Criteria may be adjusted in certain circumstances to take into account the expected impact of an event. For example, a Winter Weather Advisory may be issued for less than an inch of snow if will occur at a peak travel time, such as around the normal morning commute time, and thus potentially have a significant impact.
Severe Thunderstorm Warning
- Thunderstorm wind gusts of 58 mph or greater,
- AND/OR hail measuring 1" in diameter or larger.
- Tornado observed or indicated on radar.
- Sustained wind or frequent gusts of 35 mph or higher,
- AND visibility less than 1/4 mile in snow and/or blowing snow for 3 hours or longer.
Ice Storm Warning
- Damaging ice accumulations of 1/4" or more.
Winter Storm Warning
- Snowfall of 4" or more in 12 hours or 6" or more in 24 hours,
- OR sleet accumulation of 1/2" or more in 24 hours.
Winter Weather Advisory
- Snowfall of at least 1" but less than 4" in a 12 hour period,
- AND/OR visibility reduced to 1/4 mile or less in blowing snow,
- AND/OR sleet accumulation of less than 1/2".
Freezing Rain Advisory
- Ice accumulations of less than 1/4".
Wind Chill Warning
- Wind chills of 25 below or colder are expected. In most cases a minimum wind speed of 10 mph should be occurring or forecast before a warning is issued.
Wind Chill Advisory
- Wind chills of 10 below to 24 below are expected. In most cases a minimum wind speed of 10 mph or more should be occurring or forecast before an advisory is issued.
High Wind Warning
- Sustained non-thunderstorm wind speeds of at least 40 mph for an hour or more,
- OR non-thunderstorm wind gusts of at least 58 mph regardless of duration.
- Sustained non-thunderstorm wind speeds between 30 and 39 mph for at least one hour,
- OR non-thunderstorm wind gusts of 40 to 57 mph for any duration.
Lake Wind Advisory
- Issued when sustained non-thunderstorm wind speeds reach 20 to 29 mph for at least one hour,
- OR non-thunderstorm wind gusts reach between 35 to 39 mph.
- Widespread temperatures are forecast to be 30ºF or below for 2 hours or more during the growing season. The beginning of the spring frost/freeze season and ending of the fall frost/freeze season is determined in conjunction with the University of Kentucky Agricultural Weather Center.
- Widespread frost during the growing season. The beginning of the spring frost/freeze season and ending of the fall frost/freeze season is determined in conjunction with the University of Kentucky Agricultural Weather Center.
Excessive Heat Warning
- Issued when the heat index is expected to reach around 110ºF or higher,
- AND the minimum heat index will remain around 75ºF or higher during a 48 hour period.
- A warning would also be appropriate if heat advisory criteria are expected to be reached for 4 consecutive days.
- Issued for heat index of around 105ºF
Dense Fog Advisory
- Widespread visibility 1/4 mile or less due to dense fog.
Dense Smoke Advisory
- Widespread visibility 1/4 mile or less due to dense smoke.
Dust Storm Warning
- Widespread visibility 1/4 mile or less due to blowing dust.
Blowing Dust Advisory
- Widespread visibility of between 1/4 mile and 1 mile.
Red Flag Warning
- Sustained 20-foot wind speeds of 15 mph or greater,
- AND minimum relative humidity of 25% or less,
- AND 10-hour fuel moisture values of 8% or less.
National guidance regarding NWS Watch/Warning/Advisory products can be found in the following NWS Directives:
NWSI 10-511 WFO Severe Weather Products Specification,
NWSI 10-513 WFO Winter Weather Products Specifications,
NWSI 10-515 WFO Non-Precipitation Weather Products Specification,
NWSI 10-401 Fire Weather Services Product Specification