Kirishima-yaku in December?

I would like to visit Kirishima-yaku national park and climb mountains in December however I am concerned that I will be disappointed given that it is Winter and snow/ice may prevent the mountains from being hiked as well as the view being blocked by overcast (cloudy) weather.

My main desire is to see Mt. Shinmoedake however I am aware that it is off-limits and I was hoping to observe the mountain from the peak of Mt. Karakunidake but I fear that cloudy weather will make this impossible and therefore I do not want to waste precious time travelling here if that is the case.

Kirishima belongs to Kirishima-Kinkowan National Park. Yakushima National Park is another one.
https://www.env.go.jp/park/common/data/29_kirishima_map_e.pdf
https://www.env.go.jp/park/common/data/30_yakushima_map_e.pdf

The 30-year statistics says December is a month of sunny days.
Kumamoto City: http://www.benricho.org/weather_ratio/43_12.html
Miyazaki City: http://www.benricho.org/weather_ratio/45_12.html
Kagoshima City: http://www.benricho.org/weather_ratio/46_12.html
Naha City: http://www.benricho.org/weather_ratio/47_1_12.html

A bit less than 30% recorded snow on the ground at Mt. Karakunidake in December. December is the fourth most popular month after May, March, and November.
https://www.yamareco.com/modules/yamainfo/ptinfo.php?ptid=98

Mt. Kaimondake is also popular in December, after May, March, and April. More than 90% recorded no snow on the ground here in December.
https://www.yamareco.com/modules/yamainfo/ptinfo.php?ptid=99

Mt. Miyanouradake on Yakushima Island is not so popular in December.
https://www.yamareco.com/modules/yamainfo/ptinfo.php?ptid=100