I'm in Washington state, in a coastal area. Our temps are pretty mild, with only a few weeks a year where snow is realistically possible. Can dip below freezing throughout the winter but typically not sustained.
At sea level, in a rainy and wet climate. Concerns about the water table.
Many meats want high airflow and low humidity, whereas roots and vegetables want high humidity and less airflow so I wouldn't try to combine the two. Here for meat I just hang it in the barn, we hoverjust above freezing up until December after that it drops to just below. I have a cellar in this house but didn't in the last one due to a high water table, so you will probably just have to check your exact depth before water to know if you can dig down or not.
Yes the water table is high and the ground is soggy. So I'm hesitant to dig down. What did others do in the old days? Can I get root cellar conditions with something built above ground with an earth berm over it?
I have the same question, I am in a similar situation with you (Washington state) but on the hills not the coast.
I do have a couple of suggestions to start with. These are things that I have tried as I am learning about root cellaring.
1) Soil. You can check the gov site web soil survey (https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm) to see what soils you have in your yard and their properties. The site is extremely useful for many different things (fertility, ability to build etc) but in this case click on the soil and look at these properties:
Depth to water table: ...
Frequency of flooding: ...
Frequency of ponding: ...
2) Of course you also need to test yourself - dig a small hole and add some water (soil is already wet right now). If it does not drain in a reasonable amount of time (hours) you have a problem.
3) About your suggestion to build above ground - I think it would definitely work. Just be aware that soil is heavy and you need to move cubic yards, unless you already have a hill/slope in the right location and preferably with a northern aspect.
4) I read somewhere that a good use for an old fridge is as a "mini" cellar. You just dig a hole and put the fridge inside lying down with the door up. You can use a strawbale or some reflective insulation on top. I can see problems with this because there is no ventilation but maybe there are workarounds?
I also live in PNW. I have heard people say that they use an old fridge or freezer, above ground. It closes solidly, you can probably get one for free. Stays cold outside. Animals/bugs can't get to it. Like Skandi said, meat and veg might be better in different locations.