Winter Storms: Watch, Warning and Advisory Criteria
Types of Message
The National Weather Service issues WATCHES, WARNINGS, and ADVISORIES to alert the public to potentially dangerous winter weather events or situations.
- A WATCH is issued to alert the public that dangerous winter conditions are possible within the "WATCHED" area, generally within the next 12 to 36 hours.
- A WARNING is issued to alert the public that dangerous winter conditions are likely to occur in the "WARNED" area, generally within the next 12 to 36 hours, or are occurring.
- An ADVISORY is issued to alert the public that winter conditions are expected to cause a significant inconvenience and may be hazardous.
If caution is exercised, these situations should not be life threatening.
The exact criteria used to trigger these watches, warnings, and advisories vary throughout the United States. The following criteria are used in Maine. Criteria are the same across the State except where there is a noted difference between our two forecast areas:
Snow and/or blowing snow will combine with strong winds to produce near-zero visibility. Deep drifts and wind chill may accompany these conditions. The exact criteria used for these warnings include the following conditions which will persist for 3 hours or more.
- Sustained winds or frequent gusts to 35 mph or more, and falling and/or blowing snow which reduces visibility to 1/4 mile or less.
Winter Storm Warning
- In southern and western Maine (Gray forecast area), an average of more than 6 inches of snow/sleet is expected in 12 hours, or 9 inches in 24 hours or
- In northern and downeast Maine (Caribou forecast area), an average of more than 7 inches of snow/sleet is expected in 12 hours or 10 inches in 24 hours
Ice Storm Warning
- Freezing rain is expected to cause a glaze of ice 1/2 inch or thicker
Winter Weather Advisory
- An average of 4 inches of snow/sleet, but less than the warning amount, is expected across the area. Winter weather advisories can also be issued for mixed precipitation events or for blowing snow.
Ice Storm Advisory
- Freezing rain is expected to cause a glaze of ice on roads and sidewalks, but less than 1/2 inch is expected.
The NWS does not issue warnings or advisories for storms that produce less than 4 inches of snowfall, but these storms can be deceptively dangerous. The majority of deaths linked to snow storms are as a result of traffic accidents, and many of those accidents occur with only small accumulations of snow. Slow down as soon as snow begins to accumulate.