I'm by no means a Lojban expert, but some fiddling with http://jbovlaste.lojban.org http://jbovlaste.lojban.org leads me to "vilti'a" for "storm", a combination

I'm by no means a Lojban expert, but some fiddling with http://jbovlaste.lojban.org http://jbovlaste.lojban.org leads me to "vilti'a" for "storm", a combination of "tcima" (x1 is weather/a meteorological phenomenon [at place x2]) and "vlile" (x1 is violent/in a state of violence). You can then further refine this, e.g. by adding "lindi" (x1 is a lightning/electical arc) to get "lidvilti'a" for a thunderstorm [at place x2].