The "Waterspout Hazard Map" depicts the local threat of waterspouts for specified marine areas.  It is largely based on the likelihood that waterspouts will occur, combined with the anticipated strength of the most intense waterspout.   

Waterspout Threat Level

Threat Level Descriptions

Extreme

"An Extreme Threat to Life and Property Aboard Small Marine Craft from Waterspouts."

Within 12 miles of a marine location, an extreme likelihood (36% or greater) of a waterspout.  See description below.  

High

"A High Threat to Life and Property Aboard Small Marine Craft from Waterspouts."

Within 12 miles of a marine location, a high likelihood (26% to 35% probability) of a waterspout.  See description below.  

Moderate

"A Moderate Threat to Life and Property Aboard Small Marine Craft from Waterspouts."

Within 12 miles of a marine location, a moderate likelihood (16% to 25% probability) of a waterspout.  See description below.  

Low

"A Low Threat to Life and Property Aboard Small Marine Craft from Waterspouts."

Within 12 miles of a marine location, a low likelihood (6% to 15% probability) of a waterspout.  See description below.  

Very Low
" A Very Low Threat to Life and Property Aboard Small Marine Craft from Waterspouts."

Within 12 miles of a marine location, a very low likelihood (2% to 5% probability) of a waterspout.  See description below.  

Non-Threatening
" No Discernable Threat to Life and Property Aboard Marine Vessels from Waterspouts."

Within 12 miles of a marine location, environmental conditions do not support waterspouts.   

Note: Waterspouts form over (or move across) the nearshore waters or open waters of Lake Michigan and become a hazard for small craft.  They are treated as tornadoes over water.  There are two type of waterspouts: "fair weather" and "tornadic".  Fair weather waterspouts are usually weaker, move slowly, and may not be associated with a thunderstorm.  Tornadic waterspouts form within developing thunderstorms, or severe thunderstorms, and move much faster while being more intense.  

Waterspout - A fair weather waterspout of F0 tornado intensity (73 mph or less; 63 knots or less). 

Tornadic Waterspout - A waterspout associated with a developing thunderstorm, or severe thunderstorm, of F0 to F5 intensity.

Fujita Scale
The Fujita scale (F-scale) uses actual damage to determine a tornado’s wind speed.
F0 Gale Tornado 
40-72 mph
Some damage to chimneys. Tree branches broken off. Shallow rooted trees uprooted.
F1 Moderate Tornado
73-112 mph 
Peels surface off roofs. Mobile homes overturned. Moving autos pushed off roads. 
F2 Significant Tornado
113-157 mph
Considerable damage. Roofs torn off frame houses. Large trees snapped or uprooted. Light-object missiles generated.
F3 Severe Tornado
158-206 mph
Severe damage. Roofs and some walls torn off well constructed homes. Trains overturned. Most trees in forests uprooted. Heavy cars lifted off ground and thrown. 
F4 Devastating Tornado
207-260 mph 
Well-constructed houses leveled. Structures with weak foundations blown off some distance. Cars thrown and large missiles generated. 
F5 Incredible Tornado
261-318 mph
Strong frame houses lifted off foundations and disintegrated. Automobile-sized missiles fly through the air in excess of 100 mph. Trees debarked.

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