May 3, 1999 SPC Outlook: A Day Etched in Tornado History

The May 3, 1999, Storm Prediction Center (SPC) outlook was a high-risk forecast for severe thunderstorms, including the potential for violent tornadoes, across portions of Oklahoma and Kansas. This outlook accurately anticipated and warned the public about the catastrophic tornado outbreak that unfolded later that day, forever marking it as a pivotal moment in meteorological history and highlighting the SPC’s critical role in public safety.

The Anatomy of a High-Risk Day

Let’s dissect what made the May 3, 1999, outlook so significant. The SPC meticulously analyzes various meteorological factors to determine the likelihood and severity of severe weather. On May 3, 1999, several ingredients converged to create a volatile atmospheric environment:

Significant Atmospheric Instability

Abundant moisture streamed northward from the Gulf of Mexico, fueling the atmosphere with the necessary instability for thunderstorm development. This moisture, combined with daytime heating, created a highly unstable airmass, meaning that rising air parcels would readily accelerate upwards, leading to powerful updrafts within thunderstorms. The measure of this instability, often quantified by CAPE (Convective Available Potential Energy), was exceptionally high across the region, indicating the potential for intense storms.

Strong Wind Shear

Wind shear, the change in wind speed and direction with height, was another critical ingredient. Strong wind shear supports the development of rotating thunderstorms, known as supercells. The SPC identified a significant amount of shear present in the atmosphere, conducive to long-lived supercells capable of producing large, damaging tornadoes. This shear allowed the storms to organize and intensify, further increasing the tornado threat.

Favorable Large-Scale Forcing

A strong upper-level trough (an elongated area of low pressure) was approaching the region, providing the necessary large-scale lift to initiate thunderstorm development. This trough acted as a trigger, forcing air to rise and cool, leading to condensation and the formation of clouds and eventually, thunderstorms.

The High-Risk Designation

Based on the convergence of these factors – significant instability, strong wind shear, and favorable large-scale forcing – the SPC issued a high-risk outlook, the highest level of alert, for portions of Oklahoma and Kansas. This designation indicated a very high probability of widespread severe weather, including the potential for violent tornadoes. The SPC explicitly communicated the threat of long-track, strong to violent tornadoes in their forecast discussions.

The Devastation Unfolds

The SPC’s high-risk forecast proved tragically accurate. Numerous supercell thunderstorms developed across the region, spawning a multitude of tornadoes. The most infamous of these was the Bridge Creek-Moore, Oklahoma, tornado, an F5 on the Fujita scale (later revised to an EF5 on the Enhanced Fujita scale). This tornado caused widespread destruction, numerous fatalities, and countless injuries. Other significant tornadoes occurred across Oklahoma and Kansas, making May 3, 1999, one of the most devastating tornado outbreaks in recorded history.

Legacy and Lessons Learned

The May 3, 1999, tornado outbreak had a profound impact on the meteorological community and the public’s awareness of severe weather. The event led to:

• Increased research and understanding of supercell thunderstorms and tornadoes.
• Improvements in forecasting techniques and technology.
• Enhanced public awareness campaigns to promote tornado safety.
• Development of the Enhanced Fujita (EF) scale to provide a more accurate assessment of tornado damage.

The May 3, 1999, SPC outlook serves as a testament to the importance of accurate and timely severe weather forecasting. It also underscores the ongoing need for public education and preparedness to minimize the impact of these destructive events.

Frequently Asked Questions (FAQs)

1. What is the Storm Prediction Center (SPC)?

The Storm Prediction Center (SPC) is a part of the National Weather Service (NWS) and is responsible for forecasting severe weather, including tornadoes, across the United States. They issue outlooks, watches, and warnings to alert the public to potential threats.

2. What is a High-Risk Outlook?

A high-risk outlook is the highest level of alert issued by the SPC. It indicates a very high probability of widespread severe weather, including the potential for violent tornadoes, significant hail, and damaging winds.

3. What meteorological factors are considered when issuing a severe weather outlook?

The SPC considers several meteorological factors, including atmospheric instability (CAPE), wind shear, moisture availability, and large-scale forcing mechanisms (e.g., upper-level troughs).

4. What is CAPE (Convective Available Potential Energy)?

CAPE (Convective Available Potential Energy) is a measure of atmospheric instability. Higher CAPE values indicate a greater potential for strong updrafts within thunderstorms.

5. What is wind shear and why is it important for tornado formation?

Wind shear is the change in wind speed and direction with height. It is crucial for tornado formation because it allows thunderstorms to rotate, leading to the development of supercells.

6. What is a supercell thunderstorm?

A supercell thunderstorm is a type of thunderstorm characterized by a rotating updraft called a mesocyclone. Supercells are the most likely type of thunderstorm to produce tornadoes.

7. What is the Fujita Scale (F-Scale) and the Enhanced Fujita Scale (EF-Scale)?

The Fujita Scale (F-Scale) was used to rate the intensity of tornadoes based on the damage they caused. The Enhanced Fujita Scale (EF-Scale) is a revised version of the F-Scale that provides a more accurate assessment of tornado damage by considering a wider range of structural types.

8. What is a tornado watch?

A tornado watch means that conditions are favorable for the development of tornadoes in a specified area. It is a call for people to be aware of the potential for tornadoes and to monitor weather reports.

9. What is a tornado warning?

A tornado warning means that a tornado has been sighted or indicated by radar and poses an imminent threat to life and property. People in the warned area should take immediate shelter.

10. What should I do if a tornado warning is issued for my area?

If a tornado warning is issued for your area, seek shelter immediately in the lowest level of a sturdy building, such as a basement or storm cellar. If no underground shelter is available, go to an interior room on the lowest level, away from windows.

11. How has tornado forecasting improved since the May 3, 1999, outbreak?

Since the May 3, 1999, outbreak, tornado forecasting has improved due to advancements in radar technology, computer modeling, and understanding of atmospheric processes. Forecasters are now better able to identify and predict the formation of tornadoes.

12. What are some reliable sources for obtaining weather information and warnings?

Reliable sources for obtaining weather information and warnings include the National Weather Service (NWS), the Storm Prediction Center (SPC), local television and radio stations, and weather apps on your smartphone. Always ensure the source is official and trustworthy.