Photography of the South Dakota Tornadoes of June 23rd, 2002

On the evening of June 23, 2002 a classic tornadic supercell thunderstorm developed over extreme northern South Dakota along the North Dakota / South Dakota state line in the vicinity of Ashley, ND and Long Lake, SD. The initial series of updrafts that evolved into this supercell began approx 10-15km north of a small-scale  area of low pressure (meso-low) located at the intersection of an east/west oriented section of a quasi-stationary outflow boundary and an apparent north/south oriented surface trough that demarcated slightly drier air to the west from deeper/richer moist air to the east. 

The outflow boundary was of particular importance since its southern extent was oriented generally in an east/west fashion as opposed to further north where the boundary curved to a north/south orientation in portions of North Dakota. Mid-tropospheric flow was oriented from the west-southwest allowing for storms that developed along the southern periphery of this boundary to remain in a favorable area of enhanced low-level horizontal vorticity located just north (on the "cool side") of this boundary. This is especially true for stronger storms that develop favorable pressure pertubations located on their right flanks, the result being a rightward propagation of the storm relative to the mean tropospheric flow.

Visible satellite imagery throughout the day revealed the east/west oriented outflow boundary to be sinking southward and associated with a relatively narrow line of strato-cu. By late afternoon this boundary had become stationary and most traces of clouds along the boundary had evaporated. To the north, strong insolation had occurred for most of the day allowing the moist low level outflow air to moderate significantly while allowing surface wind direction to remain highly backed. 

The first few attempts of storm initiation were met by a somewhat hostile environment as a combination of perhaps mid-level dry air entrainment and failure for the small developing updrafts to root themselves in the boundary layer ensued. The result was a series of updraft "puffs" that could be seen on satellite imagery moving rapidly northeast from the meso-low and then glaciating as the updrafts could not be sustained further away from the favored low-level convergence/boundary zones. After more than several attempts, one particular updraft complex was successful in rooting in the boundary level and resulted in explosive growth.

The resulting updraft complex quickly became supercellular in nature as it  propagated/developed in a southeastward extent close to the center of the meso-low. Inflow winds increased in isallobaric response to the intensification of the updraft complex as a visually spectacular  beaver's tail fed rapidly westward into the now horse-shoe shaped updraft configuration. As a RFD rapidly cascaded downward on the backside of the updraft, the first tornadic circulation extended to ground as a small dust-whirl that lasted not more than two minutes. The circulation then re-intensified shortly thereafter as a larger cone funnel emerged from cloud base (tornado #2). The photos displayed below begin with the documentation of the third tornado in the series. Tornado #1 was brief and not photographically documented while tornado #2 will be added at a later date.