The extended forecasts are predicting low 80s as a high for next week. But, the temps have begun to rise here in So Cal. Yesterday was supposed to be mid-80s and it hit low-90s in the valley. My long run this past Saturday started at 5:15 am and the temp was already 72 F. Luckily, it did not go up that much until well after I was done.
If this trend continues, I would plan for warm temps during the race. Just in case though, I am taking mkymsehi's advice and getting some throw away clothes from the Salvation Army.