Lab 12: Revisiting the 2013 Moore Oklahoma Tornado - Colleen Heck

Introduction 

Over the semester, we have learned how powerful both radar and satellite can be for meteorologists. Satellite is excellent for learning about the storm from space, while radar collects accurate ground measurements. Satellites can help detect storm features with ample time before a radar might detect them on the ground. For this study, I revisited lab five from earlier in the semester, where I analyzed the Moore Oklahoma tornado on May 20, 2013. I did a radar analysis using NEXRAD data and McIDAS-V to look at storm features like hook echoes and bounded weak echo regions. Now, I will revisit the case and further analyze it using satellite observations provided by Nasa Worldview. 

On May 20, 2013, powerful convective storms swept through the heart of Oklahoma. 15 tornadoes were reported this day, ranging from EF-0 to EF-5. The EF-5, Moore tornado was one of the fatal tornadoes that swept through the city. It was estimated that it caused 2 billion dollars worth of damage. It took the lives 24 people and injured hundreds more

Figure 1. May 20, 2013 Moore, Oklahoma tornado.

Figure 2: Radar reflectivity (dBz) over Oklahoma at a 0.5 deg elevation angle on 5/20/13 at 19:47 UTC (14:47 CDT)

Figure 2 is the radar reflectivity at the time of the tornado. The radar shows a line of thunderstorms with multiple cells. While the satellite observations do not match the exact time of the radar image, they both offer the same development of the storm. 

Corrected Reflectance 

Nasa Worldview provides daily images from a couple of different satellite sources. I used Terra and Suomi NPP, both data taken at 10:30am local time (LT) and Aqua data from 1:30pm (LT).  

Figures 3 and 4 below both show satellite observations. Figure 4 shows convective activity just starting to form. There is a strict boundary along the line of convection initiation. New cells appear to be developing along the boundary. There seem to be three distinct convective cells. Figure 4 is from just three hours later, and much more convection is seen. This time, the convection is explosive and well developed. The satellite shows fully developed anvil shields that are often seen with supercell thunderstorms.

Additionally, overshooting tops from powerful updrafts appear. This satellite signature can inform meteorologists of just how strong this storm is. A closer look at the overshooting tops can be seen in figure 5. 

Some limitations of this data source have to do with time. They are collected once or twice a day at specific times. This makes it possible to miss certain features or not see them more fully developed. Luckily, scientists can use other satellite sources in real-time. 

 

Figure 3. Corrected Reflectance (True Color)  Terra / MODIS image over Oklahoma on May 20, 2013 at 10:30am CDT

 

Figure 4. Corrected Reflectance (True Color)  Aqua / MODIS image over Oklahoma on May 20, 2013 at 1:30pm CDT

Figure 5. Same as figure 4 but zoomed in to show overshooting tops 

Geostationary Layers

Unfortunately, this case was from 2013, so the Red Visible and Clean Infrared geostationary layers are not available. However, if they were available, the geostationary data could be used to see some weather signatures. 

Visible imagery channels show strong convection as having a lumpy appearance. This lumpy appearance can indicate there are overshooting tops. Additionally, the infrared imagery helps provide information on the cloud top temperatures. Convective clouds are going to have cold tops. Strong cores will have a U shape in the IR. This U shape signature can also inform scientists where the strong updrafts and overshooting tops are. 

Cloud Heights and Temperature

 

In order to determine cloud heights, I looked at two different satellite sources. First I used the Aqua / MODIS Cloud Top Temperature layer at 1:30pm after the storm had really developed. The purple area in figure 6 covers a large portion of the storm with temperatures as low as 150K. This indicates the clouds were extremely cold, most likely containing ice, and high up in the troposphere. Cloud temperatures around the storm are on the warm end at 350K, and most likely made of water. 

Cloud Top height data in figure 7 supports that these clouds were measured from extreme heights. It is estimated that the purple color is around 12,000m. Sounding data that I analyzed in lab 5 had the tropopause at just around this height.

Figure 6. Cloud Top Temperatures  Aqua / MODIS image over Oklahoma on May 20, 2013 at 1:30pm CDT

Figure 7. Cloud Top Height Suomi NPP / VIIRS image over Oklahoma on May 20, 2013 at 10:30am CDT

Precipitation Estimates 

It is not surprising that the highest rain rates are associated with these deep convective storms. High levels of reflectivity from radar data support this. Also, in lab 5, I did an analysis of the Z-R relationship and rainfall rates. Under the Marshall-Palmer relationship, rainfall rates were about 35 mm/hr, and the WSR-88D Convective relationship had values of about 50 mm/hr. Figure 8 below again is before the radar times but still shows areas that exceeded 30 mm/hr.

Figure 8. Precipitation Estimate Aqua / MODIS image over Oklahoma on May 20, 2013 at 1:30pm CDT

Environmental Conditions

The surface relative humidity layer is useful in showing the environmental conditions. Here, the majority of the moisture is east of the storm while to the west it is very dry. This is most likely why the storm developed along the boundary. The moisture east may also indicate there is still fuel for it to further develop at this time. 

Figure 9. Surface Relative Humidity Aqua / AIRS  image over Oklahoma on May 20, 2013 at 1:30pm CDT

Additional Information

Figure 10. 2010 Estimated Population Density over Oklahoma 

Figure 10 is the population density overlaid with the May 2013 storm. Here we can see some of the deepest convection is affecting some of the most populated areas of Oklahoma, shown in red. Even though the population density is not entirely accurate to the date of the storm, this layer still is helpful to see approximately how many people the storm impacted. 

The video above is a satellite loop over the course of they day where you can see just how explosive the convection of this storm was. The overshooting tops are very clear at the end!