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On Friday, January 6, 2017, much of Central Alabama received a mixed bag of wintry weather. This weather ranged from freezing rain to sleet to snow. The heaviest accumulations of sleet and snow occurred mainly near and south the Interstate 20 corridor. The highest amounts were observed in Tuscaloosa and Jefferson Counties, where up to 1.5 inches of sleet and snow fell.
An Arctic airmass began invading the region 12 to 24 hours prior to the onset of the precipitation which arrived by late morning. Cold air advection continued during the morning and into the afternoon and evening as the freezing line moved southward through the precipitation shield. Wet bulbing also aided in the cooling process as drier Arctic air was fed in from the north.
An upper level shortwave trough over the Plains combined with an abundance of moisture lurking near the Gulf Coast to result in precipitation generated by isentropic lift, or warm air advection, focused near the 750 mb level. The associated warm nose at that level caused most of the wintry precipitation to fall as sleet and freezing rain instead of snow. Precipitation rates became heavier during the late afternoon and evening which resulted in strong enough diabatic cooling, or cooling aided by the melting process, for sleet to change to snow mainly along and just north of Interstate 20. Temperatures by this point were well below freezing, and impacts became more significant. After the precipitation ended, impacts continued to increase as temperatures plunged into the teens and 20s. This caused many roads to become dangerous and impassible overnight Friday night into Saturday morning.
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