How hot is jet exaust from 40 ft.?

i was training at 29 palms ca. as a scout in the army infantry. me and one other guy had gone up antenna hill and had called for fire for about three days before the marines figured us out and sent a sea stallion full of force recon, i guess, to push us off. we were making our way down the ridge line when my buddy said, "look!". i turned just in time to see an f-4 phantom not more than, i think, 40 ft. away. it all happened so fast that it was like my eyes just took a snapshot. i could see the pilot looking right at us...it was that close. there was a blast and i remember the sensation of heat. by the time i turned to follow the jets path he was already disappearing down the valley, just a dot. i guess he was doing somewhere around 600 mph. what i never could understand though, was we we weren't flash fried on the spot.