Weather, climate, and the determination of climate normals
(Note: The following article in an excerpt from the K-State Research and Extension and Oklahoma State University publication What Is The Difference Between Weather and Climate?, MF3197, by Peter Tomlinson, K-State environmental quality specialist; Mary Knapp, K-State assistant state climatologist; Albert Sutherland, OSU assistant Extension specialist; and Amber Campbell, K-State adjunct assistant professor and project manager. The full publication is available online at: http://www.bookstore.ksre.ksu.edu/pubs/MF3197.pdf
-- Steve Watson, Agronomy eUpdate Editor)
Weather and climate are not independent. The confusion comes from weather and climate being intimately connected to each other, and this confusion is often highlighted in discussions about our changing climate. The averages of daily weather are used to monitor climate. Changes in climate lead to changes in weather patterns including extremes. An easy way to remember the difference is that climate is what you expect, like a hot summer, and weather is what you get, like a cool day in August.
Our communities and farms are affected by short-term weather events. Their long-term sustainability is affected by climate and climate variability attributed to natural processes and human activities. Figure 1 depicts how weather and climate are intertwined. Over time, the weather forms the climate and influences the environment (soil, hydrology, plants, and animals), and economic viability of our human systems.
Figure 1. Communities and farms are affected by short-term weather events. Their long-term sustainability is affected by climate (long-term weather variation or expected weather) and climate variability driven by natural and human processes.
Weather is the behavior of atmosphere at any given moment. It is what we observe on a daily or weekly basis and includes, but is not limited to, sunshine, rain, cloud cover, wind, hail, snow, sleet, freezing rain, blizzards, ice storms, and thunderstorms. We generally think about weather and how it affects our lives and activities. Weather can change from minute-to-minute, hour-to-hour, day-to-day, and season-to-season.
Climate is the long-term aggregation of weather that occurs in an area and the extent to which those conditions vary over long time intervals. When scientists talk about climate, they are looking at patterns of precipitation, temperature, humidity, sunshine, wind speed, fog, frost, and other variables, such as soil temperature and moisture, that occur over a long period in a particular place. The concept of climate has broadened and evolved in recent decades in response to the increased understanding of the underlying processes that determine climate and its variability. Earth’s climate starts with the sun, the sole energy source for our planet. Climate is influenced by interactions involving the sun, ocean, atmosphere, clouds, ice, land, and living organisms (Figure 1).
Often, this is thought of as the “climate system.” Climate varies by region as a result of local differences in these interactions. The Great Plains has a continental climate. This features wide variability from season to season and year to year, with little moderating effect from large water bodies.
Meteorologists and climatologists regularly use “normal” for placing recent climate conditions into a historical context. Climate “normals” are three-decade averages of climatological variables, including temperature (Figure 2) and precipitation. A “normal” of a particular variable (e.g., temperature) is defined as the 30-year average. The current normal period in the United States is based on 1981 through 2010 data.
Figure 2. Ottawa, Kansas daily temperature normals for the 1981-2010 period.
For example, the January minimum temperature normal for Ottawa, Kansas (19.3 degrees Fahrenheit) is computed by calculating the average minimum daily temperature in January for each year from 1981 to 2010 and then averaging those values. NOAA’s National Climatic Data Center (NCDC) released the 1981 through 2010 Normals on July 1, 2011.
Because climate normals provide a historical perspective and help us understand the unusualness of current weather, they are commonly seen on local weather news segments for comparisons with the day’s weather conditions. Graphing the high, low, and mean temperature for a single year over the normal for that location can help you visualize how well conditions fit into the typical pattern (Figure 3).
Figure 3. Ottawa, Kansas daily temperatures for 2013 compared to 1981-2010 normals.
Source: What Is The Difference Between Weather and Climate? MF3197: http://www.bookstore.ksre.ksu.edu/pubs/MF3197.pdf