For me it's all subjective. I don't like to have specific trigger points because if you've misjudged then it may be too late by the time your trigger is tripped. It means maintaining alertness but I'm ok with that.

I am about a days sail or motor east of the Golden Gate Bridge leading out of San Franciso Bay to the Pacific Ocean. If a huge storm / hurricane / tsunami / flood is predicted, it is not likely I can sail out of the narrow Delta waterways and up or down the California coastline far and fast enough to avoid such things. At this point in time, all I can do is batten down the hatches, put out extra mooring lines to the dock, and deploy extra bumpers.

My big decision is whether or not to bug out in my vehicle and abandon the boat to its fate. I am pondering what factors and data I need to make that decision, which is the genesis of this thread.

In a nutshell, you'd have to know the time that the "event" will arrive or at least a good approximation, compare that with the time you'll need to do whatever you want to do, when the arrival time coincides with your preparation time, do whatever you plan on doing.

In other words, if you know it will take you an hour to bug out and your best guess is that the "event" is one hour away from happening, activate your plan.

[A great example of specific criteria for a bug-out decision.]

Asking what things need to be known in every possible scenario is a huge job. [Only asking each to contribute what they know; the benefit of an online community.]

What you want to know is a full time job for many people, how can you expect to learn about fire behaviour, meteorology, fluid mechanics, engineering standards, and all of the other things that you'd need to know in order to make a decision about any given situation that might occur? It's impossible. [Yep, perfect information and being omnicient is not possible. I will take what I can get!]

I know for a fact that firefighters are taught about specific things to watch for before making their decision to bail out, I also know that they routinely ignore those things as do many professionals. They take their entire body of knowledge and then make a subjective decision on the fly all the time. Which is one reason why I got caught taking cover under a fire truck during a wildfire once. Even the folks who do this stuff for a living can't know all the things that might happen. [A given.]

Using a wild fire as an example, knowing that a fire is a particular distance away is only one piece of data, in order to make a well reasoned decision about when to evacuate you'd need to know the wind direction and speed, the terrain between you and the fire, the fuel load of the terrain, the number and type of any structures between you and the fire, the current and predicted weather conditions, the manpower available to get between you and the fire, the technical resources available and a few other things I'm probably forgetting. Wouldn't it be smarter to have a plan that says that if a wildfire gets within a given distance to you to evacuate? [That's exactly what I am suggesting.] You can overanalyze yourself to death. Literally. In the time you take trying to make the BEST response, you can die. I'd rather over-react then under-react. [Yep, and that is why pre-planning and thougt can be so helpful.]

I might be wrong but I don't think anyone posting here would be able to give anyone specific guidelines on what to do for every possible scenario. [ Just asking each to contribute what they can.] And frankly, I'd be very cautious in believing anyone who claims that they could do so. I've worked at a few emergency operations and controlled chaos is the best way to describe most of them. One need look no further then the recent Station Fire here in SoCal to see where otherwise intelligent, highly trained people made some fundamental errors in judgement about how and where to fight the fire. If the experts can get it wrong, how can a lay person expect to know all the stuff needed in all of the scenarios listed earlier? [Exactly, we all need all the help we can get. That is why I posted - to increase my awareness and knowledge.] It really is very subjective.

...have a copy of their respective city/county/state Emergency Management plans...This will give you an idea of what the county agencies will be looking at in order to make their decisions.