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Maps &
Diagrams

Maps and Diagrams Related to the
Great Plains Tornado Outbreak of May 3-4, 1999

  • GIS Users: A KML file depicting the damage paths for tornadoes that occurred in central Oklahoma on May 3, 1999 is available. The outlines and areas of the damage paths are color coded with relation to the parent supercell that spawned each tornado.

  • Map of the May 3, 1999 Tornado Outbreak in central Oklahoma.

  • Expanded map of the May 3-4, 1999 Great Plains Tornado Outbreak in Oklahoma and south central Kansas.

  • Tornado versus Time graph displaying individual tornadoes by storm for the May 3, 1999 Tornado Outbreak in central Oklahoma.

  • Map of the central U.S. displaying surface and upper level atmospheric features associated the May 3, 1999 Tornado Outbreak in Oklahoma and Kansas.

  • Expanded map of the western and central U.S. displaying surface and upper level atmospheric features associated the May 3, 1999 Tornado Outbreak in Oklahoma and Kansas.  A thumbnail of this image is to the right.

  • Subjectively drawn map of surface dewpoints, winds, temperatures, and frontal positions at 7 AM on May 3, 1999.

  • Subjectively drawn map of surface dewpoints, winds, and frontal positions around storm initiation time at 3:45 PM on May 3, 1999.

SYNOPSIS OF THE SURFACE AND UPPER LEVEL FEATURES

Conditions on 3 May were favorable for severe weather across much of the Plains region. The flow aloft was characterized by a large-scale trough over the western United States (Fig #1), with several smaller-scale (shortwave) troughs within the larger-scale flow. A key element on 3 May was a very intense upper-level jet stream diving southeastward from the Oregon coast toward Arizona, with maximum wind speeds in excess of 130 knots along the coast. This allowed shortwaves to “dig” well south into the southwestern states, and move rapidly as they ejected eastward into the central states. At low levels, a surface dry line extended from the Dakotas south through western Oklahoma into Texas. Warm, moist, and unstable air moved north to the east of the dry line, aided by a low-level jet stream with southerly winds in excess of 40 knots.

By late in the day, the ingredients for a significant severe weather outbreak began to come together over the southern half of the Plains. The upper-level jet turned east across New Mexico and then northeast across Oklahoma and Kansas by early evening, with a local 75-knot speed maximum near the Kansas-Oklahoma border. Thus, the strongest lower- and upper-tropospheric winds were superimposed in the area from western Oklahoma into central and eastern Kansas. Daytime heating shifted the axis of warmest surface air west to near the dry line, while the axis of maximum moisture moved slightly east into eastern Texas, Oklahoma, and Kansas. The zone of maximum instability was positioned between the two axes, and directly beneath the low-level jet axis from western Oklahoma into central and eastern Kansas. Thus initial storm formation in southwest Oklahoma, and subsequent tornadic supercell development north and northeastward into central Oklahoma and southern Kansas, occurred where both instability and vertical wind shear were maximized.

In Fig #2, an analysis of surface and upper level features over Oklahoma and southern Kansas is shown. The features represented on this map correlate to the time period where tornadic thunderstorms initiated and traveled across the area. Solid dark red (open) arrows indicate upper (low-level) jet stream axes at 00Z (7 PM CDT), while the corresponding dark red isotachs are indicated by long (short) dashed lines. The thin solid dark blue lines are 500-mb height contours at 00Z, with heavy dark blue dash-dot lines depicting axes of 500-mb shortwave troughs. The axes of maximum surface temperature and dew point at 20Z (3 PM CDT, which is just before initiation of the first supercell in southwest Oklahoma) is indicated by lines of open red circles and solid green circles (dew point). Surface low pressure centers and fronts (dry line) which were present at 20Z are indicated by lines with solid black barbs (fronts) and open brown barbs (dry line).

ADDITIONAL METEOROLOGICAL MAPS AND CHARTS



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