Friday night's cataclysmic quad-state tornado outbreak reminds us of the vulnerability of our country to tornadoes, and how the threat of these destructive storms looms menacingly real over the eastern two-thirds of the United States during any season of the year.

We're not alone; tornadoes happen in other parts of the world too, but by sheer numbers (about 1,200 on average per year) the U.S. has the dubious honor of residing at the top of the list.

The broad expanse of our country of course plays a significant role - more area equals more opportunity, but it is our geography and juxtaposition on the continent that provides the fuel for increased risk. What makes us, as in the U.S., so special?

Tornadoes tend to form where cold, dry air clashes with warm, humid air. These contrasts are maximized over the mid-latitudes, where the majority of Earth's tornadoes occur. A good-sized portion of our Lower 48 sits smack-dab in the center of that not-so sweet ordinate zone. Add in the proximity to the warm waters of the Gulf of Mexico, mid-level dry air sloping down from the Rockies, plus unfettered access to cold air from northern environs (particularly notable due to the flat topography of our Great Plains), and you bring together a nearly perfect set of otherwise harmless ingredients that can suddenly become a volatile mix of atmospheric terror.

According to the National Weather Service's Storm Prediction Center Online Tornado FAQ by Roger Edwards, there are more tornadoes in the U.S. than any other part of the world, though the author notes the data outside of the U.S. is problematic to assess since it's comparatively sparse and collected differently by each country.

Edwards wrote "a blend of recorded and inferential study indicates that the U.S. remains tops in tornado production, with secondary tornado-prone areas including the Canadian Prairie Provinces, Bangladesh, Britain, northeastern Mexico, northern Argentina and southern Brazil, and portions of southwestern Russia."

Further underscoring the worldwide risk, the National Severe Storms Laboratory of the National Oceanic and Atmospheric Administration notes that tornadoes occur in most of the world's continents, from North and South America, to Africa and Australia, to Europe and Asia, with only Arctic regions exempt.

In North America outside of the U.S., it's illustrative to see that the most vulnerable areas for tornadoes occur relatively close to the northern border of Mexico and southern border of Canada.

In Mexico, they concentrate with greatest frequency over a relatively small part of its Northeast region, where geography and topography most closely match that of the U.S. Southern Plains. Along with similar proximity to the Gulf of Mexico, effects from dynamic fronts moving east of the mountains powered by colder air surging southward from the Great Plains bring a focus of tornado risk, where violent and deadly tornadoes can occur, just as in the U.S., as evidenced by one that hit the border town of Ciudad Acuña in 2015.

To the north, Canada has a much more expansive territory of tornado risk, running across southern Alberta to Quebec. The geographical similarities of southern Canada to the U.S. Great Plains and Upper Midwest shape their contours of tornado prevalence.

The Northern Tornadoes Project, a major collaborative effort in Canada's tornado data tracking and research, offers a telling look at the country's recent tornado history. Their tracking Dashboard reveals a total of a couple hundred tornadoes over the past 5 years for all Provinces, which is about a quarter of what the U.S. sees in an average year. Still, Canada places high in the world with its share of tornadoes, though those are rarely violent one, rated at EF4 or EF5 on the 0 to 5 scale for intensity. In fact. the first recorded top of the scale tornado was in 2007 near Winnipeg Manitoba as detailed in "Environment and Climate Change Canada." By comparison, the U.S. averages several EF4 or stronger tornadoes every year, though EF5s are rare.

Within the United States, the boundaries of highest risk for tornadoes has traditionally been east of the Rockies, in the Plains, Midwest and South, but there is an expanding secondary threat area evident over the Southeast northward through the Mid-Atlantic. Recent trends are showing that part of the U.S. as having increasing susceptibility for impacts from tornadoes.

No matter where they occur, though, it's vital for each of us to understand the risk where we live, to know where and how to get alerts, and most importantly to have a plan on how to stay as safe as possible when this, the worst of weather, threatens.