National Weather Service United States Department of Commerce

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 it will occur at a peak travel time, such as around the normal morning commute time, and thus potentially have a significant impact.

Severe Weather Events...

Severe Thunderstorm Warning

  • Radar or satellite indicate and/or reliable reports of thunderstorms with:
    • ​Wind gusts equal to in excess of 58 mph
    • AND/OR hail size of 1 inch (U.S quarter size) in diameter or larger.

Tornado Warning

  • Radar indication and/or reliable reports of tornado or developing tornado.

 

Special Weather Statement

  • Strong thunderstorms that approach, or expected to approach severe criteria.
    • ​A strong thunderstorm contains one or combination of the following events:
      1. Wind gusts of 40 to 57 mph
      2. Hail less than 1 inch in diameter
      3. Frequent to continuous lightning
      4. Landspouts that are not anticipated to threaten lives and/or property
      5. Funnel clouds not expected to become a tornado threat

See NWSI 10-511 WFO Severe Weather Products Specification for additional information.

 

Flood Events...

Flash Flood Warning

  • Life or property-threatening, short-term rapid onset flooding is imminent or occurring. This can include flooding due to heavy rainfall or due to a dam or levee break.

 

Flood Warning

  • Flooding due to potentially damaging river level rises,
  • OR damaging overland flooding that is expected to persist for many hours.

 

Flood Advisory

  • Nuisance flooding due to river level rises and minor overland flooding and/or ponding of water that warrants notification of the public but less urgent than a warning.

 

Special Weather Statement

  • Heavy rainfall that is expected to cause hazardous travel conditions but is not expected to cause flooding.

See NWSI 10-922 WFO Hydrologic Products Specification for additional information.

 

Winter Weather Events...

Blizzard Warning

  • Sustained wind or frequent gusts greater than or equal to 35 mph accompanied by falling
  • AND/OR blowing snow, frequently reducing visibility to less than ¼ mile for 3 hours or more.

 

Ice Storm Warning

  • Ice accumulation of of ¼" or more on an elevated horizontal flat surface.

 

Snow Squall Warning

  • Heavy snow and gusty winds reducing visibility to ¼ mile or less with sub-freezing ambient road surfaces
  • AND/OR plunging temperatures behind an arctic front sufficient to produce flash freezes, along with a significant reduction in visibility from falling and/or blowing snow
  • AND at least a risk for a flash freeze.

 

Winter Storm Warning

  • Heavy snow accumulation of 4" or more within 48 hours or less
  • AND/OR sleet accumulation of ½" or more
  • AND/OR mixed precipitation with at least one winter hazard type (blizzard, freezing rain, sleet, or snow) meeting or exceeding warning criteria
  • OR high impact frozen precipitation outside of the normal winter season or during a critical situation (standard criteria not being met, but impacts are expected to be unusually significant).

 

Winter Weather Advisory

  • Snow accumulations of between 1 and 4", or impacts expected with 1" or less of snow
  • AND/OR Freezing rain accretions less than ¼" on an elevated horizontal flat surface
  • AND/OR Sleet accumulation less than ½"
  • AND/OR Black ice causing widespread slick roads and/or numerous accidents
  • AND/OR Blowing snow that reduces visibilities to ¼ mile or less.

 

Special Weather Statement

  • Black ice,
  • OR short-duration heavy snow bands below warning criteria.

See NWSI 10-513 WFO Winter Weather Products Specifications for additional information.

 

Non-Precipitation Events...

Blowing Dust Warning

  • Widespread synoptically driven blowing dust reducing visibilities to ¼ mile or less
  • AND winds of 25 mph or greater usually required
  • AND generally for a duration of longer than 90 minutes.

 

Blowing Dust Advisory

  • Widespread synoptically driven blowing dust reducing visibilities to 1 mile or less but greater than ¼ mile
  • AND winds of 25 mph or greater usually required
  • AND generally for a duration of longer than 90 minutes.

 

Dust Storm Warning

  • Dust storm reducing visibility to ¼ mile or less, with sudden reduction in visibility
  • AND winds of 25 mph or greater usually required
  • AND typically localized and brief in duration.

 

Dust Advisory

  • Dust reducing visibility to 1 mile or less but greater than ¼ mile, with sudden reduction in visibility
  • AND winds of 25 mph or greater usually required
  • AND typically localized and brief in duration.

 

Excessive Heat Warning

  • Maximum heat index around 110ºF or higher
  • AND the minimum heat index will remain around 75ºF or higher
  • AND conditions persist for at least 48 hours;
  • OR Heat Advisory criteria is to be met for 4 consecutive days.

 

Heat Advisory

  • Maximum heat index of around 105ºF or higher for up to 3 consecutive days.

 

Extreme Cold Warning

  • Air temperatures or wind chill values reaching or exceeding the county-level warning criteria (displayed below).

 

Cold Weather Advisory

  • Air temperatures or wind chill values reaching or exceeding the county-level warning criteria (displayed below).

 

Freeze Warning

  • Minimum shelter temperature to be under 30ºF for 2 hours or more during the growing season. The beginning and end of the growing season are determined in conjunction with the University of Kentucky Agricultural Weather Center.

 

Frost Advisory

  • Widespread frost during the growing season. The beginning and end of the growing season are determined in conjunction with the University of Kentucky Agricultural Weather Center.

 

High Wind Warning

  • Sustained non-thunderstorm wind speeds of at least 40 mph for 1 hour or more
  • OR non-thunderstorm wind gusts of 58 mph or greater for any duration.

 

Wind Advisory

  • Sustained non-thunderstorm wind speeds of 30 and 39 mph for at least 1 hour
  • OR non-thunderstorm wind gusts of 40 to 57 mph for any duration.

 

Lake Wind Advisory (for Lake Cumberland, Laurel Lake, and Cave Run Lake only)

  • Sustained non-thunderstorm wind speeds of 20 to 29 mph for at least 1 hour
  • OR non-thunderstorm wind gusts of 35 to 39 mph.

 

Dense Fog Advisory

  • Widespread fog reducing visibility to ¼ mile or less
  • OR localized fog reducing visibility to ¼ mile or less producing major impacts.

 

Dense Smoke Advisory

  • Widespread smoke reducing visibility to ¼ mile or less
  • OR localized smoke reducing visibility to ¼ mile or less producing major impacts.

 

Freezing Fog Advisory

  • Freezing fog producing light ice accretion and slippery conditions.

 

Special Weather Statement

  • Heat indices, wind chill or air temperature values near "advisory" level for an hour or two,
  • OR local areas of dense fog, dense smoke or other hazards that are below advisory criteria.

See NWSI 10-515 WFO Non-Precipitation Weather Products Specification for additional information.

 

Fire Weather Events...

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.

 

Special Weather Statement

  • Low confidence or borderline red flag conditions:
    1. ​Critically low relative humidity values
    2. Near criteria wind gusts
    3. Marginal 10-hour fuel moistures

See NWSI 10-401 Fire Weather Services Product Specification for additional information.