911-14 didn't make those winters go down in folklore

[sebastiaan1973]

 

[Beanz]

17 hours ago, Don said:

What are people's thoughts about the recent uptick in solar activity and the potential ramifications it may have on winter?

I’ve never seen anything convincing by way of scientific evidence that would make me concerned it will have any impact whatsoever

[ALL ABOARD]

Here is a prime example of cold uppers not being the everything. 

 

14th November 2019 at 108 asl South Wales 

Predicted pattern 

 

What transpired. 

 

 

Nobody had even mentioned the word snow. And I for one for all my years of lurking in these threads didn't even have a scooby it was coming. 

 

[SqueakheartLW]

My latest update based on the CFS monthly charts from weather outlook. These now only contain January to March as the December forecast has been posted on here yesterday

The latest figures translated into the following analysis. The most recent is in bold

01/11/2020 to 26/11/2020 Analysis November CET        +2.10C MILDER        November Precip        89.40% OF NOV AV
This is the current situation according to CET website. I will have the actual figure for the CET here by the next update

06/07/2020 to 30/11/2020 Analysis December CET        -0.40C COLDER        December Precip        89.45% OF DEC AV
The above December figures are my final analysis from all previous updates and the final forecast issued on 30/11/2020. See Early winter discussion thread for the forecast.

18/11/2020 to 01/12/2020 Analysis January CET        -0.21C COLDER        January Precip        103.57% OF JAN AV
04/11/2020 to 17/11/2020 Analysis January CET        -0.07C COLDER        January Precip        92.86% OF JAN AV
21/10/2020 to 03/11/2020 Analysis January CET        -0.36C COLDER        January Precip        92.86% OF JAN AV
07/10/2020 to 20/10/2020 Analysis January CET        -0.14C COLDER        January Precip        114.29% OF JAN AV
23/09/2020 to 06/10/2020 Analysis January CET        -0.36C COLDER        January Precip        103.57% OF JAN AV
06/07/2020 to 22/09/2020 Analysis January CET        -0.25C COLDER        January Precip        108.23% OF JAN AV

18/11/2020 to 01/12/2020 Analysis February CET        -0.64C COLDER        February Precip        100.00% OF FEB AV
04/11/2020 to 17/11/2020 Analysis February CET        -0.71C COLDER        February Precip        142.86% OF FEB AV
21/10/2020 to 03/11/2020 Analysis February CET        -0.36C COLDER        February Precip        121.43% OF FEB AV
07/10/2020 to 20/10/2020 Analysis February CET        -0.50C COLDER        February Precip        125.00% OF FEB AV
23/09/2020 to 06/10/2020 Analysis February CET        -0.43C COLDER        February Precip        125.00% OF FEB AV
06/07/2020 to 22/09/2020 Analysis February CET        -0.24C COLDER        February Precip        115.82% OF FEB AV

18/11/2020 to 01/12/2020 Analysis March CET        -0.86C COLDER        March Precip        114.29% OF MAR AV
04/11/2020 to 17/11/2020 Analysis March CET        -0.71C COLDER        March Precip        100.00% OF MAR AV
21/10/2020 to 03/11/2020 Analysis March CET        -0.50C COLDER        March Precip        100.00% OF MAR AV
07/10/2020 to 20/10/2020 Analysis March CET        -0.57C COLDER        March Precip        125.00% OF MAR AV
23/09/2020 to 06/10/2020 Analysis March CET        -0.43C COLDER        March Precip        110.71% OF MAR AV
06/07/2020 to 22/09/2020 Analysis March CET        -0.11C COLDER        March Precip        112.66% OF MAR AV

18/11/2020 to 01/12/2020 Analysis OVERALL NOV-MAR ANOM -0.01C COLDER        OVERALL NOV-MAR % 99.34% OF NOV-MAR AV
From now on the above overall figure includes the trending then actual anomaly for November 2020. Today it is the +2.10C provisional figure up to 26/11/2020

04/11/2020 to 17/11/2020 Analysis OVERALL NOV-MAR ANOM    -0.45C COLDER        OVERALL NOV-MAR %    105.92% OF NOV-MAR AV
21/10/2020 to 03/11/2020 Analysis OVERALL NOV-MAR ANOM    -0.38C COLDER        OVERALL NOV-MAR %    93.06% OF NOV-MAR AV
07/10/2020 to 20/10/2020 Analysis OVERALL NOV-MAR ANOM    -0.38C COLDER        OVERALL NOV-MAR %    101.43% OF NOV-MAR AV
23/09/2020 to 06/10/2020 Analysis OVERALL NOV-MAR ANOM    -0.37C COLDER        OVERALL NOV-MAR %    100.71% OF NOV-MAR AV
06/07/2020 to 22/09/2020 Analysis OVERALL NOV-MAR ANOM    -0.19C COLDER        OVERALL NOV-MAR %    104.43% OF NOV-MAR AV

November 2020

CET - So far November 2020 has performed very badly on the CET count based on the CFS prediction. It is over 2.4C above the prediction so far compared with the actual reading up to the 26/11/2020 CET value. It appears that this is going to have a huge effect on the overall figure for Nov - Mar and if we are to hit the predicted overall figure from the previous update we will need some cold months now to bring the average down a bit

Precipitation - So far CFS has performed well on the precipitation side as it was going for a drier than average November and it appears to be heading that way. How close its actual figure gets will soon be revealed but it appears CFS has this one nailed on at least

December 2020

CET - I won't say too much here about December 2020 as the main analysis is in the forecast I issued yesterday in this thread

Precipitation - As with CET see the forecast I issued yesterday

January 2021

CET - Last time my analysis brought January 2021 almost back to average with a -0.07C colder than average prediction. This time around we have trended a little colder again to -0.21C colder than average although this figure is still the 2nd least cold analysis showing for January 2021 so far. It appears we are now setting a new trend for January 2021 with a higher chance of it coming out closer to average overall. This increases the risk of a milder month maybe happening too.

Precipitation - The previous 2 updates had seen January 2021 trend drier than average. This latest update puts January 2021 back above average again but not by very much at just 103.57% of average January precipitation. This combining with the less cold CET values is making it look like a zonal Atlantic fest is on the cards for the month

February 2021

CET - February 2021 has been overall one of the coldest months in the CFS predictions, particularly the previous 2 updates. This one is no exception as it joins the club in a decent 2nd position at -0.64C colder. This keeps the recent even colder trend going even if it is less cold than the previous update. A relatively high chance of a cold February showing up at present.

Precipitation - February 2021 has maintained the overall wettest Nov-Mar month so far. The latest update has finally broken this trend as it has come in at bang on average this time with 100.00% of average precipitation predicted. Still not drier than average so very much still on track for a wetter month based on that

March 2021

CET - March 2021 has been the overall top month for coldest CET anomaly compared to average and the latest update has pushed this even colder still with a new low of -0.86C colder than average. A very back loaded winter signal has been showing up a lot in the CFS charts and is getting pushed more and more into March.

Precipitation - March 2021 maintains its wetter than average signal overall and the latest figure is no exception to this at 114.29% of March average. This wetter signal combined with the ever colder signal is making for a potentially interesting March from a snow perspective at least

Overall November 2020 - March 2021 Analysis

CET - The overall signal hasn't changed a lot for December to March but November 2020 has gone a long way out from the prediction. As this actual reading is now factored into the overall figures it has pushed them much closer to average overall for the whole period with it now showing just -0.01C colder for the whole period. December 2020 is coming out a bit colder, January is looking less cold and a potential risk for a milder month. February and March look most odds on for colder months.

Precipitation - CFS has been not that bad on this count at least for November 2020 but can it maintain this throughout the December - March period too. Overall the drier start to the winter and a wetter end signal is maintained which looks good for snow lovers as the colder period appear to be coming with the wetter ones too.

[Roger J Smith]

This winter is perhaps a bit colder than I had suggested in my outlook which was back-loaded, so if it remains back-loaded we should get a fairly solid February. 

The best performing analogues since I listed the November 12-month accumulated analogue potentials are mainly from outside that set and the best in the 20th century is (unfortunately) 1913-14 which went to a very mild February, but at least that indicates blocking potential. In more recent years, 1985-1986 and 1990-1991 have had the best Nov-Dec-Jan accumulated error vs 2020-21 actuals. Those years both featured very cold weather in February (longer duration in 1986, better snowstorm in 1991). So there's room to be optimistic at this point in what many would say is a glass half full winter. (a glass half full is of course a glass half empty) ... and the latest GFS run indicates more reason to be optimistic about February. 

Watch out for the storms around Jan 28-29, a lot of energy peaks and one of them could go into severe territory. After that, the cold should push in fairly steadily. Would be good to see the Feb 1-2 period turning more snowy on successive runs, has potential and that snow cover would be helpful in getting temperature anomalies down quickly.

This winter has been flirting with major winter synoptics and failing to find the right formula so far, but at least we're in the hunt, this is no 2013-14 or even 2019-20 so far. 

Edited January 23, 2021 by Roger J Smith

[LetItSnow!]

Sigh of relief at the ECM tonight. Knew hope wasn’t over!

[SqueakheartLW]

On 16/11/2021 at 18:49, LetItSnow! said:

Sigh of relief at the ECM tonight. Knew hope wasn’t over!

Think you might have got the wrong thread. This is last winter's one. This is the current one