Like here in America, snow during the summer in Israel is just not a reality – it wouldn’t even rain there during that time. But even if it did snow at that time of the year, it wouldn’t do crops much good.
Yet, while rain might happen during their harvest time (March and April), it wouldn’t do much to help those crops being harvested, either. So both the snow and rain mentioned here would hardly ever happen; but, even if they did, they wouldn’t really do any good.
This verse compares honoring a fool to this snow or rain. Honor is just not appropriate for a fool. If it is given, the fool won’t handle it well; it won’t do him or anyone else any real good.
In reality, even if it sounds like there might be some value here, everything mentioned in this verse just turns out to be a colossal waste of time and resources! So don’t wait for snow in summer or rain in harvest, and certainly don’t waste any honor on a fool.