While most people are taking cover when storm clouds menace, others fly directly into black and threatening skies as a first line of defense against hail.
The Alberta Severe Weather Management Society (ASWMS) has run cloud seeding operations with contractor Weather Modification Inc. of North Dakota since the mid-90s.
Cloud seeding was an initiative of insurance companies in the province.
The Society began monitoring and controlling storms shortly after a 1991 Calgary-area storm caused more than $500,000 damage. Hail suppression was introduced to reduce the amount of property damage in urban centres.
“The total cost of cloud seeding is about $6 million per year, but when a single storm can cost $500,000 in damage, a one to two per cent reduction in the severity of the storm in one day pays for the program,” said Terry Krauss, president of the ASWMS.
“But when a single storm can cost $500,000 in damage, a one to two per cent reduction in the severity of the storm in one day pays for the program.”
Hail suppression involves seeding severe storms as they head toward or develop over urban areas within the target area, which stretches between High River and Ponoka, an area referred to in the industry as “hail alley.”
“In that area, the number of severe thunderstorms is more than double compared to the rest of Alberta, Saskatchewan or Manitoba,” said Krauss.
Cloud seeding involves releasing silver iodide into the updraft of a developing storm. The particles are ice-nucleating – they attract the water in the cloud to form small ice crystals, Krauss said.
The silver iodide begins to work at a much warmer temperature than water naturally freezes, forming ice crystals at -4 degrees Celsius rather than -40 C, he said.
“It enhances the freezing of water,” said Krauss. “When you penetrate a cloud at -10 degrees on a summer day, that’s still all water.”
Hailstones form when strong updrafts carry water well above the freezing level and grow as more water freezes to them. The more liquid water in a storm cloud, the larger hail can become, which is when golf ball or baseball-sized stones occur, he said.
“We’re trying to speed up the freezing process to limit particles from growing to a large size,” said Krauss. “The amount of water stays the same, but we want to divide it into a thousand more particles. It’s called beneficial competition for cloud water and it’s very efficient.”
Some of the ice crystals formed by cloud seeding melt by the time they reach the ground, he said, reducing not only the size of hail but, often the amount that can cause damage.
Seeding a storm takes a surprisingly small amount of silver iodide. A two-hour flight would use approximately 1.3 kg of the non-toxic substance.
“To put it in perspective, a bag of fertilizer is 10 to 20 kg, so seeding on one day uses less than the equivalent of a bag of fertilizer in the amount of silver iodide,” said Krauss.
Timing is crucial for hail suppression. Seeding must take place about 30 minutes before a storm reaches a town or city, he said.
The five planes flown by Weather Modification Inc. take to the skies as soon as radar picks up potential severe weather to watch for signs of hail development. Only storms that appear to be severe and possible of producing hail are targeted.
“We’re looking for a big convector bubble and a strong updraft,” said Krauss. “If it’s a tall storm, it’s more likely there’s going to be hail. We watch the vertical structure. If it’s just dark clouds spread across the sky and it’s just raining, we’re not flying.”
This year, severe weather has resulted in more than 100 flights between June 1 and July 31, and 220 hours of flight time.
On average over the past 20 years, about 90 storms and 30 days of seeding occur between June 1 and September 15.
This year, the month of July alone recorded 74 storms on 25 days.
“We haven’t reached the average yet, but we’ve had a busy June and July,” said Krauss. “If August continues the same way we’ll be well over average.”
He said 2016 has seen an increase in stormy weather across the province, not only in hail alley.
Kirk Torneby, southern Alberta regional meteorologist for Environment Canada, said a typical year would see eight days of actual severe weather. July saw 19 days of reported severe storms, he said.
The 10-year average in Alberta is 72 hail events where stones are about the size of a nickel, but in July 2016 there were 128 severe hailstorms, he said.
“It has been an abnormally stormy year,” said Torneby. “It’s definitely not a typical summer where you get a break for a week or two with hot sunny skies.”
Referred to by meteorologists as a “bridge,” the heat wave usually seen in July is missing in 2016, he said.
There is no particular cause for unusually unstable skies, he said.
“It’s hard to determine why, or what’s changed,” said Torneby. “There hasn’t been evidence of any specific reason. Some refer to the fact we’ve come off the tail of one of the strongest El Nińos of all time, but really we can’t know.”
He said weather patterns in the foreseeable future look like they promise more of the same – temperatures in the near-normal range for this time of year with unstable air bringing storms into the late afternoons and evenings.
“It’s definitely more active than usual this year,” said Torneby. “It could be anything moving forward, it’s hard to know what’s in store.”
