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Chase Log: April 10, 2013

11 Apr

Distance: 535 miles
Tornadoes: 0
Hail: None

I may not have gotten any tornadoes, but it was a pretty exciting chase while I was on the storm near Shipman, IL!  As with every chase, I learned a few things which I will apply to the next chase.  This is usually about navigating around the storm, as that seems to be something I struggle with!

I began the day with a target of Jacksonville, IL.  All of the models had the warm front moving north, along with the surface low, which was supposed to end up near Quincy, IL in the evening.  Well that didn’t happen.  The front was basically stationary all day, with maybe a hair of northward progression.  Once I got to Springfield, I decided to head south on I-55.  At about that time a tornado watch was issued, which included a couple counties north and east of St. Louis.  I stopped at a rest stop north of Litchfield to watch a few developing cells and wait to see what happened.  I decided to target a cell that developed on the west side of St. Louis, as it was riding along the warm front.

I dropped south to SR 16 heading west.  From there I had planned to drop south on 159, but I missed it, and decided not to turn around.  The storm had been moving NNE, so I was counting on that to continue, and if it did, 159 may have been too far east.  So instead I went up to 111 south toward the town of Brighton.  I was into the rain core before reaching 111, and while I began driving south.  Around this time the storm had begun making a right turn, and took on more of an ENE path.  “Right-turners” are typically a sign of increased shear in the storm, and these are the cells to watch for when it comes to producing a tornado.

As I came out of the rain core I was greeted by a huge inflow band just in front of me, and it was BOOKING into the storm!  I don’t think I’ve ever seen and inflow band with that kind of motion.  Winds at the surface were maybe 40-50 mph, and they were warm.  Dust was being picked up off the road.  Looking to my southwest, there was no visible lowering, but a large rain-free base.  I figured with that kind of inflow, it was only a matter of time before a wall cloud formed.  Looking at the radar at this time, a nice hook was forming, though on velocity scans, no rotation was showing up.  I captured this image after the fact, but my location at this time was right inside the inflow notch.

shipman

I began traveling east to try to get back in front of it, as I was currently in a bad spot!  As I did so, a huge wall cloud formed to my south, and the whole thing was rotating.  Like a geek, I yelled (by myself in the car), “THIS THING IS GONNA DO IT!!!”  It didn’t seem like I was making any progress going east, so I decided to drop south and get behind the area of rotation to avoid being in the direct path should a tornado form!  I’m telling you, the way it was spinning, it looked like it could happen at any minute.  I’ve seen this before!  There was never a tornado warning on this cell, even after I submitted a report of a rotating wall cloud.  I’m sure this is because there wasn’t really much rotation showing on radar, but this all happened so fast, it may have been in between scans, therefore the radar never saw the rotation.

Anyway, after dropping south I found the area of tight rotation to my east.  I pulled off onto a driveway and shot some video.  I really thought it was about to happen.  Below is the video, with the area of rotation right in the center.  You can clearly see the inflow coming in from the left side.

Just as a note, if you go back to the radar image above, you’ll notice a light blue bow extending from the hook on this storm.  That is the rear-flank downdraft (RFD) or outflow.  This is the rain-cooled air wrapping around the back of the storm.  It is necessary, along with inflow, for a tornado to form.  The thing about RFD, however, is while it helps form the tornado, it is also what ends the tornado.  It will cut off the warm inflow air, and that is exactly what happened on this cell.  After getting caught in RFD rain curtains, when I emerged heading east, I could no longer see any rotation.  I could tell at that point I was on the back side of a large shelf cloud.  I wonder if the air would have been clear to the south of this cell, instead of another cell there, would the outflow have been a little bit weaker, allowing a tornado to form?

After heading back north, and then east, I got back out in front of the storm.  I could tell it was done at this time.  The remnants of the inflow tail were there, no longer moving into the storm, and the outflow was visible with a building shelf cloud.  It was beautiful structure, however!  I went to take a picture of it, but my camera batteries were dead, so I took video instead.

I wonder what this cell looked like from 8-10 miles away.  It seemed to have some great structure, and the skies were clear all around it.  Maybe one of these days I’ll have the will power to stay further back and get structure shots, but I typically like to be right in the thick of the action!

To sum up the day, I wasn’t all that disappointed, as I didn’t expect any prolific tornado-producing machines on this day.  I knew there was a narrow window of opportunity, both in terms of geographical location, as well as on any individual cell due to a lack of really good shear.  Directional shear was pretty good, especially along the front where surface winds turned to southeasterly, but speed shear in the lower levels was weak.  I figured if one did have a shot, it would be a short-lived rotation, maybe a 5-minute or less tornado.  I picked the right cell, and got to it at just the right time, it just didn’t have the right ingredients to do it.

You would think all of that time in the car (11 hours) with very little to show for it would reduce my enthusiasm to chase again, but in fact the opposite is true!  I am pumped up for the next chase now, and hoping I’ll have at least one good opportunity before I head off to PA school!

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Posted by on April 11, 2013 in Chase Logs

 

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