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Learning NAO and Snowfall Correlation

Fountainguy97

Fountainguy97

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Erwin, TN: 2000ft
Wanted to do some digging around the NAO and what impacts it has on snowfall across the area.

We always say we need the -NAO but how much do we rely on the NAO for snowfall?

I basically took the periods from 1955 to present that were either +NAO dominated or -NAO dominated. I threw the between years into a couple "neutral groups."

The NAO graph is the averaged NAO index for JFM for each year (blue). Black is the 3 or 5 year average I believe.

Take a look for yourself! I thought it was pretty cool.final 2.png

Seems that NAO doesn't make or break winter and it isn't the "fix all" for tons of snow BUT there is a clear increase in snowfall during -NAO winters.

The 2013-2019 period so far has been interesting. The mountains are seeing typical +NAO snowfall amounts but the rest of the area is seeing amounts more like -NAO winters. Could just be a couple heavy snow years as its only a 7 year average vs the other 15+ ones.

Temps are also colder for -NAO winters. Not too shocking there.

cold.png




Another interested note about recent winters.

7 of the last 10 have been +NAO
3 of the last 10 have been -NAO/neutral

this.jpg

It sounds crazy but we have not seen a -NAO winter since 2012-2013 which was more neutral than anything. The last legit -NAO winter was way back in 2010-2011..

The recent 6 year run of +NAO winters has been impressive. This is the most impressive streak of +NAO winters ever. The other streak was 1989-1995 but there were a couple winters at neutral or -nao during that.

The question is what has made the NAO so regular at being + during winter? Is it just a luck of the draw or is there some driver that is forcing our NAO to be + during winters?
 
Great analysis and a good closing question. Deserves some consideration, for sure.

In the grand scheme of things though, IMHO, and not just for snow but for winter as a whole, the AO seems more important overall ... but that's just MHO.

...and the EPO also ...
 
From the NC Climate Office:

Our results found that a negative NAO combined with a positive ENSO phase (El Niño) resulted in the most snow days on average, with an increase of 25% (or more) in snow days for all four winter months.

A positive NAO combined with a negative ENSO (La Niña) resulted in the greatest decrease in average snow days. This is due to a lack of cold air (results of a typical positive NAO), and less active subtropical jet stream (results of a typical La Niña).

NAO had the most significant impact on snow days. Even in winter months that featured La Niña conditions (typically warm and dry), combined with a negative NAO, only February saw a decrease in snow days, which suggests that the NAO has a more direct influence on NC snowfall than ENSO. The reason behind this is that the NAO directly impacts the large scale atmospheric pattern over the eastern U.S. on a daily timescale, whereas the ENSO pattern indirectly effects the eastern U.S. atmospheric pattern by altering global circulations, and does so on monthly to seasonal timescales.

https://climate.ncsu.edu/climate/patterns/nc-snowfall
 
Fountainguy97 said:
Wanted to do some digging around the NAO and what impacts it has on snowfall across the area.

We always say we need the -NAO but how much do we rely on the NAO for snowfall?

I basically took the periods from 1955 to present that were either +NAO dominated or -NAO dominated. I threw the between years into a couple "neutral groups."

The NAO graph is the averaged NAO index for JFM for each year (blue). Black is the 3 or 5 year average I believe.

Take a look for yourself! I thought it was pretty cool.View attachment 20478

Seems that NAO doesn't make or break winter and it isn't the "fix all" for tons of snow BUT there is a clear increase in snowfall during -NAO winters.

The 2013-2019 period so far has been interesting. The mountains are seeing typical +NAO snowfall amounts but the rest of the area is seeing amounts more like -NAO winters. Could just be a couple heavy snow years as its only a 7 year average vs the other 15+ ones.

Temps are also colder for -NAO winters. Not too shocking there.

View attachment 20483




Another interested note about recent winters.

7 of the last 10 have been +NAO
3 of the last 10 have been -NAO/neutral

View attachment 20480

It sounds crazy but we have not seen a -NAO winter since 2012-2013 which was more neutral than anything. The last legit -NAO winter was way back in 2010-2011..

The recent 6 year run of +NAO winters has been impressive. This is the most impressive streak of +NAO winters ever. The other streak was 1989-1995 but there were a couple winters at neutral or -nao during that.

The question is what has made the NAO so regular at being + during winter? Is it just a luck of the draw or is there some driver that is forcing our NAO to be + during winters?
Click to expand...

Even these maps show that much of GA and SC has been hardly affected by the dominant phase of the NAO. Hard daily snowfall and NAO data confirms this for places like ATL, which I've shown before. Also, a good number of major snows including some historic ones even up into NC were when there was no -NAO either immediately preceding or during. I maintain that -NAO is overrated for much of the SE for snowfall, especially south of NC/TN and these maps don't disagree. Actually, no one index is all that dominant because of the rarity/randomness of SE snows, especially deep south.
There has been more of a correlation between -NAO and SE cold during and shortly thereafter than there is between -NAO and SE snowfall during and shortly thereafter.
 
Last edited:
GaWx said:
Even these maps show that much of GA and SC has been hardly affected by the dominant phase of the NAO. Hard daily snowfall and NAO data confirms this for places like ATL, which I've shown before. Also, a good number of major snows including some historic ones even up into NC were when there was no -NAO either immediately preceding or during. I maintain that -NAO is overrated for much of the SE for snowfall, especially south of NC/TN and these maps don't disagree. Actually, no one index is all that dominant because of the rarity/randomness of SE snows, especially deep south.
There has been more of a correlation between -NAO and SE cold during and shortly thereafter than there is between -NAO and SE snowfall during and shortly thereafter.
Click to expand...

I agree. The tough part about tracking snow across the Southeast is the general random storms. This style of research is only beneficial in areas that receive ohh maybe 3+ inches on average a year.

Any less than that and your averages will be easily skewed by random storms.

There is a Correlation atleast for NC. But it seems that its not completely boom or bust. Its more like -NAO gives an extra 1-5 inches across the area than +NAO does. But even then those random snowstorms come into play and impact your averages.
 
Also, I recommend one be careful in the interpretation of these temperature comparisons because the 2nd one is centered on the very cold 1960s (colder globally, too) and is being compared to the 1st one, which is incorporating a period affected by global warming. Nevertheless, I agree that there is very likely some correlation between -NAO winters and colder winters in the SE.
 
pcbjr said:
Great analysis and a good closing question. Deserves some consideration, for sure.

In the grand scheme of things though, IMHO, and not just for snow but for winter as a whole, the AO seems more important overall ... but that's just MHO.

...and the EPO also ...
Click to expand...

I plan on breaking down the AO in a similar fashion as well. Maybe I will make a big post with all the indexes. Problem is the PNA and AO and the others are much more random. Will have to do a lot of cherry picking to find them.

NAO correlation is probably best described as "increases cold and therefore increases snowfall"
 
Tarheel1 said:
MJO is the biggest driver, period!
Click to expand...

I definitely want to do research on MJO. It drives most of our weather. I know very little about it and what makes it tick. I have seen very little research regarding MJO and Southeast Winters. Ill have to take a look.

We should have some sort of Thread with one of our smart guys breaking down each index. lol
 
If I may ... the discussion, thoughts, opinions and data being shared, without anyone getting on top of someone else, is indeed heartwarming ... great job, Folks!
 
^^^

BTW - More articles, studies etc., are most welcome (MJO or any other topic in our Wiki); I'll be glad to post them (or create a new topic) in Wiki if someone has worthwhile stuff to share! Just let me know ... :cool:
 
I guess sometimes a +NAO can be somewhat a help, sometimes it can help to shear out/squash our systems thus creating less mess but we still have to deal with close calls most of the time, -EPO we already know correlates to mix bag Miller Bs based off the maps @Webberweather53 made
 
Fountainguy97 said:
Wanted to do some digging around the NAO and what impacts it has on snowfall across the area.

We always say we need the -NAO but how much do we rely on the NAO for snowfall?

I basically took the periods from 1955 to present that were either +NAO dominated or -NAO dominated. I threw the between years into a couple "neutral groups."

The NAO graph is the averaged NAO index for JFM for each year (blue). Black is the 3 or 5 year average I believe.

Take a look for yourself! I thought it was pretty cool.View attachment 20478

Seems that NAO doesn't make or break winter and it isn't the "fix all" for tons of snow BUT there is a clear increase in snowfall during -NAO winters.

The 2013-2019 period so far has been interesting. The mountains are seeing typical +NAO snowfall amounts but the rest of the area is seeing amounts more like -NAO winters. Could just be a couple heavy snow years as its only a 7 year average vs the other 15+ ones.

Temps are also colder for -NAO winters. Not too shocking there.

View attachment 20483




Another interested note about recent winters.

7 of the last 10 have been +NAO
3 of the last 10 have been -NAO/neutral

View attachment 20480

It sounds crazy but we have not seen a -NAO winter since 2012-2013 which was more neutral than anything. The last legit -NAO winter was way back in 2010-2011..

The recent 6 year run of +NAO winters has been impressive. This is the most impressive streak of +NAO winters ever. The other streak was 1989-1995 but there were a couple winters at neutral or -nao during that.

The question is what has made the NAO so regular at being + during winter? Is it just a luck of the draw or is there some driver that is forcing our NAO to be + during winters?
Click to expand...

Ima look into the atmospheric angular momentum (AAM) and it’s effects, when it switched its phase this past spring, notice how severe weather really picked up, really don’t know much how it correlates to winter weather altho it could make ridges stronger such as the SER, anyways good stuff man ❗️❗️
 
Fountainguy97 said:
I plan on breaking down the AO in a similar fashion as well. Maybe I will make a big post with all the indexes. Problem is the PNA and AO and the others are much more random. Will have to do a lot of cherry picking to find them.
NAO correlation is probably best described as "increases cold and therefore increases snowfall"
Click to expand...

If you're willing to put the time into it, here are the day by day indices 1/1/1950-present, which allow one to pick specific snowstorms and see what the indices were in the days leading up to them and the days of:

PNA: ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.pna.index.b500101.current.ascii
AO: ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii

Also, here is the NAO in case you haven't seen it;
ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.nao.index.b500101.current.ascii

Here is the MJO day by day 6/1/1974-present (any good MJO analysis should include inside the circle, which is really just magnitudes under 1.0 for the 8 phases):
http://www.bom.gov.au/climate/mjo/graphics/rmm.74toRealtime.txt

EPO 1/1/1948-present:
ftp://ftp.cdc.noaa.gov/Public/gbates/teleconn/epo.reanalysis.t10trunc.1948-present.txt

These five table have been my focus in determining PNA, AO, NAO, MJO, and EPO correlations with winter temps and wintry precip (including ZR) for Atlanta, RDU, and some other locations in the past. Although one has to be able to dedicate a generous amount of time to analyze by the day, anyone can do these if they're dedicated.
 
GaWx said:
If you're willing to put the time into it, here are the day by day indices 1/1/1950-present, which allow one to pick specific snowstorms and see what the indices were in the days leading up to them and the days of:

PNA: ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.pna.index.b500101.current.ascii
AO: ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.ao.index.b500101.current.ascii

Also, here is the NAO in case you haven't seen it;
ftp://ftp.cpc.ncep.noaa.gov/cwlinks/norm.daily.nao.index.b500101.current.ascii

Here is the MJO day by day 6/1/1974-present (any good MJO analysis should include inside the circle, which is really just magnitudes under 1.0 for the 8 phases):
http://www.bom.gov.au/climate/mjo/graphics/rmm.74toRealtime.txt

EPO 1/1/1948-present:
ftp://ftp.cdc.noaa.gov/Public/gbates/teleconn/epo.reanalysis.t10trunc.1948-present.txt

These five table have been my focus in determining PNA, AO, NAO, MJO, and EPO correlations with winter temps and wintry precip (including ZR) for Atlanta, RDU, and some other locations in the past. Although one has to be able to dedicate a generous amount of time to analyze by the day, anyone can do these if they're dedicated.
Click to expand...


What lead times would be good to pinpoint?

2 weeks before a storm? Or closer? Or further?

How far out do these indexes have legitimate pull on incoming systems?

Obviously the day of is important but I’m wanting to see what patterns evolved that led into those storms so I/we have factors to look for before the storms happen outside of typical useful model ranges.
 
Myfrotho704_ said:
Ima look into the atmospheric angular momentum (AAM) and it’s effects, when it switched its phase this past spring, notice how severe weather really picked up, really don’t know much how it correlates to winter weather altho it could make ridges stronger such as the SER, anyways good stuff man ❗️❗️
Click to expand...

I hear AAM thrown around every now and then but not often at all.

Feel free to throw out what you find on the board! Maybe this thread should be our “index research” thread haha
 
Fountainguy97 said:
What lead times would be good to pinpoint?

2 weeks before a storm? Or closer? Or further?

How far out do these indexes have legitimate pull on incoming systems?

Obviously the day of is important but I’m wanting to see what patterns evolved that led into those storms so I/we have factors to look for before the storms happen outside of typical useful model ranges.
Click to expand...

1. This is obviously subjective/not black and white. I think a good timeframe is looking at the average of the 7-10 day period prior to a storm.
2. I've learned recently thanks to Reliant that a strong Greenland Block doesn't necessarily mean a solid -NAO or any -NAO at all. I'm sure there are some big snowstorms that immediately followed a strong Greenland Block/neutral NAO combo. I suspect that a strong Greenland Block is more crucial than an actual strong -NAO but that would be very hard to prove. That may be one reason why the snowstorm correlation with -NAO isn't as strong as one might expect. If there existed a daily Greenland block index, I bet that would have a stronger correlation.
3. Don't forget about the all important ENSO trimonthlies:
https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php

Also, Webb has his own ENSO tables back to the middle 1800s.
 
GaWx said:
1. This is obviously subjective/not black and white. I think a good timeframe is looking at the average of the 7-10 day period prior to a storm.
2. I've learned recently thanks to Reliant that a strong Greenland Block doesn't necessarily mean a solid -NAO or any -NAO at all. I'm sure there are some big snowstorms that immediately followed a strong Greenland Block/neutral NAO combo. I suspect that a strong Greenland Block is more crucial than an actual strong -NAO but that would be very hard to prove. That may be one reason why the snowstorm correlation with -NAO isn't as strong as one might expect. If there existed a daily Greenland block index, I bet that would have a stronger correlation.
3. Don't forget about the all important ENSO trimonthlies:
https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php

Also, Webb has his own ENSO tables back to the middle 1800s.
Click to expand...


Any longer than 7-10 days would probably be stretching it. It’s basically impossible to come back and say “if we get this this and this then we all get buried in snow.”
It all runs together and every single storm system will be different.


I’ll probably start by looking at some classic Miller A storms. Break it down into sub category of storm and that can probably help get a more accurate view.
 
Fountainguy97 said:
I hear AAM thrown around every now and then but not often at all.

Feel free to throw out what you find on the board! Maybe this thread should be our “index research” thread haha
Click to expand...
Oh man the AAM and GWO are great tools but I haven't been able to fully wrap my head around them. I would suggest reading into those as changes in the AAM and propagation of +/-AAM through the latitudes can often signal pattern changes

Sent from my SM-G955U using Tapatalk
 
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