From Meteorologist Eric Gardner:

Some Snow, Not as Cold:

Morning fog and freezing drizzle should push off to the east early today, but it will remain mostly cloudy as high and mid level clouds stream in from the west. Highs will generally be in the 20s and 30s today, with light winds.

Extended forecast:

We are tracking a low pressure system that brings in cold air and some moisture for the end of the week. Light snow showers are in the forecast tonight through early Friday afternoon with this system. Though accumulations aren't significant, this will still be a concern as roadways will be slippery for Friday primarily in the morning hours. For areas in northeast Wyoming and Montana, total snow accumulations look to be one inch or less for the most part. The Black Hills will generally see 0-2" with higher amounts on the eastern side of the hills. Rapid City looks to see 1-3" of snow by Friday afternoon. The South Dakota plains could expect to see 2-4" of snow accumulations with higher amounts concentrated in south central South Dakota outside of the viewing area.

We also see temperatures fall Friday night into Saturday as lows range from the teens west to single digits for folks in the plains. The good news is this now appears to be very short lived. Temperatures will rebound to more seasonable conditions as early as Saturday with temperatures rising into the upper 20s to 30s across the area with some 40s on Sunday. Another fast-moving system may trigger some light snow on Martin Luther King Day. Temperatures still holding on to be near or below average for the next 7 days in Downtown Rapid City!

Downtown Rapid City Climate Report