- Advisory: Highlights special hazardous weather conditions that are less serious than those described by a “warning.” Used for a weather event that may cause significant inconvenience and, if caution is not exercised, could lead to threatening life and/or property.
Watch: Alerts public to possibility of severe weather or some other hazardous weather element. Intended to provide enough lead time so that individuals who need to implement plans can do so.
Warning: Warns public that hazardous weather element is imminent or has a very high probability of occurring. Appropriate precautions should be taken.
- Blizzard Warning: Issued for winter storms with sustained winds or frequent gusts to 35 miles per hour or greater and considerable falling and/or blowing snow, reducing visibility to less than 1/4-mile. These conditions are expected to last at least three hours.
- Excessive Heat: Alerts are issued in the following categories:
- Advisory: Heat index above 105 degrees is anticipated.
- Watch: Conditions are favorable for the development of heat indices in excess of 105 degrees during daytime hours in combination with nighttime low temperatures of 80 degrees or higher, for 2 consecutive days.
- Warning: Heat index equals or exceeds 120 degrees for 3 hours or longer.
- Flash Flood: Flash floods take less than 6 hours to develop. Alerts are issued in the following categories:
- Watch: Flash flood conditions are possible in or near the designated area. Individuals should be alert and ready to take action.
- Warning: Flash flooding is imminent. Those in the affected area should take immediate action.
- Flood: Floods usually take 12 hours or more to develop. Alerts are issued in the following categories:
- Watch: Flooding is possible in or near the designated area. Individuals should be alert and ready to take action.
- Warning: A flood is imminent or has been reported at a certain station or river basin.
- Minor: Minimal or no property damage; possibly some public inconvenience.
- Moderate: Flooding of secondary roads; some evacuation may be required.
- Major: Extensive flooding and property damage; evacuation of people and livestock; closure of primary and secondary roads.
- Fog Advisory: Dense fog covers a widespread area and reduces visibility to 1/4-mile or less.
- Ice Storm Warning: Damaging accumulations expected during freezing rain conditions, making walking and driving extremely dangerous. Significant ice accumulations are usually 1/4-inch or greater.
- Severe Thunderstorm: Alerts are issued in the following categories:
- Watch: Conditions are favorable for the development of severe thunderstorms in and close to the designated area; usually in effect for several hours, no more than 6 hours.
- Warning: A thunderstorm has produced hail 3/4-inch or larger in diameter and/or winds equal to or exceeding 58 miles per hour.
- Snow: Alerts are issued in the following categories:
- Advisory: Over 2 inches but not expected to accumulate 6 inches or more.
- Heavy snow warning: 6 inches or more in 12 hours or less; 8 inches or more in 24 hours or less; light winds.
- Tornado: Alerts are issued in the following categories:
- Watch: Conditions are favorable for the development of tornados in and close to the designated area; usually in effect for several hours with 6 hours being the most common.
- Warning: A tornado is indicated by radar or sighted by spotters. Issued by the National Weather Service.
- Wind Advisory: Sustained winds of 30 miles per hour or greater are expected to last for one hour or longer OR gusts to 45 miles per hour or higher are expected for any duration.
- Wind Chill: Alerts are issued in the following categories:
- Advisory: Wind chills will be 35 degrees below zero or colder for a sustained period of time. Winds are expected to be at least 10 miles per hour.
- Warning: Wind chills are expected to reach 50 degrees below zero and wind speeds are 10 miles per hour or greater. (NOTE: Some areas, due to humidity, give an alert at 10 degrees below zero.)
- Winter Storm: Alerts are issued in the following categories:
- Watch: Conditions are favorable for the development of hazardous weather elements such as heavy snow and/or blizzard conditions or significant accumulations of freezing rain or sleet. Conditions may occur singly or in combination. Usually issued 24 to 48 hours in advance of event.
- Warning: Heavy snow and some windiness is imminent or very likely, perhaps in combination with sleet and/or freezing rain/drizzle. Usually issued for up to a 12-hour duration but can be extended to 24 hours.
- Winter Weather Advisory: A mixture of precipitation is expected, such as snow, sleet, and freezing rain or drizzle.
Information gathered from the NOAA Resource Guide, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Office of Public and Constituent Affairs, (202) 482-6090.