National Weather Service Weather Forecast Office

Winter Weather Threat Level

Threat Level Descriptions

Extreme

Within 12 miles of a location, there is an extreme likelihood (36% or greater) of severe winter weather capable of disrupting land and/or air travel, or creating travel conditions that result in a large number of vehicle accidents on untreated roads, or resulting in postponed indoor or outdoor activities, to completely shutting down travel and commerce in the worst situations. See winter weather descriptions below.

High

Within 12 miles of a location, there is a high likelihood (26% to 35% probability) of severe winter weather capable of disrupting land and/or air travel, or creating travel conditions that result in a large number of vehicle accidents on untreated roads, or resulting in postponed indoor or outdoor activities, to completely shutting down travel and commerce in the worst situations. See winter weather descriptions below.

Moderate

Within 12 miles of a location, there is a moderate likelihood (16% to 25% probability) of severe winter weather capable of disrupting land and/or air travel, or creating travel conditions that result in a large number of vehicle accidents on untreated roads, or resulting in postponed indoor or outdoor activities, to completely shutting down travel and commerce in the worst situations. See winter weather descriptions below.

Low

Within 12 miles of a location, there is a low likelihood (6% to 15% probability) of severe winter weather capable of disrupting land and/or air travel, or creating travel conditions that result in a large number of vehicle accidents on untreated roads, or resulting in postponed indoor or outdoor activities, to completely shutting down travel and commerce in the worst situations. See winter weather descriptions below.

Within 12 miles of a location, there is a low likelihood (2% to 5% probability) of severe winter weather capable of disrupting land and/or air travel, or creating travel conditions that result in a large number of vehicle accidents on untreated roads, or resulting in postponed indoor or outdoor activities, to completely shutting down travel and commerce in the worst situations. See winter weather descriptions below.

Within 12 miles of a location, environmental conditions do not support the occurrence of severe winter weather.

Depending on the time of the day the event occurs, amount of traffic on roads, road and air temperatures, visibilities, wind conditions, and so on, each winter weather element can have a different threat or impact on society.

• Example #1: A quick snow burst of 3 to 5 inches within a 2-hour period centered in the evening rush hour on a weekday would have a greater impact than a similar situation at 2 am Saturday morning.
• Example #2: Snow accumulations of ½ inch, or a slight glazing of freezing rain on a cold, untreated road surface could create icy conditions that result in dozens of vehicles sliding off roads into the ditches. This situation may have a high impact on society depending on the time of the day.
• Example #3: Snow accumulations of 7 inches occur over a 10-12 hour period of time, primarily during the late evening and overnight hours. Snow plow crews were ready to "go to war" due to an early Winter Storm Watch and Heavy Snow Warning, resulting in well-plowed and salted roads. This situation would have minimal impact on society.

Blizzard Warning - sustained winds or frequent wind gusts equal to or greater than 35 mph, and falling or blowing snow with visibilities near 1/4 mile or less for 3 hours or more.

Ice Storm Warning - freezing rain resulting in ice accumulations equal to or greater than ¼ inch.

Heavy Snow Warning - snow accumulations of more than 6 inches in 12 hours or less, or 8 inches or more in 24 hours or less, without strong winds.

Lake-Effect Snow Warning - lake-effect snow accumulations of more than 6 inches in 12 hours or less, or 8 inches or more in 24 hours or less, without strong winds. Snow accumulations and visibilities will vary greatly over short distances and gusty winds can accompany the snow showers. Lake-effect events are more likely to happen over counties near Lake Michigan.

Winter Storm Warning - combination of heavy snow, strong winds (sustained winds or frequent wind gusts of 20 mph or more), with or without freezing rain or sleet.

Sleet Storm Warning - sleet accumulations of 2 inches or more in 12 hours or less.

Snow Advisory - snow accumulations of 3 to 6 inches in 12 hours or less.

Lake-Effect Snow Advisory - lake-effect snow accumulations of 3 to 6 inches in 12 hours or less. Snow accumulations and visibilities will vary greatly over short distances and gusty winds can accompany the snow showers. Lake-effect events are more likely to happen over counties near Lake Michigan.

Snow and Blowing Snow Advisory - falling snow with widespread or localized blowing snow occasionally reducing visibilities to ¼ mile or less with sustained winds or wind gusts less than 35 mph.

Blowing Snow Advisory - widespread or localized blowing snow occasionally reducing visibilities to ¼ mile or less with sustained winds or wind gusts less than 35 mph.

Sleet Advisory - sleet accumulations of less than 2 inches in 12 hours or less.

Freezing Rain Advisory - ice accumulations of less than ¼ inch in 12 hours or less due to freezing rain or freezing drizzle.

Winter Weather Advisory - snow accumulations from a trace to 6 inches in combination with freezing rain, and/or freezing drizzle, and/or sleet, and/or blowing snow.