Talking about this year.
Whenever you see a huge heat difference with LGA and NYC, it's almost certainly that NYC has an overgrown jungle. Whenever LGA is colder, it's usually wind off the water in the early season.
During mid-summer, LGA and NYC should have nearly the same high temps.
You don't look at those 2 stations for differences. EWR is on a runway and NYC is in a fake jungle.
A better comparison would be LGA and NYC. Both stations are very close to eachother and have very similar climates.
LGA and NYC are fairly similar with regard to stats.
Thru 1:51am, Newark's low was 70 degrees.
And thru 7:51am, their low was 71.
So unless they fell below 70 from 7:51am to 8:51am, they did not get below 70.
JFK, NYC and LGA all fell below 70. 67 in NYC, 68 in both LGA and JFK.