It was a signal that the wind had changed direction and with it came sudden, stronger gusts.

For grazier Steve Angus, whose 1500-acre cattle farm sits in a valley below the mountain, it was a sure sign on his fire situation was about to get quite tense.

"We've been here before," the former Tharwa brigade captain and member of the ACT Bushfire Council said.

Photos taken from the front yard of his house during the 2003 fires provide the proof.

He's standing there in his protective fire gear, his house silhouetted behind him, with the entire ridge over his shoulder a hell's nest of flame and ember.

"I suspect the same thing will happen this year," he said laconically.

"We're pretty much at ground zero here. The north-westerly wind will pick up and drag the fire across this ridge right behind us sometime in in the next 36 hours.

"And it will keep going west and south."

Farmers south of Tharwa know what's coming and are prepared and calm.

ACT RFS liaison officer Chris Condon says that in the past 24 hours he has visited all 12 of the large landholders most exposed to steady march of the Orroral Valley fire.

All but one, an older woman who was on her farm alone, intend to stay and fight it.