Reno, Zone 7a...
With lots of smoke from that state to the left of us.
The smoke shouldn’t be a factor; it’s all about the heat.
Has this happened before? If so, you may need to adjust your growing ‘window’ for tomatoes so they’re not coming into maturity when they’ll likely to hit a heat wave.
I have a friend in AZ who calls me in FEBRUARY every year to tell me he’s eating fresh tomatoes; maybe planting later or earlier would help?
Is it just your San Mars that are going you a problem?