Are long, hot summers followed by cold, snowy winters?

Mark Baldwin of the Tennessee Emergency Management Agency (and a former WKU graduate) posed this question here and I did a little research to find the answer. I love when “people” say things like this about climate since “people” are almost always wrong when it comes to their memories about climate. See here for a classic example. Mark, here is some ammo to refute the “people” you have been talking to.

Here is how I approached this problem. Since Mark didn’t mention anything about precipitation in his query, I decided to only consider the hottest temperatures in KY history. Using Bowling Green as a representative station of the Mid-South, I then ranked the 15 hottest summers (June-August) and then looked at where the following December-March period ranked. Since there are 110 years of data available, a below normal winter is anything ranked 1-36, normal is 37-73, and above normal is any winter ranked 74-110.

Hot summer: winter ranking (coldest = 1; warmest = 110)
1936: 101
1921: 102
1952: 94
1943: 77
1919: 47
1931: 110
1932: 103
1901: 18
2007: NA
1980: 27
1930: 62
1934: 100
1942: 68
1899: 26
1900: 48

The average ranking of the winter that followed the 14 hottest summers was 70.2 (2007 was not counted). The 14 hottest summers had a 50% chance of being followed by an above average winter, a 28% chance of being followed by a normal winter, and only a 21% chance of being followed by a below normal winter. None of the 14 hottest summers was followed by one of the 14 coldest winters. So much for that theory.

Since Mark specified “long, hot summer” I also looked at the years with the hottest “Indian summer”, which means I ranked the 15 hottest August – October periods and performed the same analysis. As would be expected, many of the years with the hottest June -August periods were also years with the hottest August – October periods so the results were no different, with the 15 hottest August – October periods 40% likely to be followed by an above average winter, 33% likely to be followed by a normal winter, and 27% likely to be followed by a below average winter.

Since Mark also said that “people” say that cold, snow winters are preceded by hot summers, I did the same analysis in the opposite direction. In other words, I ranked the 15 coldest and 15 snowiest winters (December – March) and looked at the previous summer.

Coldest winter: previous summer rank (1 = hottest, 111 = coldest)
1978: 28
1970: 57
1899: 27
1977: 106
1984: 50
1960: 69
1963: 77
1912: 51
2001: 79
1958: 84
1979: 36
1964: 95
1915: 16
1968: 111

Again, the theory proves wrong. The average ranking for the summer that precedes the 15 coldest winters is 63.3, and summers that precede these 15 coldest winters are 43% likely to be below normal, 29% to be normal, and 28% to be above normal. The argument gets even worse when the summers preceding the 15 snowiest winters are considered.

Snowiest winters: previous summer rank (1 = hottest, 111 = coldest)
1960: 69
1978: 28
1968: 111
1936: 62
1979: 36
1948: 93
1964: 95
1977: 106
1985: 105
1942: 21
1970: 57
1951: 109
1947: 99
1965: 55
1963: 77

Note that most of our snowiest winters were also our coldest winters. In this case, the summers that preceded the 15 snowiest winters had an average ranking of 75.1!! and there was a 53% chance that the summer preceding one of the 15 snowiest winters was below normal, 33% chance it was normal, and only a 20% chance it was above normal.

Bottom Line:
The hottest summers in Mid-South history mostly occurred from 1930-1955 while the coldest and snowiest winters mostly occurred from 1960-80. Those periods do not overlap. My guess is that this “idea” originated in 1978 and 1979, both of which were cold and snowy and had previous summers that were slightly above normal (nothing as hot as 2007). What “they” conveniently forgot is that 1977, which was also a cold and snow winter, was preceded by one of the coldest summers in Bowling Green history.

In general, sea surface temperatures (SSTs) drive seasonal climate and SSTS were warm from 1930-1955 and cold from 1960-1980 and have warmed since 1980 (hence our warming trend since that time). The CPC forecast of above normal temperatures and above average precipitation is mainly due to the La Nina developing in the Pacific. I think this will be a mild and wet winter.

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