Taanit, Chapter Three, Mishnah Two
This mishnah continues to discuss situations in which they would immediately skip to the latter stages of fasting.
If [rain] falls for crops but not for the trees, for the trees but not for crops, for both of these but not for cisterns, ditches and caves they sound a blast immediately.
Light rain is good for the crops because crops dont need the rain to penetrate deep into the land. However, it is not good for the trees. Heavy rain is good for the trees but not good for the crops. Finally, it requires very heavy rain to fill up the cisterns, ditches and caves so that people will have drinking water. According to the mishnah if it rains but there is not sufficient or appropriate rain for every one of these categories, they skip the first stage and go immediately to the stage of more serious fasting, as we described in yesterdays mishnah.