Hail series: What is hail and where does it come from?

Source: NOAA Photo Library

Hail is frozen precipitation, born of the updrafts of thunderstorms. Updrafts are rising air currents, which combined with cold temperatures and water droplets, are the primary forces that create hail. Such conditions are frequently present in the middle and upper portions of thunderstorms.

Hailstone embryos form inside storm clouds on small frozen raindrops and on “snow pellets” called graupel. They grow into true hailstones by accumulating ice through a process called accretion, by capturing supercooled (below 0 °C) water droplets in cloud regions with temperatures below the freezing point, 0 °C (32 °F). Hailstones sometimes contain pebbles, leaves, twigs, nuts, and insects that have been lofted into the clouds by strong updraft winds.

For the hail embryos to grow, they must remain in a layer of supercooled water for a length of time — the longer they stay there, the larger the size. They are kept in this layer by strong updrafts that construct the great towers of the cumulonimbus (Cb) clouds. The updrafts push the Cb cloud tops high into the atmosphere, creating the environment for lightning, thunder, and the various wind characteristics of thunderstorms.

Rising air (updraft) of at least 60 km/h (40 mph) is required to form dime-size hail. Golf-ball size stones (4.5 cm diameter) form when updrafts reach approximately 100 km/h (60 mph), and softball-size hail forms inside updrafts reaching 160 km/h (100 mph; NWS). To form hailstones the size of golf balls, over ten billion supercooled droplets must be accumulated, and thus the hailstone must remain in the storm cloud for at least 5 to 10 minutes. Once a hailstone has reached a weight which the updraft can no longer support, it falls to the ground.

Hailstones form in onion-like layers of opaque and clear ice. Clear layers form when colliding water droplets freeze slowly in cloud layers that are slightly below freezing, allowing air bubbles to escape. This process is termed “wet growth”. Opaque layers, with a “milky” texture, form when colliding water droplets freeze rapidly in cloud layers that are well-below freezing. The rapidity of the freezing prevents air bubbles from escaping. This process is termed “dry growth”.

When hailstones collide inside the thunderstorm, they may break into smaller pieces or become welded together into larger irregular shapes. Large hailstones can fall at a maximum speed of 170 km/h (105 mph).

Hailstones don’t have to travel up and down in a thunderstorm cloud however.  Sometimes they drift slowly downward through the storm, accumulating water droplets and growing as they pass through supercooled water layers. These stones will have a more uniform structure, rather than layered.

Source: NOAA Photo Library

Not all hailstones survive that downward trip. Forty to seventy percent of the hailstones that form within a thunderstorm cloud melt before reaching the ground.

A series of descriptor terms are used to communicate the size of hailstones, ranging from pea-sized to softball-sized. The best way to report the size of a hailstone is to measure it with a ruler or to compare it with a commonly-known object that does not vary in size, such as a coin. Marbles, although often used as a descriptor, is not a great object to compare to due to the varying sizes of marbles.

One of the largest hailstones ever documented occurred on July 23, 2010 in South Dakota. The hailstone had a diameter of 8-inches, or about 20 cm (NWS). Jim Scarlett, meteorologist in charge at the National Weather Service in Aberdeen, SD remarked “I described this one as cantaloupe-size.” The July 23 storm sent hailstones that broke through roofs, leaving fist-size holes in interior ceilings, smashing through windshields and causing at least five injuries to stranded motorists on I-90. Dents in the ground were still visible the following day.

Weatherlogics predicts the locations of future hail storms and collects data on hail events. This information is critical to ensure we have an accurate understanding of hail risk. For more information about these services, click here.

In our next article in this series on hail, we’ll be discussing the characteristics of hailstones, storm patterns associated with hail, and weather forecasting and hail damage assessments.

Hail Series Introduction

Over the next few weeks we’ll be publishing a series about hail. Hail affects nearly everyone at one time or another. Throughout the summer months, farmers, car dealers, insurance professionals, and many others, scan the sky daily. They are watching for towering cumulus clouds that may suddenly explode with thunder and lightning, and occasionally rain down a destructive blanket of hail stones.

The annual economic impact of hail storms runs into billions of dollars. In 2012, Alberta alone experienced $700 million in insured losses due to hail (source: Insurance Bureau of Canada). Insurance companies do have a direct interest in understanding the patterns of hail so that they can better predict losses and manage their claims process more efficiently.

For the rest of us, curiosity drives our desire to understand this fascinating and ever present natural phenomena.

Over the next three weeks we’ll explore the insides of hail stones, the behaviors of hail storms, and some of the economic and social implications of this fascinating phenomena. The first post on April 23, 2018 will discuss what hail is, and how it forms.

If you have questions about this topic or would like to suggest topics for future weather-related stories, please contact us at

One of the Driest Meteorological Winters on Record Across Much of the Prairies – Except Southern Alberta

*Note: these statistics do not include the early March 2018 winter storm across the Prairies, which was technically part of meteorological spring.

It was a very dry meteorological winter (DJF) across much of the Prairies this year. Widespread parts of southern Manitoba had less than 50% of normal precipitation. The same can be said for much of southern Saskatchewan, particularly in the Regina area, and for eastern Alberta.

The contrary was true in southern Alberta, where snowfall was well above average this winter. At Calgary International Airport, 77 mm of precipitation and 87 cm of snow were recorded between December 1 and February 28, making it the 7th wettest and 4th snowiest meteorological winter since 1884. Normal is only 29 mm of precipitation and 45 cm of snowfall.

Data Issues

The precipitation amounts and their rankings are presented with a great degree of uncertainty. The methods used to measure precipitation at Environment and Climate Change Canada’s stations have changed significantly over the period of record and have become automated in the past couple decades. We have found that the new automated methods tend to produce smaller precipitation amounts as compared to previous methods, especially when there are moderate to strong winds present. These differences in methods make it difficult to accurately and confidently compare this year’s data with historical data. Nonetheless, this past winter was certainly a dry one throughout much of the southern Prairies, despite the data issues.

Another issue with the weather data in the past couple decades has been the presence of missing observations. Missing observations have occurred quite frequently at some major stations. Often times, the missing data can be retrieved in raw data formats, but sometimes an estimate must be assigned. In the case of Regina, a snowstorm on December 4-5, 2017 of this past winter was not recorded. As a result, by comparing with nearby CoCoRaHS stations, we were able to assign an estimated precipitation amount of 3 mm for the event.


In southern Alberta, a lingering deeper-than-normal snow pack may result in a delayed start to spring with cooler than normal temperatures to start the month of March, before a warming trend occurs later in the month. In southern Saskatchewan and Manitoba, an early March winter storm has increased snow depth from near record lows, to fairly healthy levels. This increase in the snow pack will be helpful in replenishing moisture in the soil, but additional spring rains will be needed to fully recover from the dry conditions last summer.

For more information about the forecast for the upcoming summer/growing season, check out our official forecast here:

Weatherlogics’ Summer Forecast for 2018

Our summer forecast for temperature, rainfall, and thunderstorms in 2018.

While it may not seem like it right now, spring is just around the corner. Meteorological spring begins on March 1, which has many people wondering what the upcoming summer has in store. We have prepared our outlook for this summer across western Canada – read on to find out more!

The weather pattern during the summer of 2017 was very dry across the southern Prairies. Rainfall totals in Winnipeg and Regina for 2017 were the 2nd or 3rd lowest on record, at only 333.7 mm (13.1 in) and 152.2 mm (6.0 in), respectively. The outlook for 2018 is a continuation of this dry pattern, but we do not expect it to be as dry as last year. The northern Prairies were on the wet side last year, and we expect this to be the case again this summer. The outlook graphic below shows our prediction for rainfall trends for the upcoming summer/growing season across the Canadian Prairies.

Weatherlogics’ summer 2018 precipitation forecast.

In terms of temperature, 2017 was warm across the western Prairies, but near- to slightly-below normal in the eastern Prairies. Like precipitation, this trend is forecast to continue in 2018, with warm conditions again in the southwestern Prairies and near-normal temperatures in the eastern Prairies. The graphic below displays our temperature forecast.

Weatherlogics’ summer 2018 temperature forecast.

Lastly, we have made our prediction for trends in thunderstorm activity across the Prairies. Overall, 2017 was a fairly quiet year for storms relative to 2015 and 2016 on the eastern Prairies. Conversely, the western Prairies were more active, seeing fairly typical thunderstorm activity. The Alberta foothills are an active thunderstorm region almost every year, so this is not an abnormal situation for that region. This year, our forecast for thunderstorms shows a slight rebound in activity across the eastern Prairies, with more activity than 2017. The western Prairies should again be active, with a similar number of storm days to last year.

Weatherlogics’ summer 2018 thunderstorm forecast.

Unfortunately, the impact of this forecast on the growing season is expected to be mostly negative, especially over southern Saskatchewan and into southern Manitoba. Last year was very dry in these regions, but crops remained surprisingly healthy as they were able to draw on residual soil moisture from previous years. This year, the situation will be different, as last year’s dry conditions depleted the reserves of soil moisture. In addition, snowfall this winter has been near record lows across a large swath of the southern Prairies, especially in southern Saskatchewan and southern Manitoba. Therefore, if significant rains do not occur at opportune times this year, crops will definitely struggle. Our best hope is for a wet spring to help replenish soil moisture before the heat of summer begins to dry the ground out once again.

The meteorologists at Weatherlogics are experts in weather forecasting and climate analysis. Don’t hesitate to contact us at if you would like to inquire about our weather solutions.

Freezing Rain Vs. Freezing Drizzle: What’s the difference?

In the winter months, one of the most feared weather conditions is freezing rain. It causes ice to accumulate on roads and sidewalks, making travel treacherous. While we all know freezing rain is dangerous, what makes it different from freezing drizzle, or even black ice? In this blog post, we investigate that question!

When you consider the difference between freezing rain and freezing drizzle, the easiest way to visualize the difference is to think of the difference between rain and drizzle. Rain consists of large drops, while drizzle is made up of much finer drops, almost like a mist in some cases. This probably gives the impression that freezing drizzle is just describing freezing rain at a lighter intensity. However, there is more to it than that.

Drizzle consists of water droplets that are less than 0.5 mm in diameter (image from:


Rain consists of water droplets that are more than 0.5 mm in diameter (image from:

To understand the difference between freezing rain and freezing drizzle, we actually need to briefly discuss a complex topic called precipitation microphysics. In short, this is referring to the very small-scale processes in clouds that cause precipitation to develop. One key concept regarding this topic is the fact that liquid water can actually exist in the atmosphere down to -40C, and the atmosphere is all liquid water at temperatures above -4C. Between -4 and -40C, there is a mix of ice and liquid, with more ice the closer the temperature gets to -40C. While a discussion about why this occurs is beyond the realm of today’s topic, keep this in mind as you continue reading.

To the average person, freezing drizzle is just low-intensity freezing rain. However, to a meteorologist the difference is much larger. Freezing rain occurs when snow is generated high up in the atmosphere, then falls through a warm layer above the ground (with temperatures above freezing), causing the snow to melt into liquid water. Before the now liquid drop of water reaches the ground, the temperature suddenly falls back below freezing, but not quickly enough for the water droplet to refreeze. As a result, the water droplet hits the ground as liquid, but immediately freezes because the ground is below-freezing. If the water droplet did have enough time to refreeze, it would be called an ice pellet (aka sleet), but that is a discussion for another day.

Freezing rain occurs when snow melts on its way to the ground and then freezes when it hits the surface (Image from:

So if freezing rain is caused by snowflakes melting before they reach the ground, how is freezing drizzle different? The difference goes back to the microphysics that were discussed earlier. In the case of freezing drizzle, a low-level cloud deck is usually present in an atmosphere where the temperature is between 0 and -10C. Since the cloud in this case is not far below freezing, it is almost entirely (if not entirely) made of liquid water. Therefore, if the cloud contains enough moisture to produce drizzle, those small liquid particles will be supercooled – below freezing – as they head toward the ground. Once they reach the ground, the drizzle droplets are deposited as ice, sometimes called “glaze” because it is often a very thin layer of ice.

Freezing drizzle occurs when the entire atmosphere is below freezing (Image from:

So we’ve learned about freezing rain and freezing drizzle, but what about black ice? Black ice isn’t actually a weather phenomena, but rather a road phenomena. According to the American Meteorological Society:

A popular alternative for glaze. A thin sheet of ice, relatively dark in appearance, may form when light rain or drizzle falls on a road surface that is at a temperature below 0°C. It may also be formed when supercooled fog droplets are intercepted by buildings, fences, and vegetation.

Black ice can form in numerous different ways. It can be the result of freezing rain or freezing drizzle, but could also be from existing water on the road freezing, or even the deposition of ice onto the road from vehicle exhaust. Regardless of its source, black ice is a very dangerous road condition because it can easily be mistaken for a wet road, or even a dry road!

When producing winter weather forecasts, the professional meteorologists at Weatherlogics closely monitor the potential for freezing rain, freezing drizzle, and black ice. While to the average person there may not seem to be much difference between freezing rain and freezing drizzle, the difference is quite important to meteorologists. The impacts are also different, as freezing rain events can be quite significant (e.g. the 1998 Eastern Canada Ice Storm), while freezing drizzle events are usually much less severe. It is especially important to consult a professional meteorologist if you are affected by these types of precipitation, since they are among the most difficult aspects of weather to predict. Our Road Weatherlogics service also provides future predictions of all winter precipitation types, including snow, freezing rain, and blowing snow.

La Niña Watch Issued; Is a Cold Winter Coming?

A La Niña Watch was issued by the Climate Prediction Center (CPC) last week. According to the CPC website, a La Niña Watch is issued when conditions are favourable for the development of La Niña conditions within the next six months.

As you’ve probably heard before, La Niña, or its “brother” El Niño, can have a big impact on winter weather in North America. In the Canadian Prairies region, La Niña usually means colder and snowier winter conditions. The graphic below summarizes why that is the case.


A typical La Niña winter brings colder conditions to the Canadian Prairies.

In La Niña years, the jet stream tends to be quite strong and remains consolidated in one band, rather than splitting into multiple streams. This tends to make it easier for frigid air to plunge down from the arctic across the Prairies. The presence of a strong jet stream in our region also allows weather systems to pass through frequently, making snow a common occurrence.

While it’s too early to say for sure whether a La Niña event will develop this winter, it is the most likely outcome at this point. The International Research Institute for Climate and Society at Columbia University has put together a graphic that shows the likelihood of various outcomes this winter. As you can see in the image below, La Niña is most likely, followed by neutral conditions (no El Niño or La Niña).

A La Niña event is currently the most likely outcome for this winter.

If you’d like more details on what to expect this winter, or need winter weather forecasts, our professional meteorologists would be happy to assist your business. Visit the contact us page to get in touch.

Will Hailstorms be More Common on the Prairies in the Future?

Will hailstorms be more common on the Canadian Prairies in the future? That question was posed by atmospheric scientists from Environment and Climate Change Canada and the University of Manitoba in a recent article titled “The changing hail threat over North America in response to anthropogenic climate change” in the journal Nature Climate Change.

Disclosure: I was involved in writing some of the code used for the data analysis in this study (see article acknowledgements). However, I was not an author of this publication and the opinions below are my own.

This study examined changes in hail across North America using three climate models that simulated future conditions between 2041 and 2070. The model was used to study changes in hail size, frequency, and seasonality. Interestingly, there was not a single uniform trend in hail across all of North America. Some parts of North America, like the southeastern United States, appear likely to see less hail due to higher freezing levels in the atmosphere. Higher freezing levels cause hail to melt before hitting the ground, reducing the size of hail stones, or eliminating them completely. Other parts of North America, like the front range of the Rocky Mountains, will probably see more hail. However, for large parts of the continent, the study found no clear trend in the number of future hail events.

Another aspect of the study examined how hail size will change in the future. In the spring, the study showed most of North America receiving larger hail, but in summer some parts of the continent will likely see larger hail, while other parts see smaller hail. This is again due to increases in temperature in some regions, which will cause hail to melt more before hitting the ground.

The last aspect of the study looked at whether the peak in hail season will change. In most of Canada peak hail season is June or July. This isn’t expected to change much on the Prairies, but in eastern Canada there does appear to be a slight trend towards an earlier peak in the hail season.

This study is quite interesting, because it’s one of the first to look specifically at how hail will change in the future. Many past studies have just examined at how severe weather in general will change, but didn’t examine the specific impacts. While this study provides good insights into future hail trends, I’ll just add one cavaet; this is only one study based on three model simulations. In science it’s important to have as much coroboration as possible for your findings. For that reason, I wouldn’t put all my proverbial eggs into this one study’s basket. I expect that we’ll see more hail studies in the future that can be compared to this article. Once we see additional research on this topic, we can determine whether we’re seeing the same trends in all the various studies, or if there is still uncertainty in future hail trends.


Weatherlogics has Canada’s most comprehensive hail database. We are also experts in meteorological research and can provide highly specialized research to meet your needs.


Forecasting Summer Weather on the Prairies

Forecasting summer weather on the Prairies is one of the great challenges in meteorology. Summer weather is volatile, ranging from searing heat, to vicious storms, to cool outbreaks of polar air. Northern parts of the Prairies can be experiencing heavy snow, while southern parts experience hot and stormy weather. So, why is the weather on the Prairies so crazy?

Summer weather on the Prairies can be volatile.

The Prairies are a confluence of regions; the arctic to the north, mountains to the west, and the boreal forest to the east. With the exception of the Rocky Mountains in Alberta, there are no features to block weather from coming across the Prairies. That means it’s easy for frigid arctic air to plunge down from the north, or for hot and humid air to surge up from the southern United States. The oceans can be a moderating influence on weather, keeping it from getting too hot or too cold, but the Prairies are far from oceans, making them susceptible to extreme weather. That means the Prairies experience a true continental climate, which is a climate of extremes – cold in the winter and hot in the summer.

It might seem like the Prairies feature a fairly uniform climate, but if you look closely there are actually many variations. In Calgary, the average temperature in January is -7.1 C, almost ten degrees warmer than Winnipeg, where the average temperature is -16.4 C. This difference in temperature exists despite the fact that Winnipeg is actually farther south than Calgary. One of the main reasons why Calgary is warmer than Winnipeg in the winter is because Calgary experiences chinooks; a warm wind that descends from the Rocky Mountains. Since Winnipeg is far from any mountain ranges, it is difficult to remove the dense, cold, arctic air mass that often settle over the city. However, the tables are turned in July, when Winnipeg’s average temperature is 19.7 C, versus only 16.5 C in Calgary. Calgary’s higher elevation of 3557 feet (783 feet in Winnipeg) puts it at a disadvantage when trying to achieve warmer summer temperatures.

Average annual temperatures across the Prairies using 1961-1990 data (image from Natural Resources Canada).

Surprisingly, precipitation is also quite variable across the Prairies. Calgary receives 418.8 mm (16.5″) of precipitation per year, which is over 100 mm (4″) less than Winnipeg (521.1 mm; 20.5″). However, the near-desert region around Medicine Hat in southeastern Alberta only receives 322.6 mm (12.7″) of precipitation per year, nearly 200 mm (8″) less than Winnipeg.

Average annual precipitation across the Prairies using 1961-2010 averages (image from Natural Resources Canada).

There are a number of factors that make predicting summer weather on the Prairies so difficult. One of the main reasons is that the jet stream is weaker in summer than in winter. This makes it more difficult for meteorologists to predict the long-term evolution of the jet stream because weaker jet streams often behave more erratically. In winter, the jet stream is strong, and therefore it is easier to predict its evolution. There is also a stronger connection between the jet stream to other global features in winter, like sea-surface temperatures (you may have heard of ENSO). Another reason why summer weather on the Prairies is hard to predict is thunderstorm activity. Thunderstorms develop almost every day across the Prairies in summer and trying to predict where they will develop is extremely difficult. It is not uncommon to go from blue skies to a raging thunderstorm within an hour or two and trying to predict when and where that will happen is nearly impossible. Sometimes these thunderstorms will also merge together, forming large convective weather systems. These convective weather systems can travel great distances, producing heavy rain and severe weather.  Such convective weather systems are actually very important to agriculture, because 30-70% of precipitation in summer on the Great Plains of North America has been attributed to thunderstorm activity (Fritsch et al., 1986).

The jet stream, shown as red arrows, tends to shift farther north and become weaker in the summer (image from Environment and Climate Change Canada).

However, there are ways to get better weather information. Firstly, it’s important to recognize the source of your weather data. If you’re just getting your forecasts online or from an app, chances are the forecast is mostly or completely automated. In other words, a computer is producing the forecast with little to no human intervention. This presents many problems, because computers often make large mistakes when trying to predict complex weather events. Only professional meteorologists can carefully analyze computer output and modify it towards a better solution. Unfortunately, there are few forecasts available that are reliably made by actual meteorologists. For example, Environment Canada’s meteorologists produce the first two days of their forecasts, but rely exclusively on computers for the rest of the forecast. Since these computers update four times per day, you can see wildly different forecasts from one hour to the next, never mind from one day to the next!

Weatherlogics’s meteorologists produce all of our forecasts, cutting out computer automation. This has resulted in great improvements in accuracy. For example, in May 2017 our forecasts were 50% more accurate than other common weather agencies in Canada. If you’d like to learn more about what we have to offer, get in touch!


Environment and Climate Change Canada: Weather at a glance (accessed June 19, 2017):

Fritsch, J. M., R. J. Kane, and C. R. Chelius, 1986: The contribution of mesoscale convective weather systems to the warm-season precipitation in the United States. J. Appl. Meteor. Climatol, 25, 1333–1345.

Natural Resources Canada: Introduction – Prairies (accessed June 19, 2017):