Autumn Warm Spells - When Summer Keeps Hangin' On
Although the general public often refers to warm spells in the fall as "Indian Summer," most occur before the first frost arrives (which, compared to the suburbs, comes weeks later to Manhattan/Central Park). This analysis goes back to 1950 and looks at warm spells that have occurred mostly in October and November (with some beginning in late September). For my purposes I focused on those that were at least four days in length.
Two-thirds of the years since 1950 have had warm spells of four or more days (including the ten of the eleven years between 2010 and 2020). Seventeen years had two or more, with 1953 experiencing four. There have been ten warm spells that lasted ten days or more, the most recent being in the autumn of 2006. The lengthiest was twenty-one days, which has occurred twice, in 1959 and 1984.
MOST ABOVE AVERAGE
There have been thirty-nine warm spells in autumn that averaged ten degrees above average or more (based on daily mean temperature). The five-day heat wave of Sept. 22-26, 1970 was the most above average, +18 degrees, with four of the five days experiencing highs in the 90s.
|LENGTHIEST AUTUMN WARM SPELLS|
|1959||Sept 21-Oct 11||21||81||65||+11|
|1984||Oct 11-31||21||70||57||+ 8|
|1973||Sept 27-Oct 15||19||74||57||+ 6|
|1995||Oct 2-14||13||76||58||+ 7|
|1986||Sept 23-Oct 4||12||79||64||+ 8|
|1994||Oct 30-Nov 9||11||69||52||+ 9|
|1970||Oct 6-15||10||74||60||+ 9|
|WARM SPELLS WITH GREATEST DEPARTURE|
|1950||Oct 29-Nov 2||5||79||58||+17|
|1971||Oct 26-Nov 3||9||72||60||+14|
Interesting study, thanks. I remember the Sept 1970 "Heat wave" well. I was still in post-college Frat Boy mode then, and my friends and I made an "emergency" trip to the Hamptons that weekend. The after-summer bonus weather was all anyone was talking about on the beach.
I'm not sure I follow the criteria for the lengthiest warm spell. The 21 days in 1959 for example. Did every day have to be above normal to constitute a warm spell? How did you determine the beginning and end dates of a warm spell?
Thanks for any clarification. I really get into this sort of arcane weather data, so I love your blog, as I have said before.
Posted by: Ken K. in NJ | 10/03/2014 at 04:59 PM
Hi Ken, the 1970 heat wave ranks #79 among my top-100 NYC weather stories. Regarding the 3-week warm spell in the fall of 1959, every day had an above average mean temp, with eleven seeing a high in the 80s and one in the 90s. Additionally, fifteen days had lows in the 60s and four in the 70s.
Posted by: Rob | 10/05/2014 at 12:16 AM