Posts Tagged With: severe weather

Do Early Tornado Events Portend for an Active Tornado Season this Spring?

After 2011’s tragic number of tornado-related deaths, and the large number of destructive tornadoes that hit densely populated areas, many people ask me if 2012 is going to be as big of a tornado year as last year. Now that we already have had deadly tornado events in February, plus the historical tornado outbreak on March 1st and 2nd in the Southeast, the interest in this year’s storm season is even more intense. The March event was historical because over 110 tornadoes were reported during the 2-day period, surpassing the largest number of tornadoes reported in any tornado outbreak in the month of March. Sadly, there were at least 40 fatalities from this outbreak.

US Tornado Deaths

provided by Harold Brooks of the National Severe Storms Laboratory

As you can see in the Figure (provided by Harold Brooks of the National Severe Storms Laboratory), the 552 deaths in 2011 were anomalously large compared to the number of deaths over the past 25 years, and so were the number of tornadoes (1,690 as reported by SPC). For comparison, in the past 10 years, we averaged 1,274 tornadoes per year in the US and an annual average of 56 deaths. In general, the National Weather Service did a great job in providing watches and warnings for the large events that caused a high proportion of deaths in 2011, with warnings often providing more than 20 minutes of advance notice. You can see from the figure below that there is a steady downward trend of tornado-related deaths in the United States over the past 50 years, which is attributable to the continuous improvements in technology and techniques made by the National Weather Service during that period. But last year was far from the norm or trend, hopefully we will not see another year like it for a long time.

Will 2012’s tornado season be as terrible as 2011? The short answer is that statistically speaking, it’s highly unlikely that the number of tornado deaths in 2012 will match or exceed the numbers in 2011. The reason for this is simply because in 2011 many EF-4 and EF-5 tornadoes struck high density urban centers, and simple odds make it unlikely this will happen again in 2012. This is not based on any physical reason other than statistical probability.

Regarding the number of tornadoes expected for this year, that is an interesting scientific question. I have talked to many people in the Norman weather community over the past couple of weeks and asked them what they thought the Spring Severe Storm season would be like. The consensus is that Spring 2012 will likely be an active severe weather year but no one believes it will be as active as 2011. I have heard this from research scientists, storm chasers and operational meteorologists. The reasons that each knowledgeable person gave me varied, but in general most people agreed that the large scale weather patterns are different now than they were in 2011 so we should expect different results.

Looking back at 2011, there were many meteorological reasons for the large number of tornadoes and strong destructive tornadoes; one of the key reasons was that a very strong jet stream set up which frequently pushed upper-level energy to the Southeast part of the U.S. contributing to the outbreaks. This is more common during La Niña events, which is a phenomenon where sea surface temperatures in the central and eastern Pacific around the equator are cooler than normal.

In early 2012 La Niña is still around, but climate forecasts for the next few months suggest that the current La Niña condition is fading fast and likely by the May time frame will be in a near neutral (normal) pattern. Another key ingredient to severe weather is warm moist air. And in the South and Southeast this winter there have been very few strong cold fronts that have penetrated all the way through the Gulf of Mexico; so Gulf sea surface temperatures are already near 70 degrees.

What does this mean for weather and storms east of the Rockies during the spring storm season? Based upon discussions with a large number of my “severe weather expert” friends, I would say there are two camps, one that believes that early events this spring in the SE will likely continue due to the large scale weather patterns and the warm moist air that is nearby, creating a good environment for storms; then as La Niña abates and upper level patterns shift, storms and tornadoes will be reduced and tend more towards climatology as we get to the May time frame, this would result in a slightly above average year for tornadoes with the biggest events in the Southeast in March and April.

The second camp is similar in that they believe that early in the year there will be the strong and frequent severe storms in the SE for the reasons stated above but this camp believes that as La Niña abates and upper patterns shift, that energy will be directed over the Central Plains causing more frequent and severe events in that region in May and June. In this scenario, we would expect a very active year in total with the number of tornadoes well above climatology.

I personally am in the second camp. I believe that the most likely scenario is for the most frequent and severe storms to be in the SE in the next two months and then we should see that energy and thus storms move west into the Central Plains culminating in a very active severe weather and tornado season.

March 1st starts the unofficial “tornado season” in the Central Plains. There will be big tornado events and sadly people will be killed. Everyone that lives east of the Rockies should own a weather radio for your home and have the iMap Weather Radio App on their iPhone (WDT launched version 2 on March 2nd, Android launches in late April). Both provide lifesaving alerts. iMap Weather Radio provides “follow-me” alerts plus an interactive map with your location and the warnings overlaid on top of radar data. Additionally, in areas where WDT has media partners you can watch their live streaming television feed within the app during severe storm events. WDT has spent three years developing iMap Weather Radio and has a fully redundant computing infrastructure to ensure that watches and warnings are delivered in a timely manner. We are very proud of the app and the alerting systems we have built, and our goal is to save lives.

Over the coming months I will post to this blog at least once a week and more often during severe weather events.

Categories: Alerting, Severe Weather, Tornado | Tags: , , , , , , , , , | Leave a comment

Making Tornadoes Less Deadly…

There has been a lot of discussion in the Norman Meteorological Community in the past few weeks over the number of deaths in the devastating tornado season we have had so far this year.  With over 550 lives lost and scores more injured it is sometimes hard to understand how these many lives are lost and people affected when we have greatly increased the capability to warn people in advance of these tragic tornadic events.

If you examine the three biggest outbreaks of the year (Alabama, Joplin, and Oklahoma) you quickly see that the National Weather Service did an amazing job of forecasting, and providing watches and warnings for these events.  Days in advance of these events, the Storm Prediction Center had strongly worded convective outlooks, that in all three cases, provided excellent heads-up to the public.  On the day of these events, strongly worded tornado watches were issued hours in advance, and tornado warnings had average lead times greater than 20 minutes for most of the tornadoes during these three events.

Today, there are many more ways that people can receive weather information then say even a decade ago with the ubiquity of Smartphones and the quality of graphics presentations by television meteorologists.  So why did so many people die?

I believe that there are many reasons for the large number of deaths this year, the first is that there were a number of large violent tornadoes that happened to hit densely populated areas.  These EF-5 and EF-4 tornadoes killed some people that did all the right things.  Some killed had received the warning, gone to a safe place in their home and yet the tornado was so strong that it did not matter; they would have needed to be underground or in a safe room to have survived.  There are others that received the warning and chose not to take any action until it was too late.  And of course there were others that believed that “I have never been hit by a tornado before when there was a tornado warning, so why would it happen to me now?” The cried wolf syndrome is a big factor.

The reality is that the science of meteorology and the tools at the disposal of meteorologists (especially Doppler weather radars) have greatly increased the capability to warn the public.  In fact, the average lead-time of tornado warnings used to be zero minutes before the NEXRAD program was implemented in the early 1990s, placing 144 Doppler radars around the United States.  Today the average lead-time to tornadoes is 14 minutes, a great leap forward in 20 years.

U.S. Tornado Count - From 2000

But the percentage of tornado warnings that are false alarms has stubbornly stayed about 75%, meaning that 3 out of 4 tornado warnings do not have a tornado reported.   The NWS continues to push the science envelope (in a positive manner) to gain more lead times for tornado warnings.  Often tornado warnings are for a period of 45 minutes and cover a fairly large area.  One thing that exacerbates the perceived false alarms is that many media outlets, smartphone apps, tornado warning sirens and other communications to the public warn for whole counties rather than the portion of the county that is actually warned for.

In my opinion, a big push needs to be made to only provide warnings for the area that is actually warned for by the NWS meteorologist, which is described by a polygon.  And I also believe that we need to somehow provide more information on the timing of the event at each location.  If what the public perceives when they receive a tornado warning, is that a tornado will occur only a small percentage of  time somewhere in my county and sometime in the next 45 minutes, it does not provide the type of information they need to narrow the warning to determine if it is an actual risk to them and when.   Thus, the natural tendency for humans is to not react at all, or to look at the skies watching to see if the warning is a real, but not reacting or moving to safety until actual observation of the tornado has occurred.

In my next blog, I will discuss how the smartphone revolution along with LBS can make a big difference in communicating warnings to the public.

Categories: Tornado, Uncategorized | Tags: , , | 2 Comments

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