#252 Comparing High-Shear, Low-CAPE Supercell Weather Events in the Southeastern United States vs. The Great Plains
Voiceover
Presenter(s)
Jasen Greco
Abstract or Description
High-shear, low-CAPE (HSLC) supercells are a phenomenon in which an anomalously high wind shear makes up for a lack of convective available potential energy (CAPE). These events are not very common, but when they do occur they generate high wind speeds and spawn numerous tornadoes. The initial conditions, severity, and longevity of HSLC supercell cases differ depending on their location in the United States. This study aims to quantify that difference by assessing and comparing HLSC cases in the Southeastern United States to HSLC cases in the Great Plains.
A total of 10 HSLC cases were observed between 2016 and 2021. 5 cases were from the Southeastern United States, and 5 cases were from the Great Plains. Each case was analyzed individually in order to determine the length of time and observe the presence of embedded supercells within the convection. Specific tornado, wind, and hail events were also observed for each case to further quantify their severity. Initial analyses of the longevity and severe weather events suggest that HSLC cases in the Southeastern United States are more impactful than those in the Great Plains.
To better understand how the convection of these cases developed over time, the National Centers for Environmental Information (NCEI) reflectivity radar was used. Additionally, the Storm Prediction Center (SPC) storm reports were observed in order to compare the amount of severe weather events for each case. These two sets of data, along with observations of embedded supercells from each case, will show the variations of HSLC cases between the Southeastern United States and the Great Plains.
Comments
Terry Shirley3 years ago
Hi Jasen - great looking poster! I found it interesting that each of your cases came from a cold season month (Oct through Feb) and there were no warm season cases. Was this by design? You mentioned that the SE cases were driven by dynamics and shear more so than the thermodynamics of the Plains. Do you think season plays a role in this? How would you expect these values to change in events during April - June? Again, great job!
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Jasen Greco3 years ago
Thank you for the comment Professor Shirley! I do believe that seasonality plays a role in the dynamical setup of these cases. Specifically, CAPE values are typically much lower in the cool season due to less instability present. This would make the CAPE values in April - June much higher than in the cool season because the heat present in these warmer months would provide much more instability for supercell cases. Wind shear would also be different in April - June because of the smaller temperature gradient present between the arctic regions and the United States. The wind shear values seen in these warmer months would be lower than those of the cooler months because of this lack of temperature gradient. Overall, the HSLC cases in my study are from only cool months because the conditions in this time of the year are ideal for high wind shear and low instability values. Thanks again for the comment!
Jacob Scheff3 years ago
Excellent work Jasen! As a non-mesoscale person I'm a bit surprised that ~900 J/kg (your Great Plains case average) is still considered "low-CAPE". With a standard deviation of ~700 J/kg in addition, that means some of your Plains cases must have had CAPE of well into the 1000s (or even 2000s at the high end?) As a relatively casual weather enthusiast I would actually think of that as quite a lot of CAPE. So what is the criterion used to call these events "low-CAPE"? I trust you're applying it correctly, but I'm just curious!
On a related note, it's also interesting that for the Southeast cases, the standard deviation of the CAPE was much larger than the average. Since there's no negative CAPE, that would imply that most of the events actually had very low CAPE but a few were much larger (i.e. a skewed distribution). Did you see any differences between these (truly) lower-CAPE and higher-CAPE cases in the Southeast?
On a related note, it's also interesting that for the Southeast cases, the standard deviation of the CAPE was much larger than the average. Since there's no negative CAPE, that would imply that most of the events actually had very low CAPE but a few were much larger (i.e. a skewed distribution). Did you see any differences between these (truly) lower-CAPE and higher-CAPE cases in the Southeast?
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Jasen Greco3 years ago
Thank you for commenting Dr. Scheff! In terms of the criterion used for low-CAPE, this is more of a relative term when used in this study. Low-CAPE implies that the CAPE seen in these cases is lower than what would be expected given their severity. It is true that some CAPE values seen in these cases get quite high, but relative to a typical supercell case their CAPE is quite low. <br /><br />As far as the difference between the higher-CAPE and lower-CAPE cases, I did notice a slight difference in the dynamical structure in regards to the higher-CAPE cases. The overall structure of these higher-CAPE cases seemed to be a bit more organized than that of the lower-CAPE cases. Overall, this did not have much of an effect on my final results because even the higher-CAPE cases did not have high enough CAPE values to alter my results. <br /><br />Thank you again for commenting!
Matthew Eastin3 years ago
Great poster Jasen! I like that you compared and contrasted HSLC cases from two regions. I am curious why cases during the cold season were chosen? Are HSLC events less common during the warm season? Lastly, how do (a) the seasonality of your cases and (b) the mean values of each instability and shear metric compare to those presented in Sherburn and Parker (2014)? I look forward to hearing about your simulation results from the summer research experience.
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Jasen Greco3 years ago
Thank you for the reply Dr. Eastin! Seasonality does play a role in HSLC cases due to a few different reasons. First, CAPE is typically lower in the winter months because of the lower instability present. Next, wind shear is higher in the cooler months because of a larger temperature gradient between the arctic region and the United States. This larger temperature gradient causes wind speeds to be larger, creating more shear. With both of these factors in play, the cold season is the ideal time for HSLC supercells because of the lower instability and faster wind speeds. HSLC supercells are typically noted as a cool season phenomenon. In regards to the Sherburn and Parker (2014) study, the seasonality of my cases matches with their seasonality. It was noted several times in that study that HSLC supercells are a cool month phenomenon, and how their cases are mainly from cooler months. With comparing my instability and shear metrics to theirs, it is clear from my observations of their results that the values I obtained are very similar to theirs. Although they did work with more cases, so their values for these parameters are a bit more established--I can see that they made sure to use cases that had almost no CAPE. Their wind shear values are also very close to mine because both of our studies aimed to have cases with anomalously high wind shears. Overall, both of our studies were very similar in terms of seasonality and the values of the parameters that we used. This shows that HSLC cases as a whole behave similarly to one another. Thank you again for commenting!
Becky Croxton3 years ago
Hi Jason,
What an awesome poster. The content is written in a way that novices like myself can understand the basis and the graphics are terrific additions. My primary recommendation is to explain a bit (in the intro and in this summary) about why this work is important. I recognize that findings indicate noteworthy differences between the two locations-- but how can folks use this information in future practice or continued research?
Nice work!
Dr. Becky Croxton
What an awesome poster. The content is written in a way that novices like myself can understand the basis and the graphics are terrific additions. My primary recommendation is to explain a bit (in the intro and in this summary) about why this work is important. I recognize that findings indicate noteworthy differences between the two locations-- but how can folks use this information in future practice or continued research?
Nice work!
Dr. Becky Croxton
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Jasen Greco3 years ago
Thank you for the feedback Dr. Croxton! I’ll be sure to apply it to future research that I complete. I really appreciate it!
Artur Wolek3 years ago
Fantastic poster and presentation. Although this area is not my expertise I was able to follow along with your methods and findings and learned a lot about this research. Great work!
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Jasen Greco3 years ago
Thank you for the comment, I’m glad you were able to understand and learn something new!