HAZARDOUS WEATHER TERMS

WATCH:  Conditions are favorable for a severe storm or flooding; but the exact timing, location, or occurrence is still uncertain.  A watch means to get prepared for the hazardous conditions.

WARNING: Hazardous weather is expected or occurring.  A warning means to take shelter.

ADVISORY: Weather conditions that cause inconvenience are expected or occurring; an advisory means to use caution.

WARNING and ADVISORY CRITERIA

THUNDERSTORMS:

TORNADO: A violently-rotating column of air from a thunderstorm in contact with the ground.

SEVERE THUNDERSTORM: A thunderstorm with hail 3/4 inch or larger and/or winds 58 mph or greater.

FLOODS:

FLASH FLOOD:  A life-threatening flood that occurs very quickly from intense rainfall over a short period of time, especially in mountainous terrain, or from a dam failure.

FLOOD: Rivers overflowing their banks or water covering a normally-dry area caused by an extended period of widespread rain, snowmelt, or ice jams.  This situation develops more slowly than a flash flood.  Melting snow causes flooding when snow melts quickly due to warm temperatures or rain falling on deep snow cover.  Ice jams occur in the spring when ice chunks jam at bends in rivers and bridge abutments; the ice acts as a dam, causing water to back up behind it.

URBAN AND SMALL STREAM FLOODING: Minor flooding of small streams, streets and low-lying areas such as underpasses and storm drains; generally not as dangerous as a flash flood.

WINTER WEATHER:

BLIZZARD:  A severe winter storm with winds 35 mph or greater AND significant snow or blowing snow with visibility less than 1/4 mile.

HEAVY SNOW:  6 inches of snow or more in 12 hours; or 8 inches of snow or more in 24 hours.

ICE STORM:  Ice accumulations that could cause extremely dangerous conditions and significant damage.

WINTER STORM WARNING:  A life-threatening winter storm with snow, ice, strong winds, and/or cold temperatures.

SNOW ADVISORY:  3 to 6 inches of snow in 12 hours; or 5 to 8 inches of snow in 24 hours.

FREEZING PRECIPITATION ADVISORY:  Light freezing precipitation that does not coat all exposed surfaces.

BLOWING SNOW ADVISORY:  Occasional visibility 1/4 mile or less; or ground blizzard conditions: Strong winds causing blowing snow and low visibility near the ground, but no snow is falling

WINTER WEATHER ADVISORY:  A combination of winter weather conditions such as light snow, light freezing precipitation, and/or strong winds.

WIND CHILL WARNING: Wind chill values -40 F or colder (see Appendix 4 for the wind chill index chart).

WIND CHILL ADVISORY: Wind chill values between -25 and -40 F (see Appendix 4 for the wind chill index chart).

WIND:

HIGH WIND WARNING:  Winds 40 mph or greater; or wind gusts 58 mph or greater.

WIND ADVISORY:  Winds 30 mph or greater; or wind gusts 45 mph or greater.

OTHER HAZARDS:

DENSE FOG ADVISORY: Visibility less than 1/4 mile.

BLOWING DUST WARNING: Visibility less than 1/4 mile over a widespread area.

BLOWING DUST ADVISORY: Visibility between 1 and 1/4 mile over a widespread area.

FREEZE WARNING: Temperatures 32 degrees or colder for a significant period of time that could kill outdoor plants at the beginning or end of the growing season.

FROST ADVISORY: Temperatures in the mid 30s with clear skies, light winds, and high humidity near the ground that could kill outdoor plants at the beginning or end of the growing season.

EXCESSIVE HEAT WARNING: Heat index values 115 F or higher for at least 3 hours with a minimum heat index of 80 F (see Appendix 4 for the heat index chart).

HEAT ADVISORY: Heat index values 105 F for at least 3 hours (see Appendix 4 for the heat index chart).

SEVERE THUNDERSTORM RISK TERMS USED IN OUTLOOKS:

SLIGHT RISK:  Severe thunderstorms are expected to be few or isolated.

MODERATE RISK:  Severe thunderstorms are expected to be more numerous or widespread.

HIGH RISK:  Severe thunderstorms with the potential for tornadoes, damaging windstorms, and/or large hail are expected.

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