The main purpose of these discussions is see how the confidence is behaving and what synoptic features are causing the low or high confidence. FEEDBACK of any kind (good, bad, terrible) is certainly welcome and should be directed to email@example.com. *If you are reading this discussion for the first time, I recommend that you first visit the project description page*.
Seems like the low confidence is mostly due to the mishandling of the storm track by the GFS. Lately the model has been having trouble on how far east to bring the main storm track. Compared to last weekend's heat spike, where the Bermuda high nosed into the Southeast, the center of the high looks to be further to the east for next week, prompting more of a southerly to south-southeasterly flow. With water temperatures off the coast still in the 50s, it seems more prudent to go with a cooler solution, even if the storm track ends up being further west. Maybe the confidence graphics are trying to depict times where the temp could potentially pop if we get some brief clearing.
As a side note, it's very interesting that last weekend's heat spike came with relatively high confidence, with the exception of New England where the confidence graphics showed low confidence about 3 to 4 days ahead of time associated with the backdoor high.