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The primary mission of the National Weather Service (NWS) is the protection of life and property through the issuances of timely and accurate forecasts and warnings. This mission was never so tested for the NWS Forecast Office in Norman, Oklahoma as it was on May 3, 1999 when 58 tornadoes taking 42 lives and injuring hundreds more occurred in the Norman area of warning responsibility. Despite these tragic results, the casualties could have been much higher had warnings been less timely or the public non-responsive. This paper will illuminate impacts of the recent infusion of technology into the forecast environment which produced significant benefits, yet important challenges for decision makers to overcome. In addition, how the concept of situation awareness (SA), while fairly new to the NWS warning environment, played a key role with regards to managing the massive amounts of data available to decision makers prior to and during the outbreak will be discussed.

The objective of this study is to gain insight into the cognitive mechanisms that enable a person to project how a system or environment will change over time. Two potential mechanisms for mental projection are examined: (1) mental simulation (performing a mental play by play) and (2) pattern matching (identifying critical features of the situation and matching those with previous experience). A study was performed in cooperation with the National Weather Service Warning Decision Training Branch in which 28 severe weather warning forecasters participated in an interval-based simulation. At three decision points in this simulation, participants were asked to assess the threat level for tornado, wind, hail, and flash flood and to delineate their rationale for each assessment. Results are presented that support the existence of pattern matching and mental simulation strategies, that suggest different strategies may be effective in different situations, and that indicate forecasters utilize both strategies.

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