You Can Too
The water potential of the air is proportional to the Kelvin temperature of times the natural logarithm of the relative humidity. You don’t need to do any arithmetic, I've plotted some lines of constant water potential in the attached charts. The important point to note is that water potential is almost independent of temperature, over the range for which our trees are growing.
Our perceptions that higher temperature means more transpiration stress comes from the fact that on any given day, the relative humidity goes down as the air heats up. I've also plotted the temperature and relative humidity that were recorded every 5 minutes for a period of 7 days, starting with the day I repotted. Notice how this ‘cloud’ reflects the daily trend we all know so well of humidity going down as the air heats up and goes back up when the atmosphere cools down again at night (on any given day, transpiration stress is greatest in the afternoon).
Generally, the warmer it is the faster plants grow, up to a point. For temperate species, growth stops when the temperature climbs above 90F to 100F because metabolic activity is consuming all the food produced by photosynthesis and then some (i.e., there is nothing left over to make more tree). More importantly, however, trees cannot recover from repotting unless the roots can grow, which means they must be at a temperature below about 90F.
I am confident that this can be done in drier climes than Anacortes, however, it is difficult for me to anticipate times when the relative humidity drops below 50%. I do not have a controlled humidity facility to explore where this limitation might be. In other words, I am (or we are) dependent upon someone living in a drier climate (e.g., in CO, WY, MT, ALB) informing me (or us) about their results with repotting after the summer solstice.
Regardless, repotting pseudotsuga menziesii var. glauca is possible at times other than 'as buds swell'.
