This is a log of the South Dakota tornadoes near Sioux Falls on September 16, 2006. This was a special short storm chase expedition (mini-chase trip) to southeastern South Dakota in the US Great Plains in September 2006. This special trip was made by myself in spite of a rather quiet storm chase season of 2006 (especially tornado-wise). This trip was from September 15 to September 17 with a total of 3 travel days, of which, one of these days were available for chasing. The first and last days were a travel days, ferrying to and from Saint Louis, Missouri and the final target near Sioux City, South Dakota. The main chase day, which was September 16, 2006, was a chase-day to remember ... This day involved two supercells, one of which was a cyclic supercell that produced three tornadoes! This was another trip dedicated to severe thunderstorm research in this area, which includes the Great Plains and the Midwestern United States. Keep in mind that this chase log is scientific evidence and portrays my on-going storm chasing research. It has been placed on this page for easy reference and meteorological interests. Please do not plagiarize or copy this document to other sites for distribution.

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The participants below are not from the "Sky-Chaser" chase team. These people often actively participate in my storm research and documentation efforts and deserve appreciation for their great help and severe weather expertise.




The following entries are all storm chases and interceptions performed in South Dakota in the Midwest United States from September 15, 2006 to September 17, 2006. This log is based on a storm chasing effort by myself - Chris Collura (Florida Skywarn storm spotter code B036 - KG4PJN). The main chase vehicle was a 2006 Ford Focus (my personal vehicle). States chased (includes travel states): IA, MO, MN, NE and SD (5 states). Total mileage: 1,451 Miles!

Communications employed are 2m VHF HAM radio, wireless Internet, and cellular phones. The ability to shoot HIGH DEFINITION video also was an advantage on this short chase trip! Other state-of-the-art equipment was also employed including video and camera gear, GPS, and a laptop computer for navigation, video / photo editing, and Internet. The main chase duties were ambidexterous, with "multi-tasking" with navigation using the GPS, radio communications, driving many miles, editing footage, and preparing forecast data.

I left Saint Louis (my place opf residence for a temporary computer IT project) on September 15 and headed west on Interstate 70 to Kansas City for the evening. Forecasted early morning on September 16 and decided to head north to Sioux City, Iowa up Interstate 29 for the primary "target area". Met up with Verne Carlson north of Omaha, NE. The main chase and target boiled down from just west of Sioux City, South Dakota (near Interstate 90) and areas around and east towards the SD / MN border. Met up with Tony Laubach as well. September 16 was a highly sucessful chase day. After finished chasing, spent the night back south in Sioux City, Iowa. September 17 was a travel day from Sioux City, Iowa back to Saint Louis, Missouri. The chase involved large expanses of the US Great Plains sometimes in the worst driving conditions imaginable, even in very remote regions.

All chases and observations are in chronological order and a chase number is assigned to each entry. Please bear in mind that all observations adhere to modern storm analysis standards and do not include all storms that occurred in a given area for a particular chase period.

Any kind of storm such as a thunderstorm, tornado, waterspout, tropical cyclone, and extratropical storm can be chased or observed. I have tried to keep this log of any storms that I have observed as accurate as possible, while using terms and expressions to abide by those used by most meteorologists and storm spotters today.

Storm chasing and observation can be extremely dangerous and may result in serious injury or death. I have received intermediate and advanced training for storm spotting in 1996. I strongly urge anyone who is to try their hand at storm spotting to get training before doing so. You must also have a good understanding of meteorology and storm dynamics. "If you don't know what you're doing, Don't do it!" Contact your local National Weather Service office for information on storm spotting and about training to become a Skywarn storm Spotter.


September 15 - This was a travel day for the rather short and "convenient" chase trip as it was on a Friday and the entire weekend was available for chasing. The chase trip began after leaving work on Friday at about 4 PM, which is a 6-month computer programing contract in Creve Coeur, Missouri. My own vehicle, a 2006 Ford Focus, was packed and used for this entire chase. I left the western Suberb of Saint Louis, MO and headed west on I-70 towards Kansas City, MO. The night was also spent here, and upon forecasting, the target area was anticipated to be anywhere from Omaha, Ne northward to Sioux Falls, SD with Sioux City, Iowa being in it's midpoint. Interstate 29 was going to be the most important northward "corridor" for the start of the actual chase.

September 16 - Today was an incredible chase day to say the least, with the simple words "dream chase" a good description. Left Kansas City, MO early after looking at data and decided on a preliminary target of Siuox City, Iowa. A powerful low pressure area was setting up in southern portions of central / western SD and backing winds were forecasted to increase in the target area along with a moisture axis of higher dewpoints (mid 60's). Shear was the big player in this case, with the left exit region of a 120 knot+ H3 (300 MB) jet stream nosing in to the target area below which had veering winds with helicities around 500 and a forecast CAPE of 3,000 alread being hinted by soundings in the area. The trip began north on I-29 through Omaha where I got breakfast and then caught up with Verne Carlson and his son chasing just north of town. We continued north on I-29 into Sioux City, Iowa where we looked at more data. It soon became clear that the best area was a bit farther north, near Sioux Falls, SD and I preached we head up that way. A weak boundary was also oriented W to E with a temperature change of about 5 degrees (cooler at 84 F near Sioux Falls, SD) as well as a dryline bulge nudging in from it's southwest. The first cumulus was noted NW of I-29 when about 40 miles south of Sioux Falls, SD and quickly became enhanced / towering. In Sioux City, we headed west on I-90 to intercept the RAPIDLY developing storm, which had a rock-hard anvil and was already severe (then tornado) warned only 45 minutes after initiation. Verne and I made it to the I-90 and Highway 81 overpass where we stopped to observe the rapidly developing wall cloud on the base of the now supercellular storm. This quickly became tornadic and produced a large tornado which eventually crossed this intersection. We moved east, then northeast as the first tornado, which lasted 15-20 minutes weakened. I continued with the storm north on Highway 19 then east on county road G where a second tornado, lasting about 2 minutes developed and destroyed a house. Verne and I separated at this point, but I met back up with him, and Tony Laubach near Trent, SD on CR G shortly after. We continued east towards Pipestone, MN where a third funnel 1/2 way to the ground was observed (possible 3rd tornado). The storm continued northeast and weakened at that point. We headed back west towards I-29 to intercept a second supercell storm near Brookings, SD but got there a bit late when the storm was at its severe (bowed segment) stage. We wrapped up the chase and headed back to Sioux City, Iowa for dinner and spent the evening there.

September 17 - Today was a travel day and included the long drive back from Sioux city, Iowa back down I-29 then east through Kansas City, MO on I-70 to Saint Louis, MO. Arrived back at my apartment in Creve Cour, MO by 4:30 PM on Sunday and began updating data and pictures. Total mileage from Friday was 1,451 miles.


The diagram above is a map showing the chase area for this trip. The heavy blue line is the chase path, including the "ferry" time to and from the target area, as well as the chase itself. The two target areas appear enclosed, and stretch from near Brookings, SD to near Omaha, NE with the first (larger) target area enclosing the final target region near Sioux Falls, SD. These areas were pretty much along the Interstate 29 corridor. The large target area was based on data and forecasting during the early morning of 9-16 and the smaller refined target after a crucial data stop in Sioux City, Iowa. Compare the target areas with those (probabilities, watches, and storm reports) of the Storm Prediction Center (SPC) and National Weather Service (NWS) below, after all, we all are looking at the same data (upper air, surface, etc)!


Above are three cropped forecast probability products for the 1630z convective outlook issued during the afternoon of 9-16-2006. These probability maps denote the possibility (in percent) of a severe weather event (any tornado, hail 3/4" or larger, and / or winds 58 MPH or higher) ocurring within 25 miles of a given point. Extreme severe weather probabilities, for events such as a strong (F2 or more) tornado, hail over 2", and winds over 65 knots (75 MPH), the areas are hatched with a dashed pattern. There are three maps from left to right in the image above. First, the tornado probability, which is at 15% probability and hatched. The second, is the probability of large hail, and is also hatched and an alarming 45%. The third, is the probability of destructive (severe) winds, which is 30% but not hatched. A summary graphic, not shown, shows an overall threat as "none", "non-severe", "slight", "moderate", or "high" risk. Based on the probabilities shown here, at least a "moderate" (or even "high") risk of severe weather is being forecasted. Also note that our refined target area above lies within some of the highest threat percentages in these diagrams!

In the diagram above, two other important products from both the SPC and National Weather Service are shown, both for the severe weather event of September 16, 2006. To the left is a tornado watch box, issued after a mesoscale discussion (not shown) for the afternoon of 9-16-2006. A watch means conditions are favorable for severe conditions in and close to the watch area. It does NOT mean they will happen, but only the strong possibility. The red parallelogram outlines the areal extent of the threat, and affected counties are color-coded within the area threatened. To the right is a storm reports graphic showing actual severe weather events that did happen and were reported. The graphic shows severe (3/4" or more) hail as a green dot (or a black triangle if over 2"), tornadoes as a red dot, and severe (58 MPH or more) winds as a blue dot (or black sqaure if over 75 MPH). Note the red dots appearing in southeastern South Dakota in the diagram to the right. Those tornadoes were from the supercell storms we chased that day!


1). September 16, 4:00 PM - Interception and observation of an extremely severe and tornadic supercell thunderstorm from near Interstate 90 and Highway 81 in McCook County, South Dakota (west of Sioux Falls) northeastward through Pipestone, Minnesota. The storm was a cyclic classic supercell thunderstorm and produced two (or even possible 3) tornadoes. The first tornado developed southwest of the intersection of Interstate 90 and Highway 81. The tornado began as a cone tornado, crossed over I-90 at the overpass of Highway 81 (the overpass took a direct hit with the core windflow of this tornado), evolved into a large (1/4 mile wide) stove-pipe tornado, then roped-out about 1 mile north of I-90 near Montrose. The tornado was on the ground for about 20 minutes and came within 1/2 mile of our observation point. Debris was noted falling from the sky and a loud "roar" heard from the tornado during it's stove-pipe phase. The Rear Flank Downdraft also hit at the same time with heavy rain, small hail, and winds gusting to 70-MPH from the west. The storm produced a second tornado, near Highway 19 and and county road G that lasted about 2 minutes and destroyed a house. The storm continued northeast towards Pipestone across the border into Minnesota. A third funnel (a thin rope half way to the ground) was noted and could have possibly been a 3rd tornado. This one lasted only about 30 seconds. The storm continued northeast of Pipestone, MN and weakened. Other conditions encountered with this storm were occasional lightning, small hail, heavy rains, and winds near 70-MPH. The main hail core (at least golfball sized) was not intercepted. Damage observed was an overturned truck on I-90, tree debris blown around, and major structural damage to a farm house near Chester, SD. Conditions causing the storms were a surface boundary / dry-line interaction, surface heating, and a low pressure system in a strongly sheared (directional shear) environment / very strong winds aloft. A 2006 Ford Focus was used to chase the storms. Documentation was still digital photos and HD video. A tornado watch was also in effect for this area until 10 PM CDT.

2). September 16, 6:30 PM - Observation and penetration of another severe thunderstorm near Flandreu, MN along Highway 34. This storm was a smaller HP supercell thunderstorm which did not produce a tornado but had a fairly large wall cloud, RFD clear area, and shelf cloud. The storm was penetrated and contained very heavy rains, 40-MPH winds, and small hail on its southern side. The storm weakened north of Pipestone, MN. Conditions causing the storms were surface boundaries, dry-line, surface heating, jet stream aloft, and a low pressure system. A 2006 Ford Focus was used to chase the storms. Documentation was still digital photos and HD video. A tornado watch was also in effect for this area until 10 PM CDT.

3). September 16, 7:30 PM - Observation of a severe thunderstorm northwest of Brookings, SD to the west of and along Interstate 29. This storm was formerly a tornado-producing supercell storm that evolved into a bow-echo / MCS structure upon our arrival to it. This storm had a linear, but spectacular appearance to it. A large shelf cloud and hail streaks were noted at about 10 miles from the storm. Part of this storm was penetrated and contained very heavy rains, 35-MPH winds, and small hail during its weakening phase. Conditions causing the storms were surface boundaries, dry-line, surface heating, jet stream aloft, and a low pressure system. A 2006 Ford Focus was used to chase the storms. Documentation was still digital photos and HD video. A tornado watch was also in effect for this area until 10 PM CDT.

This concludes the Chase Log for the South Dakota tornado chase trip in September 2006. The summary includes a total of 3 severe thunderstorms, one of which produced 2 major tornadoes and at least one additional funnel (possible tornado). The main chase vehicle conducting all chases was a 2006 Ford Focus. This information was prepared exclusively for the National Weather service and the team of Skywarn storm spotters.


The diagrams above show two radar images of the first supercell that produced the tornado near the interchange and overpass of Interstate 90 and Highway 81 roughly 15 miles west of Sioux Falls, SD. Our initial position, on the US 81 and I-90 overpass itself, appears as the two arrows to the northeast of the intense mesocyclone in both images. To the left, a base reflectivity image paints the ominous "flying eagle" shaped silouette of the classic supercell storm. Our location is pretty much at the "tail" of the "eagle" to its lower-right. The image to the right shows the storm radial velocity of the supercell (inbound and outbound speeds). Base reflectivity was over 65 (as high as 73) DBZ and had a gate-to-gate shear of more than 130 Knots (over 150 MPH). The yellow circle is the backside of the tornado. Special thanks to Doug Kiesling (BNVN or for providing these radar images from his Swift WX software and GPS navigation. The red trapezoid "fan" indicates storm motion and where the tornado can be in the next 15 minutes or so. Notice the intersection we are on is DIRECTLY in its path!

The diagram above shows another doppler radar image for reflectivity of the supercell just when it was producing the first tornado southwest of Interstate 90 and Highway 81 near Bridgewater, South Dakota. The annotation on the base reflectivity image of the supercell denotes our position on the overpass and the field of view looking southwest towards the mesocyclone / tornado. This region is called the "bear's cage" and is an extremely dangerous place to be. Anyway, the annotated view shows the line of sight relative to the radar image, and the image to the right, shows what that view (to the southwest) looked like visually at that same moment!


Video Of South Dakota Tornadoes On September 16, 2006


This is a picture of a horseshoe type "shear" funnel / vortex that deveops in convective clouds in an environment of high wind shear. There are actually two in this picture, to the lower-right. This was a complex of elevated cumulus associated with the very beginning of the weather system that would cause so much severe weather later on in the day. These fairly innocent, but highly sheared, cumulus developed northwest of Kansas City near Saint Joseph, Missouri and Interstate 29 during the morning of September 16, 2006.
Here is a picture of my vehicle, foreground, just after mounting the weather station "weatherlab" equipment on the roof and meeting up with Verne Carlson and his son (red car to the left in background). We are in Sioux City, Iowa looking at data and just about to make the crucial decision to head north into southeastern South Dakota.
Looking northwest, and about 40 miles away (we are about 40 miles south of Sioux Falls, SD and headed north on I-29), towering cumulus wells up above the agitated cumulus in the foreground. This is called convective initiation and was the first sign of convection. This puffy cloud is the SAME CLOUD that will EXPLOSIVELY develop into the raging supercell you will see in the upcoming pictures. Time here is roughly 3:15 PM CDT. The chase is on!
This is a picture looking west on Interstate 90 about 5 miles west of Sioux Falls, SD at the developing storm about 40 minutes later (roughly 3:45 PM CDT). We have already rounded the metro area of Sioux Falls off I-29 and made it west on I-90. The storm is already severe and tornado warned on rarar (radar indicated). The base of the storm is still too far away, but the rock-hard anvil edge can be seen overhead in the upper left part of the picture.
Here is another view of the well-defined anvil spreading overhead (view is high and to the southwest). The storm now is a fully developed supercell and we are still headed west on I-90 towards its southwestern (rear-flank) region. Time is about 3:55 PM CDT.
The wall cloud of the storm's southwestern flank becomes visible and begins rotating very vigorously. We are just east of Highway 81 on Interstate 90 and the time is 4:05 PM CDT. We decide to get off at the next exit as I announce on the HAM that tornado-genesis is occurring. Note the developing funnel on the lower-right side of the picture just right of the wall cloud. The timing of this chase COULD NOT have been any BETTER!
Large tornado rapidly developing just west of Bridgewater in Mc Cook County, SD and about 5 miles southwest of us! Time is 4:08 PM CDT and we are on the north side of the overpass of Highway 81 and Interstate 90. The visible funnel in this picture is not in contact with the ground, but dust and debris swirling around under it confirms the tornado touchdown. Remember, LESS than an hour ago, this storm was just an "innocent" looking puffy cumulus cloud!
Large tornado now fully developed and on the ground southwest of our location. This is coming directly at us, and this overpass we are on will soon sustain a direct hit by the core of this tornado about 10 minutes after this picture was taken. Many locals asked us if they were safe there. I just told them "No! Turn around and go back to Sioux Falls, Now! This tornado WILL cross this highway!" - Fortunately, they all listened.
Here is another picture of the tornado and my chase vehicle (with the Florida plates) in the foreground. At this point, I was taking as many still pictures and filming HD video at the same time. Many pictures I took with the tornado and chasers, vehicles, and equipment in the foeground.
Here is a picture of myself with my digital camera and the mature cone tornado in the background approaching us at the rate of one mile every two minutes. Its now 4:12 PM CDT, and the tornado is about 4 minutes from hitting the overpass.
Large tornado is roughly 2 miles southwest of our position, so its time to relocate farther east. I take one last picture of the weather station on the top of my vehicle and the approaching twister. Note the wind vane on the "weatherlab" station showing inflow winds going right into the storm!
Closeup of "corner region" of tornado at distance of less than 2 miles. Fortunately, this tornado missed Bridgewater and remained over open country until crossing Interstate 90.
This is a shot I always wanted to get with a tornado and not having to do any "special effects"! The tornado was really "closer than it appeared" as the same overpass (highway 81 over I-90) where last several pictures were taken took a direct hit from the tornado. The storm is about a mile and a half behind us. Time is roughly 4:15 PM CDT. We are headed down the road (East) on I-90 to get back into a safe position to continue documenting the tornado. Verne Carlson is leading the way in his vehicle.
The tornado has just struck the overpass of Highway 81 and I-90 dead on and is moving to the east and northeast. Time is 4:17 Pm CDT and the tornado is reaching peak width and intensity.
Here is a closer view of the lower portion of the tornado which is now just north of Interstate 90. At this point, a load "roaring" or "train" sound can be heard. Light tree and plant debris starts to "rain" down at our location. Tornado is about 1 miles northwest of us.
The tornado reaches its widest point and strongest intensity at over a quarter-mile wide (about 2,000 feet across). The tornado is now a mature stove-pipe and is about one-half a mile north of us on I-90. Note the small debris in the air. The RFD is approaching and winds suddenly blast at 70-MPH from the west as the light shining through the RFD clear-slot illuminates the back side of the stove-pipe tornado.
Rear flank downdraft (RFD) continues from the west at 60-65 MPH and tornado begins occlusion cycle, morphing from a stove-pipe to a narrower cigar-shape. The white precipitation is hail in the RFD "blob" and downdraft.
The weakening phase of the tornado like this is usually the "rope" phase. The tornado is still powerful and extremely dangerous (fortunately it is still over open fields). The narrow, twisting funnel resembles a whitish "rope". Time is about 4:22 PM CDT.
This is a picture showing the beautiful but deadly structure of the tornado rope-stage, still fully condensed. About a minute later, the visible funnel vanished and tornado number one oficially is gone by 4:25 PM CDT. The RFD still pushes outward and is loaded with rain, strong winds, and hail.
The supercell storm that produced the tornado is called a CYCLIC supercell, because when the first mesocyclone weakens, another forms and re-strengthens. A second intense area of rotation is developing just north of the "clear slot" (bright area) marked by the RFD looking north. This is highway 19 and approaching Chester, SD. Time is roughly 4:45 PM.
The RFD region is penetrated with strong winds, rain, and small hail. North of the rain hook, a rapidly spinning region of clouds called a tornado-cyclone is forming. This is where a low-level mesocyclone "tightens" up, like an ice skater pulling her arms in and spinning faster. This is tornado genesis cycle 2 of the supercell beginning.
A narrow funnel develops right in the center of the now violently spinning clouds. The funnel extends quickly earthwards at about 4:51 PM CDT.
Tornado number two from the same storm quickly develops and fully condenses to the ground. This narrow "elephant trunk" type twister is white because the light is from behind me and tyhe view is looking east. Time is 4:22 OM CDT and this is about 3 miles south of Chester, SD near Highway 19 and county road G in Minnehaha County.
Unfortunately, this short-lived tornado strikes a farm house and it is destroyed instantly. Other chasers on this storm have closer shots, showing the house simply exploding and / or disintegrating. The large "pieces" in the air near the dark debris cloud in this picture are large remnants of the house. No one was in the house that was destroyed. The tornado quickly dissapated afterwards at about 4:24 PM CDT.
The cyclic storm is followed northeast for an additional 50 miles until about 6:00 PM where is continued to produce several small funnels (or even a third tornado). In this picture, the storm weakens into a more linear / bow shape northeast of Pipestone, Minnesota. Unfortunately, the storm did not completely dissapate, as it continued towards the southwestern suburbs of Minneapolis / Saint Paul causing one death and damaging 200 homes later that evening.
This is a picture along the side of the road near Pipestone, Minnesota. Verne Carlson and myself met up with Tony Laubach and a few others with him who arrived a bit late for the first storm (they came all the way from Denver, Colorado)! Tony's van he calls "white lightning" is to the left.
Waiting for some more supercell storms to develop and move towards us, Verne and I get a chance to show Tony Laubach and his crew some tornado footage we shot earlier!
Here is Verne Carlson, right, showing off his tornado video probe. It is so funny as he is wondering to this day why he did not "deploy" this earlier on the I-90 / Highway 18 overpass - Adrenaline makes you think otherwise. The way it works is in two parts. The person on the left is holding a strap, containing a hardened case holding a battery, video camera, and transmitter. To the right is the Yagi antenna used to receive the near-microwave signal from the video device. The goal is to strap this device to a pole or guardrail in the path of a tornado, back away to a safe distance, and receive the video via the Yagi antenna and receiver.
Another small non-tornadic supercell comes up near Flandreu, MN near Highway 34. This storm did not last long, but produced this beautiful wall cloud that quickly evolved to an outflowish type shelf cloud when its RFD occluded.
Looking north, here is a view of the RFD clear-slot (although loaded with rain), on the southern side of the mini HP supercell near Flandreu, MN. The storm quickly weakened shortly after by about 6:45 PM CDT.
Another tornado was reported at about 6:55 PM CDT on a storm west of Brookings, SD, so we decided to head for it as it was the last storm of the daylight hours. We headed up I-29 but arrived at the storm northwest of Brookings at about 7:30 PM CDT. By this time, the supercell storm evolved into a bow-echo type MCS that was outflow dominant. The southern cells on this storm system were very beautiful as they were back-lit tranclucently by the setting sun.
Here is a view of the remnants of the mesocyclone of this storm, which is now mostly a linear / bow shaped MCS. The inflow portion of the wall cloud is still intact and can be seen extending from right to left into the storm (lower right portion of this picture). A slight RFD push can be seen to the left. The mesocyclone, if any, is located in the center of the picture just above the horizon. The setting sun reflecting off hail makes the clouds appear an errie green color.
A hail shaft of possibly golfball sized hail descends through a portion of the cloud base of the severe thunderstorm and causes an interesting "streaking" in the clouds. These are called "hail streaks" and can easily be seen in the upper-center this picture.

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