Climate is defined as a compilation of daily weather and extremes of weather at a specific location. A climate normal high, low and precipitation for a given location is based on 30 years of data.

This data is used to compute what the averages are on any particular day, and that data is all about to change. 

What You Need To Know

  • The climate of a location is always changing over the course of time

  • The climate normal is based on 30 years of data at a location

  • The new climate normals were released today

The climate normal is the official terminology used by the National Weather Service (NWS). It's a massive data set of information based on the reported daily high, low, wind speed, dew point, precipitation, and more of a given location.

These numbers give us daily averages, and weather extremes like a daily or monthly record are also taken into account. 

An average high, low, wind, precipitation value, cloud cover figure and more are then computed for that day, month and year. That is then tweaked to take into account the extreme weather that occurs.

Not just numbers, though

Changes around an observation site also need to be taken into account. Has new infrastructure been installed? Has a parking site near the weather station gone from gravel to pavement? Have trees been cut or a building installed?

So many seemingly subtle changes can impact one location's weather data. Here is a great blog addressing changes at the official NWS observation site.

The weather observation station atop Mount Washington in New Hampshire. Photo: Associated Press, Robert Bukaty

For example, at another observation site the data would disappear each night for several hours. Weeks were spent going through software and equipment trying to figure out the cause of missing data.

Finally, one of the engineers went to the site one night to observe what could be going on. The cause? A truck that was being parked between the weather station and the line of site communication to the building!

Striving for consistency

So in essence we are never 'normal' when it comes to weather. We are never 'supposed to have' any particular weather.

It is an average and that number changes over the course of time, hence the need for 30 years of data.

In reality, we are either at, above, below or moving through the average weather for a particular day based on 30 years of data and changes that may have been made at that particular location.

For a more in-depth look at how NOAA (National Oceanic and Atmospheric Administration) and the NWS compute these numbers, click here.