Winter 2020-2021 Outlook

[donsutherland1]

A moderate La Niña event has developed. Since 1950, 80% of La Niña events that developed in the June-July-August or later saw predominant EPO+/AO+ winter tendencies. All cases that saw the MJO in Phases 4-6 for 20 or more days experienced such tendencies.

As November progressed, the stratosphere over the Arctic region was abnormally cool. At the same time, the stratospheric polar vortex was strengthening. These developments are consistent with an atmospheric state that favors a positive AO.

As a result, even as an AO-/PNA+ pattern is likely to begin December, that pattern should eventually give way to a predominant AO+ pattern. December will likely be the coldest month relative to normal during meteorological winter in the eastern United States.

Since winter 1979-80, there have been 7 cases where December-February saw both the EPO and AO average +0.25 or above for the winter: 1998-99, 1999-00, 2001-02, 2006-07, 2007-08, 2011-12, and 2019-20. Winter 2020-21 will very likely become the 8th such case.

Key Assumptions:
1. Cold ENSO
2. Generally positive NAO
3. Negative PDO
4. Predominantly positive AO
5. Predominantly positive EPO

Given the differences in details that can occur winter-to-winter and the differing ENSO states from the EPO+/AO+ cases, a look at mean anomalies and, if possible, clustered outcomes can provide insight.

December-February Temperature Anomalies (EPO and AO +0.25 or Above):

Clustered 500 mb Scenarios:

C3S Multi-System Seasonal Forecast:

Additional factors to be considered include the observed ongoing Arctic warming. This variable can promote an increased persistence of events.

Based on all of the above factors, my estimated December-February temperature thinking is:

Colder than normal (1.0° to 2.0° below normal):

Alaska, Northwestern Canada

Near Normal (0.5° below normal to 0.5° above normal):

Pacific Northwest, British Columbia

Somewhat above normal (0.5° to 1.5° above normal):

Canada (except for southern Ontario, southern Quebec, and western Canada), West Coast (except for Pacific Northwest)

Warmer than Normal (1.0° to 3.0° above normal):

Middle Atlantic Region, New England, Plains States (Southern, Central, and Northern Plains), Southeast, Southern Ontario, Southern Quebec, Southwest

Much Warmer than Normal (More than 3.0° above normal):

Great Lakes Region

Select seasonal snowfall estimates are below:

Albany: 45"-55"
Atlanta: 0.5" or less
Baltimore: 6"-12"
Binghamton: 65"-75"
Boston: 25"-35"
Buffalo: 80"-90"
Burlington: 65"-75"
Chicago: 33"-43"
Detroit: 35"-45"
Harrisburg: 10"-20"
New York City: 8"-16"
Newark: 8"-16"
Philadelphia: 7"-14"
Providence: 20"-30"
Richmond: 4" or less
Scranton: 30"-40"
Sterling: 6"-12"
Washington, DC: 5"-10"

What could lead to higher amounts:

1. Periods of deep blocking (AO of -1.000 or below)
2. The MJO's persistently being in Phases 7, 8, 1, and 2 at a high amplitude
3. A mainly positive PNA

What could lead to lesser amounts:

1. The development of a persistently strongly positive AO, especially if coupled with a strongly positive EPO
2. The MJO's persistently being in Phases 4, 5, and 6 at a high amplitude
3. A sharply negative PDO driving a frequently strongly negative PNA

 

[billgwx]

Nicely done especially with respect to the MJO, and had came to similar conclusions. Doesn't mean we here in the NYC area can't experience periods of cold and snow (mid December potential case in point) but it's not looking like a cold/snow lover's winter here. Some other things to consider:

While October Siberian snowfall was 10th highest on record of the last 50+ years, its signal for cold and snow in the Northeast has not worked out well in recent years. Judah Cohen suspects persistently low Arctic sea ice may be playing a role here, and I also notice that in recent years North American October snowfall has been very high and may be stealing the show there.

I've wondered how the QBO could influence this winter. It's totally out of phase with the ongoing moderate ENSO phase, which has never happened before in the period of record. Looking at its potential influence alone suggests less potential for ozone transport from the tropics to the polar regions, which in turn offers less potential for weakening of the polar vortex, implying an overall a +AO phase for this winter.

Moderate La Niña events of yore in NYC were some of the coldest and snowiest in the city's history. But I think almost all were embedded in multi-year La Niña events, and featured pronounced below normal 500 mb heights over all of Canada and persistent high latitude blocking near Scandinavia, also above normal heights to a lesser degree extending from the eastern U.S across the north Atlantic to Britain, and below normal heights from the subtropical Atlantic eastward to the Middle East. Recent moderate La Niña events (all warm in NYC) all featured persistent high latitude blocking centered over central Siberia, much below normal heights centered over Alaska (+EPO), and above normal heights over most of the temperate regions.

To add local flavor to the I looked at two things: (1) average October/November temperatures in Central Park with those of DJF and (2) Central Park winter snowfall in seasons following previous winters with less than 10." Of the last 30 years, those with October/November temperature anomaly trends similar to those of this year, above normal as a whole where November positive anomalies were greater than those of October, were 80% likely to see a warm winter with below normal snowfall. The only predictor to show any skill for a cold winter overall was a cold October, but with only about 55-60% confidence. Other trends in NYC October and November anomalies (warm to cold or vice versa) had little skill. As for (2), only one following winter of record featured an ongoing moderate La Niña, (1998-99, with much below normal snowfall of 12.7 inches), and all the following winters with above normal snowfall occurred during El Niño events.

[donsutherland1]

17 hours ago, billgwx said:

Nicely done especially with respect to the MJO, and had came to similar conclusions. Doesn't mean we here in the NYC area can't experience periods of cold and snow (mid December potential case in point) but it's not looking like a cold/snow lover's winter here. Some other things to consider:

While October Siberian snowfall was 10th highest on record of the last 50+ years, its signal for cold and snow in the Northeast has not worked out well in recent years. Judah Cohen suspects persistently low Arctic sea ice may be playing a role here, and I also notice that in recent years North American October snowfall has been very high and may be stealing the show there.

I've wondered how the QBO could influence this winter. It's totally out of phase with the ongoing moderate ENSO phase, which has never happened before in the period of record. Looking at its potential influence alone suggests less potential for ozone transport from the tropics to the polar regions, which in turn offers less potential for weakening of the polar vortex, implying an overall a +AO phase for this winter.

Moderate La Niña events of yore in NYC were some of the coldest and snowiest in the city's history. But I think almost all were embedded in multi-year La Niña events, and featured pronounced below normal 500 mb heights over all of Canada and persistent high latitude blocking near Scandinavia, also above normal heights to a lesser degree extending from the eastern U.S across the north Atlantic to Britain, and below normal heights from the subtropical Atlantic eastward to the Middle East. Recent moderate La Niña events (all warm in NYC) all featured persistent high latitude blocking centered over central Siberia, much below normal heights centered over Alaska (+EPO), and above normal heights over most of the temperate regions.

To add local flavor to the I looked at two things: (1) average October/November temperatures in Central Park with those of DJF and (2) Central Park winter snowfall in seasons following previous winters with less than 10." Of the last 30 years, those with October/November temperature anomaly trends similar to those of this year, above normal as a whole where November positive anomalies were greater than those of October, were 80% likely to see a warm winter with below normal snowfall. The only predictor to show any skill for a cold winter overall was a cold October, but with only about 55-60% confidence. Other trends in NYC October and November anomalies (warm to cold or vice versa) had little skill. As for (2), only one following winter of record featured an ongoing moderate La Niña, (1998-99, with much below normal snowfall of 12.7 inches), and all the following winters with above normal snowfall occurred during El Niño events.

Thanks Bill.

I agree with you about potential periods of colder weather with opportunities for snowfall. It just doesn't appear to be a snowy winter. My 8-year-old doesn't like the idea that there won't be much snowfall, as he want to "make up" for last year's lack of sledding.

I suspect Cohen is right about the role of persistently low Arctic sea ice. That situation might well be driving the higher snowfall, as warmer air holds more moisture.
Recent moderate La Niña events haven't worked out well. Perhaps the larger area of warm SSTAs in the Pacific, which has had some impact on the MJO (more time being spent in the Maritime Continent phases) has influenced the outcome.

Interesting point about the comparison of October and November temperature anomalies. That statistic adds confidence about the possible overall nature of the coming winter.
I hope you had a great Thanksgiving Day holiday.

 

[DTWXRISK]

 

A couple of points which I think need to be mentioned because I think you are overlooking them.  Using statistics to show that something is likely to happen is all well and good until the unusual thing that is not supposed to happen does happen.

 

1000 days in a row the farmer comes out every morning and afternoon and feeds the Turkey. The Turkey becomes convinced that  it is special and chosen and that since it has  always been that way it will continue  . Then one day in the month of October when the farmer comes to feed the turkey….  well we all know what happens.

 

You seem to have discounted the idea that the moderate La Nina  is going to break down in the second half of the winter despite the overwhelming amount of data and model simulations  that show  that is going to happen.  Of course you may be discounting that or you may decide that the models are overdoing the decay of the moderate la Nina and it won't happen until spring. That was perfectly reasonable and possible. But I think it is a risk assumption to assume that the moderate La Nina is going to continue at current intensity for the entire winter.

 

The speculation or assumption that the PDO  is going to be negative and that the EPO  is going to be generally positive is also in my opinion a risky assumption given the return of the enormous blob of warm SSTAs  that have developed in the northeastern Pacific.  The last time  we had  “ the blob’  feature we were not  in  any kind of Enso event --  not   a weak moderate or  strong La Nina   and or  El  Nino.

[raindancewx]

The PDO is negative. It's not speculation. https://www.ncdc.noaa.gov/teleconnections/pdo/

202001	-1.40
202002	-1.47
202003	-1.75
202004	-1.32
202005	-0.51
202006	-0.76
202007	-0.89
202008	-1.32
202009	-1.02
202010	-0.58

Warm North Pacific does not mean +PDO. The blob idea as a unique feature is the most over rated idea of seasonal forecasting in the past decade. Same orientation in the Fall last year and ended up with a very warm winter. The Fall pattern wasn't even that different overall despite completely different tropical patterns. The Fall this year was hot west/east, cold central. Last year had more cold West, but not that different and presumably a lot of that is how close the North Atlantic/North Pacific look.

[DTWXRISK]

16 hours ago, raindancewx said:

The PDO is negative. It's not speculation. https://www.ncdc.noaa.gov/teleconnections/pdo/

202001	-1.40
202002	-1.47
202003	-1.75
202004	-1.32
202005	-0.51
202006	-0.76
202007	-0.89
202008	-1.32
202009	-1.02
202010	-0.58

Warm North Pacific does not mean +PDO. The blob idea as a unique feature is the most over rated idea of seasonal forecasting in the past decade. Same orientation in the Fall last year and ended up with a very warm winter. The Fall pattern wasn't even that different overall despite completely different tropical patterns. The Fall this year was hot west/east, cold central. Last year had more cold West, but not that different and presumably a lot of that is how close the North Atlantic/North Pacific look.

Warm North Pacific does not mean +PDO.

i did  NT  say it   did.  In no way  did I say that 

[billgwx]

On 12/1/2020 at 11:18 PM, DTWXRISK said:

 

 

A couple of points which I think need to be mentioned because I think you are overlooking them.  Using statistics to show that something is likely to happen is all well and good until the unusual thing that is not supposed to happen does happen.

 

1000 days in a row the farmer comes out every morning and afternoon and feeds the Turkey. The Turkey becomes convinced that  it is special and chosen and that since it has  always been that way it will continue  . Then one day in the month of October when the farmer comes to feed the turkey….  well we all know what happens.

 

You seem to have discounted the idea that the moderate La Nina  is going to break down in the second half of the winter despite the overwhelming amount of data and model simulations  that show  that is going to happen.  Of course you may be discounting that or you may decide that the models are overdoing the decay of the moderate la Nina and it won't happen until spring. That was perfectly reasonable and possible. But I think it is a risk assumption to assume that the moderate La Nina is going to continue at current intensity for the entire winter.

 

The speculation or assumption that the PDO  is going to be negative and that the EPO  is going to be generally positive is also in my opinion a risky assumption given the return of the enormous blob of warm SSTAs  that have developed in the northeastern Pacific.  The last time  we had  “ the blob’  feature we were not  in  any kind of Enso event --  not   a weak moderate or  strong La Nina   and or  El  Nino.

Even if you are a fan of horror movies (aka "The Blob") got to see things in greater perspective, which to me is the entire North Pacific being warm, aka -PDO. I think that will work to maintain the moderate Nina for longer, with any weakening holding off til late Feb or beyond.

[DTWXRISK]

bill    very  reasonable...

my POINT   is  not the   THE BLOB  means     XYZ...  my point is hat I have seen it with a La nina    ever  before.

maybe it  means nothing. 

 but  I  dont know that 

[raindancewx]

The northern oceans aren't a bad match to 2013, but there are still a lot of  issues with that year. The La Nina, solar activity, the Summer/Fall progression for US weather, the two hurricane seasons are completely different, sea ice extent is far lower, and 2020 follows several warm ENSO years while 2013 follows several cold ENSO years.

Can't really see blob similarities over riding all of those differences.

 

[WxMidwest]

Welcome to the jungle baby...

[billgwx]

18 hours ago, DTWXRISK said:

bill    very  reasonable...

my POINT   is  not the   THE BLOB  means     XYZ...  my point is hat I have seen it with a La nina    ever  before.

maybe it  means nothing. 

 but  I  dont know that 

Gotcha. Nor have we seen +QBO over 10.0 like we have now with a moderate La Nina. (QBO usually tends to follow ENSO phase with some lag.) Related?

[donsutherland1]

On 12/1/2020 at 11:18 PM, DTWXRISK said:

 

 

A couple of points which I think need to be mentioned because I think you are overlooking them.  Using statistics to show that something is likely to happen is all well and good until the unusual thing that is not supposed to happen does happen.

 

1000 days in a row the farmer comes out every morning and afternoon and feeds the Turkey. The Turkey becomes convinced that  it is special and chosen and that since it has  always been that way it will continue  . Then one day in the month of October when the farmer comes to feed the turkey….  well we all know what happens.

 

You seem to have discounted the idea that the moderate La Nina  is going to break down in the second half of the winter despite the overwhelming amount of data and model simulations  that show  that is going to happen.  Of course you may be discounting that or you may decide that the models are overdoing the decay of the moderate la Nina and it won't happen until spring. That was perfectly reasonable and possible. But I think it is a risk assumption to assume that the moderate La Nina is going to continue at current intensity for the entire winter.

 

The speculation or assumption that the PDO  is going to be negative and that the EPO  is going to be generally positive is also in my opinion a risky assumption given the return of the enormous blob of warm SSTAs  that have developed in the northeastern Pacific.  The last time  we had  “ the blob’  feature we were not  in  any kind of Enso event --  not   a weak moderate or  strong La Nina   and or  El  Nino.

Those are all valid points, DT.

I don’t think the current state of the La Niña will be maintained throughout the winter. I suspect it is approaching or perhaps near its peak right now and then will begin to fade. My temperature anomalies are December-February anomalies. A March 2017-type scenario is one possibility if the La Niña fades faster than I think it will. I suspect that we’ll see the ENSO Region 3.4 anomaly rise above La Niña levels (on a monthly average) in February or March, but the December-February figure will be consistent with La Niña. 

I am a bit more worried about what happens with the stratospheric polar vortex (SPV) for the second half of winter. But, as far as I know, there’s no real skill beyond a few weeks when it comes to forecasting the SPV. 

Finally, I could be wrong on a regional or larger basis when all is said and done. It wouldn’t be the first time (and almost certainly would not be the last time).