Comes from the Edinburgh slang "Stormin Norman", meaning to be on you own.
Sometimes modified to "stormer" - someone who is on his storman
Or even to be "storminated" - literally "on my own"

This is not the harshest work in the urban dictionary but if coupled with a swear word or two, someone might stab you (if you were in Glasgow).

Got the covid-19 vaccine

When you chug something and puke shortly after

To be "Stormin" on Halo Reach means to have Inclement Weather