SEA going from 100 to 103 was partly due to 100 being low hanging fruit for them and partly due to the enhanced UHI/land use changes seen at that location.
The Portland area has topped 102 in June or very early July as far back as the early 1940s, so I'd say that's more due to fall.
Sand Point actually hit 105 that day. Suburban Monroe hit 102. Paine Field hit 100. That airmass was just legit.