Severe Wind
Description:
Windstorms are defined as a storm with high winds or violent gusts. Downslope winds in Colorado are
referred to as Chinook winds, after the Native American tribe of the Pacific Northwest. Chinook winds
are warm dry wind that descends from the eastern slopes of the Rocky Mountains, causing a rapid rise
in temperature. Sometimes these winds move at considerable force.
Two main causes of high winds in Colorado during the cold season are the air pressure difference
between strong low pressure and cold high pressure systems, and Chinook winds developing along the
Front Range and mountains in the eastern half of the state. A strong low pressure system in Colorado,
coupled with a high pressure system to the west, can send a cold wind, called a Bora, through the
western part of the state and down the slopes of the eastern mountains. The result can be a cascade of
high winds from the west or northwest into the adjacent plains at speeds over 100 mph. The damage
caused by this event is usually much more widespread than that caused by a severe thunderstorm in the
warm season.
Jet stream winds over Colorado are much stronger in the winter than in the warm season, because of
the big difference in temperature from north to south across North America. Very swift west winds,
under certain conditions, can bring warm, dry Chinook winds plowing down the slopes of the eastern
mountains. These winds can also exceed 100 mph in extreme cases, again bringing the potential for
widespread damage.
Windstorm severity is difficult to quantify. Wind, by itself, has not historically caused high insured dollar
losses. That being said, windstorms in Colorado can blow shingles off roofs, knock down trees, down
power lines, and overturn large semi-trailers. Wind may also damage antennas, communication towers,
windows, siding of buildings, and vehicles. If the wind is strong enough and coming from the right
direction, older or dilapidated structures or more vulnerable construction such as car ports may
collapse. Building types, shapes, or additions that catch the wind, such as overhangs, canopies, and
eaves, also tend to be affected by high wind. A major danger from high winds is flying debris. Cold
strong winds can also bring dangerously low wind chill values, prompting a wind chill advisory or wind
chill warning.
History:
Severe wind storms pose a significant risk to life and property in the region by creating conditions that
disrupt essential systems such as public utilities, telecommunications, and transportation routes. Thus,
high winds can have destructive impacts, especially to trees, power lines, and utility services. In the
Front Range, including Denver, windstorms can occur at any time of year. Windstorms are one of
Colorado’s costliest hazards. Over the last 60 years, wind events have caused a reported $367 million in
property and crop damage. Deaths and injuries are also a result of wind events in the state with 21 and
406 respectively between 1950 and 2010. Counties with the highest number of significant wind events
tend to be located along the Front Range or northeast part of the state.
Sources:
National Climatic Data Center (NCDC)
National Weather Service
Colorado Hazard Identification and Risk Analysis
Rocky Mountain Insurance Information Association