These strange-looking images of rolled snow above are called “snow rollers” and yes, they are formed naturally! A rare occurrence, snow rollers only form during limiting conditions.
The National Geographic describes this weather phenomena as the weather equivalent of tumbleweeds. This hints that wind is what pushes the snow into these rolls. But why doesn’t this happen more often? Snow rollers only form when weather conditions have “the right mixture of moisture, snow, wind, and temperature.” The National Geographic further describes these conditions as there having to be a layer of ice with a layer of light snow on top and it must be wet enough for the snow to stick to itself. Also, winds must be around 30 mph.
Not only can snow rollers be formed by wind but, in some cases they form, by rolling downhill. As a snow rollers accumulate snow, it leaves a track behind, showing where they’ve traveled. The formation of a snow roller is very similar to the way snowmen are made. Some have compared snow rollers to the giant snowballs that roll downhill in a cartoon. They have been referred to as “snow donuts” or “snow bails”.
Some snow rollers form with a hollow center and some are packed in a swirl, similar to a cinnamon bun! Here are some pictures of the two different forms.
(A hollow snow roller.)
(A packed snow roller.)
To learn about documented snow roller events, The National Weather Service archives a few articles regarding the phenomenon.These articles include the event of December 2008 in eastern Washington and the event of March 2009 in Idaho. Some pictures the National Weather Service posted of these snow rollers can be seen below.
(Picture from the December 2008 event.)
(Picture from the March 2009 event.)
Snow rollers are just nature's anomaly. They are never dangerous, just a rare but pretty weather phenomenon.
Credit: The National Geographic and The National Weather Service
© 2019 Weather Forecaster Brittany Connelly
With the single digit high temperatures and the below freezing lows now behind us, let’s see how those bone-chilling temperatures helped with ice coverage on the Great Lakes. As shown in the graphic above, the total ice coverage on the Great Lakes is roughly 66.1%. This time last year the total lake ice coverage was about 42.2%. The roughly 24% difference from 2018 to 2019 can be attributed to the above-average temperatures in December and the rapid turn-around, (i.e., 80 degree Fahrenheit temperature change), that was experienced once the polar vortex impacted the Great Lakes region.
Believe it or not, ice-coverage is vital to the Great Lakes watershed and various ecosystems therein. Ice coverage acts as an evaporation shield to help keep the lake water from being evaporated into the atmosphere. This also reduces the amount of moisture in the atmosphere which helps to provide a source for extra low-level moisture which can often help fuel winter storms. With less ice coverage, this will produce more evaporation which, in turn, will cause more precipitation. As previously mentioned, ice on the Great Lakes acts as an “evaporation seal”—diminishing the amount of moisture being brought up to the atmosphere. The availability of more moisture in the atmosphere is what helps build winter storms, which feed off of moisture from the Great Lakes. The growing percentage of ice also helps with the region’s albedo. Albedo is the ratio of incoming radiation that is absorbed and reflected. Ice and snow, which reflects incoming solar radiation, have a high albedo due to their high reflectivity. Whereas black pavement for instance, has a low albedo to due to its lack of reflectivity and high absorption of solar radiation. In addition to albedo, ice on the Great Lakes helps regulate the ecosystem. Plankton, for instance, rely on ice to protect their populations because when ice forms over their habitat, they become more resilient and protected from warmer temperatures. Harmful algal blooms that occur in Lake Erie every year are regulated by ice because of the bacteria that causes the blooms, are killed off.
A year with low Great Lakes sea ice and a year with high Great Lakes sea ice are polar opposite in comparison. This year for instance, as of right now, we are above the 55% long-term average for lake ice. For more ice data and historical ice data visit GLERL’s website here.
To learn more about other winter weather topics, click here
©2019 Weather Forecaster Alec Kownacki
The first thought most people have when they think of winter is one thing: snow. Winters are known mostly for the white, frozen precipitation that occurs when all levels of the atmosphere (and the surface) are at the freezing mark (32 Degrees FahreNheit/0 Degrees Celsius). What happens, though, when not all levels of the troposphere, the lowest region of the atmosphere where all of our weather occurs, are below freezing? Let’s explore that idea.
The troposphere is somewhat complex. It is roughly the first 10km of the atmosphere, and is often measured in terms of pressure (millibars). When precipitation occurs, it falls through various levels of the atmosphere, often travelling through different temperatures that alter the formation of whatever precipitation is falling. When the precipitation is rain that means the temperature is above the freezing mark through at least the first couple hundred millibars of the atmosphere. However, it is often not the case that all levels of the atmosphere are above freezing, especially over much of the continental U.S. In the winter, the atmosphere goes through dramatic changes in temperature; there are different air masses that can occupy different levels. When it comes to sleet, there is likely a shallow layer of warm air in between two layers of sub-freezing temperatures. As ice crystals fall into the shallow warm layer, they melt, but only enough to melt the outer layer of the ice. As they pass through the colder layer nearest to the ground, water droplets freeze on an ice nucleus, the remaining center of the ice crystal, thereby creating sleet.
Freezing rain is a different story. Freezing rain occurs when a much deeper warm, layer is wedged above a shallow cold layer near the ground. The warm layer melts ice crystals to the point where they are rain droplets. When they pass through the shallow cold layer near the ground, they freeze on contact with any sub-freezing surface on the ground. This phenomenon occurs closer to the warm front of a cyclonic low pressure system than sleet, as the warm air is able to penetrate deeper into the atmosphere.
Its freezing rain and sleet, not snow, that often cause the most hazards to the general population. Both types of precipitation are known for the slick effect they have on roadways. They can cause black ice, or icy spots on roadways or sidewalks that are hard to spot due to their clear color. This issue is even more of a problem on elevated surfaces such as bridges and overpasses where both sides are surrounded by open air, allowing surfaces to freeze more rapidly.
The Occupational Safety and Health Administration (OSHA) also advises people to be more careful when icy weather hits. Their website lists two steps people can take to greatly reduce their risk of a life-threatening fall: wear rubber over-shoes with good treads and take slower, smaller steps.
The U.S. Department of Transportation has recorded, based on a ten-year average, over 1,800 deaths annually related to snow and icy roads. Drive safely, minimize travel in the dead of winter, and be smart and we can keep that statistic from growing even more.
To learn more about other winter weather topics, click here!
© 2019 Weather Forecaster Jacob Dolinger