Data obtained in this way is limited by the low probability of a discovery being made and reported, as well as the degree of attention given to the event by the media. Furthermore, a report is often of limited scientific value due to lack of essential detail. Even if these factors are satisfied, a report will often be only a local public interest story.
An historical survey gleans only a relatively few records (Snow et al. 1996, this volume). Only 86 out of 12,651 tornado accounts during the period 1871 to 1990 included reports of long range debris lofting. This implies a rate of just 0.72 lofting events per year.
Here we report on a nationwide effort to collect as many accounts as possible of debris lofting, transport, and fallout in 1994 and 1995. We show that lofting, long distance transport, and fallout of debris from tornadic thunderstorms occurs more frequently than is suggested by the apparent scarcity of historical accounts. Furthermore, we show that lofting can occur in conjunction with tornadoes of a wide range of intensity.
Even though this systematic study was probably not exhaustive, we did collect reports from 17 separate debris lofting events over two years, which is almost twelve times more than what the historical record would suggest. This implies a serious bias in the historical record which must be quantified.
We hypothesize that lofting events occur very frequently but most often go unreported. It would seem logical that in the aftermath of tornado events which cause significant damage (and hence produce much debris), there should be an associated pattern of fallout which is determined by the dynamics of the storm and environment. This presents a situation where the collection of data is most efficiently performed by a large number of people, covering the likely fallout area.
Since the beginning of 1994, we have utilized the following methods to help us engage the general public's participation in our data collection efforts: we let the public know of our interests through writing articles in general publications; sending informational letters to National Weather Service offices; creating a home page on the Internet (http://parker.gcn.ou.edu/Debris/Debris.html), and establishing a toll-free telephone number (1-800-3DEBRIS) to facilitate the reporting process.
For some tornado events which we learned had caused debris lofting, we followed up with a campaign for public assistance. By alerting regional media and law enforcement agencies that a tornado had recently occurred which may have produced long range fallout, we were able to inform much of the public in the region that there could be tornado-related debris in their area, and that we were seeking reports. This process significantly increased the number of items that were reported and sent directly to us. The results of our efforts are listed in Section 2 below.
Of particular interest are debris items which can be traced back to source locations. Examples are canceled checks, letters, receipts, and photos with names. We received more reports of this kind than of any other type of debris. For long range reports, traceable debris leaves little question as to the point of origin, unlike other debris, for which time of appearance is the only clue that relates it to the thunderstorm at all. Furthermore, untraceable debris usually cannot be confidently associated with any part of a tornado, or even to the tornado itself (consider a report of a fallout of tin roofing material, or of tree leaves or limbs, etc.).
Knowledge of the source and end locations of a debris item, together with its fall speed and atmospheric wind data allow analyses to be performed to estimate a three-dimensional trajectory for the item. Such analyses allow inferences to be made concerning maximum lofting altitudes and the point where debris makes the transition out of the storm environment. (Magsig et al. 1996, this volume).
We adopt a format similar to one used by Grazulis (1993) in his Significant Tornadoes 1680-1991. The first line of each event description denotes the state(s) involved, the date of the storm, the number of different locations (more than 8 km from the source) where debris was found, the farthest distance debris was known to be lofted (in km), and the highest F-scale intensity rating given to the associated tornado.
Where possible, the relationship between fallout locations and storm/tornado tracks are described. Based on the work of Anderson (1985), debris is classified as either paper, light (<1 pound), or heavy (> 1 pound).
IN APR 27, 1994 1 95 F4 LAFAYETTE - A photograph was lofted approximately 95
km from W. Lafayette, IN northeast to a field close to Akron,
IN. This fell nearly along the extended tornado track. OK-AR APR 25, 1994 3 132 EAST-CENTRAL OK - A storage shed, located near
Tuskahoma, OK, was the source for all long-range debris
items, including two canceled checks found in the vicinity of
Ft. Smith, AR (108 km and 112 km NE), and one receipt
found near Alma, AR (132 km NE). These items fell
between 8.5 and 17.6 km to the left of the storm track as
indicated by reflectivity centers (see Snow et al. 1995). TX-OK APR 26, 1994 2 65 GAINESVILLE - All long-range debris was traced back to
one damaged house in Gainesville, TX. A title deed was
found approximately 45 km northeast near Mead, OK. A
canceled check was found nearly 65 km northeast near
Caddo, OK. These debris items were deposited
approximately 5.5 km to the left of the extrapolated storm
track as indicated by reflectivity centers. TN-KY NOV 24, 1994 1 95 LATHAM - A canceled check from a home in this Weakley
County, TN, town was deposited approximately 95 km
north-northeast in Benton, KY. This is approximately 8 km
to the left of the extended northeast directed tornado track. AL-GA FEB 16, 1995 6? 150 MARSHALL CO - A canceled check was carried 13 km east
from Brashiers Chapel to Happy Home, AL. A checkbook
from the same area was deposited approximately 10 km
east in Meadowood, AL. A magazine label also from
Brashiers Chapel traveled 13 km east to the Spring Creek
Drive area. A government form was lofted northeast
approximately 35 km from Arab, AL to near South Sauty,
AL. A letter from Arab was carried nearly 150 km northeast
to Ringgold, GA. The items which were transported less
than 15 km landed to the right of the east-northeasterly
directed tornado track within 1.5 km. The form fell
approximately 8 km to the left and the letter fell
approximately 30 km to the left of the extrapolated storm
track. OK MAY 7, 1995 52 191 F3 SOUTH-CENTRAL OK - The tornado which was
responsible for lofting debris cut a path 93 km long
northeast across the Texas-Oklahoma border. Fifty-two
reports of debris found downstream from the damaged
areas were received. Many reports included multiple items.
Forty of those items were traced back to their source
locations. Paper and light debris included photographs,
slides, canceled checks, numerous receipts and other
pieces of paper, a jacket, a golf course flag, and the front
cover of a hard-cover textbook. Most debris was found
within 20 km to the left of the maximum reflectivity track.
Some reports of interest include: a jacket (with owner's
name embroidered on it) carried from a Burneyville, OK,
home 30 km north northeast to Lone Grove, OK; a 48x33
cm golf flag from the Falconhead golf course (near
Burneyville) lofted 70 km north-northeast to Davis, OK; a
14x22 cm Mary Kay beauty profile with attached carbon
copy carried from a home near St. Jo, Texas nearly 200 km
north-northeast to Seminole, OK; and a canceled check
from a Falconhead home lofted the greatest distance, 200
km north-northeast (see Magsig et al. 1996, this
volume). IL MAY 9, 1995 1 85 F? CANTRALL - An outgoing letter from a Cantrall, IL,
resident's mailbox was carried nearly 85 km northeast to
Bloomington, IL. This trajectory appears to be within 10 km
to the left of the extended tornado track estimated from local
storm reports. IL MAY 13, 1995 2 95 F4 LEWISTOWN - A canceled check was lofted east-northeast
about 65 km from Lewistown, IL, to Morton, IL. A bank
statement from the same source was found approximately
95 km northeast in Toluca, IL. IL MAY 13, 1995 1 175 F?> DALLAS CITY - A catalog order form was lofted
approximately 175 km northeast from Dallas City, IL, to a
yard near Dover, IL. IN MAY 13, 1995 2 110 F2 LINNSBURG - A receipt was lofted approximately 85 km
east-northeast from Linnsburg, IN, to Frankton, IN. A letter
from the same home in Linnsburg was carried nearly 110
km east-northeast to Cammack, IN. > TN MAY 18, 1995 2 195 F4 ETHRIDGE - A telephone directory was carried 90 km
northeast from Ethridge, TN to Christiana, TN. A canceled
check was lofted nearly 195 km northeast to Baxter, TN.
These locations are approximately 35 km and 80 km to the
left of the extended east-northeast tornado track. MA MAY 29, 1995 1 50 F3-4 GREAT BARRINGTON - Two pieces of fiberglass corrugated
roofing, about 12"x20" each, were found in a field near
Westhampton, MA. The time of appearance of the debris
provided evidence that it may have come from the storm
which produced damage in the Great Barrington, MA, area.
This implies the debris was lofted about 50 km east-
northeast, which is to the left of the east-southeast tornado
track. TX JUN 2, 1995 19 105 FRIONA / DIMMITT - A half-mile-wide tornado cut a 12-km
path northeastward across the southeast part of Friona
(Figure 1). Approximately 60 items were discovered at 19
separate locations. Most items were paper, including
numerous canceled checks and receipts. Light debris
included a 5.25" floppy disk, shingles, Plexiglas, insulation,
silk flowers (perhaps from the cemetery northeast of Friona),
sheets of tin, styrofoam, and a cassette tape. The few heavy
(> 1 lb) items included larger pieces of sheet metal, a 5'x3'
sign, a 1'x2' piece of wood from an airplane, and 3'x4' wall
tiles. Eight independent sources of long-range debris were
determined in the Friona area (located within the three
general source areas in Figure 1). A canceled check from
Dimmitt, TX, was found southeast of Canyon, TX. A
separate tornado (possibly F4) produced damage near this
town about one hour after the Friona tornado had
dissipated. The person who found the check also found a
receipt from the Friona airport, which received significant
damage. The receipt was found approximately 1 km
southwest of the check. All debris fell to the left of the
maximum reflectivity centroid track. The item lofted the
greatest distance was a canceled check from Friona, found
105 km northeast in north Amarillo, 57 km to the left of the
extended storm track. Generally debris which fell farther
away from its source also fell farther to the left of the storm
track[1].
Figure 1. Reports from Friona, TX, debris lofting event, June 2, 1995. Symbols indicate heaviest debris type found at each location.
TX JUN 8, 1995 6 126 F3> PAMPA - This event produced long-range reports of paper
debris only (checks, receipts, photos and forms). All debris
was traced back to damaged or destroyed buildings in
southwest Pampa, TX. The farthest two items, a check and
a receipt, were found 116 km and 126 km northeast,
respectively. Both were approximately 10 km to the left of
the maximum reflectivity centroid track. The other items,
which fell between 98 km and 102 km northeast, all landed
within 7 km to the right of the reflectivity track (Figure 2).
Figure 2. Reports from Pampa-Kellerville-Allison, TX, debris lofting events, June 8, 1995. Report symbol indicates heaviest debris type found at each location.
TX-OK JUN 8, 1995 2? 88? KELLERVILLE - The nearly 30-mile tornado track which
stretched from McLean to Mobeetie, via Kellerville, TX, was
the result of a storm which later produced another tornado
near Allison, TX (Figure 2). Each tornado was responsible
for long range debris transport. A check and an invoice
were found 58 km north-northeast from a source near
Kellerville, 35 km to the left of the reflectivity track. A light
shingle was also found at this location. A ripped business
form from a different Kellerville source was found 88 km
northeast, 12 km to the left of the storm track. TX-OK JUN 8, 1995 6? 95 ALLISON - All traceable debris (canceled checks)
originated from the same home near Allison, TX. The
greatest distance traveled by one of these checks was 95
km northeast. The debris pattern within the Allison fallout
area clearly shows a tendency for heavy and light items to
land closer to the storm track than paper items (Figure 2).
The light items were large pieces of styrofoam and
insulation. The one heavy item was a 4'x2' plywood board.
Debris fell between 15 km and 40 km left of the storm track.
There is a possibility that some unsourced debris may have
been lofted by the Kellerville tornado. MO JUL 4, 1995 9 140 F2 MOBERLY - Although the tornado was only rated F2 as it
cut northeast through Moberly, MO, it resulted in five reports
of heavy (> 1 lb) items downstream and four reports of light
or paper items. A 3- to 5-lb brick, which was found 45 km to
the northeast and just to the left of the extended tornado
track, was labeled with the insignia of a brick manufacturing
company which sustained significant damage in Moberly.
Unopened cans of soda (classified as light) were found 140
km northeast, approximately 25 km to the left of the
extended tornado track. The bottling company which
produces the soda had a plant destroyed in Moberly. Other
heavy items included two large signs from a tire store in
Moberly. One, 4'x6' and made of tin, was found 55 km
northeast, 10 km to the left of the extended tornado track.
The other was 3'x8' and plastic, found 75 km northeast, 8
km to the left of the track. A strip of metal measuring nearly
12 feet long and 3/4 inches wide (nearly 2 lbs) was found
85 km north-northeast, nearly 40 km to the left of the
extended tornado track. This item is thought to have come
from the Moberly storm, based on its time of appearance at
the finder's home. Paper items included a financial form
and photograph from a kennel club damaged in Moberly
found 75 and 95 km away respectively; both approximately
20 km to the left of the extended tornado track. Another
photo from the same building was found 110 km northeast
along the extended track.
This "population effect" is illustrated by the Friona, TX, case of June 8, 1995 (Figure 1). This case is unique because there is a highly populated area 100 km downstream from the damaged area. We find that the greatest geographic density of long-range reports exists within the Amarillo, TX, metropolitan area, which is near the far end of the fallout plume. Because our media campaign included both the metropolitan and rural newspapers throughout the region, we can assume that differing regional public awareness was not a major factor in the resulting report distribution.
This study further supports the idea that for long-range debris lofting to occur, a tornado need only be strong enough to produce considerable damage, and must strike structures containing loftable items. Of the lofting events for which F-scale intensity were known, four were F2, four were F3, and seven were F4.
The orientation of debris items relative to their associated storm tracks or (if storm tracks were not available) tornado tracks was determined for each event above. Figure 3 is a composite showing all debris items plotted against a single reference track. Unsourced debris and debris from events for which no track information was available was excluded. It is evident that most debris tends to land to the left of the storm/tornado track, with the fallout of heavier items generally being close on the left and paper items ranging from close on the right to distant on the left. Figure 3 is consistent with a similar plot of debris accounts from the historical record (1871-1990) by Snow et al. (1995, 1996).
With the high space-time resolution data obtained by VORTEX during the Friona and Allison events (June 2 and 8, 1995), we hope to obtain more accurate wind profiles in the storm and near storm environments, allowing for more meaningful trajectory analysis.
Figure 3. Composite pattern of 84 debris reports associated with 13 tornadic storms in 1994 and 1995. Arrow indicates reference storm track and has arbitrarily been oriented SW to NE.
Both the systematic collection of lofting accounts nationwide and the intensive study of a few well-represented events will provide a solid base on which to begin developing a numerical model to simulate the debris lofting, transport and fallout process.
Acknowledgments. The authors thank everyone who took the time to call or send in debris reports from around the country over the past two years. Dr. Chris Church provided input on earlier drafts. This work is supported by the National Science Foundation under Grant ATM9411767.
Grazulis, T.P., 1993: Significant Tornadoes 1680 - 1991. The Tornado Project of Environmental Films, 1326 pp.
Magsig, M.A., C.H. Levison, J.T. Snow, and A.L. Wyatt, 1996: Long range debris transport and fallout in Oklahoma from a tornadic thunderstorm on May 7, 1995. Preprints, 18th Conf. on Severe Local Storms, San Francisco, CA, Amer. Meteor. Soc.
Snow, J.T., A.L. Wyatt, A.K. McCarthy, E.K. Bishop, 1995: Fallout of debris from tornadic thunderstorms: An historical perspective and two examples from VORTEX. Bull. Amer. Meteor. Soc., 76, 1777-90.
______, 1996: Long range debris transport and fallout in the Ardmore, Oklahoma tornado of May 7, 1995. Preprints, 18th Conf. on Severe Local Storms, San Francisco, CA, Amer. Meteor. Soc.
[*] Corresponding author address: Carl H. Levison, School of Meteorology, 100 E. Boyd St. Suite 1310, Norman, OK 73019-0628.[Return]
[1] This fallout pattern contrasts with that in the May 7, 1995, event (Magsig et al. 1996, this volume), in which all debris fell within 20 km of the reflectivity track. The 00Z upper-air sounding from Amarillo (approximately four hours after the tornado) indicated significant veering of the wind from southeasterly to southwesterly up to 700 mb. Soundings outside the storm environment depicted a more unidirectional wind profile from the southwest. The fact that the Friona storm turned towards the east after passing the city, along with the fact that the Amarillo sounding showed no westerly winds at any altitude, seems to suggest that debris which landed farther away from the storm track exited the storm environment at higher altitudes.[Return]
The third sentence of footnote 1 should read "Sounding outside the Ardmore storm environment..." The last sentence of footnote 1 should read "The fact that the Friona storm turned towards the east after passing the city seems to suggest that debris which landed farther away from the storm track exited the storm environment at higher altitudes."
In the description of the Friona, TX, case, "cassette tape" should be changed to "strips of magnetic tape."