Case Study on the importance of a neg PDO for TN snow

[Tennwxspot]

Contrary to popular belief that a negative pdo should keep the SE more warm and less snow I have proved different at least for TN. I was looking for some graphical data for Tennessee snowfall and couldnt find any.

So I decided to put together a graph on my own. Since TN has several different cities which dictate the amounts of snowfall...I had to think of a way to get an average for the state itself. It seemed the easy way to do this was to pick the most neutral city and it's data.

Since Memphis and Chatanooga seemed to be the lower annual snowfall cities and Knoxvile and the Tri-Cities seemed to be the higher...I thought Nashville would make the best city to get an average from since it seemed to be in the middle regarding snowfall amounts and geography itself.

Here is the 50 year graph that I came up with..sorry for the jumbled numbers but you get the idea.

This graph is based on data from OHX and I have omitted 2004-05 snowfall from this graph because the data for that winter was a trace accumulation and the software won't recognize a "T" value.

Here is the source for that data

http://www.srh.noaa..../?n=monthlysnow

I knew there would be a correlation between this graph and the NAO but suprisingly there is an even better correlation between this graph and the PDO index. It appears to me that above average snowfall is more likely if you have negative PDO.

During the last cold phase of the PDO there were 6 winters in a row in the 1960's of snowfall above eleven inches and 3 of those 6 had snowfall above twenty inches. Also...during the last cold phase of the PDO there were 3 winters in the 1970s that had above twenty inches of snowfall.

Overall the cold phase of the PDO during the 60's and 70's produced anomalously higher snowfall amounts. Since we are currently seeing negative PDO values and we seemed to have entered another longterm cold phase of the PDO I thought this was very valuable information. Meaning that the PDO carries a big stick around here.

Tennessee snowfall since 1960

PDO index since 1960 with long range forecast

NAO index since 1960 with long range forecast

Despite popular beliefs that ENSO status and the NAO/AO idex are the major drivers behind our snowfall...I think this data would argue that the PDO is one of the most important indice's to be reckoned with here.

[GaWx]

Good research. I can tell you put in a lot of work.

I'd be extremely careful with considering the difference between PDO regime, which is to what you're referring, and DJF PDO for a particular winter, which can be drastically different. Examples: 1976-7 was a positive DJF PDO. Also, there are different tables with different ways to calculate the PDO. One table I frequent has 1962-3 and 1963-4 DJF's as +PDO's within a -PDO regime whereas another has them both as -PDO DJF's. Also, both tables have 1976-7, 1977-8, and 1995-6 as +PDO DJF's. These comprise 3 of the 7 20"+ winters since 1960-1.

Regarding temp.'s down here in GA based on my past research, there's no question in my mind that a +PDO DJF within a -PDO regime has been colder on average than a -PDO DJF within a -PDO regime. However, a -PDO regime does seem to be colder overall than a +PDO regime overall. What would give us the best shot at a very cold winter in 2012-3, which would be within the current -PDO regime, would be a weak El Nino with a DJF having a +PDO, -NAO, and -AO based on rather extensive research I've done and posted at this BB.

[Tennwxspot]

Good research. I can tell you put in a lot of work.

Thanks