Few years back, before I had my IR (ironically I had flown to Hawthorne KHHR airport to attend the ground school for the IR rating), I got a good scare. Classes ended around 9pm and it was dark by then. Tower had gone home, so field was uncontrolled. Fired up, listened to automated weather and taxied out. Clear and a mile, according to the AWOS. Could see all the lights on the runway and also all the city lights beyond the runway and didn’t think more of that. Took off, but almost immediately I could see the lights around me dim and then go out and was now in the soup. It came on really quick, maybe at 150ft. The marine layer from the sea had rolled in (like it often does there), but it wasn’t visible from the ground. I’d had a bit of instrument training by then, so after initial confusion I went to instruments and then popped out at around 500ft, no problem. But got my attention.