National Weather Service United States Department of Commerce
Risk Level - Legend
None
Limited
Elevated
Significant
Extreme
Risk - Limited
Risk - Elevated
Risk - Significant
Risk - Excessive
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Severe Thunderstorm Arrival Tool
Risk
Level
Risk
Level
Tornado
Fog
Hail
 
Non - Thunderstorm Winds
 
Thunderstorm Wind Gusts
Excessive Heat
Flooding
Snow and Sleet
Lightning
Ice Accumulation
Severe Thunderstorm
Arrival Tool
Frost and Freeze
Fire Weather
Excessive Cold
Coastal Flooding
Swim Risk
High Surf
Marine Hazard
 
Risk Level
Definition
None
No tornado risk.
Limited
Probability of a tornado within 25 miles of a point:
less than 10 percent.
Elevated
Probability of a tornado within 25 miles of a point:
Equal to or greater than 10 percent.
Significant
Probability of a tornado within 25 miles of a point:
Equal to or greater than 30 percent.
Extreme
Probability of a  tornado within 25 miles of a point:
Equal to or greater than 45 percent.
 
Risk Level
Definition
None
No risk of fog.
Limited
Fog with visibilities less than or equal to 1 mile.
Elevated
Fog with visibilities less than or equal to 1/2 mile
Significant
Fog with visibilities less than or equal to 1/4 mile.
Extreme
Fog with near zero visibilities.
 
Risk Level
Definition
None
No risk of hail.
Limited
Risk of sub-severe hail (less than 1")
or
Probability of severe hail (1" or greater) within 25 miles of a point:
less than 15%
Elevated
Probability of severe hail (1" or greater) within 25 miles of a point:
Equal to or greater than 15%
Significant
Probability of severe hail (1" or greater) within 25 miles of a point:
Equal to or greater than 45%
Extreme
Probability of severe hail (1" or greater) within 25 miles of a point:
Equal to or greater than 60%
 
Risk Level
Definition
None

Sustained winds < 20 mph
and
Wind gusts < 30 mph.

Limited
Sustained winds 20-29 mph
or
Wind gusts 30-44 mph.
Elevated
Sustained winds 30-39 mph
or
Wind gusts 45-57 mph.
Significant
Sustained winds 40-49 mph
or
Wind gusts 58-64 mph.
Extreme
Sustained winds > 50 mph
or
Wind gusts > 65 mph.
 
Risk Level
Definition
None
No thunderstorm wind risk.
Limited
Risk for sub-severe wind gusts (less than 58 mph)
or
Probability of severe wind gusts (58 mph or greater) within 25 miles of a point:
Less than 15%
Elevated
Probability of severe wind gusts (58 mph or greater) within 25 miles of a point:
Equal to or greater than 15%
Significant
Pprobability of severe wind gusts (58 mph or greater) within 25 miles of a point:
Equal to or greater than 45%
Extreme
Probability of severe wind gusts (58 mph or greater) within 25 miles of a point:
Equal to or greater than 60%
 
Risk Level
Definition
None
Maximum Apparent Temperature < 94
Limited
Maximum Apparent Temperature 95 to 108
Elevated

Maximum Apparent Temperature 108 to 113
OR
Maximum Apparent Temperature greater than or equal to 100 for 4 consecutive days.

Significant

Maximum Apparent Temperature 113 to 116
OR
Maximum Apparent Temperature greater than or equal to 105 for 4 consecutive days.

Extreme
Maximum Apparent Temperature greater than or equal to 116
OR
Maximum Apparent Temperataure greater than or equal to 105 for 5 consecutive days.
Note:
Apparent Temperature is defined as:
  Wind Chill Temperature during the cold season.
  Heat Index Temperature during the warm season.
 
Risk Level
Definition
None
No Flooding risk.
Limited
Risk of localized flash flooding of small streams and low water crossings, and minor flooding of poor drainage or urban areas.
Elevated

Risk of flash flooding of several low water crossings, roads, and small streams,
or
Minor River Flooding.

Significant

Risk of flash flooding of numerous roads, low water crossings, and small streams,
or
Moderate river flooding.

Extreme
Risk of widespread flash flooding of low water crossings, roads, and small strams.
or
Major river flooding.
 
Risk Level
Definition
None
No snow or sleet.
Limited
Snow and/or sleet with less than 1 inch of accumulation expected.
Elevated
Snow and/or sleet with 1 to 1.9 inches of accumulation expected.
Significant
Snow and/or sleet with 2 to 11.9 inches of accumulation expected.
Extreme
Snow and/or sleet with greater than or equal to 12 inches of accumulation expected.
 
Risk Level
Definition
None
No lightning risk
Limited
Thunderstorms expected to be isolated to scattered in coverage. 
Atmospheric conditions support cloud to ground lightning strikes in and near thunderstorms.
Elevated
Thunderstorms expected to be numerous in coverage.
  Atmospheric conditions support cloud to ground lightning strikes in and near thunderstorms.
Significant
Widespread thunderstorms are expected.
  Atmospheric conditions support cloud to ground lightning strikes in and near thunderstorms.
Extreme
Thunderstorms are expected with nearly continuous cloud to ground lightning strikes in and near thunderstorms.
 
Risk Level
Definition
None
No freezing rain or drizzle.
Limited
Very light freezing rain or drizzle with accumulation between 0.02 and 0.04 inches, OR Freezing Fog.
Elevated
Freezing rain or drizzle with accumulation between 0.05 and 0.24 inches.
Significant
Freezing rain with accumulation of 0.25 inch to 0.99 inches.
Extreme
Freezing rain with accumulation of greater than or equal to 1 inch.
 
Risk Level
Definition
None
No danger of frost or freeze causing damage to vegetation.
Limited
Patchy frost during the growing season with minor damage to unprotected vegetation.
Elevated
Frost expected during the growing season with damage to unprotected vegetation. 
This may include temperatures less than or equal to 32 degrees F for less than 3 hours.
Significant
Freeze expected (less than or equal to 32 degrees F for 3 or more hours) during the growing season with significant damage to unprotected vegetation.
Extreme
Hard freeze (less than or equal to 25 degrees F) during the growing season with catastrophic damage to unprotected vegetation.
 
Risk Level
Definition
None
Severe thunderstorms are not expected today or tonight.
Limited
Severe thunderstorms will be possible later today or tonight .
Elevated
Severe thunderstorms will be possible in the next 6 hours.
Significant
Severe thunderstorms will be possible in the next 3 hours.
The Severe Thunderstorm Arrival Tool is a resource for municipalities, counties, and SKYWARN storm spotters to plan for possible storm spotter activation on the current calendar day. Other interests can also use the Severe Thunderstorm Arrival Tool to determine the expected time frame for severe thunderstorm potential.
 
Risk Level
Definition
None
Minimum apparent temperature greater than or equal to 32 degrees F.
Limited
Minimum apparent temperature 31 to 26 deg F.
Elevated
Minimum apparent temperature 25 to 14 deg. F
Significant
Minimum apparent temperature 13 to 8 deg. F.
Extreme
Minimum apparent temperature less than or equal to 7 degrees F
Note:
Apparent Temperature is defined as:
  Wind Chill Temperature during the cold season.
  Heat Index Temperature during the warm season.
 
Risk Level
Definition
None
Open burning is usually safe with proper containers and precautions under low fire danger conditions. 
Residents should always check on local ordinances that prohibit open burning under any conditions.
Limited
Open burning is usually safe with the proper precautions.
Burning should be done in the early morning and late evening to avoid windier and drier conditions from midday through mid-afternoon. 

Residents should always check on local ordinances that prohibit open burning under any conditions.
Elevated
Any open burning is discouraged due to increased wind and lower humidity - except by experienced fire personnel
Increasing winds and lower humidity contribute to drying fuels. Fires escape control more easily and containment is difficult for inexperienced fire personnel.
Approaching Red Flag conditions.
Significant
Open burning should not be attempted.
High winds and extended dry periods lead to extreme burning conditions. Open fires can quickly escape and are very difficult to control, even for experienced fire fighters. 
Conditions exceed minimum criteria for a Red Flag Warning in most cases.
Extreme
Very strong winds, well in excess of Red Flag Criteria combined with moderate to low humidity.
Fires will spread very quickly with spot fires common. Fire control is extremely difficult due to very strong winds.
***These definitions are geared towards the general public and general emergency management and should not be confused with the standard National Fire Danger Rating System (NFDRS) adjectives used by wildland fire personnel.
The fire weather category for the Enhanced Hazardous Weather Outlook is based primarily on predicted wind, humidity and temperature, and does not account for fuel moisture from recent precipitation, snow cover and recently melted snow.  Appropriate adjustments to the fire environment must be made.
Fire weather hazard categories will normally be more restricted, generally in the "none" or "limited" categories from May 1st to September 30th due to normally predominant green and moist live vegetation.  This will be subject to change during unusual severe Spring and/or Summer drought.
 
Risk Level
Definition
None
No Coastal Flooding risk.
Limited
Winds >= 25mph and Wave Heights >= 5 feet.
These conditions could lead to isolated areas of beach erosion and coastal flooding
Elevated

Winds >=30 mph and Wave Heights >=10 feet.
These conditions could lead to scattered areas of beach erosion and coastal flooding.

Significant

Winds >=35 mph and Wave Heights >=15 feet.
These conditions could lead to significant beach erosion and coastal flooding.

Extreme
Winds >= 40 mph and Wave Heights >= 20 feet.
These conditions could lead to widespread beach erosion and coastal flooding.
 
Risk Level
Definition
None
No Swim Risk.
Limited
 A limited risk of swimming hazards imply that large waves and strong currents are not expected along the shore. However, dangerous currents can still form near river mouths and shoreline structures, such as piers or breakwalls, even during low wave heights.
Elevated

An elevated risk of swimming hazards imply that large waves and strong currents are likely along the shore. Only experienced swimmers should consider entering the water. Stay away from river mouths and shoreline stuctures. 

Significant

A significant risk of swimming hazards imply dangerous waves and currents are expected along the shore. Swimming conditions may be life threatening to anyone entering the water. 

Extreme
 
The Swim Risk grids are only generated during the swimming season, generally from mid June through the end of September
 
Risk Level
Definition
None
No High Surf Risk.
Limited
 Wave height >= 2 feet and Wave Period > 3 seconds.
Elevated

Wave Height >= 4 feet and Wave Period > 4 seconds.

Significant

Wave Height >= 6 feet and Wave Period > 5 seconds.

Extreme
 Wave Height > 8 feet.
 
Risk Level
Definition
None
No Marine Hazards Risk.
Limited
Winds >= 15 knots and/or Waves >= 2 feet.
Elevated

Winds >= 23 knots and/or Waves >= 4 feet.

Significant

Winds >= 34 knots and/or Waves >= 9 feet.

Extreme
Winds >= 48 knots and/or Waves >= 14 feet.
 
Risk Level
Definition
None
No Freezing Spray Risk.
Limited
Moderate Freezing Spray Expected
Elevated

 

Significant

Heavy Freezing Spray Expected 

Extreme
 
 
Risk Level
Definition Severe Thunderstorm Risk Day 2 to 7
None
No risk of severe thunderstorms.
Limited
Risk for severe thunderstorms with the
Probability of severe thunderstorms* within 25 miles of a point:
Less than 15%
Elevated
Probability of severe thunderstorms* within 25 miles of a point:
Equal to or greater than 15%
Significant
Probability of severe thunderstorms* within 25 miles of a point:
Equal to or greater than 45%
Extreme
Probability of severe thunderstorms* within 25 miles of a point:
Equal to or greater than 60%
Risk
Level
Severe Thunderstorms
Lightning
Flooding
Fire Weather
Fog
Non - Thunderstorm Winds
Excessive Heat
Snow and Sleet
Ice Accumulation
Frost and Freeze
Excessive Cold
Coastal Flooding
Swim Risk
High Surf
Marine Hazard