here's the common excuse for why "contrails" form:
Jets frequently make "clouds." If the air is close to 100% humidity, the added vapor from the engine's exhaust can give it just the push to make clouds of ice crystals.The shorter the contrail, the drier the air.
IF SO, THEN PLEASE EXPLAIN THIS:
there were ZERO "contrails" between 6 and 9 this morning, and after 9, the sky became full of them, when the relative humidity began at 52% at 6 and then DROPPED to 44 by 9?
by 10, when the overcast had developed, the humidty was in the 30's... it's now in the 20's..
the NWS reported clear skies (a increasingly RARE report) at 7 and 8, but only partly sunny by 9 and 10..