It actually make sense to me for JFK to be a little cooler. JFK has always radiated well at night by NYC standards, so you have some cooler lows in many setups. Then warm ups in winter are muted, often severely so, at JFK. Occasional days spiking well into the 50s or 60s will happen at Central Park but the smallest southern component to the wind will rob JFK of it and they will sit at 48 or something.