August 24 2006 central SD chase



Departed KC at 330am with a rough target of Aberdeen, SD.  A data stop in Brookings revealed a couple major wrinkles in the set-up, which necessitated over two hours

of in-depth analysis.  Ultimately I stuck with the original plan, adjusting my target a tad southwestward to Faulkton SD.  En route, I got chills while passing through

Manchester, having immediately recognized the entire area from the handful of remarkable videos from that particular day.  Things began looking up as pressed onward;

the lead disturbance's cloud canopy cleared, pressure falls resumed with surface winds becoming southeasterly again, and dewpoints held in the upper 60s right up against

the east banks of the Missouri River.  Even better, the surface low and wind shift were moving only slowly eastward, and towering cumulus were dotting the western horizon

by the time I reached Faulkton.  Not yet wanting to commit to either north or south, I watched and waited on highway 212 west of town for a few moments.






A pair of cumulonimbus rose over eastern Dewey county around 2:45pm.  The southern updraft gradually began to thrive as it crossed Lake Oahe, shown in this photo with its dissipating sidekick.  Not yet observing any development farther north, I dropped south out of Lebanon SD on gravel roads to get into better position.  (Paved roads were exceedingly scarce in this area.)

By 4:00pm, the compact storm had developed a healthy FF core and occasionally displayed weakly rotating lowerings, as in this photograph.
I navigated around the Stone Lake Public Shooting Area (unfortunately I left my rifle at home...), second-guessing my decisions as a storm nearer the ND-SD border intensified and garnered a tor-warning.  Then everything changed, so to speak... as the storm's updraft strengthened rapidly and began lowering its base (420pm), becoming a bonafide classic supercell!  A wall cloud with very impressive rotation developed soon after.
These photos of course don't show it well, but mega-zooming with the camcorder revealed that a great deal of dust was being generated near the ground directly beneath the wall cloud.  Review of video suggested this was probably not tornadic in nature.
The wall cloud took on an outflowish appearance thereafter as I was forced to jog eastward for the next south option.  Then my gravel road split before I expected it would (a GPS would have been helpful).  With the storm moving swiftly my way at 35mph, I immediately re-traced my steps on MS Streets & Trips to see where I'd goofed.
Then I glanced up and noticed a tornado was on the ground already (436pm), in spite of T/Td spreads ~22F that far west.  I found a good viewing position near what I was pretty sure was 327th Ave & 185th St (which ended up being correct).  This was in extreme northwestern Hyde county, looking west-southwest toward central Sully county.
The tornado was extremely high-based, and tracked 18 through 14 miles away from me per ABR storm survey.
The translucent tube gradually filled in with condensation & dust.  Cloud tags rotated cyclonically around, revealing the entire tornado.  The camcorder viewfinder revealed that the rate of rotation in the funnel was already respectable.

Tornado became more of a dirt-choked stovepipe and began to accelerate southeastward.

Wrapping motions were quite dramatic by this point.
The condensation funnel constricted and leaned over within outflow.
Condensation dissolved (449pm), with weak circulation hanging on a while longer within broader bowl of dirt.  Beautiful, RFD-scoured RFB above looked like a carbon copy of the post-tornadic 06/07/05 storm in southwest SD.  Cyclic formation of a new mesocyclone occurred over the next 10 minutes as I drove south and phoned the NWS to refine the location of the tornado.



Dissipating Onida tornado beneath old mesocyclone on the left; rapidly condensing cloud material on the right, which is where the new mesocyclone was born (456pm).
The beefy low-level meso took shape in 10-15 minutes, and was far lower to the ground than the previous one.

The mesocyclone crossed the road behind me at 327th Ave & 185th St.  A modest RFD blast followed.  The feature at the center of this photo then produced a vigorous dirt-churning tornado in the field immediately next to the road from 510-512pm.  Video only.

The mesocylone became very wet and disorganized as I made the 7 mile jog eastward to dry pavement (N-S Highway 47).  Upon arriving, I observed this snaky funnel extending 2/3 of the way to the ground (523pm).  No touchdown confirmed.
I drove south a few miles to get some breathing room again.  A quick look back indicated the storm was clearly re-organizing and strengthening.
I continued south.  There was nary a gravel road to be found off of this stretch of highway in Hyde county, and it appeared I'd have to go all the way south to Highmore and then take Highway 14.  Suddenly, a large lowering appeared in my side rearview mirror.  I turned around and drove back north again, filming the rapid evolution of a gorgeous truncated cone tornado ~2 miles to my northeast.  It quickly narrowed into a stovepipe, strongly resembling the taller tornado of the Stockton KS pair on 06/09/05.  Finally, just before I pulled over and snapped this photo, the tornado began to dissipate in the most interesting of ways: it broke into three pieces.  Tornado time 5:33-5:36pm.
As I headed east on Highway 14, the inflow-outflow interface of the storm became quite remarkable.
As the impressive, arcing RFD slot cut in, the storm was definitely getting "the look."  Feeling a tornado was imminent, I moved north for a closer view.  The area of interest was the agitated cone-shaped lowering above the sunflower field.  It didn't produce, and I headed back to the pavement.
The inflow band became even more pronounced as I attempted to "beat" the storm to the town of Miller.  In a strangely humorous moment, I observed a man casually exiting a roadside rest area (which consisted of a single porta-potty type unit for him and for her).  As he returned to his vehicle, he glanced nonchalantly over his shoulder at the storm.  A tornado would touch down north of the porta-potties a minute later; I can only assume he escaped the area unscathed.
I turned back west and watched as the tornado was born (6:04pm) just north of Highway 14.  My hail-ravaged car roof provided a lovely mirror image of the scene.
I was acutely aware of the rainbands closing in on me from the north.

Condensation eased up for a moment as a car whizzed in front of the tornado.

The first raindrops began to fall as condensation returned to ground level and crossed Highway 14.
A flurry of birds screamed southward to escape.
This car drove right through the tornadic circulation.
Heavy rain and pea-sized hail ensued.
The tornado moved southeast into wheat stubble fields and became a drillpress with a dynamic debris fan at ground level (much more apparent on video).  The tornado wrapped completely in rain at 6:11pm.
Headed south from Miller on Highway 45 and saw a silver-white tornado thrust out the back side of the ragged mesocyclone (possibly the same tornado as the previous one), along with a vivid double rainbow.  I observed this tornado from 6:20pm until 6:22pm, when grabbing for my digital camera again brought about its demise.  I was well behind the storm by this point.  Highway 14 continued east and then southeast out of Miller, and would put me back in the game fast... but at what expense?  I had no option but to use the side roads once again.


After many minutes of sunny driving, I drove back beneath the shadow of the supercell.  Gradually I gained enough contrast to make out the mesocyclone, which was entirely shrouded in precipitation.  After having stair-stepped 31 miles on gravel since Highway 45, I finally reached pavement near the town of Virgil and headed dutifully east.  The ridiculous inflow band came back into view, shown here.

A snaky rope tornado appeared suddenly off to my northwest (7:19pm).
The tornado moved fairly quickly east-southeast, coming out into the sun and growing thicker.
The tail end became vertical and planted itself firmly on the ground.  The tornado took on a shape nearly identical to the Cheyenne WY rope-out years ago.
In the last minute, the tornado had lengthened by about a factor of two.
At this point, a brown froth of heavy precip enveloped the tail of the tornado, while the "top" half moved out over Highway 37 and developed some wild kinks.  Rotation within this funnel was impressive.
Same shot, cropped to show the most wildly spinning portion.  As the RFD picked up, I instinctively switched to video (good call).  The tail of the tornado came into view once again.  In the craziest scene I've ever witnessed, the middle segment of the tornado bucked upward in response to the strong outflow, while the tail--stark white within the dark brown rainbands--pushed *rapidly* across the highway and into a grove of trees.  The best way I can describe the tail's behavior is to compare it to a ballerina tip-toeing as fast as she can while trying desperately not to fall down.  (Sounds strange, I'm sure.)  The tornado was literally blown apart seconds later at 7:23pm.
I stuck to highways for the remainder of the chase, which cost me the Cavour tornado.  I re-approached the supercell here from south of Carthage, where laminar low-level structure indicated that increasing CINH north of the warm front was beginning to take its toll on the storm (8:00 pm).  When I reached the updraft base near Carthage, it was very wet and very non-descript.



Soundings, maps


observed tornadoes


23Z modified RUC sounding at Miller SD

Sfc T/Td: 86/72 F

MLCAPE: 3908 J/kg

MLCINH: 0 J/kg

0-3 km MLCAPE: 127 J/kg

MLLCL: 1280 m

MLLFC: 1334 m

storm motion: 300 deg @ 32 kts

0-1 km SRH: 129 m2/s2

0-3 km SRH: 311 m2/s2


additional facts:

total mileage while actively chasing: 202 miles

total time while actively chasing: ~5 hours

total time observing the supercell: ~4 hours

total time observing tornadoes: 31 minutes

tornadoes observed: 6 (F1, F0, F0, F2, F0, F0)

distance & average speed of supercell between tornadoes 1 and 6: 91 miles @ 35mph