Rain Melting Snow and Ice

The only question is how much will be on my driveway when air temperature drops below freezing tonight.  The driveway is a 1:8 slope, so I expect it to drain off.  I'll probably drop a layer of MgCl₂ if all or most of the snow and ice is gone, so any water will be prevented from freezing.  Even a small layer won't stop the Jaguars.