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Winter 20-21 Discussion


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Opening up this thread for cross regional discussion prior to and during the winter of 20-21

 

One of the well-known 'problem areas' in recent winters has been the highly positive AO & NAO.  Here is a map showing how the 500mb pattern from the winters of 11-12 to 19-20 (last 9 winters) has compared to the winters of 02-03 to 10-11 (12-20 minus 03-11).  Getting the AO/NAO even back to neutral would be a step in the right direction.

 

IM0UIt6.png

 

 

Last winter alone, the AO numbers were kind of astounding.  The AO was +2.42 / +3.42 / +2.64 for Jan / Feb / Mar.  That's the highest on record for Jan-Mar going back to 1950

 

aOed0kC.png

 

 

The October release of the Euro Seasonal predicts the greatest potential for a -NAO to be in December, with higher values predicted for Jan-Mar.  The purple covers the range of ensemble members on the Euro Seasonal (purple line is the median).  The gray area is the model climatology.  The yellow and orange is from the analysis in the 24-year hindcast period

 

XfLSa82.png

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https://www.scribd.com/document/479516526/Winter-2020-21-Outlook

That's why I have for the winter. The gist of it is:

+NAO La Nina - but likely negative in Dec/Mar - either briefly but severely, or weakly, but persistently. A blend of 1961, 2003, 2007 is damn close on the predictive periods I use to get NAO values in winter, and very close in the four Nino zones, and in the four nino zone transitions y/y. Also, in the 24 winters following an El Nino since 1950, the winter NAO tends to behave opposite of the October NAO pattern. The -NAO pattern October now favors a +NAO winter.

As for the look of winter, most of the things I can think of that should be independent point to something less amplified but similar to 2016-17.

+NAO La Nina winters (>0.4 DJF) in aggregate are cold West / warm East. It's more reliable NW/SE, it's especially true if you throw out the super hurricane seasons like 2017.

All cold-ENSO events following two El Ninos in the last 90 years follow the above pattern to at least some extent. These are 1931, 1959, 1970, 1978, 1988, 2016 as a blend. I threw out 1942 and 2005, with different looks because they follow three El Nino winters, not two like the others.

If the models are right, and it is a strong La Nina, the blend of the sub 25.0C DJF La Ninas is also cold West/warm East (1973, 1975, 1988, 1999, 2007), with the La Ninas still following the patterns - highest ACE year (1999) is the hottest, and the La Ninas following El Ninos are much better for the West (1973, 1988, 2007).

La Ninas following an 80-160 ACE hurricane season tend to be cold NW, warm SE, again mixed SW/NE. The West will roast generally in the highest ACE La Ninas: 1995, 2005, 2017, etc.

La Ninas following El Ninos are all mild-cold - somewhere - North of a San Francisco to NE/SD line, in each of the last 10 times that scenario has happened. This is more of hot TX pattern than a hot SE or SW pattern.

The lowest sea-ice cold ENSO winters starting 2007 are all cold in the West, while the higher (relatively) sea-ice cold ENSO years are all cold in the East. This is 2007, 2012, 2016 (2020?) for the West, and 2008, 2010, 2013, 2017 for the East, with 2011 on the border. The threshold seems to be 4.3 million square km for the minimal sea-ice extent in September. We were 3.7 million this year.

The +QBO La Nina idea does not support the above ideas. But the sample is so small, that I'm not real worried about it. Especially since rising QBO from Summer to Winter with a La Nina does appear to gel fairly well with a cold NW idea. The warm October in the NW is fairly consistent with years like 1988 as well, despite being rare in a La Nina.

 

 

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The October release from the Euro Seasonal (ECMWF SEAS5) and Met Office / UKMet Seasonal (GloSea5) are similar for Dec-Feb with +EPO and +NAO, and lots of zonal flow.  They are most similar to the winter of 1998-1999.  Are they correct?  Time will tell, but they paint a grim picture for cold and snow across the lower 48. 

 

Euro and UKMet Seasonals...

 

F7TtFZw.png

 

fpAyDXu.png

 

 

1998-1999  500mb, Temperature, and Snowfall Anomalies...

 

tRgvT9W.png

 

8HvrpGB.png

 

dj8IQKu.png

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^ Other somewhat similar years to these 2 model outputs are:

2011-2012, but the +EPO/+NAO was even stronger in the analog year

2007-2008, but the negative height anomaly extended much farther south  (down into the southern plains) in the analog year

1999-2000, but the negative height anomaly was farther north from Alaska to northern Canada

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The Met Office prides itself on its predictions of the NAO with its seasonal model.  I looked at the NAO prediction from prior October seasonal model output back to Oct 2009 (this is the oldest date in the archive on the seasonal model site - https://www.metoffice.gov.uk/research/climate/seasonal-to-decadal/gpc-outlooks/ens-mean).  In looking at the charts,  I would say that in 9 of the 11 years, the October prediction of the NAO on the model was a good one.  The 2 misses were in Oct 2013 and 2015.

 

Here was the Oct seasonal output from 2010 and 2011 - both quite good with the NAO prediction (-NAO in 2010-2011 / +NAO in 2011-2012), with both of those being La Nina winters.

dfs7TC2.png

Hs8lFjl.png

 

Finally, here is a chart from the Met Office showing hindcasts for their prediction of the NAO with the GloSea5 seasonal model for the winters of 1993 to 2012.  The results are pretty good.  Note: this is the NAO prediction from the Nov1 release each year - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GL059637

 

84PSN2M.png

 

 

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The UK October output is essentially what I forecast. In the SW you tend to get ~near constant incoming precipitation divided by outgoing precipitation in each ENSO state if you calculate it annually on the Koppen classification scale. So the 1999 Summer was very cold here, and wet. Something like 40 days >=90F, compared to 90 or so this year. The following winter was hot and very dry to end up at the ~La Nina constant. I'd expect a pretty different outcome from that year given the much hotter/drier summer. 2011-12 would be interesting but I don't think it's a good match for the eastern US. I'm not a fan of 1998 either, mainly because it is a ~4C drop in Nino 3.4 from a Super El Nino, with high solar activity, and the start of a three year La Nina.

Image

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Here is an interesting thought for the winter: When is the last time, two same sign ENSO events produced the same outcome in the winter? In a row I mean.

ENSO:

2009 and 2014? No.  2014 and 2015? No  2015 and 2018? 2018 and 2019?  2006 and 2009? 2004 and 2006?

2012 and 2013? 2003 and 2012?

2017 and 2016? 2016 and 2011? 2011 and 2010? 2010 and 2008? 2007 and 2008? 2005 and 2007? 2000 and 2005?

My point with this is that 2017-2018 was a very hot/dry Western winter. So expecting the same outcome again is probably wrong, despite what CPC/IRI have.

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I really don't know what you're referring to but it doesn't look like you'll answer.

These are the hottest starts to October locally - pretty interesting set of winters.

1 1979-10-16 84.5 0
2 2020-10-16 82.0 1
- 1978-10-16 82.0 0
4 1991-10-16 81.9 0
5 1956-10-16 81.6 0
6 1963-10-16 81.5 0
7 1950-10-16 81.4 0

1950 is sort of like 2008, 1963 is extremely cold in both December & February. 1978 is very cold. 1979 is kind of a weird looking winter. 1991 had the Perfect Storm, may see something like that this month. 1991 is a very hot Plains / cold SW winter.  1956 is what CPC forecast essentially.

 

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18 hours ago, raindancewx said:

I really don't know what you're referring to but it doesn't look like you'll answer.

These are the hottest starts to October locally - pretty interesting set of winters.

1 1979-10-16 84.5 0
2 2020-10-16 82.0 1
- 1978-10-16 82.0 0
4 1991-10-16 81.9 0
5 1956-10-16 81.6 0
6 1963-10-16 81.5 0
7 1950-10-16 81.4 0

1950 is sort of like 2008, 1963 is extremely cold in both December & February. 1978 is very cold. 1979 is kind of a weird looking winter. 1991 had the Perfect Storm, may see something like that this month. 1991 is a very hot Plains / cold SW winter.  1956 is what CPC forecast essentially.

 

this storm at the end of the month, the models have been waffling back and forth on it, do you see it more like 1991 or 2012?  I see your list of analogs had 1973, 1988, 1999 and 2007 in it, and none of those had a large storm at the end of the month.

 

Personally I'd throw out 1988 and 1999 as they are 11 yr peak solar cycle years, and go with 1973 and 2007.

 

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4 minutes ago, LibertyBell said:

this storm at the end of the month, the models have been waffling back and forth on it, do you see it more like 1991 or 2012?  I see your list of analogs had 1973, 1999 and 2007 in it, and none of those had a large storm at the end of the month.

What do you mean by my list of analogs? In my forecast I gave a core blend for the winter outlook, and then noted a bunch of other years that would likely be close in either the Fall or for only regions of the country rather than nationally. I don't really like 1973 or 1999 at all for the winter. 2007 and 2012 I do like a lot, low sea ice, colder east Nino zones v. west in fall. Some similar things for the Atlantic/Pacific

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3 minutes ago, raindancewx said:

What do you mean by my list of analogs? In my forecast I gave a core blend for the winter outlook, and then noted a bunch of other years that would likely be close in either the Fall or for only regions of the country rather than nationally. I don't really like 1973 or 1999 at all for the winter. 2007 and 2012 I do like a lot, low sea ice, colder east Nino zones v. west in fall. Some similar things for the Atlantic/Pacific

I like 2012 too, actually 1973, 2007 and 2012 but I'm very cautious about using 70s analogs here, we get a lot more precip on the east coast than we used to back then.  I noticed 1973, 1988 and 1999 mentioned in an earlier post by you (on this page), I think you stated that you didn't like 1999 though but 1988 was on there.  2012 might be the best match of all, but as you'll notice in the climate subforum, sea ice was on a rapid rise at this point in 2012, and we're really lagging behind in 2020.  I'd give a slight nod to 2007 over the other years that were mentioned.

 

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I am expecting a rather broken up winter temperature regime with spells of very mild and very cold, some tendency towards a colder second half of winter relative to normal in eastern and central states, and the opposite for western  interior regions. Some powerful storms seem very likely given that energy peaks are going to be unusually concentrated. It should be the sort of winter when it would be bad luck for any region to escape a major winter event at some point. It could be a very active lake effect snow season. 

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I'm tempted to say "yes", but it'd be a bit arrogant at this point since the storm is still in the future and could fall apart or something. The rule is an upper low or closed low will appear in the SW domain, somewhere 30-38N, between Los Angeles and Dallas ten days after a 10 point drop in the daily SOI in one or two days. It doesn't work in June-September when the super subtropical highs that make the desert the desert are too strong. But someone looked at all the major SOI drops from 1990-2015 of 10 points and made a composite of it in winter, the "look" is for a low over the four corners. French name for the guy on Twitter, Jacque or something.

15 Oct 2020 1011.26 1009.50 -7.29 11.94 8.69
14 Oct 2020 1012.74 1010.20 -2.26 12.44 8.84
13 Oct 2020 1014.49 1010.00 10.31 12.58 8.77

If you look at the forecasts for Colorado/Northern NM, the low placement is right on time with the 17 point drop between 10/13 and 10/15, using the ten day rule. I find that the drops of 10 points with the SOI still very positive do lead to storms over the SW, but they tend to be completely moisture starved, and little more than dry cold fronts. That's why the recent drop coincides with a pretty big system on the models, but prior drops do not (although there was originally a system depicted around 10/13 following the crash early October). I had mentioned 10/24 in my forecast (from 10/10) as the approximate end of the dry spell in NM that began after the 9/9 system brought snow to NM and CO after highs in the mid 90s. 

More generally, I think the PDO looking more neutral lately and the Euro depicting a weakening La Nina are consistent with a storm down here. When La Ninas weaken or El Ninos strengthen (warming either way), the SW tends to get wet or cold.

 

ezgif-3-26e2c1ecd29d.gif

These are the years with accumulating snow in Albuquerque in October if it happens. It's a ~once a decade event since the 1930s.

Monsoon Oct Nov Dec Jan Feb March April May Oct-May
1932 0.4 0.0 2.0 0.6 0.0 0.9 0.6 0.0 4.5
1967 0.2 1.0 2.8 0.0 2.0 1.4 0.0 0.0 7.4
1970 0.5 0.0 0.5 3.0 2.3 0.5 0.0 0.0 6.8
1973 0.3 0.6 0.1 9.3 0.6 2.0 0.0 0.0 12.9
1979 0.9 0.8 2.7 0.0 0.9 3.1 0.0 0.0 8.4
1986 3.2 0.6 0.2 4.9 4.9 0.2 2.2 0.0 16.2
1991 2.5 1.5 2.1 5.6 0.0 1.0 0.0 0.0 12.7
1996 1.1 2.5 0.0 4.7 0.9 0.3 2.9 0.0 12.4
2004 0.2 1.7 0.3 0.0 0.0 4.2 0.5 0.0 6.9
2009 0.8 0.0 0.7 1.0 0.9 0.8 0.0 0.0 4.2

The cold ENSO years with snow in October are pretty snowy/cold here in general: 1932 is frigid, 1967 is cold, the coldest day in the last 130 years here is in January 1971 (high of -1 I believe, low of -17), 1973-74 is snowy, and 1996-97 is pretty cold and snowy here. On Tropical Tidbits, 1967 is currently one of the top five SST matches globally for the past month, it's kind of a poor man's 1988.

 

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I was toying with something like that originally but moved away from it for a few reasons. Weatherbell's original 2020-21 outlook was basically your blend, +2012, i.e.  2016, 2017, 2018, 2019, 2012 as a blend.

1) The blend of those four years is very wet nationally. I think this is a pretty dry pattern for a lot of the US. Month to date, TX to CO and West has seen essentially no moisture this month (it will change soon though). 2016 and 2017 are night and day different for Western precip - record wetness in California one, and then ~5 months with no rain/snow in the other for places like Amarillo.

2) February 2019 is one of the coldest months on record for large areas of the US. I don't think we'll repeat it this year. The cold shot late January 2019 also rivalled the cold shots in the 1976-77 winter for severity in the Plains/Midwest/East.

3) 2018/2019 all had near record warmth in Nino 4 - which we don't have. Nino 4 is somewhat colder than the 1951-2010 average now. Just in the absence of the super hot Nino 4, I'd expect much more wintry conditions in the East in December (though I'd still go warmer than average).

4) Those are generally +PDO winters, which ties in with the precip being heavy.

5) I find La Nina strength/El Nino strength in an ONI /SST sense doesn't matter too much. But the year/year trends that match tend to produce similar teleconnections. So 2018 is a big warm up year over year in Nino 3.4, but the other three are cool downs.

 

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17 hours ago, raindancewx said:

I was toying with something like that originally but moved away from it for a few reasons. Weatherbell's original 2020-21 outlook was basically your blend, +2012, i.e.  2016, 2017, 2018, 2019, 2012 as a blend.

1) The blend of those four years is very wet nationally. I think this is a pretty dry pattern for a lot of the US. Month to date, TX to CO and West has seen essentially no moisture this month (it will change soon though). 2016 and 2017 are night and day different for Western precip - record wetness in California one, and then ~5 months with no rain/snow in the other for places like Amarillo.

2) February 2019 is one of the coldest months on record for large areas of the US. I don't think we'll repeat it this year. The cold shot late January 2019 also rivalled the cold shots in the 1976-77 winter for severity in the Plains/Midwest/East.

3) 2018/2019 all had near record warmth in Nino 4 - which we don't have. Nino 4 is somewhat colder than the 1951-2010 average now. Just in the absence of the super hot Nino 4, I'd expect much more wintry conditions in the East in December (though I'd still go warmer than average).

4) Those are generally +PDO winters, which ties in with the precip being heavy.

5) I find La Nina strength/El Nino strength in an ONI /SST sense doesn't matter too much. But the year/year trends that match tend to produce similar teleconnections. So 2018 is a big warm up year over year in Nino 3.4, but the other three are cool downs.

 

Its not the only factor, but you mean to say that you see very little commonality between like ENSO states of similar intensity?

 

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21 hours ago, griteater said:

My first guess on winter...

Curvua6.png

GFsA40w.png

s5WBrcn.png

g9FUQxM.png

 

You don't have an issue with the fact that half of your analogue seasons are opposite ENSO state? Of course, that doesn't mean they can't end up similar sensible weather wise.....

I would assume that you expect the Aleutian ridge to be flat, then?

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50 minutes ago, 40/70 Benchmark said:

You don't have an issue with the fact that half of your analogue seasons are opposite ENSO state? Of course, that doesn't mean they can't end up similar sensible weather wise.....

I would assume that you expect the Aleutian ridge to be flat, then?

40/70 - thing is, at 500mb, a composite of the last 2 winters (below) looks like La Nina instead of El Nino with NPac ridge and -PNA.  So, when I composited the last 4, it came out to kind of what I had in my head for this winter in the big picture. 

+QBO this winter would favor a more poleward NPac ridge.  That composite of mine does have a poleward ridge (no negative anomalies in Alaska), but it's biased to the NW.  4 of the last 5 mod-strong Ninas with a poleward NPac ridge were biased to the NW ('56, '71, '74, '11) .  '89 is the lone exception.  One thing that would support the idea of a suppressed NPac ridge would be a strong +AO.  The seasonal models favor a suppressed ridge at the moment.  AO/NAO are always a challenge to figure out.

Anyway, those are some thoughts on it...hope I will have time to put more into it the next 2 weeks...my work has been busier than normal of late.

 

wiGkkoR.png

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19 minutes ago, griteater said:

40/70 - thing is, at 500mb, a composite of the last 2 winters (below) looks like La Nina instead of El Nino with NPac ridge and -PNA.  So, when I composited the last 4, it came out to kind of what I had in my head for this winter in the big picture. 

+QBO this winter would favor a more poleward NPac ridge.  That composite of mine does have a poleward ridge (no negative anomalies in Alaska), but it's biased to the NW.  4 of the last 5 mod-strong Ninas with a poleward NPac ridge were biased to the NW ('56, '71, '74, '11) .  '89 is the lone exception.  One thing that would support the idea of a suppressed NPac ridge would be a strong +AO.  The seasonal models favor a suppressed ridge at the moment.  AO/NAO are always a challenge to figure out.

Anyway, those are some thoughts on it...hope I will have time to put more into it the next 2 weeks...my work has been busier than normal of late.

 

wiGkkoR.png

That makes sense.

Thank you.

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7 hours ago, 40/70 Benchmark said:

Its not the only factor, but you mean to say that you see very little commonality between like ENSO states of similar intensity?

 

Pick three similar years in Nino 3.4 in winter and see how close any of them are nationally when you ignore the other factors. These are the winters I consider La Ninas from 1931 to 2019. Look at 1984 and 1933, or 2011 and 1995 as an extreme example:

1933-1984

La Nina 3.4 DJF
1973 24.63
1988 24.83
1975 24.90
1999 24.95
2007 24.98
1998 25.07
1970 25.09
2010 25.21
1955 25.22
1949 25.26
1942 25.31
1950 25.41
1933 25.51
1984 25.55
1954 25.56
1964 25.69
1938 25.72
2017 25.72
1995 25.74
2011 25.76
1971 25.76
2008 25.79
2005 25.80
2000 25.87
1974 25.93
1983 26.00
1956 26.10
2016 26.30
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12 hours ago, raindancewx said:

Pick three similar years in Nino 3.4 in winter and see how close any of them are nationally when you ignore the other factors. These are the winters I consider La Ninas from 1931 to 2019. Look at 1984 and 1933, or 2011 and 1995 as an extreme example:

1933-1984

La Nina 3.4 DJF
1973 24.63
1988 24.83
1975 24.90
1999 24.95
2007 24.98
1998 25.07
1970 25.09
2010 25.21
1955 25.22
1949 25.26
1942 25.31
1950 25.41
1933 25.51
1984 25.55
1954 25.56
1964 25.69
1938 25.72
2017 25.72
1995 25.74
2011 25.76
1971 25.76
2008 25.79
2005 25.80
2000 25.87
1974 25.93
1983 26.00
1956 26.10
2016 26.30

I wouldn't argue that point, however, do think that the course of lease regret is to consider intensity when parsing potential analogs. I agree with you that there are many other important factors. I do understand why it is less important for you since you focus on sensible weather in your analogs.

I think that there is a very good argument to be made for using MEI to sort by intensity, rather than ONI, though.

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