Site Investigations

The Severe Weather Damage Site Investigator

TORRO’s most productive area of research involves members conducting tornado damage site investigations.

Our aims are:
  • To establish the most likely cause of the damage (i.e. tornado, downburst, other thunderstorm-related winds etc).
  • To record the type of damage and its locations (usually with descriptive notes and photographs).
  • To obtain statements from eyewitnesses.
  • To assist with media enquiries at the scene (usually only applies to the larger events).
Once the site investigation is complete: This research helps to ensure that events are properly recorded and logged. Without it, many events would remain unrecorded, and the nature and extent of the damage illusive. For example, the true extent of damage is often considerably larger than may initially be indicated by media reports or eyewitness information. It is only by careful site investigation that we can truly hope to understand more about the incidence and distribution of severe local storms and their associated damage in the UK and Ireland.

A large team of scientists, researchers and enthusiasts carry out various activities to support the site investigations. These range from obtaining satellite images, radar data, synoptic charts and other reports, to providing maps and live assistance to the investigator. TORRO hopes that by directly involving its members in such activities, they will learn more about tornadoes and other severe weather events. Visiting damage sites is often a fascinating experience, and it is hard to leave without a greater appreciation of the power of tornadoes and other damaging wind events. It is only by conducting this important research that we can hope to develop a credible database of tornado and other storm-related damage events for the UK and Ireland.

TORRO has a core network of members who are willing to undertake site investigation work. Our network of potential site investigators spans the furthest reaches of the UK and Ireland. Members have a wide range of experience levels, but in practice no prior knowledge is required: the main requirement is for careful and accurate documentation of the facts. With sufficient information, analysis of the findings at a later date can usually determine the cause of the damage, even if this is not established at the time of the site investigation.

In some events, members are alerted to the risk of severe weather by TORRO convective discussions and advisories. This helps us to keep an eye out for any damage reports, which in turn can help ensure a quick response, should anything occur. It is not unusual for an investigator local to an event to attend the scene well before the press has arrived, sometimes within an hour or so. TORRO also has good links with the UK Meteorological Office, and is grateful for the many hundreds of reports that they deliver to us.

Below is a set of guidelines for site investigation activities. Bear in mind that site investigators don’t need a detailed understanding of the meteorology relating to an event. The primary aim of any investigator should be to produce an accurate and complete (as far as possible) documentation of the damage. All that is needed is willingness and a desire to learn.

Guidelines to Achieving Successful Site Investigations

  • All investigators are expected to behave in a responsible and courteous manner. Remember that people may have been injured, or may have suffered property structural damage or lost personal belongings. Please be sensitive to this possibility.
  • Investigators are reminded that they undertake investigations entirely voluntarily, and at their own risk: TORRO cannot be held responsible for any loss or damage associated with individual investigations. Do use common sense to assess potential dangers such as fallen power lines: where in doubt, don’t take the risk!
  • In advance of any possible events, members may keep up-to-date by checking for TORRO advisories, watches or discussions (the best information can normally be found on The Forum, but forecasts are also posted on the main TORRO website). Attention can then be focused on periods and areas at risk. We recommend that members check the forum regularly during identified periods of risk – to keep informed of any developments and reports.
  • Damage reports usually make it onto the forum initially, and may then be passed-on to the nearest member to that location. If the exact location is not known, investigators may have to contact the press for more information (in addition, some Fire and Rescue services also post incident locations on their websites). However, damage reports usually contain sufficient information to provide a starting point for the site investigations.
  • Attending the site as soon as possible after the event is recommended, since damage may be cleared away quickly, particularly in suburban and urban areas. However, site investigation will usually provide some useful information several days, if not weeks, later (for example, damage to trees in rural areas may be clearly evident months later).
  • Although not essential to the site investigation, investigators may find it useful to have a rough idea of the likely direction of any damage tracks. Such information may be derived, for example, from available radar data which can show the movement of individual storm cells. This information can often be found on the forum soon after a report is received. In the UK, damage tracks are typically orientated from somewhere between west and south towards a point between north and east, though of course there are exceptions to this rule.
  • Once a damage path is identified (if one can be) a useful approach is to look along extensions of the line in both directions (e.g. for a SW – NE track, check locations along extensions of the track to the NE and SW). Marking the track on a map is to be recommended, not only for documentation purposes, but also because roads and footpaths which cross extensions of the path can be easily identified, and then checked. This approach helps to establish the overall length of the path, and its start and end points. Damage along a path can be intermittent, so it is worth checking several points that lie on any possible extension to a path, even if damage is not found at an intervening point.
  • Take photographs of damage, paying particular attention to any unusual damage. Photographs provide excellent detail, which helps with post-investigation discussions about the nature of the event, in addition to providing a lasting record.
  • Add the locations of all observed damage to your map. Even where no obvious pattern in damage locations is apparent, the information could be vital in order to clarify the nature of the event. If a path is found, another approach which may be useful is to find the start point, and then walk the entire length on foot, noting all damage (e.g. as in 'Fig 1' below).
  • On scene, endeavour to note the type of damage, movement direction of projectiles and fall direction of snapped or uprooted trees. Noting the dimensions and materials of projectiles is also useful.
  • Although there is no requirement to establish the cause of the damage at the time (this can be done later, for example by an overall analysis of the documented damage patterns), the following points may be helpful:
    • In the case of tornadoes, a ‘surgically’ well-defined and narrow damage-path is common, along which significant damage is seen, but away from which there is little sign of damage;
    • For cyclonically (anti-clockwise) rotating vortices, projectiles may be thrown to the left of the direction in which the vortex advanced (i.e. looking down-track). This effect is usually not apparent, however, for fast-moving, weak tornadoes.
    • A diverging pattern of damage and throw directions, with no clear path, is a good indication of downburst (severe, non-tornadic) winds
  • Map the damage locations in detail. In some cases, a tornado may lift and touch down again repeatedly resulting in a more fragmented trail of damage.
  • A reliable source of information will come from eyewitnesses or people who have suffered damage to their homes. It may be necessary to knock on a few doors. Damage tracks will often pass over private land – please get permission from the owner before entering any private land.

Writing-up your site investigation findings

A formal write-up of site-investigations is not compulsory. However, many investigators find that writing out the results helps in consolidation of findings and in drawing final conclusions about the cause of the event. Furthermore, a good write-up provides a lasting record of the event and an example for future investigators to follow. TORRO aims to publish site investigation reports in its affiliated journal, the International Journal of Meteorology. Where needed, help and advice in writing-up the results are always on hand – just ask on the forum or contact us via the TORRO website.

Site investigation reports will typically contain the following:
  1. Date, time and location of the event.
  2. Date and time of site investigation(s).
  3. Approximate damage track length and width.
  4. Maximum intensity based on the TORRO Tornado Intensity (T) scale.
  5. A graphic overview of the damage track with damage markers (e.g. as in Fig 1).
  6. Descriptions of the damage observed at various points, or the most significant instances of damage.
  7. Photographs of the damage.
  8. A conclusion as to the most likely cause of the damage (i.e. tornado, downburst etc.). An ‘open verdict’ is perfectly acceptable where uncertainty remains.

  9. Additionally, reports may include the following:

  10. A radar sequence for that period (e.g. Fig 2).
  11. A synoptic analysis map for that day (e.g. Fig 3).
  12. Radiosonde data (i.e. tephigrams, aka skew-t diagrams).
This additional information is used for analysis of the meteorological conditions relating to an event. It is not a vital part of a site-investigation report, but if an author wishes to include this information, it can usually be obtained by request via the TORRO forum. Alternatively, the following websites can be used:
Sounding data: University of Wyoming
Synoptic charts from the Met Office

When complete, also consider posting your report directly onto the TORRO forum, where it can immediately be read by other members. The tornado and severe weather database is compiled partly by using information from the forum; therefore, by posting investigation results on the forum, you will ensure that the details of the event will make it into the database.

Fig 1. (Farnborough Tornado Track December 2006)
Google map Courtesy © Google Earth

Fig 2. Save radar images for that period on that day
Radar Courtesy © Netweather radar

Fig 3. Example synoptic map
Synoptic map Courtesy © UKMO

Please print off our Tornado Site Investigation Check List.
Compare site damage with the International Tornado Intensity Scale.
The latest forecasts from TORRO can be found on the TORRO Forecast section of the website.