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Snow in New Orleans? That's like a blizzard in Coffs Harbour

Anthony Sharwood
Image: New Orleans looking a lot more like New York City in midwinter after this week's rare heavy snowfall. Source: @smichaelmorrow on Instagram
Image: New Orleans looking a lot more like New York City in midwinter after this week's rare heavy snowfall. Source: @smichaelmorrow on Instagram

Many Australians have been wondering how it was possible for snow to fall in subtropical parts of America like Florida, southern Mississippi and New Orleans on Louisiana’s Gulf of Mexico coastline. This story explains what happened.

The images this week of New Orleans have been especially stunning, with up to 30cm of snow lending an almost magical appearance to the signature Spanish, French and Creole architecture of the city’s famous Bourbon Street district.

Image: Ute-skiing in New Orleans. A new thing for everybody's tourism bucket list. Source: @paulmorsephoto on Instagram.

To put that in perspective, New Orleans is on the same latitude (or at least the northern hemisphere equivalent) as Coffs Harbour on the New South Wales Mid North Coast. As most Aussie know, Coffs Harbour is the home of the Big Banana and would never, ever see snow.

So how did it happen in New Orleans?

America's weather is different to Australia's in several key ways, most of them related to geography.

For example, the prevalence of tornadoes in America is due to a combination of huge mountains (the Rockies) to the west of "tornado alley", the heat of the great plains, and the moisture feed from the Gulf of Mexico. Australia has no equivalent.

With regard to cold snaps like this week, the USA is connected to the polar region by land. This is a crucial difference between the continents of North America and Australia.

  • By contrast, Australia is separated from Antarctica by the vast Southern Ocean. This famously ferocious water body might not seem like a warm place in winter, but the ocean still retains enough heat for the air above it to warm up a lot more as it moves into the mid-latitudes.
  • When a northern hemisphere polar outbreak occurs over North America and winds push weather systems south, frigid polar air can easily travel across Canada and into the USA as far as the Gulf of Mexico coast without warming up too much.
  • Land, not water, lies between subtropical latitudes and the poles in North America. That, in a nutshell, is why places like New Orleans will occasionally see snow.

However, this particular event was still remarkable for the sheer quantity of snow that fell. Usually, northern parts of states like Mississippi, Louisiana, Texas and Alabama see heavier snowfalls in systems like this.

Image: Snow clearly visible along America's Gulf of Mexico coastline with New Orleans located on the tip of land in the centre of the image. Source: NASA Worldview.

But as the map above shows, snow was concentrated along the Gulf of Mexico coastline in the south of those states, while there was no snow in towns like Kosciusko Mississippi (a central Mississippi town named after the same guy as Australia’s highest mountain but spelled without the z, which also happens to be the birthplace of Oprah Winfrey!)

The story with this event is that warm, moist air along the Gulf coast interacted with the frigid Arctic air, creating localised heavy coastal precipitation which in this case fell as snow.

Image: That's definitely close to a foot (approx 30cm) of snow on those New Orleans cars. Source: Hailey McCaskell @hailzzzyea on Instagram.

Meanwhile after New Orleans dipped well below –10°C this week, it is forecast to warm dramatically to 21°C next Wednesday with a minimum of 17°C, with showers of the distinctly unfrozen variety. That’s close to, or even a little above, the January average.

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