a mist is a sink of invention & sand is a mean of place & wind is a mean of shepherd ->  a storm is a source of rain / snow  a storm is a source of rain / snow & a sb is a mean of mist ->  a thunderstorm is a source of rain / snow  a thunderstorm is a source of rain / snow & tepid rear effect closer as they try by -> cold fronts will cause rain / snow as they pass by