While we're discussing UHI, can we talk about how garbage the GFS is at simulating it, especially during the day? It consistently overheats the big cities by 5-8 or even 10 degrees on warm days. Below is the 2:00 PM forecast from the 12z GFS:
GFS forecast for NYC: 92. Actual: 86
GFS forecast for BOS: 95. Actual: 84
IIRC this was an issue during the winter as well, especially during those marginal March storms, although the bias was less pronounced compared to the summer.