Storm Reports including tornadoes in southeast South Dakota for June 24-25, 2009

Several tornadoes hit portions of southeast South Dakota on the evening of June 24. These tornadoes were associated with two supercells that developed.  A supercell is a thunderstorm which has a rotating updraft and is responsible for a majority of tornadoes that affect the United States. The first supercell developed shortly after 7 pm CDT southwest of Huron, South Dakota.   This storm moved east-southeast toward Virgil.  Around 8:07 pm CDT, the first tornado was reported 1 mile south of Virgil.  On the image below, a hook echo can be seen on the reflectivity on the left.  It is within this hook echo that the tornadic circulation will form.  The right image shows the storm relative velocity and two circulations are seen - one south of Virgil and the second near Alpena.  It is believed that the western circulation near Virgil was the one that produced the tornado.  Finally, at the same time the tornado occurred, destructive hail was occuring south of Virgil.  Up to golf ball size hail was reported which resulted in over 6 square miles of crop damage south of Virgil.

Below is a picture of the storm taken at 8:06 pm CDT. 

Photo taken by Nick Hartley, Brookings Register

The storm continued to move southeast.  By 9:40 pm, the supercell was located north of Fulton, South Dakota.  This is where the storm produce two tornadoes near Fulton.  On the radar picture below, a hook echo is apparent north of Fulton (left).  A very strong circulation can be seen on the storm relative velocity image (right).

Picture of the tornado north of Fulton at 9:43 pm CDT.

Photo courtesy of Nick Hartley, Brookings Register

Finally, around 11 pm CDT, a second supercell began to develop between Mitchell and Chamberlain in Aurora County, South Dakota. This was a classic splitting supercell.  A splitting supercell is one in which there is a left-moving supercell with an anticyclonic rotation and a right-moving supercell with a cyclonic circulation.  Typically the anticyclonic supercell will produce large hail but rarely produce a tornado while the cyclonic supercell can produce tornadoes in addition to large hail.   The right-moving supercell did produce a weak tornado 15 miles east of Platte in Douglas County around 12:25 am CDT as well as golf ball size hail west of Stickney.  The left-moving supercell produced 1 inch hail northeast of Plankinton.

At 11:30 pm CDT, the supercell was just beginning to split.  On the reflectivity image, it still appears as a single storm.  However, one can see an indentation on the southwest and northwest side of the storm indicative of inflow and two updrafts.  When looking at the storm relative velocity image, two circulations are evident.  On the southwest side storm, collocated with the inflow, there is a strong cyclonic circulation.  On the north side of the storm a strong anticyclonic circulation can be see where the inflow was forming with the left-moving supercell.

At 11:50 pm CDT, the supercell has split into two storms.  The left-moving supercell has begun to move to the east-northeast north of Plankinton and the right-moving supercell has begun to move south-southeast west of Stickney.  The left-moving supercell maintains a strong anticyclonic circulation on the north side of the storm.  Also, the inflow of warm and moist air is on the north side of the storm which results in a storm shape that is the "reverse" of what we typically see with a supercell thunderstorm with a broad "hook" on the north side.  The right-moving supercell has a strong and broad cyclonic circulation.  There is a broad hook on the southwest side of the storm and large hail, up to golf ball size, was falling east of the hook.

The final radar image, from 12:05 am CDT, shows that the supercells have completely split.  The left-moving supercell continues to show a strong anticyclonic circulation along the Davison and Aurora County border north of Mount Vernon.  The broad hook echo remains apparent where the circulation is located.  The much larger right-moving supercell has moved south and is approaching the Douglas County line.  A strong cyclonic circulation continues to be evident on the southwest side of the storm.  After this time, the left-moving supercell weakened after moving into Davison County while the right moving supercell continue to produce large hail and a few damaging wind gusts as it moved across Douglas County and into Bon Homme County after 1:00 am CDT.

A summary of reports from June 24-25, 2009.

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1033 PM CDT THU JUN 25 2009

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0745 PM     HAIL             2 WNW VIRGIL            44.30N 98.46W
06/24/2009  E0.75 INCH       BEADLE             SD   TRAINED SPOTTER

0750 PM     HAIL             6 S HURON               44.28N 98.21W
06/24/2009  E0.75 INCH       BEADLE             SD   EMERGENCY MNGR

0757 PM     HAIL             2 WNW VIRGIL            44.30N 98.46W
06/24/2009  E1.00 INCH       BEADLE             SD   TRAINED SPOTTER

0759 PM     HAIL             2 NW VIRGIL             44.31N 98.46W
06/24/2009  E1.00 INCH       BEADLE             SD   PUBLIC

0802 PM     HAIL             1 WSW VIRGIL            44.29N 98.45W
06/24/2009  E1.75 INCH       BEADLE             SD   EMERGENCY MNGR

0807 PM     TORNADO          1 S VIRGIL              44.28N 98.43W
06/24/2009                   BEADLE             SD   PUBLIC

            WEAK MULTIPLE VORTEX TORNADO.

0815 PM     HAIL             4 N ALPENA              44.24N 98.37W
06/24/2009  E1.75 INCH       BEADLE             SD   PUBLIC

            6 SQUARE MILES OF CROPS WAS DESTROYED BY LARGE HAIL.

0850 PM     HAIL             7 N FORESTBURG          44.13N 98.11W
06/24/2009  E1.75 INCH       SANBORN            SD   PUBLIC

            GROUND WHITE FROM LARGE HAIL

0850 PM     HAIL             8 NNE FORESTBURG        44.13N 98.05W
06/24/2009  E1.00 INCH       SANBORN            SD   TRAINED SPOTTER

0900 PM     TORNADO          3 S ARTESIAN            43.97N 97.92W
06/24/2009                   SANBORN            SD   PUBLIC

            RAIN WRAPPED TORNADO.

0910 PM     HAIL             ARTESIAN                44.01N 97.92W
06/24/2009  E2.00 INCH       SANBORN            SD   TRAINED SPOTTER

            DAMAGED NUMEROUS CAR WINDOWS, STRONG WINDS BROKE SMALL
            BRANCHES

0915 PM     HAIL             4 ESE FORESTBURG        44.00N 98.03W
06/24/2009  E1.75 INCH       SANBORN            SD   LAW ENFORCEMENT

0941 PM     TORNADO          3 N FULTON              43.77N 97.82W
06/24/2009                   HANSON             SD   STORM CHASER

            TWO TORNADOES

0942 PM     TORNADO          3 E FULTON              43.73N 97.76W
06/24/2009                   HANSON             SD   EMERGENCY MNGR

1015 PM     TSTM WND GST     3 NE EMERY              43.63N 97.58W
06/24/2009  E60.00 MPH       MCCOOK             SD   PUBLIC

            NUMEROUS BRANCHES DOWN, LASTED 15 MINUTES

1026 PM     TORNADO          1 N BRIDGEWATER         43.56N 97.50W
06/24/2009                   MCCOOK             SD   STORM CHASER

1033 PM     HAIL             1 N DOLTON              43.51N 97.38W
06/24/2009  E2.00 INCH       MCCOOK             SD   TRAINED SPOTTER

1104 PM     HAIL             2 W PARKER              43.40N 97.18W
06/24/2009  E1.00 INCH       TURNER             SD   EMERGENCY MNGR

1104 PM     TORNADO          3 S MARION              43.38N 97.26W
06/24/2009                   TURNER             SD   EMERGENCY MNGR

1118 PM     HAIL             HURLEY                  43.28N 97.09W
06/24/2009  E1.75 INCH       TURNER             SD   BROADCAST MEDIA

1139 PM     TORNADO          VIBORG                  43.17N 97.08W
06/24/2009                   TURNER             SD   BROADCAST MEDIA

1149 PM     HAIL             8 SW PLANKINTON         43.64N 98.60W
06/24/2009  E1.75 INCH       AURORA             SD   FIRE DEPT/RESCUE

1154 PM     HAIL             6 WNW STICKNEY          43.61N 98.55W
06/24/2009  E1.75 INCH       AURORA             SD   LAW ENFORCEMENT

1204 AM     HAIL             2 NE CENTERVILLE        43.14N 96.93W
06/25/2009  E1.00 INCH       TURNER             SD   TRAINED SPOTTER

1205 AM     HAIL             7 NE PLANKINTON         43.79N 98.38W
06/25/2009  E1.00 INCH       AURORA             SD   PUBLIC

1215 AM     HAIL             7 NNW MOUNT VERNON      43.81N 98.31W
06/25/2009  E0.88 INCH       DAVISON            SD   TRAINED SPOTTER

1218 AM     TSTM WND GST     BERESFORD               43.08N 96.78W
06/25/2009  E60.00 MPH       UNION              SD   FIRE DEPT/RESCUE

1227 AM     TORNADO          15 E PLATTE             43.39N 98.55W
06/25/2009                   DOUGLAS            SD   LAW ENFORCEMENT

1230 AM     HEAVY RAIN       4 ESE DELMONT           43.24N 98.09W
06/25/2009  E2.00 INCH       HUTCHINSON         SD   TRAINED SPOTTER

            OCCURRED IN 15-20 MINUTES, BUT NO FLOODING CAUSED

1232 AM     FUNNEL CLOUD     2 W CORSICA             43.42N 98.45W
06/25/2009                   DOUGLAS            SD   LAW ENFORCEMENT

1245 AM     FUNNEL CLOUD     8 SW CORSICA            43.34N 98.52W
06/25/2009                   DOUGLAS            SD   LAW ENFORCEMENT

1250 AM     HAIL             5 NW DELMONT            43.32N 98.23W
06/25/2009  E1.00 INCH       DOUGLAS            SD   TRAINED SPOTTER

1257 AM     HAIL             HAWARDEN                43.00N 96.48W
06/25/2009  E0.88 INCH       SIOUX              IA   TRAINED SPOTTER

1259 AM     HAIL             2 N CHATSWORTH          42.95N 96.51W
06/25/2009  E1.00 INCH       SIOUX              IA   EMERGENCY MNGR

0100 AM     HAIL             ARMOUR                  43.32N 98.34W
06/25/2009  E0.88 INCH       DOUGLAS            SD   LAW ENFORCEMENT

0100 AM     HAIL             3 W ARMOUR              43.32N 98.40W
06/25/2009  E1.00 INCH       DOUGLAS            SD   LAW ENFORCEMENT

            CROP DAMAGE

0100 AM     HAIL             6 S HAWARDEN            42.92N 96.48W
06/25/2009  E1.00 INCH       SIOUX              IA   EMERGENCY MNGR

            CROP DAMAGE

0105 AM     TSTM WND DMG     9 N AVON                43.14N 98.06W
06/25/2009                   BON HOMME          SD   PUBLIC

            LARGE TREE BRANCHES BROKEN OFF LARGE COTTONWOOD,
            PEA-SIZED HAIL

0110 AM     FLASH FLOOD      ARMOUR                  43.32N 98.34W
06/25/2009                   DOUGLAS            SD   LAW ENFORCEMENT

            WATER 4-6 INCHES DEEP OVER ROAD

0115 AM     TSTM WND DMG     11 NNE WAGNER           43.23N 98.22W
06/25/2009                   CHARLES MIX        SD   PUBLIC

            TREE BRANCHES DOWN

0136 AM     HAIL             BRUNSVILLE              42.81N 96.27W
06/25/2009  E1.00 INCH       PLYMOUTH           IA   TRAINED SPOTTER

0145 AM     FLASH FLOOD      9 N AVON                43.14N 98.06W
06/25/2009                   BON HOMME          SD   PUBLIC

            CREEK RUNNING OUT OF ITS BANKS, CULVERTS WASHED OUT,
            RECEIVED 2.5 INCHES OF RAIN IN 1 HOUR

0145 AM     HAIL             7 NE AVON               43.09N 97.97W
06/25/2009  E1.00 INCH       BON HOMME          SD   TRAINED SPOTTER

            CROPS WERE DAMAGED BY COMBINATION OF LARGE HAIL AND WIND

0145 AM     TSTM WND GST     7 NE AVON               43.09N 97.97W
06/25/2009  E60.00 MPH       BON HOMME          SD   TRAINED SPOTTER

            SEVERAL BRANCHES KNOCKED DOWN BY THUNDERSTORM WIND GUSTS.


0224 AM     HAIL             5 SSE TABOR             42.88N 97.62W
06/25/2009  E1.00 INCH       YANKTON            SD   TRAINED SPOTTER