Warning Criteria

TYPE OF ISSUANCE 

What is Expected To Occur

WINTER WEATHER ADVISORY

When any of the following is expected within the next 12 to 24 hours:
 

Blowing Snow…

• Visibility substantially reduced over a wide area due to wind-driven snow with winds less than 35 mph. Usually NOT issued for localized occurrences.

Freezing Rain…

• Any accretion of freezing rain or freezing drizzle on road surfaces

Mixed Precipitation…

• Winter weather event having more than one predominant hazard (ie., snow and ice, snow and sleet, or snow, ice & sleet) meeting or exceeding advisory criteria for at least one of the precipitation elements, but remaining below warning criteria.

Snow…

• 4 inches averaged over a forecast zone in 12 hours

Snow and Blowing Snow…

• 4 inches snowfall averaged over a forecast zone in 12 hours with visibility substantially reduced over a wide area due to wind-driven snow with winds less than 35 mph.

Wind Chill…

• Wind chill index between -20°F and -34°F for at least 3 hours with a sustained wind speed of at least 10 mph.

WINTER STORM WARNING

When any of the following is expected within the next 12 to 36 hours:
 

Blizzard…

• Sustained winds or frequent gusts > 35 mph AND considerable falling and/or blowing snow frequently reducing visibility < ¼ for > 3 hours (Blizzard conditions need to be the predominant condition over a 3 hour period)

Heavy Snow…

• Snowfall >= 6 inches in one event for Bangor region and Downeast.
• Snowfall >= 8 inches in one event (36 hrs total, but must fall within 12) for the area north of a line from Dexter to Indian Township.

Ice Storm…

• ½ inch or greater accretion of freezing rain in any zone

Sleet…

• Pure sleet >= 1”

Wind Chill…

• Wind chill index less than -35°F for at least 3 hours with a sustained wind of at least 10 mph.

Winter Storm…

• Winter weather event having more than one predominant hazard {ie. heavy snow and blowing snow (below blizzard conditions), snow and ice, snow and sleet, sleet and ice, or snow, sleet and ice} meeting or exceeding warning criteria for at least one of the precipitation elements.

WIND ADVISORY

Sustained winds 31-39 mph (27-34 kts) for at least 1 hour; OR any gusts to 46-57 mph (40-49 kts)

HIGH WIND WARNING

Sustained winds 40-73 mph (≥35 kts) for at least 1 hour; OR any gusts ≥ 58 mph (≥50 kts)

SEVERE THUNDERSTORM WARNING

Thunderstorms with wind gusts ≥ 58 mph (50 kts) AND/OR hail ≥1" in diameter

TORNADO WARNING

Likelihood of a tornado within the given area based on radar or actual sighting; usually accompanied by conditions indicated above for "Severe Thunderstorm Warning"

FLOOD ADVISORY

Expected inundation of some low lying and poor drainage areas, resulting in a nuisance to the public but not a threat to life and property.

FLASH FLOOD WARNING

Rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within a short timeframe from the onset of heavy rain.  A dam or levee failure, or water released from an ice jam is also considered

FLOOD WARNING

Expected overflow or inundation by water which causes or will cause damage and/or a threat to life

RIVER FLOOD WARNING

Water level at a River Forecast point along a main stem river (such as the Penobscot, Aroostook, Saint John) is expected to reach or exceed flood stage

EXCESSIVE HEAT WARNING

Daytime heat indices of ≥ 105°F for 2 or more hours

HEAT ADVISORY

Daytime heat indices of 95ºF-104ºF for 2 or more hours

DENSE FOG ADVISORY

Widespread visibility ≤1/4 mile for at least 3 hours

FREEZING FOG ADVISORY

Very light ice accumulation from predominantly FZFG

FROST ADVISORY

Issued under clear, light wind conditions with forecast minimum shelter temperature 33-36ºF during growing season

FREEZE WARNING

When minimum shelter temperature drops to < 32ºF during growing season

RED FLAG WARNING

• The mean of 1 hour and 10 hour fuel moistures are less than 10% in combination with the following weather conditions

• Less than 30% Relative Humidity and frequent gusts or sustained winds above 25 mph. 

SMALL CRAFT ADVISORY

Sustained winds or frequent gusts of 29-38 mph (25-33kts) AND/OR Seas ≥ 5 feet within 24 hours

GALE WARNING

Sustained winds or frequent gusts of 39-55 mph (34-47kts) within 24hrs from a non-tropical system

STORM WARNING

Sustained winds or frequent gusts 55-73 mph (48-63kts) within 24 hours from a non-tropical system

HURRICANE FORCE WIND WARNING

Sustained winds or frequent gusts ≥ 74 mph (≥ 64kts) (> 2hrs) within 24 hours from a non-tropical system for coastal waters only

TROPICAL STORM WARNING

Sustained winds 39-73 mph (34-63kts) (no gust criteria) associated with a tropical storm expected to affect a specified area within 24 hours

HURRICANE WARNING

Sustained winds ≥ 74 mph (64kts) (no gust criteria) associated with a hurricane expected to affect a specified area within 24 hours

SPECIAL MARINE WARNING

Brief/sudden occurrence of sustained wind or frequent gusts ≥ 34 knots, usually associated with thunderstorms; AND/OR hail ≥3/4" in diameter; also issued for waterspouts

COASTAL FLOOD ADVISORY

Minor coastal flooding expected within 12 hours.  Examples include: splash over causing a few roads briefly impassable, standing water in parking lots, etc.

COASTAL FLOOD WARNING

Coastal flooding expected within 12 hours; widespread serious coastal flooding which damages property AND/OR is a threat to life

FREEZING SPRAY ADVISORY

Light to moderate accumulation of ice is expected on vessels.

HEAVY FREEZING SPRAY WARNING

An heavy accumulation of freezing water droplets on a vessel at a rate of 2 cm per hour or greater caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement