I'm making a Region of a planet with very high humidity, mostly covered in fog at ground level. I am open to having seasonal changes and would like there to be a few sunny days lets say 1 out of 15, that figure is completely changeable. I need the fog to be pretty thick, thick enough to use Electroperseption for sight and have hydrolysis be used for breathing and getting hydrogen to float. How would I make this work without the planet being entirely underwater? Thanks.
Should FOG1 look like Venus, it is because it will in some aspects be similar to it and because this is an image of Venus. :)
FOG1 is a predomenetly metallic (read 90%+) super-earth orbiting a long lived, dim K-Type star. Its planetary attributes are:
$$M = 7,5 Me$$ $$R = 1,3871 Re$$ $$gravity = 3,898 G (38,228 m/s^2)$$ $$Vescape = 26 km/s$$
Its average surface temperature is 320 K (47 °C), just shy of the dreaded runaway greenhouse effect. This is why it's parent star has to be so dim and small, because it will live longer and get brighter slower. Using an M-type star would be even better, but would mean that the planet is tidally locked and I wasn't sure if OP would like that. The low mass of its parent star is also the reason why FOG1 lacks an hydrogen+helium atmosphere. While it should have one due to its temperature and escape velocity making the atmospheric escape of these gases implausible, there was little of these gases around when the solar system formed and the parent star was a flare star in its youth and stripped most of the atmosphere away.
Now how do I create the fog? Firstly FOG1 is an ocean planet with less than ten percent land cover. Most of this landmass are low island continents near the equator. Surprisingly FOGG1 has significantly less water than Earth, but because its gravity is almost four times stronger its profile is flatter than Earth's. The highest mountain is only 2.5 kilometers high due to the higher stresses the rock will be under and the stronger erosion. The surface mostly consisting of water and the high temperatures will make sure that there is a lot of water in the atmosphere, because I optimized the setup to get the optimal vapor pressure out of it. This is why there will be a global cloud cover, resulting in a Venus-like appearance. The equatorial landmasses will be in a zone of maximum evaporation, creating an extremely wet version of tropical climate. Torrential rain, extremely humid air and fog whenever it isn't raining will be the result.
A bonus is that the clouds will and extremely low in FOG1 as the scale hight of its atmosphere will be only 2.35 km instead of Earths 8.5 km. Assuming that the hight of Cumulonimbus clouds can be found at scales with the scale hight, we can find these on FOG1 at min: 128m, avg: 2128m and max: 3410 m. This will give you a continuous oppressive cloud cover which could plausibly envelop all land above 100 m all the time under the right (story appropriate) circumstances.
EDIT1: One could of cause do something similar with a planet of lower mass, trading the low cloud layer for higher mountains. However, I thought that a super-earth would be more interesting to explore. Additionally, this planet might very well be superhabitable. The island continents and shallow oceans will create a lot of room for very biodiverse kelp- and land forests and the oceans might be filled with mighty sea monsters feeding of these very rich marine ecosystems. Incidentally these kelp forests could justify the electroperception you want. Your species lives a semi-aquatic lifestyle. They spend a lot of time in the water of the kelp forests where their electroperception is really useful as the environment makes vision somewhat impractical. However, they rest and live on the shoreline as the dangerous and numerous sea-borne predetors can't reach them there. Their electroperception is useless there and limited to a range if centi or decimeters, but they can rely on other senses.