The fog wasn’t announced, that is true. I have the HAL messaging system on my phone, and the first mention of a fog warning from the Met came at 04:04 AM this morning. The first message sent by HAL APOC at 03:59 mentioned just sunny and settled weather.
The first message from the Met mentioned fog from 04:00 to 08:00, then subsequently extended until 11:00. As a result, flow rates restrictions were instituted until 3PM.