Historical Warm Streaks in Minnesota

Unusually warm conditions have dominated the last 18+ months in Minnesota, but how does this warm episode stack up historically?

To answer this question, we examined monthly average temperatures for the state of Minnesota going back to 1895, and compared those values to the averages from the entire 1895-2016 record. We looked at warm streaks, which are runs of consecutive months that are warmer than the long-term averages, and also warm periods, which we defined as regimes of predominantly warm conditions with no more than two consective months that were cooler than average. We note that we could have come up with countless other definitions.

For historical comparisons, we simply counted the total months involved in each streak or period, computed the average temperature departures, and also calculated the "total accumulated warmth" (TAW), which is the sum of all temperature departures through the duration of each episode.

Whichever way we look at it, the current warm episode is indeed making history. As Table 1 shows, the 18-month streak (through February 2017), is the longest on record and also has the greatest accumulated warmth, with a TAW of 99.3 F. Based on average monthly departures, the streaks from 1986 to 1987 and 1999-2000 were more intense, but those streaks were also less than half the duration of the current one. It is safe to say that Minnesota has never seen a warm streak like the one presently underway.

Table 1. Minnesota warm streaks, ranked by duration.

                       Duration  Avg. Monthly          
     Date Range        (Months)  Departure(F)   TAW (F)
-------------------------------------------------------
Sep 2015 - Feb 2017*      18        5.5         99.3
Jul 2011 - Sep 2012       15        5.3         79.4
Apr 1941 - Apr 1942       13        3.5         45.8
Jul 1998 - Jul 1999       13        3.5         45.3
Sep 2005 - Aug 2006       12        4.4         53.1
Dec 1986 - Jul 1987        8        7.1         57.0
Dec 1920 - Jul 1921        8        4.0         32.1
Sep 2004 - Apr 2005        8        3.9         31.3
Nov 1999 - May 2000        7        6.5         45.2
Sep 1994 - Mar 1995        7        3.9         27.5
Mar 1988 - Sep 1988        7        3.5         24.8
May 2007 - Nov 2007        7        2.6         18.0

*ongoing

Of the warm periods, which include gaps of one or two cool months, the most significant episode stretched from September 2004 through November 2007, when 33 of 39 months were warm and when the total accumulated warmth through those 39 months was 125.2 degrees F. The present warm episode currently ranks #2, possibly still gaining ground, depending on whether it can avoid three consecutive cool months.

Table 2. Minnesota warm periods, ranked by total accumulated warmth (TAW). 

                       Duration   Warm     Avg. Monthly          
     Date Range        (Months)  Months    Departure(F)   TAW (F)
------------------------------------------------------------------
Sep 2004 - Nov 2007       39       33          3.2        125.2
Jun 2014 - Feb 2017*      33       28          3.4        110.0 
Jan 1986 - Jan 1989       37       28          2.6         96.4
Jul 1997 - Jul 1999       23       21          4.0         91.6
Nov 1999 - Feb 2002       28       21          3.3         91.5
Jul 2011 - Feb 2013       20       19          4.4         88.8
Feb 1930 - Aug 1932       31       24          2.6         80.2
Sep 1940 - Apr 1942       20       17          2.6         51.9
Sep 1920 - Nov 1922       27       20          1.8         48.1
Jul 1989 - Aug 1991       26       17          1.7         43.4
Feb 1952 - Feb 1954       25       16          1.5         38.2
Oct 1962 - Jul 1964       22       16          1.7         36.8


*ongoing

Of the warm periods, which include gaps of one or two

 
Last modified: March 17, 2017
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