Jan 18, 2012 11:00 AM MST - An arctic cold front is now sweeping across southwest South Dakota...bringing a rapid drop in temperatures. The temperature at NWS Rapid City dropped 15ºF within half an hour. Winds quickly switched to the north and increased...producing wind chills down to -5ºF and colder. Below is a graph from NWS Rapid City showing the rapid temperature drop at 8:30 AM MST. Further below is a surface plot showing the location of the cold front at 10:00 AM MST. Notice the temperature difference between areas north (colder) and south (warmer) of the front. Also notice the difference in wind speed and direction. Winds behind the front are from the north and stronger. This shows the arctic air quickly pushing southward toward the Nebraska/South Dakota border.