National Weather Service United States Department of Commerce

Storm System To Lift From The Southern U.S. To Great Lakes Over The Next Couple Of Days

A storm will develop, intensify and lift northward from the southern Plains to the Great Lakes over the next two days. The weather hazards of most concern today are severe thunderstorms with damaging winds, isolated large hail and tornadoes and heavy rain with possible flooding in the Lower Mississippi Valley and Mid South. Then on Thursday, a zone of heavy snow may fall in Iowa and Wisconsin. Read More >

Definitions of Weather Watches, Warnings and Advisories

 

Winter Weather/Cold Weather

 

 


                      Fire Weather

 

 

 

Fog / Wind /Severe Weather

 


                       Misc

 

 

Flooding

 

 

 

 


 

Heat

 

Hazardous Weather Outlook

The Hazardous Weather Outlook will describe potential hazardous weather and hydrologic information of concern in Days 1 through 7.

The outlook contains two segments: One segment for the marine zones and adjacent land-based (i.e., coastal) zones and the other segment for the rest of the land-based zones. Each segment of the HWO will contain 3 sections: short term through Day 1, long term for Days 2-7, and spotter information.

Public Information Statement

A narrative statement issued by a NWS Spokane that can be used for: 
 

1) Disseminating observations and accumulation reports during and after a weather event. (i.e. Snowfall/rain totals, observed wind speeds, etc)

2) A current or expected nonhazardous event of general interest to the public that can usually be covered with a single message (e.g., unusual atmospheric phenomena such as sun dogs, halos, aurora borealis, lenticular clouds, and stories about a long-term dry/cold/wet/warm spell). 

3) Public educational information and activities, such as storm safety rules, awareness activities, storm drills, etc. 

4) Information regarding service changes, service limitations, interruptions due to reduced or lost power or equipment outages, or special information clarifying interpretation of NWS data. For example, this product may be used to inform users of radar equipment outages or special information clarifying interpretation of radar data originating from an unusual source which may be mistaken for precipitation (such as chaff drops, smoke plumes, etc., that produces echoes on the radar display.

Local Storm Report

A product issued by local NWS offices to inform users of reports of severe and/or significant weather-related events

 

Short Term Forecast (Nowcast)

A product used to convey information regarding weather or hydrologic events in the next few hours.

 

Air Stagnation Advisory

Issued for atmospheric conditions stable enough to cause air pollutants to accumulate in a given area.

Criteria include:

1) Morning and afternoon mixing height of 1,500 ft AGL or less

AND

2) Morning and afternoon transport winds of 10 kts or less

AND

3) Conditions to continue for at least 72 hours 

AND

4) Conditions are underway or are expected to start within 24 hours

 

Air Quality Alert

Used to relay non-routine air quality alert messages issued by state and local agencies.  It is only meant to convey the official information from the state and local air quality agencies.

Criteria:

 1) Air quality conditions reach or are expected to reach "unhealthy" or worse (AQI 151 to 200 or above)

 

Dense Smoke Advisory

Visibilities at or below 1/4 of a mile. 

 

Dust Advisory

A sudden drop in visibility to one mile or less, but greater than 1/4 mile, resulting in widespread or localized blowing dust. 

Blowing Dust Advisory

Long duration event of widespread or localized blowing dust reducing visibilities to one mile or less, but greater than 1/4 mile.

Dust Storm Warning

A sudden drop in visibility to 1/4 mile or less resulting in widespread or localized blowing dust.

Blowing Dust Storm Warning

A long duration event of widespread or localized blowing dust reducing visibilities to 1/4 mile or less.

Dust Storm Warning

Widespread or localized blowing dust reducing visibilities to 1/4 mile or less.

 

Ash Fall Advisory

Airborne ash plume resulting in ongoing deposition at the surface. Ashfall may originate directly from a volcanic eruption or from the re-suspension (by wind) of a significant amount of relic ash.

 

Winter Storm Watch

A Winter Storm Watch is issued when there is the potential for significant and hazardous winter weather within 12 to 48 hours. It does not mean that significant and hazardous winter weather will occur...it only means it is possible.

Significant and hazardous winter weather is defined as a combination of:

1) Heavy snow (Criteria for heavy snow found here)

AND/OR

2) Sleet accumulations of 1/2" or greater

AND/OR

3) Ice accumulations of 1/4" or greater

AND/OR 

4) Sustained winds or frequent gusts of 35 mph or greater with visibility frequently at or below 1/4 mile in snow or blowing snow for 3 or more hours (Blizzard)

AND/OR

5) Wind Chill forecast or observed at or below -20°F with a wind of 10 mph or greater, in all valley and plateau locations with population centers. 


Blizzard Warning

A Blizzard Warning means that the following conditions are occurring or expected within the next 12 to 18 hours.


1) Snow and/or blowing snow reducing visibility to 1/4 mile or less for 3 hours or longer


AND


2)  Sustained winds of 35 mph or greater or frequent gusts to 35 mph or greater.


There is no temperature requirement that must be met to achieve blizzard conditions.


Winter Storm Warning

A Winter Storm Warning is issued when a significant combination of hazardous winter weather is occurring or imminent.

Significant and hazardous winter weather is defined as a combination of:

1) Heavy snow (Criteria for heavy snow found here)

AND/OR

2) Sleet accumulations of 1/2" or greater

AND/OR

3) Ice accumulations of 1/4" or greater

AND/OR 

4) Sustained winds or frequent gusts of 35 mph or greater with visibility frequently at or below 1/4 mile in snow or blowing snow for 3 or more hours (Blizzard)

AND/OR

5) Wind Chill forecast or observed at or below -20°F with a wind of 10 mph or greater.

 

Ice Storm Warning

An Ice Storm Warning is issued when ¼ inch or more of ice accumulation is occurring or is expected to occur. 


Winter Weather Advisory

A Winter Weather Advisory will be issued for winter weather expected to cause a significant inconvenience, but not serious enough to warrant a warning. 

Winter weather causing a significant inconvenience is defined as a combination of:

1) Heavy snow (Criteria for heavy snow found here)

AND/OR

2) Blowing Snow reducing visibilities to 1/4 mile or less with winds less than 35 mph

AND/OR

3) Sustained wind or frequent guest of 25 to 34 mph accompanied by falling and blowing snow, occassionally reducing visibilities to 1/4 mile or less, for 3 hours or more. 

AND/OR

4) Freezing rain accumulation less than 1/4"

AND/OR

5) Sleet accumulation less than 1/2"


Freeze Warning

A Freeze Warning is issued when significant, widespread freezing temperatures are expected.

A Freeze Warning is issued in the autumn until the end of the growing season (marked by the occurrence of first widespread freeze).

 

Wind Chill Watch

A Wind Chill Watch is issued when wind chills at or below -10°F with a wind of 10 mph or greater are POSSIBLE. 


Wind Chill Advisory

A Wind Chill Advisory is issued when wind chills at or below -10°F with a wind of 10 mph or greater are expected. 


Wind Chill Warning

A Wind Chill Warning is issued when wind chills at or below -20°F with a wind of 10 mph or greater are expected.  


Dense Fog Advisory

A Dense Fog Advisory is issued when widespread fog is expected to reduce visibilities to 1/4 mile or less.


High Wind Watch

A High Wind Watch is issued when the following conditions are POSSIBLE:

1) For valley locations: sustained winds of 40 mph or higher and/or gusts of 58 mph or higher

OR

2) For mountain locations: sustained winds of 50 mph or higher and/or gusts of 75 mph or higher


High Wind Warning

A High Wind Warning is issued when the following conditions are expected:

1) For valley locations: sustained winds of 40 mph or higher and/or gusts of 58 mph or higher

OR

2) For mountain locations: sustained winds of 50 mph or higher and/or gusts of 75 mph or higher



Wind Advisory

A Wind Advisory is issued when, in valley locations, sustained winds of 30-39 mph and/or gusts of 45-57 mph are expected. (not issued for mountain locations)

 

Special Weather Statement

Issued for hazards that have not yet reached warning or advisory status or that do not have a specific code of their own, such as widespread funnel clouds. Commonly used when radar indicates a strong thunderstorm is producing small hail or high winds whose strength does not reach the criteria to be designated a severe thunderstorm.


Severe Thunderstorm Watch

A Severe Thunderstorm Watch is issued when severe thunderstorms are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.

Severe thunderstorms are defined as follows:

1) Winds of 58 mph or higher

AND/OR

2) Hail 1 inch in diameter or larger.


Severe Thunderstorm Warning

A Severe Thunderstorm Warning is issued when severe thunderstorms are occurring or imminent in the warning area.

Severe thunderstorms are defined as follows:

1) Winds of 58 mph or higher

AND/OR

2) Hail 1 inch in diameter or larger.

 

Severe Weather Statement

Provides follow up information on severe weather conditions (severe thunderstorm or tornadoes) which have occurred or are currently occurring.


Tornado Watch

A Tornado Watch is issued when severe thunderstorms and tornadoes are possible in and near the watch area. It does not mean that they will occur. It only means they are possible.

Severe thunderstorms are defined as follows:

1) Winds of 58 mph or higher

AND/OR

2) Hail 1 inch in diameter or larger.


Tornado Warning

A Tornado Warning is issued when a tornado is imminent. When a tornado warning is issued, seek safe shelter immediately.
 

Hydrologic Outlook

Issued when a flood potential exists in a time beyond 48 hours from the start of the event. 

Flash Flood Watch

A Flash Flood Watch is issued when conditions are favorable for rapidly rising water to poses an immediate hazard to life and property. It does not mean that flash flooding will occur, but it is possible.


Flash Flood Warning

A Flash Flood Warning is issued when rapidly rising water poses an immediate hazard to life and property. 


Flood Watch

A Flood Watch is issued when conditions are favorable for flooding. Issued 6-48 hours before the event. It does not mean flooding will occur, but it is possible.


Flood Warning

A Flood Warning is issued when flooding is imminent or occurring.

 

Areal Flood Watch

Issued to inform public if general area wide flooding is expected. Issued 6-48 hours ahead of the event. 

 

Areal Flood Warning

Issued when confidence is high of flooding severe enough to result in significant threat to lives and property. 


Heat Advisory

A Heat Advisory is issued when the Heat Risk reaches a Level 2  based on the National Weather Service's HeatRisk scale (below). The HeatRisk scale is a ranges from 0-4 and indicates the level of heat concern for a location. HeatRisk takes into account: 

  1. how significantly above normal the temperatures are at a location,
  2. the time of the year (for example, is this early season heat that you likely haven't become used to, or late season heat that you have become more used to),
  3. the duration of unusual heat (for example, are temperatures overnight at levels that would lower heat stress, or will warm overnight low temperatures continue to add to heat stress into the next day), and
  4. if those temperatures are at levels that pose an elevated risk for heat complications, such as heat stress, based on peer reviewed science.

                                                                                        

 

Excessive Heat Watch

An Excessive Heat Watch is issued when the Heat Risk has the potential to reach a Level 3 or 4  based on the National Weather Service's HeatRisk scale (below). The HeatRisk scale is a ranges from 0-4 and indicates the level of heat concern for a location. HeatRisk takes into account: 

  1. how significantly above normal the temperatures are at a location,
  2. the time of the year (for example, is this early season heat that you likely haven't become used to, or late season heat that you have become more used to),
  3. the duration of unusual heat (for example, are temperatures overnight at levels that would lower heat stress, or will warm overnight low temperatures continue to add to heat stress into the next day), and
  4. if those temperatures are at levels that pose an elevated risk for heat complications, such as heat stress, based on peer reviewed science.

                                                                                        

 

Excessive Heat Warning

An Excessive Heat Warning is issued when the Heat Risk will reach a Level 3 or 4 based on the National Weather Service's HeatRisk scale (below). The HeatRisk scale is a ranges from 0-4 and indicates the level of heat concern for a location. HeatRisk takes into account: 

  1. how significantly above normal the temperatures are at a location,
  2. the time of the year (for example, is this early season heat that you likely haven't become used to, or late season heat that you have become more used to),
  3. the duration of unusual heat (for example, are temperatures overnight at levels that would lower heat stress, or will warm overnight low temperatures continue to add to heat stress into the next day), and
  4. if those temperatures are at levels that pose an elevated risk for heat complications, such as heat stress, based on peer reviewed science.

                                                                                        


Fire Weather Watch

A Fire Weather Watch is issued to alert fire officials and firefighters of potentially dangerous fire weather conditions within the next 18 to 96 hours. They are issued when the there is a high potential for the development of a Red Flag event meaning: 

1) Abundant lightning and dry fuels

2)Sustained surface winds exceeding 15 MPH AND

       -RH less than 15% in the Columbia Basin

       -RH less than 20% in the valleys

       -RH less than 25% in the mountains

3) High level Hains Index in conjuction with low RH of 15% or less

4) An unusually unstable atmosphere


Red Flag Warning

A Red Flag Warning is issued to alert fire officials and firefighters of potentially dangerous fire weather conditions within the next 12 to 24 hours. They are issued when the following criteria are met:

1) Abundant lightning and dry fuels

2)Sustained surface winds exceeding 15 MPH AND

       -RH less than 15% in the Columbia Basin

       -RH less than 20% in the valleys

       -RH less than 25% in the mountains

3) High level Hains Index in conjuction with low RH of 15% or less

4) An unusually unstable atmosphere