AUSTIN, Texas - Friday’s forecast high is in the mid-90s which puts it about 16° above ‘normal’. Makes sense, Austin isn’t supposed to be in the mid-90s this early in the year. But where does that ‘normal’ number come from?
Well, if you average all the historical data going back to 1897 then the average high temperature will be about 3° cooler than the ‘normal’ temperature. Why is that? Because the ‘normal’ temperature is actually calculated as a rolling average of the past 30 years.
According to Keith White, a meteorologist and climate team lead at the National Weather Service for the Austin/San Antonio office the climate program was started in the 1930s. Back then about 30 years was all they had.
"What they had, in most locations, was about 30 years of data," says White. "In fact in Austin data started in 1897 so the first set was 1901 to 1930."
So why 30 years? According to White, "the history of it is that 30 years is what they had available when the first started and they’ve just stuck with that over time."
In addition to historical posterity, there is a more scientific reason. "30 years is long enough that it gives us a good look at a long-term average," says White.
This year the shifting normal will likely include a small increase in afternoon high temperatures in the summer and a small increase in overnight low temperatures. These temperature changes won’t be significant but will serve as an indicator of the gradual but steady warming of the climate.
"In terms of temperature we do typically see those impacts of climate change," says White. "As we remove the ten years from the 80s and add the ten years from 2011 to 2020 we will see some nominal increase in temperature."
While the warming trend is expected, the trends are definitely regional. Texas will overall see a warming trend, but parts of the northern plains will see a slight decrease in 30-year normal temperature, especially in the spring months when late-season cold intrusions are becoming more intense and frequent.
But beyond the changing climate numbers, the 30-year rolling averages actually have some impact on daily life. "These data are used for planning purposes for a lot of different sectors," says White, "agriculture, electricity load planning, building heating or cooling requirements, all sectors of the economy benefit from these data sets."
The new 30-year climate data set will be released in May 2021.
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