Alister Alders: your new Saltwire Network weather report

We have been hearing the term ‘atmospheric river’ a lot over the past few weeks.

An atmospheric river brought deadly flooding, mudslides and road washouts to parts of southern B.C. An atmospheric river was also responsible for the significant rainfall that washed out roads and cut off some communities in Atlantic Canada last week.

But the term is new to most of us, and many have been asking me just what exactly is an atmospheric river?

Atmospheric rivers are long, narrow bands in the atmosphere that carry water vapor from locations like the tropics and subtropics into the midlatitudes.

They can be thought of “like rivers in the sky,” according to the National Oceanic and Atmospheric Administration.

NOAA adds atmospheric rivers can carry an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River.

According to NASA, there are about 11 atmospheric rivers present on earth at any time. Most are weak and provide a normal, beneficial amount of rain or snowfall. Atlantic Canada has experienced past weather events where moisture from the tropics fueled our weather systems.

However, some atmospheric rivers are powerful enough to cause extreme rainfall and strong winds, especially if they stall over a region.

Terrain also plays a role — mountains can enhance the rain or snow associated with atmospheric rivers.

Some may be wondering if climate change is going to have an impact in the frequency and severity of atmospheric rivers. A 2018 study led by researchers from NASA’S Jet Propulsion Laboratory found atmospheric rivers will become 10 per cent less frequent by the end of this century, but 25 per cent longer and wider, and they could become more intense.

Warmer atmospheric and ocean temperatures could allow atmospheric rivers to hold more moisture, which in turn could lead to more severe weather events.

I want to answer your weather questions! You can email them to me: weather@saltwire.com or use the hashtag #Askallister on social media.