With the torrential rains that swept through parts of the Milwaukee Metro Area on July 22, 2010, we compiled graphs of the number of days 1 inch or greater of liquid precipitation fell in the Milwaukee and Madison areas. In this narrative, "high precipitation event" is defined as a day in which one inch or greater of liquid precipitation fell. There is a slight upward trend in both Madison's and Milwaukee's graph, with Milwaukee's being more noticeable in recent years.
Graph for Milwaukee
Graph for Madison
Within the graphs we see many years with numerous days of high precipitation events, but we also see plenty of years with a low number of high precipitation events. These oscillations are what make up the "normals" we can judge a certain year against. For example, if in the past two years we received 2 days and 8 days of high precipitation events respectively, the average would be about 5 days of high precipitation events per year. That same process is how the National Weather Service calculates the "normals" or "averages" for a day, month, or year. However, unlike the previous example this data is taken from the past 30 years. With a broad dataset, it can give you a good idea of what to expect climatically months in advance, but on a daily basis you are more likely to fall above or below the average for the day.
Averages do provide meteorologists, climatologists, and the general public with valuable information however. By watching the trends in which average temperatures move, climatologists can track climate change and continue research on the subject, determining its source and impacts on the environment. Also, if you were planning a trip months in advance, you may want to see the average precipitation to calculate your risk of getting rained on.
You can keep track of Milwaukee and Madison Area climates in our climate section of the webpage here.
Justin Weber, Student Volunteer