First, was the tornado outbreak over the United States a couple of weeks ago, and in particular, a F3 tornado that went through Michigan and actually crossed an ice-covered lake where it appears to pull up ice. If you haven’t seen the video, I would highly recommend taking a look.

The second item has been the record-shattering heat over a good chunk of the western and central U.S. I don’t have room to go into all the details, but a heat dome brought record temperatures for March to many locations with some of them seeing temperatures that would have broken April all-time records. With persistent arctic high pressure to our north, these extreme temperatures have been kept south of the border, but southern Minnesota did see a record high of 31 C.

Last on our list is an article that came out indicating that there is a good chance we will see the development of El Niño conditions across the Pacific later this year and it could be a very strong El Niño. We will look at that topic in April.

OK, now on to our main topic.

In our last article we looked at the composition of the atmosphere, breaking it down into a heterosphere and homosphere. Then we looked at the atmosphere from a temperature point of view and proceeded to break it down into four regions or layers — the thermosphere, mesosphere, stratosphere, and troposphere. We finished off by saying that one of these layers is responsible for most, if not all, of our weather. So, in this issue we will get back on track and extend our understanding of weather and the atmosphere by beginning our look at the atmosphere and surface energy balances.

To begin to understand how solar energy is spent as it reaches the Earth’s surface, and thus understand our surface energy budget, we need to look at the pathways in which solar energy can travel once it reaches the Earth’s surface.

Where the rays go

Earth receives energy from the Sun in the form of shortwave radiation. When this energy is turned into heat, it takes on the form of long-wave radiation. A good portion of both of these types of radiation passes through our atmosphere in the process known as transmission. When we are looking at shortwave radiation reaching the Earth’s surface, we call it insolation, and it is this insolation that is the driving force behind all of our weather.

Insolation is comprised of shortwave radiation that is transmitted directly to the ground, along with diffused or scattered radiation (indirect radiation). As shortwave radiation travels through our atmosphere some of it interacts with gas, dust, pollutants, water droplets and water vapour, changing the direction of the shortwave radiation — or scattering it. This scattering is what causes the sky to be blue during the day and why sunsets and sunrises take on a reddish hue.

The principle behind why we see these colours is known as Rayleigh scattering; named after the English physicist Lord Rayleigh, who came up this principle back in 1881. The principle relates wavelength to the size of the particles that are causing the scattering.

The general rule is: the shorter the wavelength, the greater the scattering; the longer the wavelength, the less the scattering.

Small gas molecules will scatter shorter wavelengths (remember with visible light, blues and violets have the shortest wavelengths, while oranges and reds have the longest wavelengths). So, since short waves are scattered the most and the molecules in our atmosphere scatter short waves, we end up having the lower atmosphere dominated by scattered blue waves.

At sunrise and sunset, the angle of the Sun is such that the insolation has to travel through much more atmosphere than during the day. The short blue wave lengths are still scattered, but now they encounter so much scattering only the longer orange and red wave lengths are left to reach our eyes — so we tend to see these colours.

Action and refraction

Another thing that happens to shortwave radiation as it enters the atmosphere is that it refracts. Refraction is the bending of light as it passes from one medium to the next. In this case, it is passing from the virtual vacuum of space to our dense atmosphere.

We have all seen examples of refraction. Rainbows are created when light passes through dense water drops causing the different wavelengths of light to refract at different rates. Mirages are another example of refraction. Most of us have experienced mirages on warm days along a highway when you stare down the highway and see what appears to be something floating above the road. In this case, it is the hot air above the highway that causes the light to be refracted.

One interesting note about refraction is that without it, the amount of daylight we receive would be about eight minutes less each day. When the sun sets or rises, the light refracts as it passes from space into our atmosphere. This refraction allows us to “see” the Sun when it is actually below the horizon. In the morning we see the sun rise four minutes before it actually moves above the horizon and at sunset we continue to see the Sun for four minutes after it has actually dropped below the horizon.

Next we will take a break from learning about the weather and take a look back at our extended winter to see how the numbers stacked up.

The post Why is the sky blue? appeared first on Manitoba Co-operator.

In this issue we are going to look at what takes a regular old thunderstorm and turns it into a severe thunderstorm, or occasionally, into a thunderstorm that you truly remember.

Typically for severe thunderstorms to develop we have a hot humid air mass in place at the surface and the air a few thousand meters up is very cold. This provides an environment where rising air will continue to rise, or we would say there is plenty of lift.

Venting

Add to this a strong jet stream overhead that will vent the accumulating air at the top of the storm, and we are ready for severe thunderstorms. Over the last few weeks or so, we have had plenty of cold air aloft, but we didn’t really have a lot of hot and humid air at the surface, but there was enough heat and humidity at the surface to generate rising air. Combine this with several occurrences of strong jet streams overhead and we ended up seeing some severe thunderstorms develop. The question then is, what can Mother Nature add to the mix to make things even worse?

The first and probably most important “extra” ingredient that can be added to the mix is to have the wind change direction with altitude. Remember that the atmosphere is three-dimensional; that is, air can flow horizontally, but this horizontal direction can change as you move upwards. Why would this have an impact on our storm?

To put it in a nutshell, this change of direction can cause the developing storm to rotate. Picture what would happen if you took a rising parcel of air and push on it from the south when it is at the surface. Then as it rises a couple of thousand feet the wind switches direction and now blows from the east. Then a few thousand feet further up it is blowing from the northwest. What would happen to our rising parcel of air? It would get twisted — it would start to rotate.

Spinning

If we can get air to rotate counterclockwise it will start to create an area of low pressure. Air flows, or spirals inwards, in a counterclockwise rotation. This means the air will be converging or bunching up near the center of this rotation. This converging air can either move downwards or upwards. Since the ground is in the way for the air to move downwards, plus the air is unstable which means it already wants to move upwards, this results in upwards moving air — often forced to move upwards very fast. So, if we can get our severe storm rotating, a small-scale area of low pressure can form and that helps the air to rise even more than it would without the rotation. When this occurs, it is referred to as a super cell thunderstorm, or a mesocyclone.

The second thing a rotating thunderstorm can do is to nicely separate the area of updrafts and downdrafts. This is important, since the downdrafts, even with a severe thunderstorm, will eventually cut the updraft off from its source of warm moist air. Once this happens the storm quickly weakens.

In a rotating thunderstorm, the source of warm moist air is maintained, giving these storms a long life and a lot of moisture to produce heavy rain. This is something parts of the Prairies would like to see sooner than later.

Tornadoes

Another aspect of the storm a rotating column of air can provide is the conditions for tornadoes to form. While we still do not fully understand how tornadoes are formed, we do know that rotating thunderstorms can and often do produce tornadoes.

It is believed that rotating columns of air can get squeezed into a narrower shape. As this happens, the wind speeds increase, eventually producing the tornado. It’s the whole theory of the conservation of angular momentum. Take a large thing that is spinning slowly like a big wide column of air and shrink it down, the objects rotational speed needs to increase and visa-versa.

The classic example of this is the spinning figure skater pulling in their arms to increase their rate of rotation, but more on this when we take a closer look at tornadoes.

Like most things in nature, thunderstorms rarely behave like a textbook example. Even when all the ingredients are there, sometimes no storms will form, or sometimes some key ingredient is missing yet we get a really severe storm — this is what makes weather so interesting.

Missing

As we know, not every thunderstorm that develops becomes severe, in fact, much of our summer rainfall comes from garden-variety thunderstorms. These can be air mass thunderstorms, which, as the name indicates, develop in the middle of a typical warm summer air mass. Because they are in the middle of an air mass, a number of the key ingredients for severe storms are missing.

As I mentioned earlier, usually in the middle of an air mass, the temperature will not decrease that rapidly with height. The wind will usually remain constant with height, and there will probably not be a jet stream overhead. Nonetheless, we can still have enough heat and humidity for the air to rise, and thunderstorms will form.

Since these storms don’t rotate or have any way to vent the rising air from the top of the storm, they rarely last long. The accumulating air at the top of the storm will eventually fall back down as a downdraft, wiping out the updraft and essentially killing the storm. The whole process from the start of the storm to the downdraft killing it can be anywhere from 30 minutes to an hour or two.

While these storms are short lived, they can give brief periods of heavy rain and the odd, good gust of wind, especially when the downdraft first hits the ground.

The same thing can occur with frontal storms, where all but one or two of the main ingredients could be in place, thunderstorms will form, but they just can’t pull everything together to go from just garden variety storm to a severe storm.

These storms often provide us with just the right amount of precipitation just when we needed it during the summer.

In the next issue we will start to examine all the different types of severe weather that can accompany severe thunderstorms.

The post The ingredients of a Prairie thunderstorm appeared first on Manitoba Co-operator.

• super-cell theory;
• rear-flank downdraft theory;
• tornado vortex theory; and
• multiple vortex theory

The first two are tied together because they both involve super-cell thunderstorms. Thunderstorms are fueled by warm, moist air near the surface and colder air aloft. What makes a super-cell thunderstorm different from a regular thunderstorm is the ability for the storm to sustain a rotating updraft.

These storms can rotate due to wind shear, or the change in wind speed and direction with height. As a super-cell thunderstorm evolves and the updraft intensifies, it draws in warm, moist air, which helps drive further storm development.

With the right type of wind shear, the updraft becomes tilted. This helps keep the updraft separate from the downdraft, allowing the storm to continue growing. Also, the tilting starts to stretch and squeeze the rotating column of air vertically, making the rotating air spin faster.

This stretching and squeezing of the rising, rotating air column is what scientists believe leads to development of tornadoes, but the exact mechanism is still not fully understood.

This leads to the second theory, rear-flank downdraft.

As the super-cell thunderstorm evolves, a region of cool, descending air develops on the backside of the storm. This is the downdraft that all storms have, but due to the wind shear tilting the storm, it does not come crashing down outside the main updraft area.Instead, this downdraft is able to interact with the updraft by enhancing the low-level inflow and rotation, which in turn can be pulled into the updraft of the super cell, leading to increased likelihood of a tornado.

The tornado vortex theory is similar to the super-cell theory. In fact, it almost simplifies the super-cell theory. It states that tornadoes form when horizontal spinning air in the storm updraft is tilted vertically by a strong updraft. These updrafts can move very fast and as the air rises, it stretches and contracts the rotating column of air, much like a figure skater pulling in their arms when spinning.

This causes an increase in spin rate due to conservation of angular momentum, a process known as vortex stretching, and the intensified spinning motion within the storm may lead to formation of a tornado.

The last is multiple vortex theory. As the name suggests, the main vertex within a thunderstorm contains multiple smaller vortices rotating within the main circulation. These can appear as satellite tornadoes or as sub-vortices within the primary tornado.

This phenomenon results in a tornado with a more intricate appearance, often displaying a spiral pattern of swirling winds within the main funnel.

According to this theory, the main column of rising, rotating air serves as the parent vortex and provides the circulation or rotation necessary for tornado formation. As the parent vortex intensifies, it can spawn smaller satellite vortices. These are typically found rotating around the main funnel cloud and this is why we often see unique and intricate structures in tornadoes.

The interactions between these satellite vortices can create a complex pattern as the individual vortices merge, split and interact with each other. This can result in the rapid change in shape, size and intensity of the tornado.

It is not known how these satellite vortexes are formed. If you remember our discussion on formation of areas of low pressure and how they can randomly spin up along a boundary of opposite moving air, then picture the same thing happening on a much smaller scale but at a much faster speed.

The constantly changing environment within the storm, and the physical landscape it travels over, can cause these satellite vortices to spin up, grow larger and then simply die away.

I think all the theories bring something to the table and as with most complex systems, it is probably a combination that leads to formation of tornadoes. The one thing the theories have in common is the need for a strong, well-established thunderstorm that either has rotation or is in an environment where columns of air can gain rotation.

Hopefully, as technology gets better, research will eventually lead to the definitive answer on the formation of tornadoes, and that in turn leads to better warnings.

Next on our list of severe summer weather is something the kills more people than any other severe weather event: heat waves.

The post The four theories of tornado formation appeared first on Manitoba Co-operator.

At least 64 people, including six children, lost their lives in Kentucky after a raft of tornadoes tore through six states.

“We have a 200-mile swath through Kentucky that has pulled-down grain systems, destroyed chicken hatcheries and of course blown-over barns,” said Ryan Quarles, Kentucky’s agriculture commissioner.

The destruction in the Midwest could further raise already high chicken prices and add to supply-chain headaches that have made it difficult for farmers to replace tractor parts.

Poultry is Kentucky’s top agricultural commodity, and at least a dozen chicken barns collapsed, Quarles said. The state is working with the U.S. Environmental Protection Agency to properly kill and dispose of chickens housed in barns that were destroyed, he said.

President Joe Biden will visit the state on Wednesday to survey the damage.

One Pilgrim’s Pride chicken hatchery was a total loss, and another is expected to be offline until spring after suffering significant damage, the company said in a statement. It added that other company hatcheries are supplying chickens to farmers near Mayfield, a town of 10,000 that suffered some of the worst damage from the tornadoes.

Pilgrim’s, mostly owned by Brazilian meatpacker JBS, is evaluating damage to a local feedmill, while a production plant is expected to be fully operational on Wednesday, the statement said.

The loss of the hatchery in Mayfield “automatically triggers a multi-month delay in the processing and raising of chickens because the hatchery simply is not there anymore to supply the farmers,” Quarles said.

Mayfield is in Kentucky’s top county for agricultural sales, accounting for six per cent of the state’s total farm business, according to U.S. Department of Agriculture data, though the state is not a top grain producer. Kentucky held 1.5 per cent of U.S. corn stocks in December 2020, USDA said.

“Lots of farmer elevators damaged. Some small feed mills have damage with indefinite timelines,” said Andrew Jackson, broker at Producers Hedge, in Lancaster, Kentucky.

Mayfield Grain Co., a crop handler, had roofs ripped off of parts of a storage system that holds six million bushels of grain in Mayfield, Quarles said. That’s enough corn to fill two Panamax vessels — each ship the length of two football fields.

Photos on Twitter showed yellow corn visible from the tops of bins that lost their roofs. The company had no immediate comment.

“You have millions of bushels of corn, much of which was just freshly harvested, being exposed to the elements, being damaged,” Quarles said.

“We’re looking for ways to recover spilled grain but also divert the storage and movement of grain to other facilities around the state.”

Quarles said the agriculture department will help farmers find buyers for grain amid reduced demand for feed from livestock and poultry producers who suffered losses.

Hutson Inc., a company that sells Deere equipment, said its flagship store in Mayfield was “destroyed by one of the worst natural disasters to ever hit the state.”

Workers “waded through debris and used what equipment they could salvage to assist with rescue efforts at a candle plant located next to us that had mass casualties,” CEO Josh Waggener said in a statement online.

Deere said it is in touch with Waggener and working with Hutson to provide financial assistance to the community.

— Reporting for Reuters by Tom Polansek, Christopher Walljasper and Mark Weinraub in Chicago.

The post U.S. tornadoes destroy chickens, tractors, silos appeared first on Manitoba Co-operator.

I figure I can cover the cold snap and heatwave in the next issue, so while we have not had much in the way of severe weather this year, let us dig into this still poorly understood topic.

What are tornadoes, and how do they form? We have looked at this topic several times over the years, but I think it is important to re-examine it. A classic definition of a tornado is a violently rotating column of air that extends from a thunderstorm to the ground, which may or may not be visible as a funnel cloud. For this rotating column of air to be classified as a tornado, it must touch the ground.

As to how tornadoes form, the real answer is, we just do not know. Tornadoes usually develop from supercell thunderstorms, which are difficult to predict. Even if we were able to accurately predict where and when these thunderstorms would develop, the intense part of the thunderstorm usually only covers an area of a few hundred square kilometres. Within these few hundred square kilometres, the really severe weather may only occur in a small area of maybe 10 to 20 square km. Now, if we look at the size of tornadoes, we will find that they range from as small as about 40 metres to as large as two km across, with the average width being around 100-200 metres. This means that, as far as weather phenomena are concerned, tornadoes are very small, which makes them very hard to study first-hand.

To begin our look at tornadoes, let us first take a look at one of the weakest members of the tornado family and something we do see around Manitoba: the cold air funnel.

Manitoba only sees around 15 tornadoes on average each year, making them fairly rare; however, cold-air funnel clouds, also referred to as cold-core funnels, are a little more common. Personally, I have never seen a tornado, but I have seen a cold-air funnel. All tornadoes develop out of what we refer to as a funnel cloud. In strong thunderstorms, these funnels elongate and may eventually touch the ground to become tornadoes, but a funnel cloud all by itself is not considered a tornado. While a fair bit of research has been done on tornadoes and the storms that produce them, very little research has been done on cold-air funnels; therefore, we know very little about them.

In general, cold-air funnels form in environments where we would not typically expect severe weather to develop (hot, muggy, unstable air); rather, they usually form when there is a large pool of cold air aloft that is most often associated with an upper-level low. These conditions provide two critical ingredients that are believed to be necessary for the development of cold-air funnels: instability and vorticity.

If you think back to when we talked about instability in the atmosphere, you’ll remember that warm air will rise and cold air will sink. If the atmosphere is unstable, you need either really warm air at the surface, or very cold air in the upper atmosphere. This is why there needs to be a pool of cold air aloft for cold air funnels to form, because this provides the first ingredient: instability, or rising air.

Spin machine

The second ingredient is vorticity. This simply means spinning air. Areas of low pressure are large areas of spinning air, too large to form into a funnel cloud or tornado. But within this large area of spinning air, smaller regions get “spun up,” creating what meteorologists call a vorticity-rich environment, containing a lot of little eddies of spinning air. Now, what scientists believe happens is that one of these small eddies of spinning air gets caught in an updraft. This updraft then pulls on and elongates the eddy, causing it to contract in width, and, just like figure skaters pulling their arms in during a spin, this causes the rotation to speed up, creating a funnel cloud.

These funnel clouds are generally very weak and short-lived and will rarely become strong enough, or last long enough, to touch down. If they do touch down, they can then be referred to as tornadoes, but even then, they rarely cause much damage, often comparable to that of a very strong dust devil. In fact, when these cold air funnels do touch down, they are sometimes referred to as ‘land spouts.’

Since the potential exists for cold air funnels to touch down as tornadoes, Environment Canada has to issue special weather statements to warn the public about them. Since they rarely touch down, and even when they do, they rarely cause damage, such statements will usually urge the public to be watchful for these to occur and to take precautions, if necessary, i.e., you do not have to go diving for the nearest storm shelter if you see one of them forming.

In the next issue, we will take a break from tornadoes as another month has come and gone, so we will do our usual look back at June’s weather across the Prairies and then look ahead to see what the next three months might have in store.

The post Cold air and cold-core funnels appeared first on Manitoba Co-operator.

Areas around Brandon, Rapid City and north towards Riding Mountain National Park reported widespread flooding June 28-29.

Brandon airport reported 155 millimetres of rain in a matter of hours, according to Environment and Climate Change Canada (ECCC), leaving the eastern entrance to the facility impassible and surrounding fields totally underwater.

Elsewhere, ECCC reported 156 millimetres in Oak River, 153 millimetres in Minnedosa, 120 millimetres in Alonsa, and 115 millimetres in Newdale.

“The rainfall was highly localized,” ECCC has said. “Only 19 mm was reported at a site 20 kilometres southeast of Brandon, while the city itself received over seven times that amount.”

In Oakburn, residents reported golf-ball sized hail while a “rain-wrapped tornado touched down briefly near Rapid City,” ECCC has said.

The Municipality of Oakview, which includes Rapid City, has announced a state of emergency in the wake of the storm. The region has reported snapped trees and property damage, as well as flooding.

Clayton Robins, who farms near Rivers, says his farm has been mercifully unharmed, despite about five inches of rain.

“Our ravines are running like crazy again and we’ve certainly gotten some ponding on our fields but, actually, the number of acres that look to be damaged is relatively small compared to what I saw on my way into work this morning, where whole fields are covered and huge chunks of land.”

Robins, who also works in Brandon, noted the challenge of navigating what he says is a sudden labyrinth of road closures and roads that have since turned into fords.

Water was still overflowing ditches and across many highways and rural roads as of the afternoon June 29, and widespread road closures were in effect. The TransCanada Highway directly east of Brandon was closed due to floodwaters June 29, while Highway 10 reported closures north of Forrest and again north of Minnedosa. Highway 25 between Highway 10 and Provincial Road 270, Provincial Road 270 from the TransCanada Highway to Rapid City, Highway 24 west of Rapid City and Highway 19 in Riding Mountain National Park are also reporting closures.

Rural roads fared little better.

“We had to turn around at least four different times,” Robins said. “We probably drove through some spots that we, maybe, in hindsight shouldn’t have tried. The water was going over the road, in some spots, at least once every mile.”

Those floodwaters may have since swelled, he noted, pointing to the topography of his region and rain that fell further to the north.

“There’s definitely a lot of water that’s laying and moving still all though this area and it’ll be a few days before a lot of this disappears, I think,” he said.

Northwest and Interlake

In the northwest and Interlake, rains were more welcome.

Apart from the 120 millimetres fallen over Alonsa, Ste. Rose du Lac reported about 30 millimetres, according to the province’s Ag weather network, while, closer to the Saskatchewan border, Inglis reported just over 15 millimetres.

Pam Iwanchysko, livestock specialist with the province based in the northwest, said rains near Roblin and Swan River were not enough to disperse the region’s previously dry conditions, although the area around Dauphin reported two to three inches.

The rain was, “needed for annual crops, so it was welcome,” she said.

The rain should help bolster the outlook for a second cut for hay growers, she said, although it will hinder first cut now.

Ray Bittner, Iwanchysko’s counterpart in the Interlake, said storms damaged some buildings and trees due to high winds and dropped anywhere from two and a half to five and a half inches.

But our area was so desperate for rain, this was a general blessing,” he said.

Both Iwanchysko and Bittner had previously expressed concern over hay yields and dry pasture conditions in the week prior to the storms.

The weather may not be done with the region yet. ECCC has again forecasted thunderstorms for western and eastern Manitoba.

The post Floodwaters rise in western Manitoba appeared first on Manitoba Co-operator.

Before we begin our look at tornadoes I think we have to step back a little bit and discuss: “How can you know if a storm is capable of producing severe weather?” The answer is actually not that easy. The first thing is to check with Environment Canada (EC) for watches and warnings. If a watch is issued by EC it means the potential exists for severe thunderstorms, but they have not yet developed in your area. When you hear there is a watch, you should watch the sky for any development, and if any storms do develop, they have the potential to become severe. If EC issues a warning, this means a thunderstorm with some or all the characteristics of a severe storm has developed and has been confirmed by an eyewitness or radar. This means you should take precautions immediately.

If you are out in the field without access to a radio or the internet, what can you watch out for? First of all, recognize the conditions: how warm and humid is the air? Remember, a moist atmosphere means there is a lot of energy available. Look for a dark or threatening sky — look closely at the area between the storm and the ground, and if you can see through it, the storm is likely not severe yet. Lots of lightning or nearly continuous thunder are good indications of a severe storm. As the storm approaches, keep an eye out for features such as a green sky and mammatus clouds (clouds that look like bag-like sacks that hang beneath a cloud); these conditions usually indicate the storm contains huge amounts of water and has very strong up- and downdrafts. Finally, watch out for any kind of rotation within the storm. This means the storm has become very strong and has the capability of producing a tornado.

Storms quick to form

In this day and age, most of us have internet access nearly 24-7 and if you depend on the weather you usually have one or more weather apps available to quickly check to see what is happening. The best way to know what is going on with a developing thunderstorm is to check out EC radar. While this tool can allow you to see just where a storm is developing and how it is moving over time, you need to remember that thunderstorms can be very dynamic. Storms can develop very quickly, going from almost nothing to a severe storm in less than 20 minutes. Conversely, powerful storms can collapse almost as quickly. Often, when we have an outbreak of severe weather, thunderstorms are developing and collapsing along a line. Radar will show a very strong storm about to hit your area only to have it collapse and weaken just as another storm fires up and becomes severe a few kilometres away. So, while using weather apps and watching radar can be helpful, when severe weather develops and is moving into your area, always prepare for the worst and be thankful if it doesn’t happen.

The word “tornado” for most people brings about a feeling of awe and even a little fear. Unless you have already witnessed a tornado first hand, many who are interested in weather secretly wish they could safely experience the awesome beauty and power of a tornado.

Worldwide, Canada is second only to the United States in the number of tornadoes occurring each year, with an average of about 70 reported. Southern Ontario experiences the highest number of tornadoes, followed by southern Manitoba, Saskatchewan and central Alberta. While these areas report most of Canada’s tornadoes, they have occurred in nearly all regions of Canada.

Tornadoes can strike at any time of the year, but in Canada, tornado season runs from April to October, with the peak months being June, July and August. This differs from the U.S., where tornadoes peak in April and May. This is due to the amount of cold air that is available for severe storm development. In the spring, the southern and central U.S. have become quite hot, but cold air is still closely available to help develop thunderstorms. By midsummer, most of the cold air has retreated well into Canada, putting our region into warm conditions, however, we still have cold air fairly close by to our north.

Unfortunately, it appears as though I’m running out of space to finish up on our topic of tornadoes in this issue. Next week we’ll take a break from the topic of severe weather to look back at how this spring turned out and take a look ahead to see what the latest summer forecasts are calling for. Guess we’ll have to pick up on tornadoes after that.

The post Continuing with severe summer weather: Tornadoes appeared first on Manitoba Co-operator.

After that, even the weather models turned against me. They were showing only about a week of cold weather and most of that period looked as if it would be cloudy. I was hoping the clouds would keep the frost away, but a couple of clear to partly cloudy nights allowed for just enough cooling to allow temperatures to drop a couple of degrees below 0 C. Now the weather models show the cold weather sticking around until about the middle of October. I will revisit the long-range fall forecasts next week, but let’s just say that it doesn’t look like much in the way of warm, sunny weather coming any time soon.

For this article I thought we’d do a bit of global weather roundup, starting with August’s global temperatures. It appears August was the fifth warmest on record, according to both NASA and NOAA. The other top four warmest Augusts were in 2016, 2017, 2014 and 2015. This makes it five years in a row that the planet has recorded record-breaking August heat. Looking at the global August temperature of the lower eight km of the atmosphere as measured by satellite, it was the ninth-warmest August on record, according to the University of Alabama-Huntsville.

During August, 186 major weather stations reported new all-time heat records. Japan led the way with 92 records, then South Korea with 28, followed by Portugal with 16, North Korea, 15 and Canada, 14. No stations reported breaking any all-time cold records during the month. There have been 35 national monthly heat records across the globe so far this year. This means that a place in one of those countries has recorded the warmest temperature ever recorded for that country. There have been no monthly cold records. So far in 2018, there have been five all-time national heat records and, just like with the other heat records, there have been no all-time national cold records so far this year.

No Northwest Passage this year

Moving to the polar regions, it looks like the Arctic sea ice is at or near its seasonal minimum as the sun is now setting on the Far North. As of September 17, the sea ice extent was at 4.6 million square km, 1.69 million below the 1981-to-2010 long-term average. If this holds, then this minimum will come in as the sixth-lowest year on record. Cooler-than-average temperatures during July, which slowed the ice melt, were one of the main reasons for the slightly higher-than-expected minimum. The Northwest Passage remained clogged with ice this year and will not become navigable, but the Northern Sea route has been mostly ice free and navigable. To the south, in the Antarctic, sea ice extent is nearing its maximum and is currently running nearly two standard deviations below the long-term average.

The next weather story would be Hurricane Florence. After gaining strength and peaking at a Category 4 storm in the days leading up to its landfall in South Carolina, Florence fortunately dropped down to a Category 1 storm, sparing the region from the catastrophic winds and associated damage that a Category 4 storm would have wrought. That was where the good news ended, though. As the storm approached shore, it slowed down, thanks to a strong ridge of high pressure situated over eastern North America. This slow motion kept part of the storm’s circulation over the ocean and allowed the weakened system to tap into large amounts of moisture. This moisture was then dumped over the Carolinas in the form of heavy rainfall to the tune of over a metre (1,000 mm) in some areas! Florence easily broke the record for the heaviest rainfall from a tropical storm for this part of the U.S.

The final story comes from a little closer to home and is one of those weather stories you would rather not hear about. I’m talking about the devastating tornadoes that hit the Ottawa and Gatineau regions of Ontario and Quebec on Sept. 21. Environment Canada reports two tornadoes moved through this region. The first was classified as an F3 and it moved through Dunrobin, Ont., before moving on to Gatineau. A second, weaker tornado was recorded to have touched down over the south Ottawa neighbourhood of Arlington Woods. Early reports are listing over 275 buildings either damaged or destroyed, with upward of 175,000 customers without power after the storm. Ontario Hydro is expecting some customers to be without power for up to a week. As I write this article, luckily no one has been reported killed, but two people have been admitted to hospital in critical condition.

As we leave the summer season behind in our region, along with the accompanying thunderstorms, our thoughts and prayers go out to these folks.

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Southern Manitoba is taking stock after major storms on June 14 brought a confirmed tornado touchdown near Waskada, Man., while a wide swath near the international border saw anywhere from quarter and toonie-sized hail to ice chunks the size of softballs. Total crop damage has yet to be determined.

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We have a hot, humid air mass in place; the air a few thousand feet up is very cold, providing for good lift; and we have a strong jet stream overhead providing the venting at the top of the storm. Everything is in place for a severe thunderstorm, but what can Mother Nature add to the mix to make things even worse?

The first and probably most important “extra” ingredient that can be added to the mix is to have the wind change direction with altitude. Remember that the atmosphere is three dimensional; that is, air can flow horizontally, but this horizontal direction can change as you move upward. Why would this have an impact on our storm?

To put it in a nutshell, this change of direction can cause the developing storm to rotate. Picture what would happen if you took a rising parcel of air and pushed on it from the south when it was at the surface. Then, as it rose up a couple of thousand feet, the wind switched direction and now blew from the east. Then, a few thousand feet farther up, it changed again and was blowing from the northwest. What would happen to our rising parcel of air? It would get twisted; it would start to rotate.

Remember that if we can get air to rotate counterclockwise, we have an area of low pressure. Air flows inward in a counterclockwise rotation and is then forced to move upward. One thing we can get, if we get our severe storm rotating, is a small-scale area of low pressure that helps the air to rise even more than it would without the rotation. The second thing a rotating thunderstorm can do is to separate the area of updrafts and downdrafts. This is important, since the downdrafts, even with a severe thunderstorm, will eventually cut the updraft off from its source of warm, moist air. In a rotating thunderstorm, the source of warm, moist air is maintained, giving these storms a long life and a lot of moisture to produce heavy rains.

Another aspect to the storm that a rotating column of air can provide is a tornado. While we still do not understand exactly how tornadoes are formed, we do know that rotating thunderstorms can produce tornadoes. It is believed that rotating columns of air can get squeezed into a narrower shape; as this happens, the wind speeds increase, eventually producing the tornado.

Like most things in nature, thunderstorms rarely behave like a textbook example of a thunderstorm. Even when all the ingredients are there, no storm may form, or sometimes a key ingredient is missing, yet we still get a really severe storm; this is what makes weather so interesting.

Downdraft versus updraft

Of course, not every thunderstorm that develops becomes severe; in fact, much of our summer rainfall comes from your garden-variety thunderstorm, or what we call an air mass thunderstorm. These storms, as the name indicates, develop in the middle of a typical warm summer air mass. Because they are in the middle of an air mass, a number of the key ingredients for severe storms are missing.

Usually, in the middle of an air mass, temperature will not decrease very rapidly with height. The wind will usually remain constant with height, and there will probably not be a jet stream overhead. Nonetheless, we can still have enough heat and humidity for air to rise and thunderstorms to form. Since these storms don’t rotate or have any way to vent the rising air from the top of the storm, they rarely last long. The accumulating air at the top of the storm will eventually fall back down as a downdraft and this will wipe out the updraft, essentially killing the storm. The whole process, from the start of the storm to the downdraft killing it, can be anywhere from 30 minutes to one hour.

While these storms are short lived they can give brief periods of heavy rain and the odd good gust of wind, especially when the downdraft first hits the ground. These storms often provide us with just the right amount of precipitation when we need it during the summer.

I hope you now know just a little bit more about the nature of severe thunderstorms. Next issue we’ll take a look at the latest long-range summer and fall forecasts, to see if they are still predicting warmer- and drier-than-average conditions, or if they are starting to swing toward a cooler and wetter pattern.

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