**This week Bob Henson and I introduced the world to the concept of an index which has the potential to rank and statistically compare surface temperature records.**

**For a detailed explanation see:**

**So for this post let’s do some calculations using the ETI for some very recently set records. These come from March 21st, 2017 and are listed here: https://www.ncdc.noaa.gov/cdo-web/datatools/records**

**First, the current algorithm and formula for the Extreme Temperature Index are presented here:**

**Let’s start with one of the hotter records that was set that day: Big Spring, TX, which got up to 94 F and broke their record by 2F (I took the averages or norms for the min and max from Midland, TX, which is close to Big Spring):**

**Now let’s take another site which also broke its record by 2 degrees on the same day, Marshfield, MO, which is near Springfield (from where I took the average max/min):**

**Despite the fact that Big Spring had the hotter record, using the ETI method, Marshfield set a statistically more significant one due to the fact that its period of record, or n, was longer and the difference between the average max and min was less.**

**Let’s take a look at a couple more. Nashville, AR established a new record of 87 also in 3/21/17. Since this station is near Texarkana, AR I am taking the average max/mins from that station:**

**The next is from Sheridan, AR, which also set a new record of 87 but is a relatively new station. Sheridan is near Little Rock, so I plugged in LIT’s average max/mins:**

**The ETI for Sheridan is higher since the difference between the old record and new is weighted higher in the algorithm than other factors such as period of record.**

**Another method for looking at the viability of an algorithm is to hold all the variables constant while changing one. The ETI has three variables. Using some simple math I have made three tables that show the ETI number changing while one variable increases.**

**The first shows n, or the period of record, increasing. I choose 30 years as a starting point since that figure is the bare minimum period of record keeping for a station to be eligible in the NCEI database.**

**The second shows the difference between the average maximum and minimum changing. Why is this important? Again, T sub d is a reflection of how “continental” or how far inland a station is, and is taken into account in the ETI.**

**The third, and as you can see most weighted variable looking at how much the ETI number changes, is the difference between the old and new record.**

**With time, I will be adding more ETI calculations to this post. Drop me a note if you want me to calculate a specific ETI for a set record…. maybe one near you.😊**

**The Climate Guy**

Great write up. Thanks for your hard work.

Is it possible for you to post a tweet when you do a new article?

I tend to see it sooner via Twitter, than anywhere else.

Thanks

Rick Highsmith