If you wait until after the precipitation, it will melt and spread out into a puddle on your sidewalk and ice will form again, leaving you with a slippery mess.

You’ll also want to keep in mind that once snow starts falling and temperatures drop below 32 degrees Fahrenheit, rock salt becomes ineffective because its ability to melt ice is compromised by the low temperature. And if you’re dealing with temperatures above 50 degrees Fahrenheit, your application of rock salt may be too late—it won’t work as a deicer for very long under those conditions anyway!