Tornado Index # 20040420.17.13
Note: This approximate tornado path has been generated from data provided by the SPC.
The Tornado History Project generates approximate paths through separate historical archives provided by the Storm Prediction Center (SPC) and the National Climatic Data Center (NCDC). Paths generated from the NCDC data are typically more detailed, but neither archive gives exact path information. There are several reasons that paths may be inaccurate:
- Tornado touchdown and liftoff coordinates were recorded with only 2 digits of decimal precision (i.e. [33.72, -86.15] vs [33.71689, -86.15463]). As a consequence, the observed points on the map may be slightly off from actual. Note that beginning in 2009, up to 4 digits of decimal precision are given.
- Coordinates have not historically been calculated via GPS (Global Positioning System). Thus, tornado touchdown and liftoff coordinates should be considered as estimates only.
- Tornadoes may not have been in contact with the ground for the entire path as depicted on the map. Storm damage in any location depicted under the "path" should not be inferred.
- Although paths are drawn as straight lines between any two sets of coordinates, the tornado may have "zigzagged" in some way.
- Although paths are drawn as uniform thin lines on the map, it is likely that the tornado changed size over its lifetime. Damage in any location depicted under (or not under) the "path" should not be inferred.
Even with the above in mind, the data is the best available. If you see a path that is depicted incorrectly, please post a comment in the tornado forum indicating why you belive the path to be incorrect.
Paths generated from NCDC data are typically more detailed due to the way coordinates are listed in each archive:
- SPC database - A maximum of 2 coordinates (touchdown and liftoff) is given for each tornado, or each state segment of a tornado if it is a multi-state tornado. Thus the vast majority of paths are depicted as simple straight lines.
- NCDC database - Some tornadoes have mutliple sets of coordinates within any state, generally corresponding to entry and exit points by county. Thus, since more coordinates have been used to draw the path, the depicted path should be more accurate. Having said that, most tornadoes do not have additional path data in the NCDC archive. When they do, paths are drawn from the NCDC data.
The following statistics and definitions are derived from the Storm Prediction Center (SPC) historical tornado archive. The Tornado History Project can
not guarantee the accuracy of the underlying data within the SPC historical tornado archive. However, the data as presented here is guaranteed to
match the SPC data, except where noted.
Some definitions will not be given since they are obvious (i.e. "Date", "Time", etc...)
Special Note: This site uses a unique index number to identify each tornado. This index number is not a part of the official historical tornado archive.
E (Error) (tornado search table only) - A yellow box indicates that the tornado record contains a suspected error. A red box indicates that the tornado record contains an error and has been modified from the official source. Hover over the box for the error text.
Map/Forum (tornado search table only) - Clickable icons for further content related to a tornado.
State - The state or states affected by a tornado.
Fujita - The Fujita scale is an attempt to classify damage from a tornado. F0 being the least damaging, F5 the most. For 2007 and beyond, the Enhanced Fujita (EF) is given.
Fat. - The number of fatalities attributed to the tornado.
Inj. - The number of injuries attributed to the tornado.
Width - Width in yards. It is unclear if this indicates a maximum width or mean width.
Length - Length of tornado path in miles. Note the entire track length is not necessarily all on the ground (some tornadoes "hop and skip".)
Damage - Prior to 1996, this is a range by dollar amount. For 1996 and later, actual damage estimates are in millions.
Crop Loss - Added in 2007. Given in millions of dollars.
Lat/Lon - Contains two sets of coordinates:
- Touchdown Latitude/Longitude - For single state tornadoes, and the overall record for multi-state tornadoes, the approximate touchdown location in
decimal degrees. For the state specific records of multi-state tornadoes, entry point into the state in decimal degrees.
- Liftoff Latitude/Longitude - For single state tornadoes, and the overall record for multi-state tornadoes, the approximate liftoff location in
decimal degrees. For the state specific records of multi-state tornadoes, the exit or lift-off point from the state in decimal degrees.
St. #. - The state tornado number assigned to the tornado for that specific state for that specific year. Generally, state tornado
numbers were assigned in the order the tornado occurred, but that is not always the case.
SPC # - The tornado number as assigned by the SPC. Tornado numbers are not unique and reset each year. Generally, tornado numbers were assigned in the order the tornado occurred, but that is not always the case.
|Date (y/m/d)||Time||Fujita||Fatalities||Injuries||Width||Length||Damage||Crop Loss||Touchdown Lat/Lon||Liftoff Lat/Lon||SPC #||State #|
|2004-04-20||18:35:00 3||1||0||0||75||6||-||-||41.05 / -87.95||41.1 / -87.85||813|
|Affected States||Affected Counties|