NWC REU 2018
May 21 - July 31



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NWS Tornado Warnings: A Regional Analysis

Ronald Kennedy, Jr.


What is already known:

  • Brooks and Correia (2018) looked at the National Tornado Warning Performance from 1986 – 2016. They found a change occurred in 2012.
  • My focus is on the regional analysis of what Brooks and Correia (2018) did nationally and the time-period around the change in 2012.
  • Metrics of interests: Probability of Detection (POD), False Alarm Ratio (FAR), Bias, and Critical Success Index (CSI).

What this study adds:

  • The most significant change in performance nationally took place in 2012 when POD and FAR decrease.
  • Central region changes first followed by southern and eastern. The change in the threshold of warnings led to a reduction in FAR (and POD).
  • Using data from the performance diagram can show changes in multiple metrics.


Sergeant JP Finley used a 2 x 2 contingency table to forecast tornado occurrences. This table allowed a user to obtain probability of detection (POD), false alarm ratio (FAR), critical success index (CSI), Success ratio (SR), and the Bias. These metrics help evaluate help provide the value and quality of a forecast. Recent studies of national weather service tornado warning performance for the Central, Eastern, and Sothern regions from 1986 - 2011. This study found a major decrease in false alarm ratio (FAR), probability of detection (POD) starting 2012 for the Central region, while the Southern and Eastern region displayed no change in false alarm ratio (FAR) or probability of detection (POD) until the following year. A warning forecaster has lots of information to consider before issuing a warning. They have radar, spotter reports, environmental conditions, historical data sets, etc. These elements all play a role in the weight of evidence required to issue a warning or not. If there is enough weight of evidence to issue a warning that goes above the threshold set in place most times the forecaster will issue a warning. This of the paper will be the regional analysis of regional performance focusing specifically on the time-period around the change in 2012.

Full Paper [PDF]