Berlin in September will be my third marathon. My first in December was 3:14 and second in March was 3:00.
For both of those marathons, the training and race occurred under ideal weather conditions in the upper 40s and lower 50s.
Now even at 4am is is 80 degrees with a 75 degree dew point and all my paces suck. For some context, in February I was doing my long runs at 7:15 pace on average for 18-22 miles at a heart rate between 150 and 155 bpm. It felt awesome. In April and May, as the weather crept into the 60s and 70s, my long run pace for an equivalent effort went to 7:30 or 7:45 pace and it did not feel so awesome generating and dissipating so much heat.
Today I was going to do a 20 mile long run at 8:00 pace, but after 10 miles I started slowing down and my heart rate was approaching 160 so I stopped because I knew I was approach 10k level effort. It was 81 degrees with a 75 degree dew point.
If I'm struggling so much in the heat even with a 2L hydration vest with electrolytes and energy gels, I don't see how I will be able to run sub 2:55 in Berlin.
Should I be doing my long runs, marathon pace work, and speed work indoors on a treadmill and keep the rest of my easy runs outside?