Storm Chasing Fever - Blog - Rozel, Kansas Tornado - May 18, 2013 Case Study
Rozel, Kansas Tornado - May 18, 2013 Case Study
Mar 15, 2014
Today's blog entry is to explain the broad synoptic atmospheric overview that led to the tornadoes on May 18, 2013, including the Rozel, Kansas EF4 tornado. I will also review what meteorological parameters I utilized to help me pick a storm chasing target area.
The Storm Prediction Center had issued a moderate risk of severe weather across Kansas and Oklahoma for the possibility of tornadoes, large hail and damaging winds. The tornado threat was elevated over Kansas, but questionable due to weaker 500 mb flow and higher LCLs (more on this later).
A surface low was expected to develop across southwestern Kansas during the afternoon with a dry-line expected to surge east into the better moisture axis and instability. This combined with the marginal wind shear, would help promote supercell storms.
Before we picked our target area, the first parameters I checked were for upper air disturbances that help promote sources of lifting air parcels and atmospheric wind shear.
So, let's first review the 300mb (30,000ft), 500mb (18,000ft) and 850mb (5,000ft) layers of the atmosphere for May 18, 2013 at 7:00PM CDT, 20 minutes before the Rozel, Kansas tornado.
The map shows a strong jet maximum entering the western U.S. with some upper-level divergence noted downstream over Kansas, but is more prominent over Oklahoma. Divergence helps air at the surface rise. The left exit region of the jet is still further west of the plains which supports the most intense upward motion. To conclude, there is broad divergence over the entire area to promote storms across the region.
The map highlights a northwest to southeast line which is a trough axis. Vertical lift will be present across the Nebraska, Kansas and Oklahoma region.
The winds on this map are out of the south-southeast direction. This helps bring strong deep moisture advection in the boundary layer for the storms to tap into. The low-level winds will also help increase helicity and low-level shear.
Overall, the general target area based on upper air dynamics is over Kansas. While not a major severe weather outbreak is likely, with these features alone, we need to analyze other factors. Let's look at wind shear.
The 0-6km shear was 35 knots; on the low-end side of supercells but just enough to keep the updrafts and downdrafts separate. The higher the numbers, the greater chance of supercells.
In my experience, if 0-6km shear looks good, you want to explore 0-1km shear. Values over 20 knots raises a flag for tornado development. In this case, at the time of the Rozel, Kansas tornado, low-level shear increased dramatically from 20-30 knots in the 0-1km layer.
Cape is the amount of energy for air parcels to rise. The higher the number, the stronger the upward motion. Values at this time were between 3,000 - 5,000 j/kg which are on the very high side. The low and mid-level lapse rates were also very steep. From a stablity side, these parameters are looking very healthy for severe storms. Dewpoints were streaming north/northwest from the gulf of mexico ranging from 62-70 degrees from Texas, Oklahoma, and Kansas. The moisture was deep, east of the dry-line.
Keep in mind, most parameters might look great, but it only takes one to have a tornado outbreak fail to materialize. There was one big fly in the ointment on May 18. Can you take a guess? High LCL's. What are LCL's? It stands for the Lifting Condensation Level.
While traveling towards Kansas in the early afternoon, there was extreme mixing occurring across
northern Oklahoma. Our car temperature reached 101 degrees at 3pm. The dew point was also on the low side. Originally, we figured the dry-line was east of us, but it wasn't, only 20 miles west with towering cumulus clouds developing and having a hard time sustaining due to the deep boundary layer mixing. The towering cumulus began to form into storms a few hours later, but to only die off after forming. Lifting Condensation Levels values were extremely high the storms bases were very high-based. Tornadoes have a harder time forming with high cloud bases, and usually prefer low-cloud bases.
Let's provide a brief overview during storm imitation. For more, read the full account of the May 18, 2013 Rozel, Kansas Tornado Storm chasing log.
The first severe storm of the day was across Interstate 70 (see radar below). This storm did prompt a tornado warning with confirmed rotation, but from my knowledge the tornado was rain-wrapped or not visible due to low visibility. The storm we had followed for about an hour to the south, slowly became better organized and it was still isolated. There were more storms across northern Oklahoma, but they were multi-celluar in nature. We didn't want that. My chase partners were starting to get impatient (as they should) about ditching the middle storm, east of Dodge City and travel north towards Ness City/Hays area. It was a crap-shoot, but the storm's updraft base was descending and interacting with the better moisture transport from the south. If it stayed isolated, I thought no reason to ditch this one and get suckered to the storm to the north. A little patience and the rest was history.
Supercells near I-70, Rozel, KS Supercell begins to form - May 18, 2013
So what was our result? First, Storm Chasing is luck, and we were lucky to sit, be patient with the Rozel storm and let it develop from start to finish. From a scientific stand-point it was interesting to watch it develop from a measly high-based thundershower with little organization, to a produce an EF4 large cone tornado. To our amazement, two additional tornadoes formed to our north and east, near Sandford, Kansas for a total of three tornadoes documented. Interestingly, the supercell storm to our north appeared to have slightly better tornado parameters, but that's the luck of the draw.
Studying severe weather parameters does help, but they only should be used as a guide. There are many storm chasers and meteorologists that analyze other parameters (Significant Tornado Parameters, Supercell Composite, etc) but, I didn't cover these, in this blog and it would take weeks to write this blog entry. Please feel free to do research and learn as you go. I don't claim to know it all and never will. If I did, storm chasing and forecasting would become stale and boring. Everyone knows, the atmosphere will do what it wants and the mysteries involved is what makes the science of meteorology simply fascinating. For me, this is what storm chasing is all about.