Retrieving date ranges with the r platform
If louisville_weather$DATE is formatted as POSIXct, the month can be extracted, thanks @RockScience, with

lvmonth &lt;- format(louisville_weather$DATE, "%m")


It's a character variable.  So, filtering

louisville_weather &lt;- louisville_weather[lvmonth == "01", ]


should extract your weather for January.

Hope you'll find it cold enough to balance the warmth of datascience.SX !