There’s a ‘new normal’ when it comes to Rochester weather

Weather Blog
Courtesy of the National Weather Service, Buffalo, NY

We’ve all heard it before during this pandemic. We have to adjust to “a new normal”. But did you ever stop and think that the term “new normal” heard so often over the last year may also be applicable to our weather?

The temperature portion of the graph above shows normal temperature ranges and averages over the course of a year in Rochester (precipitation is in the bottom portion). You’ve probably heard on many occasions a meteorologist talk about today’s high temperature in Rochester and how above or below normal it was. But did you ever wonder how that’s calculated and what exactly IS normal?

According to NOAA, the National Weather Service, and their glossary, the term normal is defined as the ” long-term average value of a meteorological parameter (i.e., temperature, humidity, etc.) for a certain area.

Every 30 years, climatologists from NOAA (National Oceanic and Atmospheric Administration) compile and review thirty years of weather and climate data from sites across the United States. That data include temperature, precipitation, and a variety of other parameters. Calculations are made to fill in missing data and corrections need to be made for discrepancies that might arise when a weather station changes locations. Bottom line: it’s not just a simple average.

So why is 30 years the standard? In 1935, the International Meteorological Organization—now known as the World Meteorological Organization—instructed member nations to calculate “climate normals” using a 30-year period, beginning with 1901–1930. The premise originates from a general rule in statistics that says at least 30 values (numbers) are needed to get a reliable estimate of a mean or average. That is why NOAA scientists have traditionally defined those normals as averages over 30 years simply because of the accepted convention—not because it’s the only logical or perfect way to define a climate normal. NOAA also provides other reference time periods as needed for climate change studies (say 1901-2010). Data for Rochester as measured at the Airport, goes back to the early 1930s, but some records date as far back as the 1830s!

Typical automated weather station (ASOS) used in climate monitoring. Courtesy of NOAA

Fast forward to today! Climatologists from NOAA are currently compiling and reviewing the last 30 years of weather and climate data from across the U.S. to serve as the nation’s updated climate “normals” for the next 10 years. What’s normal NOW is based on data from 1981 to 2010. This new 30-year dataset will span from 1991 to 2020 and is scheduled for release and use in May 2021.


It will look MUCH different for some, as the 1980s are dropped and the record setting warmth of the 2010s are factored into the data. The fastest warming places will see a significant bump up in the averages, while others, like the Northern Plains, actually may COOL a bit! According to Mike Palecki, project manager for NOAA’s 1991 to 2020 Climate Normals, “The new Normals are a better baseline for today’s climate, helping inform activities in many economic sectors,” Palecki added, “This shift will result in there being fewer ‘above normal’ temperature days in most of the U.S. at the start of this decade compared to recent years that used the previous Normals cycle.


All of this is important to many different sectors of society, such as business, as more recent data helps them better assess the risks that they face now. The construction industry, for example, may want to know the average number of days in which there is precipitation at any given locale. That number can be incorporated into their business model to help make plans.

Climate will continue to change in the U.S. during this decade, so we will need to go through this process all over again in 2031! In the meantime, get ready for the “new normal” when it comes to perspective to your weather forecast!

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