I posted this recently in another thread so I won't repeat the entire message. You can plan for some unusual things. For example, my GRE scanners, with their 20 files or programs, each have the NIFC radio system (National Interagency Fire Center) frequencies for large incidents in one bank. I have it in Bank 19 of every program so I can always punch it in without having to look up where I've put it. I have all the NIFOG, FEMA, state and local large incident frequencies in Bank 20. In my newest scanner, a 325P2, I have NIFC in System 1 and the NIFOG, Et al., in System 2. In this way I don't have to duplicate either one of them in every geographic area system in the rest of the memory. If an area has a large fire or a significant weather or geological event I have the frequencies I need with a quick punch on the keyboard. In my California files I have Bank 18 set up with all the large fire frequencies that Cal Fire uses and any of the other fire mutual aid frequencies that often get used on fires in the state's jurisdiction. My 325P2 has those in System 3.
To find these systems, go to the main database page. At the top of the map click on "Nationwide Frequencies." Then click "National Interagency Fire Center." Enter the entire list into you scanner. When that is done, click on "Federal Disaster" and "National Interoperability" and program those in. It depends on what scanner you are using as to how you arrange the banks, lists or systems. Don't combine them all into one huge master grouping. The scanner will take too long to get through them all. Don't scan them every day, it will slow up your other scanning.
To the OP, I don't know if this helps you, because I don't know what you like to listen to. I would bet that if people could not hear law enforcement in busy large cities, 80% of the people here would lose interest in scanning. Encryption may take us to that scenario. For me, a retired U.S. Forest Service employee who wore a wildland fire hat and a law enforcement hat every day, I like listening to natural resource agencies and agencies or departments that have a significant wildland fire workload. If I lived in L.A. County, which I did until I went out of state to college, I would program all the federal natural resource agencies in a separate system. This would have the Angeles, Cleveland, Los Padres and San Bernardino National Forests, the Bureau of Land Management's California Desert District, the National Park Service's Santa Monica National Recreation Area, the Bureau of Indian Affairs, the U.S. Geological Survey and the Army Corps of Engineers in one bank or system. I would throw in the CA Dept. of Fish and Wildlife and State Parks in there as well. I would put Cal Fire's San Bernardino, Monte Vista (San Diego) and Riverside units frequencies in my scanner there. Cal Fire can be very busy and I don't like to listen to them as much as I like the first bank or system. Sometimes I don't like a scanner being very busy. A lot of traffic in southern California on Cal Fire frequencies is medically related and in Riverside County Cal Fire is the county fire department by contract. A lot of times I want to hear natural resource agency radio traffic and nothing more. It was my career and it is my main interest when listening to a scanner. There aren't a lot of us. Everyone's interests are different and I don't know your preferences.
I might even set up a system or group within a system that has the VHF High commands and tacs that the L.A. County Fire Department uses on larger incidents. I don't know if they use these for wildland fires only or if they use them on other types of incidents. I think they set up portable repeaters, which have a limited receiving distance, so anything north of Sylmar would be out of range for a SF Valley or L.A. Basin resident. They wisely set up a VHF High system for large incidents, especially large wildland fires as that is what is used on wildland fires at the state and federal level all over the U.S.
The State of California and agencies in southern California, specifically L.A. County, have some mutual aid frequencies that aren't in the NIFOG. A bank or group of those might be the ticket for picking up on unusual events. Look in the database for those. The L.A. Sheriff's office has some UHF frequencies for mutual aid. Those might be worth putting in a group or bank that otherwise doesn't get a lot of traffic. I have multiple scanners in my home, and sometimes I have just the NIFC and NIFOG banks in them, just in case. I have that scanner on all the time, even at night so I'm alerted to uncommon as you said.
Keep in mind that PaulNdaOC is correct and unusual can happen at any time and the first indication of it you get is on a frequency you wouldn't expect it to be on. I've even heard the start of some big incidents on business frequencies. You can't scan everything, with a couple dozen scanners and pick up that first bit of radio traffic that leads to large consequences. They just happen. However I disagree that you can't plan for them, just scan the types of banks or groups I've explained here. On occasion you can pick up on some big things that haven't hit the media yet.
I've written a lot in a longish post, I hope something here is useful to you.
