I think monitoring first responder channels is the way to go for the earliest warnings in your local area.

Most other stuff comes thru channels that have to be "activated" by the PIO machines of agencies.


When the big floods hit Colorado 2 years ago I heard, in real time during my early morning commute, the fireman who'd gone up a canyon to check on something as he was reporting his situation from up a tree using a handheld radio. Flood waters had come down and started washing his truck away so he climbed a tree.
He carefully gave dispatch his name, agency and home phone number in case he drowned. (!)

From that I had a pretty good idea that there was badness going on in the canyons.

News stations started doing gee-whiz coverage a few hours later.

When it was time to bail out of work and go home, I tried to use the scanner to figure out what routes were open. That idea failed. Every channel was utterly clogged with continuous traffic since the flooding was so widespread across the area I needed to transit to get home.

Only my personal knowledge of multiple back road routes home got me there before some of the bridges washed away.