National Weather Service United States Department of Commerce

Storm Impacting the Northwest U.S.; Fire Weather Conditions in Southern California; Severe Weather in the South

A Pacific storm is bringing areas of low elevation rain, moderate to heavy mountain snow, and high winds to the Northwest. Strong Santa Ana winds and very dry conditions are producing elevated to critical fire weather conditions in southern California. Isolated strong to severe thunderstorms are possible through early Wednesday morning across parts of northeast Texas into western Tennessee. Read More >

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.