The Great I-40 Snow Drought

[mempho]

First off, my apologies to DWagner who has a snow drought thread ongoing, but I had most of this post thought out earlier this weekend and I had to take some time to do some analysis on this.  I originally posted the first part of this as a reply on the WMC weather blog on Friday.  I think that this is a much different thread on the "drought" in that it has two key differences:

1)  A focus on statistical analysis (which is flat even though there is evidence that this stuff is cyclical)
2)  A focus on both Nashville and Memphis (something that is of great interest to many of the posters)

In any case, I realize that I'm new here and I do want to be gracious to the forum here and its members.  Mods, please feel free to do as you see fit...so if you feel the need to merge or whatever, go ahead. 

Almost all of you are aware of the snow drought that has plagued the I-40 corridor in Tennessee.  It is the extent of it that many of you may not be aware of.  The intent of this post is two-fold:

1)   To inform interested parties about the extent of the snow drought
2)   To seek answers through collaboration with a community of like-minded and interested people

First, the extent of the snow drought is something that most of you will find quite astonishing. 

Nashville

Snowfall records have been kept in Nashville since the winter of 1884-85.  As of this writing, there have been 124 complete seasons recorded for Nashville.  In these 123 years, Nashville has had:

3 Seasons of 30” or more (2.4%)
16 Seasons of 20” or more (12.9%)
25 Seasons of 15” or more (20.2%)
31 Seasons of 12” or more (25.0%)
51 Seasons of 7” or more (41.1%)

In the past 20 years, Nashville has recorded:

1 Season of 20” or more
2 Seasons of 15” or more
2 Seasons of 12” or more
3 Seasons of 7” or more

So, in an average 20-year period, Nashville should have between:

1)   8 seasons of 7” or more (Compared to only 3)
2)   5 seasons of 12” or more (Compared to only 2)
3)   4 seasons of 15” or more (Compared to only 2)
4)   2-3 seasons of 20” or more (Compared to only 1)
5)   0-1 seasons of 30” or more (Compared to 0)

Now, the probability calculation of having 3 seasons or less of 7” or more is as follows:

1   0.000352
2   0.002336
3   0.009781

The sum of these probabilities is about 1.2% or it’s about 1 in 83 that any given year will begin a snowfall drought of this magnitude.

This is, indeed, a very bad snow drought.  But it gets worse, much, much worse as you travel to the southwest down Interstate 40. 

Memphis

Snowfall records have been kept in Memphis since the winter of 1889-90, and, in those 119 years, Memphis has had:
5 Seasons of 20″ or more (4.2%)
10 Seasons of 15″ or more (8.4%)
18 Seasons of 12″ or more (15.1%)
30 Seasons of 7″ or more (25.2%)
Now, we haven’t had more than 7″ since 1987-88 even though the probability of such a year is better than 1 in 4!
That’s 20 years without hitting a 1 in 4 chance! Statistically speaking, the probability of such a streak would be 0.748 to the 20th power or about 0.3%, or about 1 in 333!!
If you find these numbers unbelievable, as a local television met did before running the numbers, feel free to look at the source:

http://www.srh.noaa.gov/meg/memsnow.php

The Question
So, I bring this up for the two reasons that I brought up in the outset of the post.  I ask you the following:
1)   What do you think of the numbers posted? 
2)   Do you think they are a temporary aberration or permanent?
3)   Do you think snowfall was way “above normal” at the start of the record-keeping or do you tend to believe that it is way “below normal” now for the area?
4)   What is your hypothesis for the cause of this (please no unintelligent canned answers.  I don’t mind someone saying “climate change” or something but I'd prefer it to be well-reasoned and insightful)?
5)     If you think this is cyclical, what do you think it will take to get back to the days of more plentiful snowfall?

[David]

Did you see any patterns in your research like 30 year trends ?

[mempho]

Did you see any patterns in your research like 30 year trends ?

While there is quite a bit of "clumping" with respect to the really good years, there is nothing that even comes close to approaching this.  By my count, there are two different 12-year stretches without a double-digit season in Memphis, but there were still some relatively decent years in the middle (by Memphis standards).  The current stretch of 20 years without a double-digit season or even a 7 inch season has never been anywhere close to happening since records were kept. 

There is a great deal of cycling on the 15"+ seasons, however (at least by just looking at it).

[Thundersnow]

Great write-up, mempho.  And, welcome to the forum!

While my research may not have been as thorough as yours, here is some info I researched a while back in this thread:  Cyclical Snowfall Averages.

Special attention to the following graphics:

"Rolling" 30-year average as recorded in Nashville 1914/15 - 2006/07: 

The graph is a rolling year-by-year calculation of the previous 30 years of snowfall averages.  For example, the value for the season 1914-1915 was the 30-year average starting with the 1884-1885 season and ending with the 1914-1915 season... and the graphic continues a sliding 30-year average from that point forward (so that the value for the season 2006-2007 is the 30 year average starting with 1976-1977 onward... you get the idea).

What you can visually see in that graphic was a steady decline in snowfall averages during the 1920s and 1930s.  That average leveled out rather low through the 1940s.  But, then, during the 1950s, we begin to see a rise in snowfall averages.  During the snowy 60s, the averages really skyrocket and stay high through the 1970s and 1980s.  Since the 1980s, the current snow drought takes us back roughly to where this area was during the 1940s.

Here's a similar graphic I derived from calcuations from the snowfall data in Memphis:


Same general idea... but maybe even a bit more pronounced.

I would appreciate your thoughts.

[tennessee storm09]

i really honestly think it cycles in years of 30. and like i said before its about time to start going the other direction. so hopefully snowy years are in the near future again.

[Clay]

First off, my apologies to DWagner who has a snow drought thread ongoing, but I had most of this post thought out earlier this weekend and I had to take some time to do some analysis on this.  I originally posted the first part of this as a reply on the WMC weather blog on Friday.  I think that this is a much different thread on the "drought" in that it has two key differences:

1)  A focus on statistical analysis (which is flat even though there is evidence that this stuff is cyclical)
2)  A focus on both Nashville and Memphis (something that is of great interest to many of the posters)

In any case, I realize that I'm new here and I do want to be gracious to the forum here and its members.  Mods, please feel free to do as you see fit...so if you feel the need to merge or whatever, go ahead. 

Almost all of you are aware of the snow drought that has plagued the I-40 corridor in Tennessee.  It is the extent of it that many of you may not be aware of.  The intent of this post is two-fold:

1)   To inform interested parties about the extent of the snow drought
2)   To seek answers through collaboration with a community of like-minded and interested people

First, the extent of the snow drought is something that most of you will find quite astonishing. 

Nashville

Snowfall records have been kept in Nashville since the winter of 1884-85.  As of this writing, there have been 124 complete seasons recorded for Nashville.  In these 123 years, Nashville has had:

3 Seasons of 30” or more (2.4%)
16 Seasons of 20” or more (12.9%)
25 Seasons of 15” or more (20.2%)
31 Seasons of 12” or more (25.0%)
51 Seasons of 7” or more (41.1%)

In the past 20 years, Nashville has recorded:

1 Season of 20” or more
2 Seasons of 15” or more
2 Seasons of 12” or more
3 Seasons of 7” or more

So, in an average 20-year period, Nashville should have between:

1)   8 seasons of 7” or more (Compared to only 3)
2)   5 seasons of 12” or more (Compared to only 2)
3)   4 seasons of 15” or more (Compared to only 2)
4)   2-3 seasons of 20” or more (Compared to only 1)
5)   0-1 seasons of 30” or more (Compared to 0)

Now, the probability calculation of having 3 seasons or less of 7” or more is as follows:

1   0.000352
2   0.002336
3   0.009781

The sum of these probabilities is about 1.2% or it’s about 1 in 83 that any given year will begin a snowfall drought of this magnitude.

This is, indeed, a very bad snow drought.  But it gets worse, much, much worse as you travel to the southwest down Interstate 40. 

Memphis

Snowfall records have been kept in Memphis since the winter of 1889-90, and, in those 119 years, Memphis has had:
5 Seasons of 20″ or more (4.2%)
10 Seasons of 15″ or more (8.4%)
18 Seasons of 12″ or more (15.1%)
30 Seasons of 7″ or more (25.2%)
Now, we haven’t had more than 7″ since 1987-88 even though the probability of such a year is better than 1 in 4!
That’s 20 years without hitting a 1 in 4 chance! Statistically speaking, the probability of such a streak would be 0.748 to the 20th power or about 0.3%, or about 1 in 333!!
If you find these numbers unbelievable, as a local television met did before running the numbers, feel free to look at the source:

http://www.srh.noaa.gov/meg/memsnow.php

The Question
So, I bring this up for the two reasons that I brought up in the outset of the post.  I ask you the following:
1)   What do you think of the numbers posted? 
2)   Do you think they are a temporary aberration or permanent?
3)   Do you think snowfall was way “above normal” at the start of the record-keeping or do you tend to believe that it is way “below normal” now for the area?
4)   What is your hypothesis for the cause of this (please no unintelligent canned answers.  I don’t mind someone saying “climate change” or something but I'd prefer it to be well-reasoned and insightful)?
5)     If you think this is cyclical, what do you think it will take to get back to the days of more plentiful snowfall?

Excellent post. Welcome to TNWX. You especially along with our other new members will surely be an asset and welcome addition to the forum.    

[JJJackson]

I have updated the 30-year rolling average for Memphis to also include data points for 10 and 20 years. Helps to illustrate how the occasional "big" snow impacts the short-term. Hope it's useful. Great topic and research.

[Cameron K.]

Mempho, you aught to tell a little about your self in the introduction forum. Obviously you have good knowledge, what are your backgrounds, ect?

[Thundersnow]

Mempho, my attempt at the questions you pose:

The Question
So, I bring this up for the two reasons that I brought up in the outset of the post.  I ask you the following:
1)   What do you think of the numbers posted?

The information is accurate and consistent with what I have observed in looking at the same data.  I appreciate seeing some of the percentages and other stats you've presented from the data.
 

2)   Do you think they are a temporary aberration or permanent?

I don't know the answer to that with certainty.  But, I tend to believe that it is a temporary statistical lull in snowfall averages.

3)   Do you think snowfall was way “above normal” at the start of the record-keeping or do you tend to believe that it is way “below normal” now for the area?

The point of my also posting the graphics I did above illustrates what I believe the historical data to show... the definition of "normal" is in a constant state of change.  A 125-year average will flatten out the ups and downs to a certain value.  Yet, any given 30-year period will show a different average.  It truly depends on what defines "normal."

4)   What is your hypothesis for the cause of this (please no unintelligent canned answers.  I don’t mind someone saying “climate change” or something but I'd prefer it to be well-reasoned and insightful)?

I don't have a solid hypothesis for why it is.  I can only repeat what has been hypothesized by others, which include anything from sunspot cycles to AGW (manmade global warming) to other observable but yet to be understood cycles in nature.  There is evidence of cyclical ice ages and warm periods in earth's past.

5)     If you think this is cyclical, what do you think it will take to get back to the days of more plentiful snowfall?

This is similar to my answer for #2.  But, I believe the earth is in a constant state of change, and colder, snowier winters will tend to cycle back at some point.  Do I have solid scientific evidence for that?  Nah, not really.  It's just a hunch.

[Thundersnow]

I have updated the 30-year rolling average for Memphis to also include data points for 10 and 20 years. Helps to illustrate how the occasional "big" snow impacts the short-term. Hope it's useful. Great topic and research.

Yep.  When I was graphing my findings with Excel, I tried different intervals to calculate the averages, including 10, 15, and 20 years, etc.  Longer spans of time tend to "smooth out" the look of the averages over time.  30 years was what I went with simply because that is the number of years that climatological averages are usually based on.  But, big events certainly make all the difference.  What we have seen in the data shows some clustering of the big events. 

[lyngo]

Wrong phase of the Pacific Decadal Oscillation?  I don't know.  I firmly believe it's cyclical in nature w/ a little bad luck thrown in.  I agree w/ those who believe we're nearing (if not already beginning) a period of cooler climate overall.  It would not surprise me at all for our winters to get progressively worse (more snowfall) in the next few years.  I could go on and on but my point is that I think it's primarily cyclical and better days lie ahead.

[Eric]

First off, my apologies to DWagner who has a snow drought thread ongoing, but I had most of this post thought out earlier this weekend and I had to take some time to do some analysis on this.  I originally posted the first part of this as a reply on the WMC weather blog on Friday.  I think that this is a much different thread on the "drought" in that it has two key differences:

1)  A focus on statistical analysis (which is flat even though there is evidence that this stuff is cyclical)
2)  A focus on both Nashville and Memphis (something that is of great interest to many of the posters)

In any case, I realize that I'm new here and I do want to be gracious to the forum here and its members.  Mods, please feel free to do as you see fit...so if you feel the need to merge or whatever, go ahead. 

Almost all of you are aware of the snow drought that has plagued the I-40 corridor in Tennessee.  It is the extent of it that many of you may not be aware of.  The intent of this post is two-fold:

1)   To inform interested parties about the extent of the snow drought
2)   To seek answers through collaboration with a community of like-minded and interested people

First, the extent of the snow drought is something that most of you will find quite astonishing. 

Nashville

Snowfall records have been kept in Nashville since the winter of 1884-85.  As of this writing, there have been 124 complete seasons recorded for Nashville.  In these 123 years, Nashville has had:

3 Seasons of 30” or more (2.4%)
16 Seasons of 20” or more (12.9%)
25 Seasons of 15” or more (20.2%)
31 Seasons of 12” or more (25.0%)
51 Seasons of 7” or more (41.1%)

In the past 20 years, Nashville has recorded:

1 Season of 20” or more
2 Seasons of 15” or more
2 Seasons of 12” or more
3 Seasons of 7” or more

So, in an average 20-year period, Nashville should have between:

1)   8 seasons of 7” or more (Compared to only 3)
2)   5 seasons of 12” or more (Compared to only 2)
3)   4 seasons of 15” or more (Compared to only 2)
4)   2-3 seasons of 20” or more (Compared to only 1)
5)   0-1 seasons of 30” or more (Compared to 0)

Now, the probability calculation of having 3 seasons or less of 7” or more is as follows:

1   0.000352
2   0.002336
3   0.009781

The sum of these probabilities is about 1.2% or it’s about 1 in 83 that any given year will begin a snowfall drought of this magnitude.

This is, indeed, a very bad snow drought.  But it gets worse, much, much worse as you travel to the southwest down Interstate 40. 

Memphis

Snowfall records have been kept in Memphis since the winter of 1889-90, and, in those 119 years, Memphis has had:
5 Seasons of 20″ or more (4.2%)
10 Seasons of 15″ or more (8.4%)
18 Seasons of 12″ or more (15.1%)
30 Seasons of 7″ or more (25.2%)
Now, we haven’t had more than 7″ since 1987-88 even though the probability of such a year is better than 1 in 4!
That’s 20 years without hitting a 1 in 4 chance! Statistically speaking, the probability of such a streak would be 0.748 to the 20th power or about 0.3%, or about 1 in 333!!
If you find these numbers unbelievable, as a local television met did before running the numbers, feel free to look at the source:

http://www.srh.noaa.gov/meg/memsnow.php

The Question
So, I bring this up for the two reasons that I brought up in the outset of the post.  I ask you the following:
1)   What do you think of the numbers posted? 
2)   Do you think they are a temporary aberration or permanent?
3)   Do you think snowfall was way “above normal” at the start of the record-keeping or do you tend to believe that it is way “below normal” now for the area?
4)   What is your hypothesis for the cause of this (please no unintelligent canned answers.  I don’t mind someone saying “climate change” or something but I'd prefer it to be well-reasoned and insightful)?
5)     If you think this is cyclical, what do you think it will take to get back to the days of more plentiful snowfall?

Excellent post and nicely done!  Thank you for posting your information.  In case I haven't welcomed you the forum yet....WELCOME!

[Curt]

Nice write up Mempho and welcome!

The last 20 years have been torture for me winter wx wise. I cannot believe that we are in such a statewide snow drought, but especially at KMEM. Howver, there have been several years where areas around, and I mean suburbs have recorded normal or even above average amounts vs KMEM(ie '96, '97, '02, '03, '06, and '08.) Even parts of the Metro recorded 6-8 inches from that freak storm in Feb '04. I know why KMEM is not an accurate recording station on radiational cooling nights, but why the heck for snow amounts.

Now for Nashville, go figure. It seems that awful "Warm-Nose" snow bust in '06 was just icing on the cake for the drought there. I will never figure that one out.

[Clay]

Nice write up Mempho and welcome!

The last 20 years have been torture for me winter wx wise. I cannot believe that we are in such a statewide snow drought, but especially at KMEM. Howver, there have been several years where areas around, and I mean suburbs have recorded normal or even above average amounts vs KMEM(ie '96, '97, '02, '03, '06, and '08.) Even parts of the Metro recorded 6-8 inches from that freak storm in Feb '04. I know why KMEM is not an accurate recording station on radiational cooling nights, but why the heck for snow amounts.

Now for Nashville, go figure. It seems that awful "Warm-Nose" snow bust in '06 was just icing on the cake for the drought there. I will never figure that one out.

The March of 08 event I just about thought they took a yard stick measured snow right off the landing tarmac. It seemed ridiculous until everyone realized BNA and East Nashville were just that unlucky. Ron reported less than the airport if I recall correctly. I live 7 miles WSW of BNA and roughly 150 higher in elevation and recorded just over 4" of snow.

[snowdog]

Great stats and thanks for putting all that down. 

I think this is our new climate for the area as I stated in another thread. I think our new climate average will be around 5" for BNA.  Do I have sound reasoning for this?  No not really.  Just having lived here for 31 years and observing.  Nashville has always been known to be "on the line" when it came to winter events but I think the line has moved north some what. 

I dont totally poopoo the cyclical argument either.  Unfortunately, the data we have is such a small sample size it is hard to really tell.  This would have been a great year to cash in on some snow.  Low sun activity and a colder than normal January didnt do us any good.  It will be ineresting to see what the long term effects of lower sun activity are in the next few years.