Weather Lessons for Everyone from the Cold Conveyor Belt Wizard

#0505 "Ominous

The meteorological journey to get to this point started nine months ago. Some of the science steps were absolutely essential to justify the observations we are about to assert. Some strides were more for background, nice to know information. But where are we after this gestation period of these meteorological concepts?

The cold conveyor belt (CCB blue arrow) holds lessons that the can teach everyone. We have already established how the cold conveyor belt can control the phase of the precipitation in some surprising ways. The cold conveyor belt can also reveal the characteristics of the entire mid-latitude storm through the Conveyor Belt Conceptual Model and the Weather Machine. Here is how that wizard works.

The premise is that a warm conveyor belt and storm is approaching your region. You are located within or under the Cold Conveyor Belt. This is what you observe:

The surface wind (the cold conveyor belt as measured in the earth frame of reference) has a westerly component. I used the large green arrow in the graphic to depict the surface wind result of the vector addition. This is the typical mid latitude storm that is moving steadily with the jet stream across the landscape. Cirrostratus arrives on the western horizon but the surface winds stay out of the southwest. The system crosses the area without hesitation. The precipitation, if there is any, comes and goes quickly. Stronger westerly winds signal the passage of the cold front and the system. The speed of the system relative to the earth (purple arrow) is faster than the atmospheric frame winds in the cold conveyor belt (blue arrow). The vector addition of these winds leaves a surface wind with a westerly component - the green arrow in the graphic.

The surface wind (the cold conveyor belt measured in the earth frame of reference) is calm. The mid latitude storm that is moving a bit slower across the landscape. Cirrostratus arrives on the western horizon and the surface winds gradually decrease in speed. The cirrus is slow to thicken up into altostratus.  The precipitation, if there is any, will arrive slower and last a bit longer. The calm winds will shift to the west with the passage of the cold front and the system. The speed of the system relative to the earth is about equal to the winds in the cold conveyor belt so that the vector addition of these purple and blue arrow winds balances out to provide the "calm before the storm".

The surface wind (the cold conveyor belt measured in the earth frame of reference) has an easterly component. The mid latitude storm is moving slowly across the landscape. Cirrostratus arrives on the western horizon and the surface winds gradually increase from the east. The cirrus is really slow to thicken up into altostratus.  The precipitation, if there is any, will arrive very slowly and last much longer. The easterly winds will shift to the west when the cold front arrives - but the storm is likely to last a while. The speed of the system relative to the earth (purple arrow) is slower than the winds in the cold conveyor belt (blue arrow) so that the vector addition of these winds generates surface winds out of the east – which are never good for man or beast.

In the previous three examples only the speed of the system was adjusted to arrive at the different evaluations of the storm. The strength of the wind in the conveyor belt system can also be adjusted. For example as the storm intensifies, the conveyor belt winds in the weather machine will also increase with speed. The effects of this can be evaluated by observing the results at the surface within the cold conveyor belt.

A fast moving system that still produces an easterly cold conveyor belt wind at the surface is a very strong storm indeed. It may cross the region quickly but the strength of the circulations will make it a force to be reckoned with. In general, the stronger the easterly surface winds in the cold conveyor belt, the more likely that the storm will last longer and probably be more intense as well.

By observing the surface wind in the cold conveyor belt portion of the storm, a keen observer can estimate how fast the system will cross their region as well as the intensity of the storm. If the observers also remember how to read the lines in the sky and have their right fingers handy, then they might also deduce which portion of the warm conveyor belt is likely to cross their position.

A Closer Look at Lines in the Sky 

Observing Warm Conveyor Belts and Forecasting Your Own Weather 

It took almost nine months to carefully establish the linkages between observing the surface wind to really understanding the weather. The pioneers had it figured out by observational trial and error. Their crops and lives depended on it. They recorded their findings in rhymes. Their weather poems and ditties would fill several books.

Personally, my meteorological training was much more book based. My university background was theoretical physics with an emphasis on nuclear. Back in 1976 I needed to pass a crash course in meteorology in order to stay employed with the then Atmospheric Environment Service of Canada. Fine academic textbooks on meteorology  (James R. Holton comes to mind) did not prepare me for the real world though. Happily, my plein air painting and the arrival of remote sensing did. I spent all of my career trying to really understand the weather from a more personal and natural perspective more akin to that of the pioneers.

Environment-based education is a current movement trying to reconnect students with the natural world. That is the unstated goal of my Art and Science Blog. The timing to present this material during COVID-19 was intentional. Observations of the natural world and the Cold Conveyor Belt in this example, can teach a lot. Technology and tablets may be glitzy but nature is real. Immersing yourself in the environment along with nature is where you can really begin to learn and to live. I would like to suggest some reading. The Last Child in the Woods and the Nature Principle by Richard Louv would be a good place to start.

Warmest regards and keep your paddle in the water,
Phil the Forecaster

PS: The real weather is always more complicated but these conceptual models will help you figure that out…

The Cold Conveyor Belt - The Wizard Controlling the Precipitation Type

#0418 "Sheena's Sky" Phil was about to learn
some meteorology from this one trick pony...

I am a firm believer in making mistakes. Ask anyone. I feel that you need to keep pushing the knowledge envelope to become skilled. Strive to learn. If you are not making mistakes, you are not learning. Nature is the best teacher and it is best to be always paying attention. One never knows when the next natural lesson will be presented.

Conveyor Belt Conceptual Model of a Mid-Latitude Storm
The humble Blue Arrow is the Cold Conveyor Belt but ignore
this Wizard of the Weather at your own risk.

I recall one Day Shift at the Ontario Storm Prediction Centre in the early 1990’s. The Cold Conveyor Belt taught me a lot. I made a tremendous number of mistakes – but I never made those mistakes again. A large and severe winter storm with a good feed of Gulf of Mexico moisture was developing with a huge warm conveyor belt. The equally impressive dry conveyor belt was carving a path through the dry slot in the comma cloud pattern. I was all over these dramatic patterns in the severe storm and excited to provide an accurate warning service.  I was in charge. Or was I? Then it happened.

Rain started to fall in the eastern forecast regions. This was a winter storm! No problem, we will fix the heavy snowfall warnings. The rain changed to freezing rain. Big problem! We had to really adjust the warnings. The freezing rain changed to ice pellets. What next? The ice pellets changed to heavy snow. Wonderful! We finally caught up to the weather that we were originally warning for but we had spent the morning back pedaling and confused. I learned a lot. I made even more mistakes. That day was burnt into my memory more than any of the forecast successes. The humble Cold Conveyor Belt had ruled the day and the weather. The Cold Conveyor Belt Wizard was pulling the strings behind the curtain of the three dimensional deformation zone.

Rain Sounding

The cold conveyor belt originates from low levels in the atmosphere poleward and east of the low pressure center. The cold and dry air is drawn toward the low. The operative word is actually “dry” instead of cold. In this case the temperature started above freezing but the dew-point was well below freezing.

The snow flakes were in their free-fall at 1 metre per second. Those flakes melted in the last kilometre of their descent. That explained the winter storm starting as rain.

Freezing Rain

The energy required to melt the snow flakes along with the saturation of that lowest kilometer of air created a profile with an above freezing layer of air aloft and below freezing near the ground. That explained the rain changing to super-cooled water droplets. These super-cooled water droplets freeze on contact producing a treacherous ice glaze on exposed surface - freezing rain.

Ice Pellets Type A

The continued cooling and saturation of the air mass increased the amount of cold air at the surface. The super-cooled water droplets were freezing within the deeper cold layer at the ground thus converting the freezing rain to less dangerous ice pellets.

Snow

The continued loss of energy required to melt the snow flakes and saturate the air mass in the lowest kilometre cooled the entire profile to the wet-bulb temperature and eliminated the above freezing layer aloft. The falling snow would fall that lowest kilometer and remain unchanged as large dendritic flakes. These large flakes would accumulate quickly and verify our original warning. Before that happened though the cold conveyor belt had been exceedingly dry and taught me a lot of lessons.

I quietly slid the term wet-bulb temperature in the previous paragraph. At 100% relative humidity, the wet-bulb temperature is equal to the air temperature (dry-bulb temperature). In dry air, the wet-bulb temperature is achieved by evapourating water into the air parcels and taking the latent heat required to do that evapouration from the air parcel itself. The wet-bulb temperature is a conservative property of air as it moves in the conveyor belts of a storm. The wet-bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only.

The cold conveyor belt taught lessons about precipitation typing and the wet-bulb temperature that day. It also taught about the perils of being distracted by large and energetic patterns while neglecting the subtle features of the wizard behind the deformation zone curtain. This weather is now called a "wintry mix" by the media thus side-stepping the potential challenges and science. I feel it is best to understand and work with nature - and never leave home during a freezing rain event.

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick

Next is how the Cold Conveyor Belt can make you a better weather observer.