Roads may become impassable for most vehicles. These are the most dangerous winter storms and can be especially severe when combined with temperatures below 10 degrees. This means the expected winds will average 40 miles an hour or more for at least 1 hour or winds gusts will be greater than 58 miles an hour. Trees and power lines can be blown down. This means life threatening cold with wind chill temperatures computed to be -40 degrees or less for at least 3 hours.
Longer exposures can be fatal.
The snowfall is usually expected to begin within the next 12 hours. This is issued when the visibility will be significantly reduced, or when the roads become snow covered over a large area. Advisories, in general, are issued for weather conditions that are expected to cause significant inconveniences and may be hazardous, These situations are normally not life threatening if caution is exercised. This is issued for average wind speeds between 31 and 39 miles an hour, or for frequent wind gusts between 46 and 57 miles an hour. Lake effect snow usually occurs in narrow bands over limited areas.