Baby it's cold outside! Yes the holidays are back and cold weather gripping much of the U.S. is causing shorts to cover positions in natural gas. The rise in natural gas prices may even start to make coal-fired plants more economical. That view could go mainstream if the EPA decides to officially give states some flexibility in meeting new standards for coal fired plants. This has me thinking the recent rally in coal stocks such as Walter Energy (WLTGQ), Peabody Coal (BTU) and Alpha Natural Resources (NYSE: ANR) may see continued upside. That could also mean that investors should look at putting some coal in their Christmas stockings this year, even shares of out-of-favor Arch Coal (NYSE: ACI).