Western Washington is experiencing an extreme (for us) heat event, in what is normally a mild marine climate. Mid Sunday morning it seemed my end fed wire antenna was being detuned by the heat. The SWR would jump way high, I would rematch with my autotuner, then once I began a CW call of CQ FD the SWR would spike again. Lowered power to 50 watts, same thing again. Finally went QRT.  73, Tad