The National Weather Service issues a litany of notices before and during inclement weather events. They can be important signals on how to respond.

Significant winter weather for a watch means 5 or more inches of snow and/or sleet within 12 hours, or 7 inches of snow/sleet within 24 hours, or ice accumulation that could cause damage to trees and powerlines, or life-threatening combinations of snow and/or ice with wind.

The National Weather Service released a winter weather advisory at 10:38 a.m. on Friday valid from Saturday midnight until Sunday 6 p.m. for Lawrence, Limestone, Madison, Morgan, Marshall, Jackson, DeKalb and Cullman counties.

Follow live updates as a winter storm is expected to bring heavy snowfall, icy roads and cold temperatures from the southern states to the Northeast.

This index, from NOAA's National Weather Service, attempts to scale the impacts from winter weather, taking into account factors such as snowfall, accumulated snow on rooftops, ice accumulation, the potential for a flash freeze, and blowing snow. Not all factors are in play in a given winter storm.

ERCOT, which operates the Texas power grid, has issued an advisory for "extreme cold weather" in Texas. TEXAS, USA — The Electric Reliability Council of Texas (ERCOT) has issued an advisory for "extreme cold weather" ahead of the expected winter storm in Texas this weekend.

Wednesday morning's snow on top of existing road conditions has resulted in some school closings in southeast Michigan.

The National Weather Service issued a winter weather watch, storm warning or advisory for 30 states on Thursday, Jan. 22 morning ahead of a massive winter storm slated to bring nearly three feet of snow,