May 25, 2013

Storm Retrospective: Kinsley/Rozel Tornadoes, May 18, 2013

John Monteverdi
Thom Trimble 

All images copyright © John Monteverdi and Thom Trimble

The storm that eventually produced at least two major tornadoes  near Rozel, KS formed southwest of Kinsley, KS at around 6:45 PM CDT.  

The storm developed, we believe, in a narrow slot of inflow air that had about 3F higher dew points and slightly lower temperatures than did the surrounding air being ingested by storms further north and south.  I've drawn an arrow on the 2100 UTC surface chart to show the flow of air into the storm genesis area.  Note that the dew points on the upstream portion of the arrow are in the 70s.

I wish I could say I had foreseen that narrow jet of air.   But I hadn't.   It's that kind of mesoscale detail that cannot be forecast in advance.  And the luck here was that we were in the exact position at which that kind of feature could really cause explosive development of a storm.   It certainly did in this case.

The storm immediately had a bell shaped lowering (see image to bottom center). Within in a few minutes it had a very good visual appearance with a rain core out to its northeast and something like an RFD cut developing too.

Arrow indicates approximate path of what we think
was a moist inflow jet that the storm intercepted.

We stayed with this storm for an hour or so and  during that time were treated to an absolutely fabulous example of a storm proceeding through the supercell cascade.  While the storm was about 5 miles west of us, the southeast winds really kidked up a notch....probably 20-30 mph.  We believe that the  inflow jet, as explained above, was being intercepted by the storm.   I got a dewpoint of 70.8F on my Kestrel and  a temperature of 84F.  We commented  that it was hard to figure why the storm had such a high base and no wall cloud.     

Bell shaped lowering on rapidly developing storm
west of Kinsley KS.  

Shortly after the development of that inflow jet,  though, the storm base lowered and the RFD slot sharpened.  The updraft area showed signs of bvecoming an RFD occlusion...and, then a nub formed on the north side of the horeshoe base (see picture below)  That rapidly descended visually and became a large tornado, somewhere between a wedge and cone.

Horeshoe base, showing rear flank downdraft cut, and developing cloud base circulation
(the nub above the centered tree).   

About 2 minutes after previous image.   Tornado circulation now developing at ground level.

This is the instant of initial contact of the tornado with the ground.  It's zoomed, but you can see the same trees and farm buildings that are to the left of the distant forming funnel in the picture above.

The good news is that we got great digital stills of the whole thing, and also video.  The bad news is that things happened so quickly that I never had an opportunity to setup the good video camera on a tripod.  Nevertheless, I have video documentaiton of the first tornado development on the lowered base.  

The radar below shows the storm when the tornado cycled up to its strongest.  Our position is shown as the yellow circle.   The names plotted there are the other chasers and storm spotters who were reporting their positions.  The purple triangle is a Tornado Vortex Signature.

GRLevel3 Radar Plot of Kinsley/Rozel storm at time of tornado genesis.   Our location shown as yellow circle.  The magenta triangle is not the tornado but a radar signature called Tornado Vortex Signature. (Time shown is PDT)

Tornado damage (blue and yellow..estimated by
ground survey;  red estimated by DOWS)
(Image courtesy of NWS)
The tornado moved northeastward, as shown on the graphic on the right, until the process known as tornado or RFD occlusion completed.  The tornado turned to the left, cyclonically, around the mesocyclone.  The red symbol at right is the only location where the tornado was sampled by the mobile doppler radar (Doppler on Wheels--DOWS).  There the winds were measured at 165-185 mph and the circulation width at the ground at 3300 feet.  On this basis the tornado was rated an EF4.

At the time the tornado was most intense, the radar signature was extremely impressive.  I've included at right the radar plot from the DOWS at that time below.

DOWS radar plot corresponding to red
symbol above.  Upper left, reflectivity;  Upper right, storm
relative velocity.  (Image Courtesy of NWS)

The tornado was extremely impressive visually for nearly its entire life cycle.   Its visual appearance varied from a cone to a wedge.  It was quite obvious that the funnel was extremely large and had violent circulation around it.

We drove north towards Rozel and the tornado began to narrow...and at first we thought it had begun the roping out process.   But shortly after that the trunk redeveloped with lofted debris north of town.   I told Thom I thought another tornado might develop back along the flanking line, which by that time was east of we were in roaring RFD (warm) air.  

These three images were taken over a five minute period and correspond to when tornado #1 was at its most intense.  We were located about 2 miles south of Rozel at the time and the pictures are shot looking northwest.
Tornado begins to narrow at its base just west of Rozel.

New tornado formed east of Rozel rapidly as first tornado was in
the process of dissipating.  Setting sun provided wonderful
color to all cloud features.

We turned east and moved through Rozel.   We wondered why the police had roadblocked several roads east of the first tornado. Out of the murk, we could then see another fully developed cone...nearly a wedge briefly back along the flanking line.  We barely got pictures of it.

This also was a very substantial tornado, as you can see in the picture at left.  The setting sun began to produced unusual orange and purple highlights on this thing.  It really was gorgeous, towering above us to the east.

The DOWS did not manage to redeploy so quickly to sample the rotation with this tornado.  But it probably would have been at least an EF2 from the looks of it, though that is very difficult to judge from visual appearance alone.
Meanwhile, back at the original occlusion point, the original tornado was still pulsing, but in a downward trend.  At one point it redeveloped a massive cone.

While we were watching the second tornado that formed further southeast along the flanking line, yet another tornado
seemed to appear to the north.

We're debating whether that was a new tornado, or the remnant of the original tornado as the main updraft area probably had crossed the road at that point. That tornado refused to give up the ghost, so to speak.   It took nearly 30 minutes for it to finally rope out to nothing.

To the right  are some pictures of the rope out phase of tornado 1 (or perhaps, as explained above,  it was tornado 3).   We were getting confused in the darkness and the episodes of good and poor visibility  And while it was doing that, it still had a substantial ground level circulation. Finally, even the tiny remnant of the funnel seemingly floating disconnected was associated with ground level debris.

Thom and I agree that tornado 1 was the strongest, and largest, tornado we've seen in our chase careers.  And now that we've had several days to consider what we saw and experience,  we agree that it was the most phenomenal chase of our chase experiences together.

From the decision to get us there, to the good fortune that made us stay in place in Kinsley instead of going north or south, to the road we chose with absolutely perfect vantage points, all was just about perfect.

Last remnants of the rope out phase of Tornado 1 (or it may have been a third tornado).  The last portion of the
funnel seemed to float free, yet it was still associated with circulation at ground level and debris.