An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak...
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![Page 1: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/1.jpg)
An Overview of Environmental Conditions and Forecast
Implications of the 3 May 1999 Tornado Outbreak
Richard L. Thompson and Roger Edwards
Presentation by Chris Fisher
![Page 2: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/2.jpg)
Overview
• Brief Introduction of the Outbreak• Synoptic Scale Characteristics• Moisture and Instability• Vertical Shear• Convective Initiation• Conclusion
![Page 3: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/3.jpg)
Introduction
• Late Afternoon and Evening of May 3, 1999• 69 Tornadoes, 10 which were Supercells• Central/Northern Oklahoma and Southern
Kansas• Violent tornadoes occurred in the Oklahoma
City and Wichita metropolitan areas• Poor Numerical Model Forecast meant that
outbreak was not initially predicted.
![Page 4: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/4.jpg)
![Page 5: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/5.jpg)
•500 mb heights•Trough located over the Western United States•Short Wave trough progresses from Arizona to Western Oklahoma and Kansas
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•Surface dew points in the middle to upper 60’s degrees F•Drylines present•Fronts become more occluded
![Page 7: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/7.jpg)
•Strong dew points and high daytime surface temperatures in southwest Oklahoma contributed to large values of CAPE and weak values of CIN.
![Page 8: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/8.jpg)
•Moist boundary layer in the lowest 1km•Elevated mixed layer from 825mb to 600mb•CAPE value of 2434 J/kg at Norman Ok at 1200UTC on May 03
![Page 9: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/9.jpg)
•General 20-45kt strengthening of the flow in the 4-10km layer•According to previous research, an observed strengthening of the lower and middle tropospheric flow during the afternoon, generally below 8km, is an indication of enhanced supercell potential.•Increasing mid-upper tropospheric winds resulted in sufficient deep layer vertical shear.
![Page 10: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/10.jpg)
•BRN values of 55 m^2/s^2 in Frederick, OK at 2042 UTC on May 3rd
•BRN values of 166 m^2/s^2 in Purcell, OK at 0200 UTC on May 4th
•SRH values of 338 m^2/s^2 in Purcell
![Page 11: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/11.jpg)
![Page 12: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/12.jpg)
•Convection formed under a gap in the cirrus canopy between the two drylines•Storm A moves across the confluence boundary 20 minutes prior to the first significant tornado of the outbreak•Storm A and B combined produced a total of 35 tornadoes, including an F5 that moved across southern Oklahoma City
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![Page 14: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/14.jpg)
•Eta Model Forecasts of 300mb (a,b) and 500mb (c,d)•Model showed the possibility of Severe Weather but the tornado outbreak was not anticipated due to poor forecasts of the mid-upper tropospheric winds
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•Eta Model initial analyses of 300-mb geopotential height (dam), divergence (solid lines 1 × 10−5 s−1, dashed lines represent convergence), and negative absolute geostrophic vorticity (shaded area, with gradations at 0, −1 × 10−5 s−1, −5 × 10−5 s−1, and −10 × 10−5 s−1) at (a) 1800 UTC 3 May 1999, and (b) 0000 UTC 4 May 1999. The shaded areas of negative absolute geostrophic vorticity represent areas of inertial instability. (Courtesy of D. Schultz, National Severe Storms Laboratory.)
![Page 16: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/16.jpg)
CONCLUSION
• General Characteristics of severe weather outbreak were observed
• Trough located over the 4 corners region and deep low pressure in the high plains
• Unstable warm sector• Mid-upper jet moved eastward from the
trough during the afternoon of the outbreak
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CONCLUSION
• Large area of high clouds overspread the drylines and warm sector complicating forecasts for convective development
• Tornado threat was not realized due to poor model forecasts of the mid and upper level flow, and deep layered vertical shear
• Observational data suggested a greater threat of supercells.
![Page 18: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/18.jpg)
CONCLUSION
• Sufficient CAPE values (3000-5000 J/Kg)• Sufficient vertical shear (excess of 20 m/s)• BRN shear greater than 40 m^2 s^2• 0-3 km SRH values of 150-300 m^2s^2• Initial storms did not evolve into a squall line
meaning that supercells remained in a favorable environment, allowing them to produce a large number of tornadoes (due to weak convergence along the dryline)
![Page 19: An Overview of Environmental Conditions and Forecast Implications of the 3 May 1999 Tornado Outbreak Richard L. Thompson and Roger Edwards Presentation.](https://reader036.fdocuments.in/reader036/viewer/2022062714/56649d2d5503460f94a038c2/html5/thumbnails/19.jpg)
QUESTIONS????