Temperatures are expected to approach record highs in Boston today, where runners are set for the 108th Boston Marathon. Highs should be in the mid-80s -- some 30 degrees warmer than the average high for April. The hottest marathon weather was a sizzling 96 in 1976. The field of 20-thousand-400 official entrants is the second largest in the event's history. The largest was in 1996 when more than 38-thousand runners marked the Marathon's 100th anniversary. This year's 26-point-two mile race is a watershed for the women, who for the first time in Boston Marathon history, will leave the Hopkinton starting line about a half-hour before the men's field and the horde of recreational runners.