Is Late August/Early September Heat More Frequent Nowadays?

Today the temperatures reached the lower and mid 90s across not only Ohio but much of the lower Great Lakes and Ohio Valley. The question of whether or not late season heat is becoming more frequent in northern Ohio always surfaces during heat like this.  

High temperatures August 27th:

Heat Index reading on August 27th:

So how do we answer this question?  First what time period are we looking at when we say "late August/early September"?  I like to use the last week of August and first week of September. A fourteen day period that is a decent duration sample size.

August 25 to September 7

What about temperature?  First, let's take look how many instances each year the high temperatures reach 90 degrees or higher during this 14 day period? (Given the forecast we could conceivable hit 90° four times by the end of the week).

Contrary to some of our recollections, its been 6 years since we had a late August stretch of 90+ similar to this year.  This actually occurred the most frequently in the 1950s. The early 2000s are a close second with high occurrences in 2010, 2012, 2016 and 2018.  With the exception of a few years like 1973, 1983, 1991 and 1993 it rarely happened in the 1960s, 70s, 80s and 1990s.  

What was interesting about the late August/early September of 1953 period was that we were above 90 degrees eleven of the fourteen days. 

The top number is the high temperature. The bottom number is the highest heat index that day.  Notice the extreme humidity didn't accompany the heat initially. In fact, dew points were very dry the first 6 days of that stretch from August 25 through the 30th. It wasn't until later in the period -- day 7 of the 11 day stretch -- that the heat index rose above 100° for 4 straight days.

Now compare 1953 and its 10 days above 90° to the 7 day stretch in 2018.

What about the overall average high temperatures during this 14 day period.  Are there any changes locally?  Here is a look each year since 1980. 2016 and 2018 were well above normal in high temperatures as was 2010 and 2012.  

Were these warm, late season stretches just relegated to northern Ohio?

Notice that most of these late season hot periods were centered over the Great Lakes, Ohio Valley and portions of New England and eastern Canada while the western US experiences well below normal temperatures.  Below are the temperatures above normal (warm colors) and below normal (cool colors) across the US and Canada.

The bottom line is that long hot stretches don't happen every year in late August/early September like many remember.