Well i would be delighted to kick things off in this new thundery argument. Thunder, is the sound created by a lightning discharge. If thundery rain is forecast then the forecaster expects there to be convection embedded in either a frontal rain band, or an MCS. He expects some lightning, somewhere. If conditions do not seem likely to produce convection sufficient to produce lightning, then he will forecast rain, heavy or light or whatever. If a shower passes above an observer, and no lightning is seen or thunder heard, then it should be described as a shower. He can describe the rain as heavy, torrential, light, moderate, blustery, tropical etc etc but NOT Thundery, for obvious reasons.