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Stormy weather: Preparing property to ride out more frequent & severe convective storms

Peter J. Gore Willse, PE., FSPE, a research expert from AXA XL gives advice on how to prepare your property for stormy weather, minimalizing property damage and insurance losses.

26 Aug 2019

Warm air rises. It’s a lesson that many of us remember from science class. When it does, carrying moisture with it, it results in a weather condition that allows a storm to develop.

Convective storms are essentially thunderstorms, which – depending on whatever other meteorological conditions are present – can often bring with them other weather hazards including lightning, heavy rain, hail and, in some instances, tornadoes. As recent data shows, convective storms are becoming a more frequent and costly occurrences. To minimize property damage and subsequent insurance losses when one of these storms rolls in, we are taking a hard look at how we can better protect properties. 

Not exclusive to Tornado Alley 

Peak tornado season in the US typically occurs from March through May in the southern states; late June through August in the northernmost states, but tornados could occur at any time. In 2019, there has been a steady stream of tornadoes, hail, straight-line wind and convective storms across the US, and not just in Tornado Alley, which refers to more tornado prone areas like Texas, Oklahoma, Kansas, South Dakota, Illinois, Iowa, Missouri, Nebraska, Colorado, North Dakota, Ohio, and Minnesota. Nearly 4,400 reports of tornadoes, hail and straight-line winds were reported in May of this year alone. Among them, more than 362 tornadoes were recorded, the highest since 2015, when 381 tornado events hit during the month of May.

Tornado season in Europe and western Russia occurs from May to August, but tornadoes have occurred in December and January. According to Dr Pieter Groenemeijer, director of the European Severe Storms Laboratory, Europe has an average of 300 every year. The worst tornado outbreak in Europe occurred on 23 November 1981 in the United Kingdom where 104 tornadoes occurred. Most of these were weak tornadoes but 57 were classified as F1 and 2 were classified as F2 events. Between 31 August and 14 September 1994 there were 23 tornadoes in northern Italy. On 9 June 1984 there were 22 tornadoes in western Russia. There was 1 tornado classified as an F4 and 1 classified as an F5.

Asia is not without their season, tornadoes occur mainly between April and November. There were only a few reported tornadoes in the 1990’s.

From the Australian Bureau of Meteorology, there is no defined tornado season in Australia. Tornadoes are more commonly occur in late spring to early summer but can happen any time. Most of the tornadoes occur in Western Australia, southeastern South Australia, and from the area around south-eastern Queensland to the far north coast of New South Wales. The islands of New Zealand are also prone to tornadoes.

With growing frequency

Some meteorologists and scientists are carefully watching tornado activity and noticing shifts in timing and frequency. According to recent coverage in Scientific American, scientists say they are observing ‘macro-scale’ changes in tornado frequency and variability across the US. And, an analysis of federal disaster spending since 1954 shows that tornadoes are becoming costlier. According to Federal Emergency Management Agency (FEMA) data, the agency has spent $7 billion since 2001 on tornado-related damage, which includes $5.3 billion repairing roads, utilities and other public facilities and another $1.7 billion paid to owners of tornado-damaged homes and businesses.

Scientists say they are observing ‘macro-scale’ changes in tornado frequency and variability across the US.
US Tornado data analysis by NOAA’s National Severe Storms Lab are also indicating startling trends. The number of EF1 or higher tornados, says NOAA, has remained constant since the 1970s, however, frequency is changing, as the May 2019 activity suggests. In the 1970s, there were about 150 days per year with at least one confirmed tornado in the US. According to NOAA scientists, that number fell to between 90 and 100 days in recent years.
Over the same period, the number of days with dozens of tornadoes – 30 or more – have increased by a factor of five, from one day every other year to 2.5 days annually.
NOAA’s National Severe Storms Lab

A heftier price tag

According to Karen Clark & Co’s latest estimates, annual property losses for tornados and other convective storms are now said to be approaching $25 billion annually, which is higher than hurricane and earthquake perils combined.

While tornados can bring costly property damages, hail is the actually the biggest driver in convective storm damage. There were 6,045 major hail storms in 2017, according to the most recent statistics from NOAA’s Severe Storms database. According to various industry sources, during the past five years, insurance claims related to wind and hail damage on a national basis accounted for almost 40 percent of all insured losses, averaging approximately $15 billion annually. And that figure appears to be growing each year.

Storm prep

Convective storms seem to crop up out of nowhere. Once there’s a severe storm or tornado alert, it’s probably too late to do much more than find a secure place to ride out the storm. Before storms roll in, however, there are a number of things commercial property owners can do to minimize damage and destruction. Preparations to consider:

  1. Get the roof right. Inspect it, repair it and check the roof, wall and foundation connections to minimize areas where wind – and water – can enter the facility.
  2. Perform routine maintenance including securing attached structures to minimize risk of significant damage, prevent vegetation on the property from becoming flying debris.
  3. Have a plan: Know where to go when a severe storm or tornado threatens – and set up a plan on how to communicate with employees and families.
  4. Finally, close ALL windows and doors. This will help keep the roof on, according to the Insurance Institute for Business and Home Safety (IBHS). Closing windows and doors helps compartmentalize the pressure inside a business or home into smaller areas, thus reducing the force on the roof by as much as 30%, giving the roof a better chance of staying intact.

AXA XL Risk Consulting property engineers have developed a number of guidelines to help their clients fortify properties to prevent losses.

Resilient building

In addition, before tornado season, think about retrofitting your commercial property to be more resilient, or if you are building new, take advantage of the numerous advances in materials and construction processes that are available today.

If your building or facility is in one of the areas affected by severe convective storms, especially tornadoes, think about building or retrofitting for wind resistance. Advances in building materials and techniques have come a long way to improving the resiliency of construction and retrofitting might be less expensive than one might think.

There has been a lot of research on what it takes to build resilient buildings. In 2013, Florida International University’s International Hurricane Research Center’s Wall of Wind™ facility tested pre-Hurricane Andrew building codes against post-Hurricane building codes by stimulating a Category 5 windstorm with 12 massive fans cranked up to 160 mph. Video confirms that both roofs were torn up, but the new one –based on new building codes – mainly lost shingles.

As a result, building codes in Florida and other storm-prone areas have been substantially strengthened to ensure better outcomes. Going beyond emergency preparedness and disaster preparedness, the Insurance Institute for Business & Home Safety plays a critical role in improving property resiliency by conducting building safety and mitigation research at its research center in South Carolina. At the facility, engineers test the performance of full-scale residential and commercial structures during simulated severe weather events including wind and hailstorms. From this research, IBHS helped design and manufacture resilient homes in Florida and the Carolinas. When the Category 4 Hurricanes Florence and Michael hit the US in 2018, the IBHS test homes survived intact.

Funded by private industry, federal and state agencies, IBHS has also developed a voluntary set of national standards for resilient construction including FORTIED Home™ and FORTIFIED Commercial™. The programs help design professionals work with building owners to choose a desired level of protection that best suits budgets and resilience goals.

While we can’t harness Mother Nature, there are now alternatives available to help commercial property insureds withstand weather’s wrath more effectively than ever before.

About the Author
Peter J. Gore Willse, PE., FSPE is Director of Research for AXA XL Risk Consulting. To learn more about convective storm prep and resilience, contact Pete at

View original blog here.