Alberta Clippers and Prairie Schooners

#2611 "Winter Tree Tunnel" 
20x16 inches oils gallery wrapped
40 centimetres of Singleton snow
after a Prairie Schooner

In the past few Science Stories, we have established how lee cyclogenesis is linked to conserving the spin of a figure skater. We briefly investigated how the temperatures of the equatorial Pacific Ocean influences the location of the jet stream and why there were more Alberta Clippers in a LaNiña year like 2022.  These storms are an essential part of the global balance. Weather results from an imbalance in one or all of the basic components of the energy cycle: heat, cold, water, electrical charge and there are certainly other forms of energy to juggle and try to distribute judiciously.

In advance of a low pressure area (a storm), warm and moist air is moved northward. In the wake of that low, cold and relatively dry air is moved southward. The pressure pattern that results is really a wave in the atmosphere … the downstream ridge is separated from the upstream trough by the storm and the next upstream ridge. Together the atmospheric wave which is the storm attempts to keep the earth in balance. The wavelength is from one ridge to the next. 

The impact of an atmospheric wave is related to its size - just like waves on the ocean. Winter weather can also have more impact than summer. Although severe summer convection can be extremely exciting and dangerous, the impacts on society and the economy are often more important with the winds, temperature and precipitation of “ordinary”, everyday winter weather. Such is the case with Alberta Clippers and this is where we have been headed all along. 

Genesis Stage of an Alberta Clipper

The impacts of Alberta clippers also vary with the size of the storm. The scale of an individual clipper varies with the strength of the jet stream crossing the Rockies, the size and intensity of the lee cyclogenesis and the temperature contrast across the frontal zone. There are other factors for sure but let’s keep this simple. We will even start with some history. 

The name “Alberta Clipper” was coined in the late 1960s by Rheinhart Harms, a meteorologist at the U.S. National Weather Service Office in Milwaukee, Wisconsin. Rheinhart witnessed the rapid speed of these snow storms as they crossed the Prairies. I undoubtedly heard the term when I entered the world of meteorology in the 1970s. It would take until the 1990s for that phrase to enter the scientific literature.

Alberta clippers are frequent winter forecast challenges and can occur every few days in rapid succession just as they did in February 2022. The first clue is to witness the jet stream crossing the Alberta Rockies nearly perpendicularly. A chinook arch is typical when those westerly winds charge down the lee slopes to dig the lee the trough. The chinook brings relatively warm weather approaching 10 °C even in the middle of winter. Lee cyclogenesis follows as the energy of the jet stream and the “figure skater” is transformed into a low pressure area and wave that then ripples along with the jet stream.

The clippers approach fast. Snowfall amounts with these systems tend to be small with only 3 to 8 cm being typical. The lack of moisture and short duration keep the accumulation well below the warning impact threshold of 15 cm per 12 hours. 

The wind and the wind chills can be more important for the typical clipper. Temperatures typically drop 15 to 20 Celsius degrees in just a few hours behind the clipper cold front. Blowing and drifting of even the small amounts of snow can make travel treacherous in whiteout conditions. These situations can approach warning criteria. 

Alberta Clipper crossing the Great Lakes

As the clipper cross the Great Lakes, the dynamics of the storm can change. When combined, the five great lakes represent a huge source of heat and moisture as well as lower friction. The inland seas also provide the opportunity for the generation of snowsqualls when those strong, cold Arctic winds blow over the open waters of the lakes. Snowsqualls bring significant snow accumulations onshore as well as extensive whiteout conditions  – that is another story that we call lake-effect snow. Suffice it to say that Alberta Clippers can take on a different and potentially dangerous character when they cross the Great Lakes to affect Ontario, Quebec and the north-eastern United States. 

I spent a large part of my meteorological career very concerned about how Alberta Clippers would influence my forecast regions. In the early 1990’s I was looking for a simple way to differentiate between the impact and the threat of each of these storms emerging every few days from the Rockies of Alberta. The larger the storm, the more probable that warning criteria would be breached and this could all be summarized by the speed of the clipper. 

I started using the phrase “Prairie Schooner” to describe these larger storms that would produce warning criteria weather. Clippers were built for speed but for me, schooners delivered the goods! Often, clippers were rebuilt into schooners as they crossed the “Great Lakes Aggregate” as we described the combined effects of those inland seas. As I recall, clippers would sail along at about 30 knots but schooners moved slower at only 20 knots. I kept careful histories of the track and speed of these storms emerging from Alberta. Any clipper that was slowing down to 20 knots was doing so for good meteorological reasons and I would get ready to hoist the warnings and rebrand that weather event as a Prairie Schooner. 

The science of the storm was all embedded in the speed of the system. Temperature contrast, precipitation rate and duration, latent heat … there is a long list that goes into determining the size of the storm. And size determines the wavelength which governs the speed. 

In 2005 my meteorological career took me to COMET (https://www.comet.ucar.edu/) in Boulder, Colorado. I recall that the acronym stands for something like “Cooperative Program for Operational Meteorology, Education and Training” but no one in that office even uses that anymore. Some of these Blogs were turned into Training Modules by the professional team of instructional designers, scientists, graphic artists, multimedia developers, and information technologists of COMET, UCAR and NOAA’s National Weather Service. After seven years in Boulder, I gradually retired during the course of the last decade – but not totally. 

The distinction between Alberta Clippers and Prairie Schooners has possibly been forgotten or perhaps I did not explain the concepts well enough. This Blog was intended to mend the sails on that ship – the concepts are simple, effective and fun at the same time. 

Next week we will explain why small Alberta Clippers are faster than Prairie Schooners. It will all make sense with the assistance of meteorologist Carl-Gustaf Arvid Rossby and our friend the figure skater as we conserve spin also known as angular momentum. 

Warmest regards and keep your paddle in the water, be safe,

Phil the Forecaster Chadwick