National Weather Service United States Department of Commerce
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Experimental Enhanced Hazardous Weather Outlook


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Severe Thunderstorm Risk
24 Hr. Hazards
Day 1
Severe Thunderstorm Arrival Tool






Tornado






Hail






Thunderstorm Wind Gust






Severe Thunderstorms
Lightning
Flooding
Fire Weather
Grassland Fire Weather Index
Fog
Non Thunderstorm Winds
Excessive Heat
Snow & Sleet
Ice Accumulation
Frost & Freeze
Excessive Cold
Severe Thunderstorm Arrival Tool Legend         Severe Thunderstorm Safety Tips
 
Risk Level
Definition
None
Severe thunderstorms are not expected today or tonight.
Later Today or Tonight
Severe thunderstorms will be possible later today or tonight .
Next 6 hours
Severe thunderstorms will be possible in the next 6 hours.
Next 3 hours
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.
Tornado Risk Legend         Tornado Safety Tips
 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.
Hail Risk Legend         Severe Thunderstorm Safety Tips
 
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%
Thunderstorm Wind Gust Risk Legend         Severe Thunderstorm Safety Tips
 
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
Probability 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%
Severe Thunderstorm Legend         Severe Thunderstorm Safety Tips
 
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%
Lightning Legend         Lightning Safety Tips
 
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.
Flooding Legend         Flooding Safety Tips
 
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 streams.
or
Major river flooding.
Fire Weather Legend         Wildfire Weather Safety Tips
 
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.
Grassland Fire Weather Legend         Wildfire Weather Safety Tips         Grassland Fire Danger Index
 
Risk Level
Definition
Low-Moderate
Favorable to marginal weather conditions with moderate to high moisture content of grasses and other dry organic material on the ground, indicating that the probability of a fast moving fire is low to a slight potential. Outdoor burning under these conditions can usually be performed with reasonable safety precautions, but should be monitored. Difficulty of fire suppression: Headfire can generally be stopped by road and tracks in low conditions and with water under moderate conditions.
High
Unfavorable weather conditions and low moisture content of grasses and other dry organic material on the ground, indicating that there is a high potential for fire to spread. Outdoor burning should be restricted to early morning or evening hours when wind speeds are usually lower and the relative humidity is higher. Burning is still favorable for well-planned burns by experienced land management personnel. Difficulty of fire suppression: Headfire attack generally successful with water.
Very High
Very poor weather conditions and very low moisture content of grasses and other dry organic material on the ground, indicating that dangerous burning conditions exist. Fires will spread rapidly and show erratic behavior. Outdoor burning is not recommended other than for experienced land management personnel. Difficulty of fire suppression: Direct headfire attack will become increasingly difficult. Spot fires are more likely.
Extreme (GFDI 50-75)
Extreme weather conditions and very low moisture content of grasses and other dry organic material on the ground, indicating that critical burning conditions exist. All fires have the potential to become large and spread quickly and become erratic with extreme fire behavioral characteristics. Difficulty of fire suppression: Direct attack on a headfire will generally fail. Back burn from a secure good line with adequate manpower and equipment. Flanks may become more difficult to control in shifting or erratic winds. Spot fires are likely.
Extreme (GFDI > 75)
Extreme grassland fire weather conditions that are rarely experienced in our area. Very high winds and low humidity with very dry cured grasses. Any fire that starts will spread rapidly and almost impossible to control. Fire suppression: Direct attack will likely fail, especially in heavy fuel loads.
The Grassland Fire Danger Index (GFDI) is a numerical value that indicates the potential for grassland fires to experience extreme fire behavior. The GFDI combines the curing (%), temperature (deg C), relative humidity (%), and the average of the sustained wind and wind gust speed (km/hr).
Fog Legend         Fog Safety Tips
 
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.
Non Thunderstorm Wind Legend         Wind Safety Tips     Boating Safety Tips
 
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.
Excessive Heat Legend         Excessive Heat Safety Tips
 
Risk Level
Definition
None
Maximum Apparent Temperature < 95
Limited
Maximum Apparent Temperature 95 to 104
Elevated

Maximum Apparent Temperature 105 to 109
OR
Maximum Apparent Temperature greater than or equal to 100 for 4 consecutive days.

Significant

Maximum Apparent Temperature 110 to 114
OR
Maximum Apparent Temperature greater than or equal to 105 for 4 consecutive days.

Extreme
Maximum Apparent Temperature greater than or equal to 115
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.
Snow and Sleet Legend         Winter Weather Safety Tips
 
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 5.9 inches of accumulation expected.
Significant
Snow and/or sleet with 6 to 11.9 inches of accumulation expected.
Extreme
Snow and/or sleet with greater than or equal to 12 inches of accumulation expected.
Ice Accumulation Legend         Winter Weather Safety Tips
 
Risk Level
Definition
None
No freezing rain or drizzle.
Limited
Very light freezing rain or drizzle with up to a thin glaze, OR Freezing Fog.
Elevated
Freezing rain or drizzle with accumulation less than 1/4 inch.
Significant
Freezing rain with accumulation of 1/4 inch to less than 1 inch.
Extreme
Freezing rain with accumulation of greater than or equal to 1 inch.
Frost and Freeze Legend
 
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 28 degrees F) during the growing season with catastrophic damage to unprotected vegetation.
Excessive Cold Legend         Extreme Cold Safety Tips
 
Risk Level
Definition
None
Minimum apparent temperature greater than or equal to 10 degrees F.
Limited
Minimum apparent temperature -9 to 9 deg F.
Elevated
Minimum apparent temperature -10 to -24 deg. F
Significant
Minimum apparent temperature -25 to -34 deg. F.
Extreme
Minimum apparent temperature less than or equal to -35 degrees F
Note:
Apparent Temperature is defined as:
  Wind Chill Temperature during the cold season.
  Heat Index Temperature during the warm season.

The Experimental Enhanced Hazardous Weather Outlook is an experimental product that will be posted to this page for evaluation. We encourage your comments or suggestions for improvements using the electronic survey provided. Your feedback will help us determine product utility, if modifications are needed, and whether the product should become part of our operational suite. | Product Description Document

The Experimental Enhanced Hazardous Weather Outlook is a decision support service that supports preparedness and response efforts prior to and during hazardous weather.  This service provides decision makers with convenient access to potential weather hazard information by graphically depicting the risk of weather hazards out through seven days.