Up until December, all 11 winter months (December-February) since January 2011 had average temperatures that were warmer in Harpswell than Portland (on average by about 1 degree). In December, Harpswell was 1.5 degrees cooler than Portland - a very big change from previous winter months. Not sure why that would be, especially since water temperatures are warmer than normal this winter. Perhaps it is just a random weather feature. So far, January has been warmer in Harpswell than Portland, so perhaps December was just another example of the randomness weather.
All 12 summer months (June-August) had cooler average temperatures in Harpswell than Portland. Spring temperatures in Harpswell and Portland are about the same; fall temps also tend to be warmer in Harpswell, like winter. The blue dots on the graph show the selected differential that I used in 2014 to determine normal temperatures in Harpswell. Clearly 4 years is not enough time to determine the long term average differential; it's a work in progress.