When salt works, doesn't in cold weather
One of the things about this cold snap that hasn't been talked about much is the fact that salt doesn't work very well in these bitterly cold temperatures.
Take a look at the chart, you can see that at a temperature of 30 degrees, one pound of salt will melt 46 pounds of ice.
As the temperature drops, the salt's effectiveness slows to the point that when you get down near 10 degrees and below, salt hardly works at all.
Keep in mind that this is for nighttime temperatures; salt is effective at these very cold temperatures in sunshine.
However, this can be dangerous in a situation where salt is applied to some snow the previous day and melts that snow.
Then, if the overnight temperature drops, that snow melt (which essentially becomes a saltwater solution) can refreeze into a layer of ice.
So, remember this whenever temperatures drop this low.
What can you do if salt isn't going to work?
Use other ice melting products such as magnesium chloride (that's what I use at home).
Not only does magnesium chloride work down to temperatures of -20 to -25 degrees, but it's also much more environmentally friendly: salt is very caustic to your lawn, pets, and plants, whereas magnesium chloride is almost like fertilizer.
The only drawback is that magnesium chloride costs about three times as much as salt...but I consider it a very wise investment.