Number of Days with Temperatures Above 32F at Milwaukee- any Trend?

We took a look at the long-term temperatures observed for Milwaukee, and calculated the number consecutive days with temperatures above 32F - that is, the minimum temperature for any calendar day had to be above the freezing mark of 32F.  In a rough sense, we were looking for the number of consecutive days each year that plants had a chance to grow or survive.  We found some interesting trends, but in general, there has been a lengthening of the growing season since the 1960s, but we haven't exceeded what was observed in some of the years during the perod of 1900 to 1934 (click on the image for a larger version). 

Below is a graph of the annual average temperaure for Milwaukee - it also shows an upward trend in recent years.  However, keep in mind that the location of the observations moved from the downtown area to Mitchell Field (click on the image for a larger version).

Some climate researchers have noted that a good portion of the increase in temperatures in the past couple decades was due to warmer overnight minimum temperatures - in other words night-time temperatures increased more than the daytime temperaures.  So, we went back into the record books to count the number of days each year with minimum temperatures at or above 70 F.  The hot summer of 1995 really stands out, as well as some of those hot years in the early 1930s.  The year of 1921 stands out as well with 34 days with minimum temperatures at or above 70F.  The graph below shows the results (click on the image for a larger version).

Spreadsheet data for graphs used in this story were originally compiled by Andy Corrao, a severe weather spotter, and later updated by Courtney Obergfell, a Student Employee (SCEP).

...Rusty Kapela, WCM

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