If you read climate summaries often, you know that most descriptions of what the climate was like in a particular month or year is put in terms of a departure from normal. But what is ‘normal’? For climatologists, ‘normal’ is a 30-year average of temperature or precipitation which is intended to describe the expected climate for the next ten years or so. The current set of normals is based on the 1981-2010 period. They are updated every ten years, so the new normal period of 1991-2020 is in the process of being computed now that 2020 is over. The numbers have to go through quality control before the statistics are done, so it takes a while for the data to be tabulated and published (that’s why they don’t update every year–too much work!). You can read more about it in Forbes.com at https://www.forbes.com/sites/marshallshepherd/2021/01/02/what-is-normal-climate-where-you-livethe-answer-changes-in-2021/?sh=6cea696811b9 as described by Dr. Marshall Shepherd of the UGA Atmospheric Sciences program.
If you are interested in getting a look at how the normals for your area are likely to change, you can use the Iowa Environmental Mesonet site to show how the 1981-2010 period compares to the 1991-2020 period for stations across the US as well as climate divisions. For the Atlanta GA long-term record for minimum temperatures, the frequency distribution is shown below. As you can see, the highest minimum temperatures are increasing and the lowest minimum temperatures are decreasing (you can break it down by season or month at the web site as well as pick different stations). Give it a try and see how removing the 1980s and replacing them with the 2010s affect the 30-year averages.
