GRAND RAPIDS, Mich. (WOOD) — Every 30 years, the National Oceanic and Atmospheric Administration updates the climate standards that meteorologists use as a guide for “what’s normal” for each weather station.
This has been done for years, and is a standard practice by NOAA These 30-year climate normals are most used by broadcast and forecast meteorologists to give people an idea of how the weather on a given day compares to usual. It is not the same as long-term climate data, which can go back hundreds of years.
According to NOAA, “Member states of the World Meteorological Organization are required to calculate their country’s normals at 10-year intervals. The decadal update is the equivalent of the census for those who use the data. It replaces the previous set of U.S. normals, which cover all 50 states and U.S. territories such as Puerto Rico and Guam.”
WHAT DOES IT MEAN?
Basically, it means that we are no longer comparing our day-to-day highs, lows, snow and rain to weather history from 1981 to 2010. As of Tuesday, we are comparing it to weather history for our area from 1991 to 2020.
When a summer is classified in a forecast as being “wetter than usual,” it means it is wetter than the averages of the summers from 1991 to 2020, instead of the summers from 1981 to 2010.
WHY DOES IT MATTER?
Most of the time, the fact that the climate normals have been updated will not impact you very much. However, there are some interesting trends when we compare the previous three decades to our now current decades. When comparing the chunk of years between 1981 to 2010 and 1991 to 2020, there are some shifts that have occurred.
All four seasons experienced some warming, the least of which was spring when comparing the older 30-year data to the more recent data.
The newer data was also wetter than the previous 30 years for three of the four seasons. The only season that trended drier was fall.
There was also an increase in annual snowfall. When using the 1981-2010 average, Grand Rapids saw about 74.9″ of snow a year. The new data set of 1991-2020 shows an average of about 77.6″ of snow falling on average.
SOMETHING TO KEEP IN MIND
If the overall shift is warmer and wetter from the current three decades to the previous three decades, then it is important to keep in mind when comparing a daily number that it is being compared to an already slightly warmer and wetter average.
For example, if our summer this year comes in 0.4 degrees warmer than usual (usual being 1991-2020 data), it would have been 0.8 degrees warmer than average if we would have compared it to the previous “average” (1981-2010).