Fallout of Debris from Tornadic Thunderstorms

FALLOUT OF DEBRIS FROM TORNADIC THUNDERSTORMS:
An Historical Perspective And Two Examples From VORTEX

John T. Snow[*] and Amy Lee Wyatt
College of Geosciences
The University of Oklahoma
Norman, Oklahoma

Ann K. McCarthy
Department of Earth and Atmospheric Sciences
St. Louis University
St. Louis, Missouri

Eric K. Bishop
School of Meteorology
The University of Oklahoma
Norman, Oklahoma

ABSTRACT

We report preliminary results of an investigation of debris lofted by tornadoes, its long- distance transport by thunderstorms, and its subsequent fallout. We begin with a review of historical accounts, including the unique study of the1984 Barneveld, Wisconsin tornado by Anderson. Our review shows that long-distance transport and fallout of debris have occurred and that distances involved have been significant. We then report first-hand evidence of these phenomena in two events with F2 tornadoes: the Tuskahoma, Oklahoma tornado of 25 April 1994 and the Gainesville, Texas tornadoes of 26 April 1994. In both cases, traceable material in the form of canceled checks, bills-of-sale, invoices, and legal documents were reported to us. We were able to locate the source locations for several of these items. We close with some conjectures on the implications of these first findings.

1. INTRODUCTION

Several times each year tornadoes strike communities in the United States, damaging homes, businesses, and other structures. Great efforts have been made to understand how tornadic winds damage structures. Less attention has been given to other, closely related phenomena. While there have been a few efforts to investigate low altitude lofting and deposition of material by tornadic windfields (usually motivated by an interest in missile hazards), the lofting of debris to great heights, its long-distance transport, and its fallout far downstream from its source have received little attention. Indeed, most of our knowledge of such phenomena is anecdotal -- the newspaper clipping reproduced in Figure 1 is typical. These phenomena pose interesting scientific questions and challenges, and are the subject of this paper.

Figure 1. Account from San Francisco Chronicle (December 3, 1992) describing debris lofted by a tornado near Florence, Mississippi on November 21, 1992. The debris was recovered approximately 30 miles (50 kilometers) downstream. The tornado was rated F3 at the time it went through Florence; later in its 128-mile (205-km) track, it was rated as F4.

1.1 The Barneveld, Wisconsin Tornado

Motivation for this study was provided by Anderson's (1985a) investigation of debris lofting, long-distance transport, and fallout that accompanied the 7/8 June 1984 outbreak of tornadoes in southern Wisconsin. As shown in Figure 2a, seven tornadoes were produced in southern Wisconsin by a complex of thunderstorms (see Anderson, 1985b, for a description of this storm). One of these, a violent tornado (rated F5 on the Fujita Intensity Scale; Fujita, 1971, 1973), destroyed approximately 90% of the small village of Barneveld. A large amount of debris from this village was lofted, transported, and deposited in a wide swath running from southwest to northeast across Wisconsin. In the days following the outbreak, Anderson and his students conducted a ground survey and a mail and telephone campaign to obtain data on the fallout of debris. His results are summarized in Figure 2b.

Figure 2a. Mapping showing the tracks of the seven tornadoes produced in Wisconsin outbreak of 7/8 June 1984 (taken from Storm Data, June 1984, 26(6)).

Figure 2b. Debris fallout pattern resulting from the Barneveld tornado (from Anderson, 1985a).

Anderson classified fallout from this storm as follows:

Paper: This consisted of many different types of paper items -- most important were checks, letters, bills, and invoices. (Such items can be called "traceable paper", since they contain addresses that allow the source to be identified.) Anderson reports:
"Paper debris was found throughout the contiguous area with a wider extent than the light debris. Paper debris was found in widely scattered locations north of the contiguous area reaching the town of Bonduel, some 20 miles northwest of the city of Green Bay. The maximum width of this scattered paper was 23 miles at 110 miles downstream of Barneveld."
Light (< 1 pound): This consisted of tarpaper, shingles, soffit, insulation bits, etc... from buildings, bank pouches, and occasionally bundles of light materials such as canceled bank checks and statements in envelopes. In the BarnevelD storm:
"A bank pouch lettered 'Barneveld State Bank' was found in Mayville, 86 miles ENE of Barneveld." (This pouch is also notable since it was the one item of light material found outside the contiguous debris area.) "The lighter materials are not deposited symmetrically around the heavy debris path but lie more to the east, making the heavy debris path lie nearer the western edge of the contiguous deposit area."
Heavy (> 1 pound): This consists of pieces of plywood, aluminum siding, boards, etc... from buildings. Anderson states "..., the heavy material lies along a narrow path from Barneveld to east of Redgranite, about 85 miles in length. The path of the heavy material shows branching at three places along its length, and it is partially interrupted in the Portage region."

1.2 Objectives

While showing conclusively that lofting, debris transport, and fallout occur, Anderson's study is the only one of its type in modern times (see Peterson, 1993, for discussion of three early European studies; these are mentioned briefly below). It does not provide a sufficient basis from which to judge either how often these phenomena occur or what happens in tornadoes of lesser intensity. We would like to be able to answer questions such as

How common is the high altitude lofting, long-distance transport, and subsequent fallout of debris such as occurred following the Barneveld tornado?
Is long-distance transport a phenomenon associated only with thunderstorms that produce the most intense tornadoes?
What is the maximum distance debris is likely to be transported?
How is the distribution of fallout related to storm structure?

As an application, we would like to be able to assess the risk posed by lofting, long- distance transport, and fallout of hazardous material (e.g., toxic chemical or radioactive material, medical waste in bulk storage, or even contaminated soil from a Superfund site) from tornadic thunderstorms. If lofting of material high into a thunderstorm, followed by its transport and fallout downstream, is a common event, then tornadoes pose serious hazards well beyond the direct impact of their high winds.

In an attempt to answer such questions, we recently began a three-year effort to gather data on lofting, transport, and fallout from tornadic thunderstorms. The objective of this study is to collect several data sets containing detailed information on these phenomena and on the thunderstorms causing them. For this reason, while we seek reports of fallout occurring anywhere in the U.S. during all seasons of the year, we are focusing our efforts on storms occurring in the VORTEX region during the intensive observing periods of that program (described briefly in Section 3). Here we report on some preliminary work and our first year's efforts. Specifically, in Section 2 we discuss evidence gleaned from a survey of historical records. In Section 3 we present evidence from two events with F2 tornadoes that occurred in the spring of 1994.

2. HISTORICAL EVIDENCE

A review of accounts of tornadoes -- by no means exhaustive -- finds a number of reports of debris being transported long distances. While many of these accounts -- especially those prior to 1950 or so -- are highly subjective and likely exaggerated, when taken together, they provide useful insights on lofting, transport, and fallout. In Grazulis (1993) [1], for the period 1871 through 1990, 86 out of 12,651 tornado accounts provided 121 reports of debris found more than five miles downstream, while a review of other publications on significant tornadic events which occurred in this same 120-year period provided an additional 42 reports. A tabulation of these 163 reports, giving dates, locations, F-scales and transport distances, is given in Table A1 of the Appendix [2]. (It is interesting to speculate why lofting, transport, and fallout have not attracted more scientific scrutiny. Possibly it reflects scientists' dislike of working with anecdotal and circumstantial data provided by laypersons, the type of data central to an initial investigation of these phenomena. Further, this complex chain of events -- lofting, long-distance transport, fallout -- occurring in the rapidly varying environment in and around a thunderstorm has probably been impractical to explore outside a focused field program such as VORTEX.)

Items reported to have been transported by tornadic thunderstorms range from paper products, such as canceled checks and photographs, to large, heavy objects, such as an airplane wing and a carton of deer hides [3]. In an account of the Tri-State tornado of 18 March 1925, Felknor (1992, pp. 73-74) cites the Murphysboro Daily Independent: "... a bond for a deed was blown to Lawrenceville [Illinois], 125 miles away." In a detailed discussion of the 9 June 1953 tornado in Worchester, Massachusetts, O'Toole (1993, p. 255), reports

"Emily McNutt of South Weymouth found a wedding gown in her backyard. It was dirty, as would have been expected, but was intact and in surprisingly good condition. A label sewn into the gown read 'McDonald, Worchester', indicating that the gown had been blown some fifty miles to its final landing place."

As another example typical of many reports, in a discussion of the Jordan, Iowa tornadoes of 12/13 June 1976 , Stanford (1987, pp. 95-97) reports

"Several days after the tornadoes, a photograph was returned to Jordan by a couple who had found it in their cornfield near Ackley, Iowa, more than 50 miles northeast of Jordan. The couple wondered if the photograph, about 16 by 20 inches, had possibly come from Jordan. Neighbors recognized the children shown in the photograph and it was returned to its owners, a family whose home had been destroyed in Jordan. Prior to the storm, the photograph had been hanging on a wall in their home."

Figure 3. Annual number of tornado events with long-distance debris transport and fallout for the 120-year period 1871-1990. Tornado events for which more than one debris report were noted were counted only once. Total number of events: 93.

The year-by-year distribution of the 93 tornado events which yielded the 163 reports in Table A1 is plotted in Figure 3. This distribution shows that although tornadoes with reports of long-distance transport occur with regular frequency, more than half (50 events, 90 reports) occurred in the fifty years prior to 1920. In the period 1871 through 1990, the number of tornadoes reported annually has increased from less than 100 in the period 1871-1916 (Fujita, 1987, p. 36) to greater than 1100 in 1990. Therefore, the number of tornado events with reports of long-distance debris transport, per year, as a fraction of the total number of recorded tornadoes for that year, has decreased in recent years. We conjecture that this is due in part to a shift (beginning in the early 1950's and with increased emphasis since the mid-1970's) by the operational and research communities from detailed analyses of each year's relatively few significant events, to a risk-assessment approach that is focused on characterizing the intensities for all tornadoes that occur in a given year. In using the current F-scale for this characterization, only damage in the path of a tornado need be assessed to ascertain intensity. Entries in Storm Data, the official government publication containing these characterizations, tend to be short and limited to items that substantiate estimates of intensity. Further, this broader approach to documenting tornadoes has increased most notably the number of weak (F0 and F1) tornadoes reported each year, events for which debris lofting and long-distance transport seem less likely.

Figure 4. Plot of number of debris reports as a function of type and distance for the 120-year period 1871-1990. Debris categorized as paper, light (weighing less than one pound), heavy (weighing more than one pound) or unknown weight (not paper). Total number of reports plotted: 163. As a result of an arbitrarily selected cutoff used in screening the tornado data base, there are no reports in the interval 0 to 5 miles.

Figure 4 shows the number distribution of the 163 debris reports as a function of debris type and distance transported. Using the definitions discussed in Section 1.1, the transported items were categorized as "paper", "light", or "heavy". If the account of an event was unclear as to the size or weight of the debris, the item was classified as having "unknown" weight; such accounts typically included phrases like "pieces of..." or "...buildings were destroyed. Debris was carried ... miles away." (While it would be desirable to also characterize transported objects in terms of their aerodynamic shapes, this proved impractical due to the lack of information in most historical accounts. An important exception is "paper", especially personal bank checks, since such items are very often of standard size.)

The overall shape of the distribution in Figure 4 is roughly what one would anticipate. Most items fall out fairly close to their points of origin. Heavy items tend to come down closest to their source locations, followed by light items. Paper items, the lightest materials, are carried the farthest downstream as indicated by the long tail of the distribution. The secondary peak in the distribution which occurs at a distance of 85-90 miles (135-145 kilometers) in Figure 4 (and also in Figure 5) is due to multiple reports of debris found at the same location, all associated with the F4 Great Bend, Kansas tornado of 10 November 1915.

Figure 4 suggests that most heavy debris falls out within 50 miles (80 kilometers) of its source, while most light debris falls out within 90 miles (145 kilometers) from its source. Paper debris, on the other hand, can be deposited much farther. The farthest reported distance for any fallout is 210 miles (335 kilometers); this was a canceled check, found in Palmyra, Nebraska, transported by the thunderstorm that produced the 1915 Great Bend, Kansas tornado. This tornadic thunderstorm also transported light and heavy objects farther than any other storm on record. Clothing, shingles, and fragments of books were found in Glasco, 87 miles (140 kilometers) to the northeast of Great Bend. A sack of flour, categorized as heavy, was found about 110 miles (175 kilometers) to the northeast. (Grazulis, 1993, personal communication, noted this to be "perhaps the longest distance ever recorded for an object weighing more than one pound.") This particular report may be anomalous, since the second-farthest report of transport of a "heavy" item is only 50 miles (80 kilometers).

Debris Reports

F scale Heavy Light Paper Unknown All types

F2 3 2 1 4 10

F3 3 9 7 15 34

F4 20 28 32 22 102

F5 4 2 8 3 17

Total 30 41 48 44 163

F scale	Heavy	Light	Paper	Unknown	All types
F2	3	2	1	4	10
F3	3	9	7	15	34
F4	20	28	32	22	102
F5	4	2	8	3	17
Total	30	41	48	44	163

Table 1. The distribution of 163 reports of paper, light, heavy or unknown weight debris as a function of tornado F-scale for the 120-year period 1871-1990. The number of tornadoes with debris reports for each F-scale value is listed in parentheses in the first column. Total number of tornado events with debris reports for the period is 93.

Table 1 displays the 163 debris reports as a function of F-scale. These and subsequent statistics using the F-scale must be interpreted with caution, especially if inferences are to be made about tornado dynamics and wind speeds, as the Fujita Intensity Scale is really a tornado damage rating scale -- see Doswell and Burgess (1988) for a discussion of this point. (Recall that the F-scale value assigned to an event characterizes the most severe damage observed; typically this will have occurred over only a small portion of the tornado's track.) While there is some correlation between damage rating and tornado strength, the correlation is not a perfect one. Further uncertainties enter in the assignment of F-scale values from anecdotal information. The net effect is that the F-scale value assigned to many events probably contains an uncertainty approaching +/- 1; there also appears to be a tendency to err on the high side in many events.

In Table 1, there are no data on fallout linked to F0 or F1 tornadoes since Grazulis focused on strong (F2 and F3) and violent (F4 and F5) tornadoes. The largest number of reports of long-distance debris transport (about 75% of the total) are associated with violent tornadoes, particularly those rated F4 in intensity. While the number of reports associated with F5 tornadoes appears small, this is a result of the fact that damage of this intensity is very rare (on the order of 0.1% of all tornadoes, based on tornado accounts 1953 through 1990). Similarly, F4 events are also a small fraction of all tornadoes (on the order of 1%). Hence, that 57 violent events appear here suggests that a relatively high percentage of violent tornadoes (roughly 4%) leads to long-distance debris fallout. In contrast, while there are some reports of long-distance debris transport by strong tornadoes, the number here is a relatively small percentage of all such events (roughly 0.4%). Since strong events account for roughly 28% of all tornadoes, this suggests debris transport by thunderstorms producing such events is rare.

Figure 5. Plot of number of debris reports as a function of F-scale and distance for the 120-year period 1871-1990. Overall distribution is the same as in Figure 4, but each bar is now differently proportioned.

Figure 5 shows the same number distribution as Figure 4, but with the bars now showing dependence on F-scale. The items which traveled the farthest distances, 205 and 210 miles, were both transported by thunderstorms producing F4 tornadoes. The greatest distance traveled by debris associated with an F2 tornado was 130 miles by a piece of copper plate from the 20 March 1888 tornado in Calhoun, Georgia (Grazulis, 1993).

Figure 6. Composite pattern of 68 debris reports associated with 31 tornadic storms, 1871-1990. The arrow indicates "storm direction", and has arbitrarily been oriented SW to NE. Debris items are plotted by azimuth and distance from their source.

Sixty-eight debris reports from 31 of the 93 tornado events represented in Table A1 -- ones in which the descriptions of the fallout were particularly detailed -- were combined to produce Figure 6, a composite plot of fallout locations with respect to estimated storm motion. Cases used in the plot were those in which the debris report was linked to a town name, or in which a direction and distance from the debris source was given. For example, on 25 April 1957 in southeastern Nebraska, Grazulis (1993, p. 1005) reports that an F4 tornado

"...moved ENE for 2 m N of Geneva, passing 1 m N of Friend, hitting the west half of Milford and ending 2 m N of Pleasant Dale...Milford debris was carried 40 miles to the NE, falling at Wahoo."

Locations of fallout finds and source points were given in 48 reports. In the other 20 reports, a direction and distance from the source were provided. (Although there were actually 83 usable reports, only 68 are plotted in Figure 6; the other 15 overlap, i.e., same event, same type, same fallout location.)

Using latitude and longitude coordinates of the noted towns or other locations, an azimuth and distance from the source was computed for each fallout site. The direction of storm movement for each event was estimated very roughly (to within +/- 10 °, say) as the direction of the line tangent to the beginning portion of the tornado track; here this will be referred to as "storm direction". The tracks were then rotated to align along a common direction (here drawn aesthetically as 225 °, or from southwest to northeast) and relative debris locations plotted accordingly. Because of the limited number of reports, no effort was made to stratify these data by tornado intensity.

Figure 6 shows that, of the 68 debris items plotted, 53 items (78%) fell to the left [4] of the composite "storm direction". Of the 15 items which fell to the right, only two items (one "paper" and one "light") fell beyond -10 °. Therefore, 66 items of debris (97% of the reports) fell either approximately along (i.e., within 10 ° to the right or left) or to the left of "storm direction".

Relative to the "storm direction", the composite debris pattern shown in Figure 6 suggests the most concentrated area of debris is between 10 ° and 35 °, that is, to the left of the composite "storm direction"; fifty-four percent of the points fall in this area. Thirty-two percent fall along the "storm direction". Paper was scattered the farthest, for distances as great as 210 miles, between angles of -40 ° and 70 °. Light debris was found up to 87 miles downstream, between angles of -38 ° and 75 °. Heavy items, with the exception of the flour sack, were carried up to 50 miles, between angles of -10 ° and 75 °. Items of unknown weight were carried up to 130 miles, between angles of -5 ° and 80 ° with respect to "storm direction".

This pattern of long-distance debris transport and fallout has similarities to that found by Anderson for the Barneveld tornado. In constructing a fallout map, Anderson found that the "...contiguous area of debris [lay] mainly to the west and north of the Barneveld-Arlington-Markesan tornado path.", that is, most of the fallout was to the left of the storm's track. Similarly, Peterson (1993) has described three European events in which the debris was to the left of the tornado track. These events include the St. Claude, France tornado of 1890; the Woldegk, Germany tornado on 29 June 1764; and the 24 July 1930 tornado in the Treviso-Udine district of Italy.

3. TWO RECENT EXAMPLES

3.1 VORTEX

The Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX) is a project being conducted by the NOAA National Severe Storms Laboratory in partnership with researchers from numerous universities and other federal agencies. Its goal is to gain better understanding of how tornadoes form, the role of the environment in producing tornadic storms, the structure of tornadoes, and how tornadoes produce their incredible damage. In a study area covering the southern half of Kansas, most of Oklahoma, and parts of the Texas panhandle and northern Texas, project participants are investigating target storms using portable and airborne Doppler radars; vehicular-mounted weather stations; movie, video, and still photography teams; and mobile facilities for launching weather balloons. This "mobile laboratory" supplements and complements the array of fixed WSR-88D radars, ASOS and conventional observing stations, and Oklahoma Mesonetwork stations in the study area. The first intensive observing period for VORTEX was 1 April through 15 June1994; the second intensive observing period is planned for the same ten weeks in 1995.

3.2 The Tornado Debris Research Project

The Tornado Debris Research Project, administered from the School of Meteorology at the University of Oklahoma, aims to study debris transported long distances by tornadic thunderstorms, especially those which occur within the VORTEX study area. The goal of the project is to locate "traceable debris" and infer a trajectory for the debris based on the dynamics of the transporting storm and the structure of the wind field in the mesoscale environment.

In order to locate debris, assistance from the public is essential. Prior to the start of a VORTEX intensive observing period, contact letters are sent to law enforcement, emergency management, and news media personnel in the study area and also "downwind" in Kansas, Missouri and Arkansas. These contact letters acquaint these individuals with the project, and indicate what will happen when a tornado strikes. When a tornado is reported to have caused significant damage within the study area, a press release is sent by facsimile to news media and emergency management personnel in counties downstream from where the tornado struck. The press release asks the public to be on the lookout for debris which may have been transported by the tornado. Debris reports are directed to the Tornado Debris Research Project via the Tornado Debris Hotline (1-800-3DEBRIS), by electronic mail to debris@metgem.gcn.ou.edu, or by regular mail. Persons who discover debris are asked to note what the item is, the specific location where it was found, the time it was found, and if there are any identifying marks or writing that might indicate its origin. Most debris items are then sent to the Tornado Debris Research Project for further study and an attempt to return the items to their owners. Through this procedure we have identified small amounts of fallout associated with two tornadoes that occurred in the VORTEX study area in April 1994.

3.3 The Tuskahoma/Talihina, Oklahoma Tornado Of 25 April 1994

At approximately 6:45 p.m. on 25 April 1994, a tornado of unknown intensity touched down in southeastern Oklahoma, just north of Tuskahoma. Reports obtained from the Tulsa, Oklahoma and Fort Smith, Arkansas offices of the National Weather Service suggest that this tornado was the first in a sequence of brief touchdowns and short damage tracks along a 20-mile (30-kilometer) long path running to the northeast, passing through and finally ending to the northeast of Talihina, Oklahoma. In Talihina, F2 damage was reported. Radar imagery showed that the storm which produced this sequence of tornadoes subsequently moved to the northeast over Sebastian, Crawford, Logan, Franklin, Johnson and Newton counties in Arkansas.

After receiving a post-storm survey report from the Meteorologist-in-Charge at the Fort Smith, Arkansas National Weather Service office, press releases were sent to newspapers in Poteau, Oklahoma and Clarksville, Fayetteville, Fort Smith, Greenwood, Huntsville, Springdale and Van Buren, Arkansas in order to alert the public to watch for debris that may have been transported by the tornado.

Two residents of Fort Smith, Arkansas and a third from Alma, Arkansas, a suburban community about 10 miles (15 kilometers) to the northeast of Fort Smith, responded to the press releases, reporting that they had found canceled checks and a receipt which were likely transported by the thunderstorm. The items were from a defunct gas company formerly located in Clayton, Oklahoma. Subsequent interviews with the former owners of the gas company revealed that the items had been in a storage shed which was demolished by this storm. The shed was near Tuskahoma, nearly 70 miles (115 kilometers) from Fort Smith and 80 miles (130 kilometers) from Alma.

3.4 The Gainesville, Texas Tornadoes of 26 April 1994

At approximately 3:20 p.m. on 26 April 1994 two tornadoes hit Gainesville, Texas, causing extensive damage to homes and property in Gainesville and rural Cooke County. The first tornado, rated F2, touched down on the west side of town and tracked six to eight miles east-northeast. The second tornado, also rated F2, touched down three minutes after and about one-half to three-quarter miles south of the first, and moved east-northeast, remaining on the ground for three to four miles. This second tornado was reported to have been rotating anti-cyclonically. Radar showed that the storm which produced the tornadoes moved to the northeast over Love, Marshall, Bryan, Johnston, and Atoka counties in Oklahoma.

News releases informing the public of possible debris fallout from this storm were sent to newspapers in Gainesville, Texas; and Ardmore, Durant, Konawa, Madill, Seminole, Tishomingo, Wetumka, and Wewoka, Oklahoma. Six telephone calls or letters reporting debris finds were received in response to the news releases.

For four of the six reports, the source of the debris was determined. These four debris items, which landed at three separate locations, were all traced to a ranch site about four miles north-northeast of downtown Gainesville. A canceled check and a page from a bank statement were both found on property four miles northeast of the source location. A title deed from the sale of property was found near Lake Texoma in Bryan County, Oklahoma, a distance of nearly 40 miles (65 kilometers) from the source. A second canceled check was found in Caddo, Oklahoma, nearly 60 miles (95 kilometers) from the source.

In addition, three photographs were retrieved from a pasture approximately two miles north of the Gainesville city limit. The source of the photographs has not been determined. Part of another canceled check of unknown origin was also found in Gainesville. Further, siding and other building materials of unknown origin were found approximately one mile (1.2 kilometer) west of Gainesville; all nearby buildings were undamaged by the storm.

4. CLOSING CONJECTURES

It is premature to draw general conclusions about these phenomena. However, the historical record and our experiences in the spring of 1994 suggest the following points:

Debris, sometimes large pieces, does fall from some tornadic storms well downstream from its source. While most lofted material falls out locally, we suspect a small amount of debris is carried upward in or around the tornado core and transferred into the circulation of the mesocyclone. The rising air in the mesocyclone apparently carries the material still higher into the parent storm. Exactly how high material is lofted and how the transfer occurs remains unclear.
Consistent with Anderson's findings, composited historical data contains hints that there is organization in how fallout occurs downstream. The large majority of historical accounts of long-distance transport of debris place the fallout to the left of the direction of storm movement. There is also a suggestion of a concentrated band of material within the overall fallout pattern. Possibly this tendency for fallout to be concentrated to the left of storm movement reflects the nature of the sheared flow through which the falling items descend, where the low-level wind direction veers with height. Still another possibility is that the debris rotates around the mesocyclone as it is carried aloft. However, that a few items of debris fall out well to the right of the "storm direction" is worrisome, especially if one is attempting to predict the fallout of hazardous material.
The historical record suggests that fallout is mainly from thunderstorms that have produced tornadoes rated F3 or greater in intensity (though we must recall the uncertainties in the F-scale values when making this assertion). Somewhat in contrast, our first-hand experiences in 1994 show that thunderstorms which have produced F2 tornadoes can also produce long-distance transport and fallout, a point that is only weakly indicated by the historical record. Indeed, it may be significant that we found long-distance transport and fallout in the first two F2 events we investigated, suggesting that perhaps these phenomena occur much more commonly than the historical data would suggest.

The number of events for which we have first hand data remains at two, a sample too small to fully answer the questions raised in Section 1.2. We are hopeful of obtaining additional cases in 1995 with the second VORTEX intensive observing period. Just before the onset of the spring storm season, we will also be advertising nationwide for reports of fallout, advising National Weather Service offices and media meteorologists of our project.

We close by noting that in addition to the interest inherent in these phenomena in their own right, lofting to high altitudes and long-distance debris transport by tornadic thunderstorms constitute challenges for numerical modelers to duplicate, and provide a unique means of testing certain types of cloud and mesoscale models. Replicating observed fallout patterns will require combining the dynamics of a cloud model with a model for the aerodynamic behavior of "typical" debris particles. It requires consideration of both in-storm winds and adjacent environmental flow. However, simulation of fallout does not require a cloud model coupled with an aerodynamic model for the debris. Rather, since debris should not significantly modify the wind field, one can run a cloud model through a storm's life cycle, then go back and use the resulting four-dimensional wind field to predict debris trajectories. Such a simulation could become a prediction model for use by emergency management personnel. Again, the high quality, temporally and spatially dense measurements of environmental conditions to be made during VORTEX should facilitate such research.

ACKNOWLEDGMENTS

The late Dr. Charles E. Anderson provided the inspiration for this work through his study of the Barneveld, Wisconsin tornado. The historical review could not have been done without the extensive analysis of tornado records that has been carried out by Mr. Thomas P. Grazulis over the last decade. Christopher R. Church, a partner in our field work, made useful comments on an early draft of this article and provided insights on how to interpret Table 1. Mr. Michael Magsig and Mr. Carl Levison read several rough drafts and provided excellent sounding boards. Special thanks are due Mr. Stephen Cale of the Durant Daily Democrat, and the other individuals who provided us with reports of debris and fallout: Ms. B.J. Riggs; Mrs. Vernon Dunn; Ms. Renee Fair, WCM in the NWSO - Fort Smith, Arkansas; Mr. Steve Piltz, WCM in the NWSO - Tulsa; Mr. Jay Hilgartner, Meteorologist, KFSM-TV, Fort Smith, Arkansas; Mr. Fred Roush, MIC, NWSO - Fort Smith, Arkansas; J. D. and Linda Fite, Kiamichi Valley Gas Co.; Ms. Odell Mosley; Mr. Lloyd Swain; Paul and Stephanie Sidener; Mr. Lynn Colson; Ms. Maggie Hill; Ms. Betty Brewer; Mr. Cleveland Dennis; and Mr. Greg Stumpf of the NOAA National Severe Storms Laboratory. Dr. T.T. Fujita and two anonymous reviewers made several valuable suggestions that improved the final draft. This work is supported by the National Science Foundation under Grant ATM9411767.

[APPENDIX]

REFERENCES

Anderson, C.E., 1985a: The fall-out pattern for debris for the Barneveld, WI tornado: an F-5 storm. 14th Conf. on Severe Local Storms, American Meteorological Society, Boston, MA. 264-266

Anderson, C.E., 1985b: The Barneveld tornado: a new type of tornadic storm in the form a spiral mesolow. 14th Conf. on Severe Local Storms, American Meteorological Society, Boston, MA. 289-292.

Corliss, W.R., 1983: Tornados [sic], Dark Days, Anomalous Precipitation, And Related Weather Phenomena. The Sourcebook Project, Glen Arm, MD, 196 pp.

Davies-Jones, R.P., 1981: Acquisition and analysis of severe storms and tornado field observations. Section 4 (pp. 21-66) of Summary of AEC-ERDA-NRC Supported Research At NSSL 1973-1979 (J.T. Lee, ed.), NOAA Technical Memorandum ERL NSSL-90, 93 pp.

Doswell, C.A. III, and D.W. Burgess, 1988: On some issues of United States tornado climatology. Mon. Wea. Rev., 116, 495-501.

Felknor, P.S., 1992: The Tri-State Tornado. Iowa State University Press, 131 pp.

Fujita, T.T., 1971: Proposed characterization of tornadoes and hurricanes by area and intensity. Satellite and Mesometeorology Research Project Research Paper 91, Department of the Geophysical Sciences, The University of Chicago, Chicago, IL. 44 pp.

Fujita, T.T., 1973: Experimental classification of tornadoes in FPP scale. Satellite and Mesometeorology Research Project Research Paper 98, Department of the Geophysical Sciences, The University of Chicago, Chicago, IL. 15 pp.

Fujita, T.T., 1987: U.S. Tornadoes. Part One: 70-Year Statistics. Satellite and Mesometeorology Research Project Research Paper 218, Department of the Geophysical Sciences, The University of Chicago, Chicago, IL, 122 pp.

Grazulis, T.P., 1980: Indiana Killer Tornadoes, poster.

_____, 1993: Significant Tornadoes 1680 - 1991. The Tornado Project of Environmental Films, 1326 pp.

Hayes, M.W., 1927: The St. Louis Tornado of September 29, 1927. Mon. Wea. Rev., 55, 405-407.

The Oklahoma Daily, 1994: Tornado victims rebuild, recall. The University of Oklahoma Publications Board, April 27.

O'Toole, J.M., 1993: Tornado! 84 Minutes, 94 Lives. Databooks, 284 pp.

Peterson, R.E, 1993: Far-field tornado debris patterns. 17th Conference on Severe Local Storms, American Meteorological Society, Boston, MA. pp. 319-322.

Smith, H.E., Jr., 1982: Killer Weather. Dodd, Mead & Company, 224 pp.

Stanford, J.L., 1987: Tornado: Accounts of Tornadoes in Iowa, 2nd Edition. Iowa State University Press, 143 pp.

Tanner, R.W. (Ed.), 1990: Southwestern Nebraska Tornado of June 15th. Storm Data, 32(6), 25-27.

Walz, F.J., 1917: Tornado of March 23, 1917, at New Albany, Ind. Mon. Wea. Rev., 45, 169-171.

FOOTNOTES

* Corresponding author address: Dr. John T. Snow, College of Geosciences, The University of Oklahoma, Sarkeys Energy Center Suite 710, 100 East Boyd St., Norman, OK 73019-0628 [Return]

[1] Grazulis investigated accounts of tornadoes of F2 or greater intensity, and/or those which caused loss of life. Further, he notes that in collecting data for his study, his focus was not on recording debris reports, but on estimating damage intensity to determine F-scale values. He recalls "...I noted debris carried > 5 miles [but] my focus was never on long distance debris. I passed over many more examples. I focused on heavy debris > 500 lbs. carried > 1 mile in my searches." (T.P. Grazulis, 1993, personal communication) [Return]

[2] We note that Corliss (1983) documents many "falls" of anomalous materials -- such as frogs and fishes -- from showers and thundershowers. While many of these accounts are likely exaggerations or misinterpretations, there are enough reports to suggest such events to occur and that the underlying mechanism is related to that discussed here.[Return]

[3] It is probably safe to assert that most debris that is transported long distances lands in unpopulated areas or else is accepted as common litter. It is likely most fallout is detritus and blends into the landscape. Probably only a very few items, novel enough to excite curiosity with their appearance in the local environment, are reported.[Return]

[4] Here we denote positive angles as being drawn counterclockwise from the composite "storm direction", i.e., to the left of the "storm direction." Negative angles are drawn clockwise from this composite direction.[Return]