ROCHESTER, NY (WROC) – Anyone looking at infrared satellite images over the last few days was likely to notice a curious feature. A giant “cloud” engulfed much of Canada, seeping southward into the United States. Here’s the catch: skies were largely clear. So what gives?

Satellite Imagery

One of the primary ways we look at clouds is using visible satellite imagery, but it only takes us so far. Satellites use light to help produce the images you see us often use on TV to show you cloud cover over an area. Once the sun goes down, we lose that daylight needed to be able to see those clouds. When we want to see clouds at night, we turn to a different source known as infrared imagery.

Infrared Imagery

Instead of using light to detect clouds, infrared uses radiation coming off of cloud tops to detect their temperatures, which are displayed using a color scale. The taller the clouds stretch into the sky, the colder the tops are. Temperatures around -20 degrees will show up as blue on infrared imagery, and are typically the temperature that cloud tops can be, which is why you see nearly the entire country of Canada covered in what appears to be a giant cloud.

Clouds that are present in the atmosphere no matter what level they fall at are typically colder than what temperatures are at the surface. This is why we’re able to separate them from everything else; the exception here being when temperatures get very, very cold in extremely cold places such as Canada.

So all in all, the air over Canada is just so cold that it’s picking it up as if they were cold cloud tops. There’s no giant, menacing cloud taking over the entirety of Canada. We’ll save that for the movies.

Notice the real clouds have a much more fluid movement to them with time in comparison. You can also see in the loop above the initial presence of the cold temperatures over the surface of Canada as the blue and purple colors. As temperatures gradually warmed throughout the course of the day the blue and purple colors retreated a bit to the north. Pretty neat, huh?

Where is this cold going?

The next several days will feature a decent shot of this cold air, and it’s not just us either that will be feeling the chill. The extent of this cold air over Canada is stretching over Montana, North and South Dakota, Minnesota, and as far south as Kansas, Oklahoma and Texas.

By Friday most of the upper half of the U.S. will be engulfed in this frigid air with actual temperatures in Montana around 20 below zero. Now just imagine what the wind chills will be there. Here in Rochester, we’ll be looking at a single digit morning with below zero wind chills. We won’t be quite as cold as folks up north, but we’ll definitely be bundling up.

Another way we can see where parcels, or chunks of this arctic air are coming from way up in the atmosphere is using the HYSPLIT model courtesy of NOAA. In the image below you can see the trajectory of air over just the past 48 hours is coming right from the heart of where the cold is now.


Plus, the coming days will feature even more of this cold air for Western New York including into the weekend. Get the latest on the local forecast HERE.

~Meteorologist Christine Gregory