about 9 P.M. Eastern Standard Time
A giant high pressure system with its center in northern Oklahoma promised warm fair weather across America . Another , centered east of the Ural Mountains , forecast clear weather for most of Europe and northern Asia . A low pressure trough between was dropping light warm rain on the green fields of England , but from Seattle to Washington , D. C , from Stettin to Vladivostock the sun was rising or setting in clear skies . Then about 9 P.M. Eastern Standard Time , a thickening mist descended over warm and drowsy southwest South Carolina . It was a fog that was not a fog , observers said afterwards , because there was no damp , no coldness -- just a steady loss of visibility until a man could n't see his hand held up in front of his face , even though a bright moon was shining . Most of the reporting night shift at the Aiken hydrogen bomb plant never reached the tightly-guarded gates . Those who did were not allowed in .