May & Summer Temperatures in Philly, Not Much There any Longer

[Rainshadow]

First off let me say, I don’t know if it really matters with the way recent summers have been going lately.  This as always is for PHL.

This is a 67 year look from 1950 (modern enso era). During that period the average May temperature has been 63.6 degrees and the average summer temperature 75.4 degrees.  We don’t need Captain Obvious to tell us both have warmed lately. 

These yearly breakdowns have no met significance, more with the sheet I was working on (and just wanted to separate from 2000 onward).

From 1950 thru 1977, there were 10 above average Mays and 6 above average summers. From 1978-99 there were 11 above average Mays & Summers and since 2000, there have been 12 above average Mays and 14 above average summers.

When I was texting Tom, the recent history (since 2000) of the five below average Mays were all followed by warmer than average summers were etched in my brain. Then again 14 of the 17 summers since 2000 have been above average, so what does it matter what May does or doesnt do?

Anyway if we look at the 64 year sample (three were tossed because those Mays were exactly average): When May was below average 18 summers were below average and 13 summers were above average.  When May was above average, 18 summers were above average and 15 summers were below average.  So if this were pre 2000, climo would say we have a 70% likelihood of a cooler summer; since 2000 we have been running the contrarian result (which again is easy because nearly every summer is warm).

The last summer the cool May worked was in 1997 and that was a developing el nino as is currently predicted.  Which brings me to the smaller sample size of Mays in which el nino got going by late summer (with previous winter either la nina or enso neutral). 

I counted 9 years, 4 with below average (1963, 1976, 1997 and 2002) Mays.  Three of them did average below average summers, but I would look at this (hopeful) sample size as being rather small.   

  

[Mitchg]

I think precipitation may be of more statistical significance, worth a look.