Chilly weather means frozen soil in many areas of the country. But just because the ground is solid, doesn't mean water can't seep in. It seems odd to water during the cold, blustery months, but winter plant loss of recent transplants (past year or two) is more often caused by lack of water than by freezing temperatures.
When plants go dormant, they still need moisture. The biochemical processes that make plants cold-tolerant continue producing high concentrations of dissolved sugars and amino acids in the winter. They need water to do this.