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Moore, OK Tornado Frequency

Over the last two days, severe weather has returned to the Central Plains in the U.S. This recent outbreak was by no means historic but it has become the most active severe weather outbreak thus far in 2015, with eight tornadoes, 31 wind reports and 162 hail reports, 13 of which were reported as 2″or larger.  Given the tornado wind damage that occurred in the towns of Moore and Sand Springs, OK, it comes as no surprise that PCS issued its first Wind and Thunderstorm CAT bulletin of the year, although it is abnormally late for such an issuance, due to the lack of severe weather.  In fact, since 2000, typically the insurance industry would have experienced just over 3, nearly 4 PCS loss events with an average of $1.3B in losses by the end of the first quarter.

BMS iVision March 25 Hail Analysis

BMS iVision March 25 Hail Analysis

Above is a look at the BMS iVision Verisk Climate hail size swath overlaid with the various Storm Prediction Center Local Storm Reports from the March 25 severe weather outbreak over the south-central plains.

There are no official tracks or ratings of the two tornadoes that impacted the cities of Moore and Sand Springs yet – those will come later today from the Tulsa and Norman, OK National Weather Service (“NWS”) offices – but, sadly, it has been verified that the Sand Springs tornado was the first deadly storm of the season. This comes later than the 20-year average for the first killer tornado of a given season (typically, February 11), but one month earlier than that of the 2014 season, which occurred on April 25.

The tornado that hit Moore, thankfully, looks to be not nearly as devastating as the same tornadoes that hit the city in 1999 (F5), 2003(F4) and 2013(F5). It is interesting, nonetheless, because it is not only the fourth tornado to hit the same general area in the last 17 years, but it also tracked in an unusual direction.

OKC Tornado Track 1880 - 2013

OKC Area Tornado Track 1880 – 2013

The image above, created by the NWS office in Norman from the work of Tom Grazulis, a tornado historian, shows many tornadoes that track over the Moore/Oklahoma City area travel in a northeast direction. The tornado yesterday, however, tracks in an atypical southeast direction, as the preliminary NWS map below illustrates.

Prelimimary NWS March 25 Moore, OK Tornado Track

Preliminary NWS March 25 Moore, OK Tornado Track

The other thing that becomes apparent from analysis of the 156 documented tornadoes that have occurred in the Oklahoma City metro area (OKC), is this location appears to be a magnet for tornadoes – it experiences an average of just over one each year. Since weak tornadoes were not always documented prior to 1950, this number is likely well underestimated, according to NWS. In fact, Grazulis’ study confirms the OKC region has experienced 13 violent tornadoes (F/EF4 or stronger) since 1880, including the May 19, 2013 and May 20, 2013 tornadoes in Shawnee and Moore, respectively. Also through 2013, OKC experienced two or more tornadoes on the same day 26 separate times, with only three time periods since 1950 with an over two-year lapse between tornadoes.

However, OKC and Moore are not the only areas that have experienced similar tornado frequency. Statistical work from Florida State University’s Jim Elsner suggests there are many areas comparable to the size of Moore with just as many or more tornadoes occurring since 1950, as shown in the image below.

FSU Jim Elsner  analysis of areas comparable to the size of Moore, OK with as many or more tornadoes than Moore since 1950.

FSU Jim Elsner analysis of areas comparable to the size of Moore, OK with as many or more tornadoes than Moore since 1950.

So, as the insurance industry prepares for the severe weather season, it is already apparent that Tornado Alley is appropriately named, since there are many areas within this region that experience the same tornado frequency as Moore. But, there is still no clear reason why, in recent years, Moore keeps getting hit by tornadoes. Studies have shown the affects of urban environments can sometimes enhance rain from thunderstorms downwind of cities (and Moore is just south of OKC), but little work has been done to determine if cities actually impact tornado formation.  Future work in the insurance industry might answer these questions.

 

Unusual Weather we’re Having, Ain’t It?

I have been saving this title for awhile, and with the recent 75th anniversary of the release of The Wizard of Oz, in which the cowardly lion says this line as he notices the fallen snow on the poppy field, I find it a fitting start to a discussion about extreme weather. Interestingly, this might also be the first case where a blockbuster movie promotes the idea that average weather can manifest into “extreme weather,” such as a garden-variety tornado in Kansas turning ugly and transporting people to alternate universes.

Images courtesy of Warner Bros. Entertainment

As a meteorologist, I often run into self-proclaimed armchair meteorologists all the time. It has never been easier to get weather information via a blog, Twitter, or on television, which now has at least four cable channels devoted solely to weather. Because weather impacts almost everyone on a daily basis and changes often, it is closely watched. However, with this accessibility of information, one can easily become brainwashed with the idea that normal weather is somehow extreme.

The Media Research Center has just released what I think is fascinating research. The Center analyzed broadcast television network transcripts for morning and evening shows looking for stories using the phrase “extreme weather” between July 1, 2004 and July 1, 2005, and also between July 1, 2013 and July 1, 2014. Ten years ago, ABC, CBS, and NBC barely used the phrase. Now, its use is prolific, despite scientific disagreement regarding extreme weather trends, as discussed in the most recent Intergovernmental Panel on Climate Change Fifth Assessment Report (Chapter 2).

According to the Media Research Center, between July, 2004 and July, 2005, the three networks only used the phrase “extreme weather” in 18 stories on morning and evening news shows in that entire year, even though there were several opportunities to use the phrase when reporting on the 13 named storms that impacted the U.S. during that period.

Now, the familiar phrase of the networks, “if it bleeds, it leads” has taken a backseat to “extreme weather.” In the past year (July, 2013 through July, 2014), the same network news shows discussed extreme weather 988 percent more often, in a whopping 196 stories. That is more than enough stories to see, on average, one every other day. Here is a short video montage to illustrate:

This is despite lower occurrences of severe weather (e.g., hail, wind, tornado) and hurricanes than were observed during the same period 10 years ago.

The Media Research Center study states that “extreme weather” was frequently used by the networks to describe fairly normal weather events, such as heat waves, droughts, tornadoes, hurricanes and winter storms, and they often included the phrase in onscreen graphics or chyrons during weather stories. ABC even has an extreme weather team, dedicated to covering such events. We also get footage from storm chasers that make a living driving into the worst weather.

Since some people still read the old-fashioned newspaper, let’s analyze the 162-year history of the New York Times, which can be done using a tool for graphing the frequency of use of certain words and phrases called the Chronicle.

It is interesting to note that the 1933 hurricane on Long Island or a major drought in 1988 were not considered extreme weather events. The disproportionally high use of the phrase “extreme weather” started after 2005.

The publishing of news is inherently an ephemeral act. A big story will consume public attention for a day, a month or a year, only to fade from memory as quickly as it erupted. There is no doubt that weather events get more attention in this day and age of instant communication and technology, and the speed with which this information is shared certainly has an influence on how people think. It is important to remember that extreme weather is completely natural and there will always be extreme weather somewhere, as the atmosphere is in a constant battle to reach equilibrium. In fact, it is less likely to have a day that is perfectly average than to have one that is one or two standard deviations above or below the average. However, the use of the phrase “extreme weather” in the media occurs with alarming regularity and is undoubtedly influencing the insurance industry.

Severe Weather in a Warming World

Andy Siffert, BMS’ resident Meteorologist, discusses Severe Weather in a Warming World

As we have all seen in the media it would appear that on May 15 Mother Nature has turned on the severe convective storm season, which to date had been historically quiet in terms of insurance losses and severe convective storm reports.

Since May 15 the preliminary tornado count stands at 305 tornadoes, but considering the nation is currently at the climatological peak of the severe convective storm season and the tornadoes are occurring precisely where historically they should occur, the impacts of the severe weather should be expected and can be easily explained by understanding the current weather pattern.

The reason we have seen the recent uptick in severe weather activity to more normal levels is the spring of 2013 has been climatologically cooler than normal over the eastern two-thirds of the country, which has kept instability levels low. This is most likely due to a weather pattern associated with the a negative phase of the Arctic Oscillation (AO), which has kept a low amplitude jet stream pattern in place over the eastern portion of the U.S., allowing cool air from Canada to spill southwards into the U.S. blocking warm moist air northward progression from the Gulf of Mexico.

Starting in mid May a shift in the jet stream winds resulted in a weather pattern that allowed for frequent weather systems to draw upon the warm moist air from the Gulf of Mexico to clash with the cooler, drier air moving east off the Rocky Mountains. This different weather pattern has provided the main ingredients necessary to produce what have been widespread multi-day severe weather events.

Understanding weather patterns can fluctuate explains the last three years of tornado activity, which have experienced both a record minimum and record maximum tornado count. These two extremes of recent tornado surplus (2011) and the current tornado drought are rare and considering they are back to back it makes the occurrence even more unusual. However, these patterns have resulted in several contradictory views on the impact a warming world might have on severe convective storms in the U.S. In a warming world should we experience more seasons like 2011 or fewer tornadoes like 2012? Are extreme tornadoes like Moore, OK, a result of this warming world?

In the latest BMS Introspect – Severe Weather in a Warming World and Its Impact to the Insurance Industry we attempt to answer these questions.