聳物: sobikimono (an archaic renku word for "rising things"). This category is the complementary opposite of "precipitation." Whereas the latter involves falling forms of water (rain, snow, sleet...), this category includes rising phenomena such as mist and smoke.
A warning about mist: it can be associated with two different seasons in Japanese tradition. As 霞 kasumi it can refer to "spring mist"; as 霧 kiri it can refer to "autumn mist." In my own translations of Issa, I use the word "mist" to denote the spring thing and "fog" to denote the autumn one. Smoke is a safely seasonless riser.