EXPLAINER: Normal high and low temperature changes

RICHMOND, VA (WWBT) - You may have missed it but there's been a change in our First Warning Weather forecast. What is considered our normal daily high and low temperatures have changed.

We talk about our normal high and low temperature all the time during our weathercasts.  It's a good way to describe the weather of the day.  And it almost never happens that our actual high and low temperature is average, but it happened yesterday.

When we tell you the average for a certain day, we are using what's called the "30 year climate normal" it's produced by the national climatic data center and it's an average taken over 30 years, and it's updated every 10 years.

And our 10-year update just happened.

Until recently, we were using the 1971-2000 data, but now our averages are based on 1981-2010.  And that's produced a noticeable jump up in our average high and low temperatures.

For example, our average high temperature for August used to be 85.7 degrees.  But the new data shows it to be 87.6 degrees.

Some adjustments contributed the almost 2 degree jump. The NCDC tweaks airport data to try to make the temperatures more accurate.

Add that to the fact that the very warm 2000s are replacing the relatively cool 1970s, and you come up with a noticeable difference year-round.

So, if you notice a change on our almanac display on TV -- now you'll know why!

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