Tornado in Ripley County, IN - March 8, 2009

March 8, 2009
Tornado In Ripley County, IN

During a period from April to September in 2008, National Weather Service offices gained access to data from forty five Terminal Doppler Weather Surveillance Radars (TDWRs) at major airports across the country. Reflectivity data has also recently become available to the public in the RIDGE 2 radar display mosaic. The Wilmington, OH (ILN) County Warning Area (CWA) has been fortunate to have a TDWR located at major airports near Dayton, Columbus, and Cincinnati. The TDWRs bring the potential for data sampling at lower levels of a storm, more frequent radar data at the lowest levels, more detailed information given a storm's closer proximity to the radar, and ultimately more information for warning forecasters. On March 8, 2009, the Cincinnati-Northern Kentucky International Airport radar (TCVG) provided data which helped detect rotation associated with a brief tornado touchdown.

TDWRs provide a radar scanning strategy which provides new data at the lowest elevation tilt every minute. In comparison, the WSR-88Ds can provide radar scans at the lowest tilt every four and a half minutes in their fastest scanning strategy. During the Ripley County tornado, the radar provided valuable reflectivity and storm relative motion (SRM) velocity data. In Figure 1, the TCVG SRM shows the broad rotation of the storm tightening into a couplet. The couplet is not visible from KIND, but more of a broad rotation is evident with the storm. The storm touched down briefly at approximately 2122Z. Notice the couplet on TCVG from 2121Z-2124Z. The 0.5 degree elevation scans from KIND provided data of the storm at 2120Z and 2124Z, missing the first three minutes of the couplet. In Figure 2, seen below, KILN shows no evidence of a tightening circulation. The reflectivity data from TCVG indicates an apparent cell merger on a pre-existing storm scale boundary. This suggests that the tornado may have developed from a non-descending mesocyclone. These processes can be difficult to detect using WSR-88D data since they are often short-lived and develop just a few thousand feet above ground level. The addition of one minute data from the 0.1 degree elevation scan of TCVG in this case provided the ability to see short-lived reflectivity and velocity signatures which occurred between scans from both KILN and KIND. TCVG provided more scans by the minute, detecting the evolution of the storm.

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PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE WILMINGTON OH
414 PM EDT MON MAR 9 2009

...EF1 TORNADO CONFIRMED IN NORTHEAST RIPLEY COUNTY...

A NATIONAL WEATHER SERVICE DAMAGE SURVEY HAS CONFIRMED A TORNADO
TOUCHDOWN IN NORTHEAST RIPLEY COUNTY ABOUT THREE MILES SOUTH OF
SUNMAN ON SUNDAY AFTERNOON MARCH 8.

THE TORNADO BRIEFLY TOUCHED DOWN IN TWO LOCATIONS JUST WEST AND
NORTH OF THE INTERSECTION OF INDIANA STATE ROUTES 101 AND 48. THE
FIRST AREA OF DAMAGE OCCURRED ON A PROPERTY LOCATED ALONG STATE
ROUTE 48 ABOUT A QUARTER MILE WEST OF THE INTERSECTION OF STATE
ROUTES 48 AND 101. A LARGE TWO-STORY BARN SUSTAINED ROOF DAMAGE
AND HAD BOTH METAL GARAGE DOORS BLOWN OUT. MUCH OF THE NORTH-
FACING WALL OF THE GARAGE AND SEVERAL SMALL OBJECTS IN THE BARN
WERE BLOWN OUT AND THROWN INTO AN ADJACENT CORNFIELD TO THE
NORTHEAST. A SECOND SMALLER BARN BEHIND THE HOME HAD THE BACK PART
OF ITS METAL ROOF PEELED OR REMOVED. TWO CEDAR TREES IN THE
VICINITY OF THE LARGE BARN WERE UPROOTED. THE HOMEOWNER AND HIS
SON BOTH WITNESSED THE TORNADO LIFT UP IN THE CORNFIELD AND THEN
COME BACK DOWN IN THE VICINITY OF STATE ROUTE 101 JUST NORTH OF
ITS INTERSECTION WITH STATE ROUTE 48. IT WAS IN THIS LOCATION THAT
THE SECOND AREA OF DAMAGE WAS LOCATED.

THE MOST SIGNIFICANT DAMAGE WAS IN THIS LOCATION ALONG STATE ROUTE
101...TO A STAND-ALONE GARAGE AND THE BACK PORTION OF A HOUSE. THE
FRONT PART OF THE GARAGE HAD ITS ROOF COMPLETELY REMOVED AND
DEPOSITED IN A FEW PARTS IN THE FIELD TO THE EAST OF THE
PROPERTY. SEVERAL PIECES OF THE ROOF TRUSSES AND FIBERGLASS WERE
SCATTERED BEHIND THE GARAGE AS WELL. INSULATION WAS STUCK TO THE
ENTIRE SOUTH SIDE OF THE GARAGE...AND THE WEST-FACING GARAGE DOOR
WAS BLOWN OUT. THE BACK PART OF THE GARAGE REMAINED LARGELY INTACT
WITH LITTLE ROOF DAMAGE. THE HOMEOWNERS INDICATED THAT THIS PART
OF THE GARAGE WAS BUILT AT A LATER TIME THAN THE FRONT PART OF THE
GARAGE. ADDITIONAL DAMAGE OCCURRED TO A BACK ROOM TO THE HOUSE.
THIS WAS AN ADDITION TO THE HOUSE...BUILT AT THE SAME TIME AS THE
FRONT PORTION OF THE GARAGE WHICH SUSTAINED THE BRUNT OF THE
DAMAGE. THE ENTIRE ROOM WAS SHIFTED OFF THE FOUNDATION BY AS MUCH
AS SIX INCHES AND THE DOOR WAS BLOWN OUT. SEVERAL MAPLE TREES
ALONG THE BACK EDGE OF THE PROPERTY WERE KNOCKED DOWN.

BASED ON THE TYPE OF DAMAGE TO THE STRUCTURES AND HOW THEY WERE
BUILT...ESTIMATED MAXIMUM WINDS ARE 85 TO 90 MPH WHICH CORRELATES
TO THE LOW END OF THE EF1 CATEGORY. EF1 WINDS RANGE FROM 86 TO 109
MPH. THE BROKEN PATH LENGTH WAS ABOUT 0.5 MILES. PATH WIDTH WAS
ABOUT 25 YARDS.

$$

Radar Images

4-Panel Radar Imagery of Storm


TCVG 4-Panel Radar Imagery

TCVG 4-Panel Radar Imagery

TCVG 4-Panel Radar Imagery

TCVG 4-Panel Radar Imagery

TCVG 4-Panel Radar Imagery

The resolution of radar data decreases the further a storm is away the radar. Range limitations provide challenges for forecasters, as their furthest most counties are not sampled as well by the WSR-88D radar. The resolution decreases with range and the lowest levels are not sampled at all. TDWRs can provide data at a finer resolution than the WSR-88s with a smaller data bin size. In this case, the storm was approximately 65 nm from KILN and 60 nm from KIND. Both the KIND and KILN 0.5 degree elevation SRM data show only weak rotation at this distance from the radar. Thus, the low-level rotation was poorly sampled by the WSR-88Ds, and not sampled at all below 5,000 feet. Fortunately, the TDWR was approximately 33 nm from the storm, providing higher resolution scans of the storm, especially in the lowest tilt where the couplet was more evident. Although the range on the WSR-88Ds is greater, the proximity of TCVG to the storm in this case provided more detailed scans.

Despite the fact that TDWRs have less range in comparison to the WSR-88Ds, their scans provide a lower elevation angle (0.1 or 0.3 degrees). TCVG's lowest elevation angle in this scanning strategy is at a 0.1 degree tilt, where the WSR-88Ds provide a 0.5 degree tilt. With the storm being closer to TCVG, the 0.1 degree elevation scan provided data of the storm at approximately 1,100ft AGL. Meanwhile, the 0.5 degree elevation scan of both KIND and KILN displayed data at 5,400ft and 5,800ft AGL respectively. Notice in Figure 4, the TCVG SRM velocity couplet is well-defined at the 0.1 degree tilt, whereas the KILN SRM shows inconclusive data. The WSR-88Ds could not sample the most valuable data near the surface which is sampled by TCVG.

The radar data provided by TCVG revealed a well-defined rotation with the storm as it moved into northeast Ripley County and approached the Dearborn County line. The lower tilted beam, proximity to the radar, and faster scanning at the lowest tilt of the TDWR provided data which corresponded with a brief touchdown of a weak tornado. This supplemental information was beneficial for forecasters. In this case, WSR-88D data was limited, and could not detect the low-level rotation as adequately as the TDWR data. Although the TDWR provided more detail in this case, there still are limitations which are not covered in this study. The storm's proximity to the radar can vary the quality of the data provided by both the WSR-88Ds and TDWRs. The Ripley County storm is proof that the TDWRs can provide beneficial supplemental data to the WSR-88Ds in certain scenarios.

Storm Damage Photos: