The Spencer SD Tornado of 30 May 1998

Meteorological Data & Analyses from SPC

NOTE: More data and analyses (upper air, radar, satellite) will be added as time and resources permit.

SURFACE

    Regional surface plots, not analyzed [31-34K GIFs]:

    1. 17Z (noon CDT)
    2. 18Z (1 pm CDT)
    3. 19Z (2 pm CDT)
    4. 20Z (3 pm CDT)
    5. 21Z (4 pm CDT)
    6. 22Z (5 pm CDT)
    7. 23Z (6 pm CDT)
    8. 00Z (7 pm CDT)
    9. 01Z (8 pm CDT)
    10. 02Z (9 pm CDT)
    11. 03Z (10 pm CDT)

Notes: Tornado moved across Spencer between 0038Z-0044Z. If printing surface plot GIFs from your browser, use landscape mode. Images will usually print on two or three 8X11 pages or one 11X17 page, depending on your browser and printer settings. You may also save to disk; then re-size or crop (if necessary) and print from a graphics program like L-View, XV or Photoshop.

UPPER AIR

    Skew-T Soundings [19-20K GIFs]:

    1. 12Z Valley, NE (7 am CDT) unmodified
    2. 18Z Valley, NE (1 pm CDT) unmodified
    3. 00Z Valley, NE (7 pm CDT) unmodified
    4. Javascript loop of Valley, NE soundings. This is a 3-frame, 56K loop which may take a minute or two to load on slower connections.
    5. Modified 00Z Valley, NE sounding with interpretation
    Upper-air Maps [33-37K GIFs]:
    1. 30/12Z (7 am CDT) mandatory-level raob plots: 250 mb, 500 mb, 700 mb, 850 mb, 925 mb
    2. 31/00Z (7 pm CDT) mandatory-level raob plots: 250 mb, 500 mb, 700 mb, 850 mb, 925 mb

Notes: All thermodynamic sounding parameters were derived using a virtual temperature (Tv) correction and mean-mixed (lowest 100 mb layer) lifted parcel. For more info on the Tv correction, see this reference:

  1. Doswell, C. A., III, and E. N. Rasmussen, 1994: The effect of neglecting the virtual temperature correction on CAPE calculations. Wea. Forecasting, 9, 625-629.

Soundings are on a black background (default to the original analysis software) for easier viewing. To print with white background, download the image to disc, call it up in a graphics program and invert the colors, then print from the graphics program.

RADAR

    Animated reflectivity/velocity snapshot from Sioux Falls WSR-88D at 0133Z (8:33 pm CDT) -- 133K GIF courtesy NWSFO FSD.

SATELLITE

    GOES-8 IR, enhanced with MB-color curve [53-73K GIFs]:

    1. 1445Z (9:45 am CDT) -- Thunderstorm complex over northeast NE/southeast SD/northwest IA is anchored by a supercell, and is laying out an outflow boundary (unseen).
    2. 1515Z (10:15 am CDT) -- Supercell will move SE across IA for several hours before weakening.
    3. 1545Z (10:45 am CDT) -- Dense cirrus/cirrostratus canopy over NE will retard surface heating over most of NE all day; but not over SD.
    4. 1615Z (11:15 am CDT)
    5. 1645Z (11:45 am CDT)
    6. 1715Z (12:15 am CDT)
    7. 1745Z (12:45 am CDT)
    8. 1815Z (1:15 pm CDT)
    9. 1845Z (1:45 pm CDT)
    10. 1915Z (2:15 pm CDT) -- IA convective complex will keep weakening.
    11. 1945Z (2:45 pm CDT) -- Intensifying line of thunderstorms over southeastern MT will move ESE across western SD.
    12. 2015Z (3:15 pm CDT)
    13. 2045Z (3:45 pm CDT)
    14. 2115Z (4:15 pm CDT)
    15. 2145Z (4:45 pm CDT) -- Towering cumulus and nascent cumulonimbi developing near dryline, ahead of frontal MCS.
    16. 2215Z (5:15 pm CDT) -- MCS near cold front and surface low, isolated thunderstorm briefly develops over southeast SD near Missouri River.
    17. 2245Z (5:45 pm CDT) -- Southeast SD storm moves near Gannvalley, MCS moving ESE across central SD.
    18. 2315Z (6:15 pm CDT) -- Gannvalley storm weakening over Jerauld County, central SD MCS weakening (warming tops), squall line developing to its E.
    19. 2345Z (6:45 pm CDT) -- Cold tops over squall line, early stages of Artesia supercell (small green area S of squall line). Old detached Jerauld County anvil flying into MN.
    20. 0015Z (7:15 pm CDT) -- Coldest tops (tan/yellow) over SW portion of developing line, anvil expanding from Artesian supercell.
    21. 0045Z (7:45 pm CDT) -- Coldest tops over squall line and Artesian supercell. Southwestern most blue anhancement is intensifying future Spencer storm.
    22. 0115Z (8:15 pm CDT) -- Coldest tops over merger of squall line and Artesian supercell. Southernmost light blue represents highest tops of Spencer supercell. Here is a photo of the Fulton tornado in progress at this moment.
    23. 0145Z (8:45 pm CDT) -- Tornado leaving Spencer, enhanced-V signature with warming cloud tops.
    24. 0215Z (9:15 pm CDT) -- Southwesternmost overshooting top (brown) is now atop Alexandria storm and anchors enhanced-V signature
    25. 0245Z (9:45 pm CDT) -- Cloud tops warming with Spencer/Alexandria complex, Spencer/Alexandria convection outflow-dominant and weakening as indicated by surface and radar observations
    26. 0315Z (10:15 pm CDT)
    27. 0345Z (10:45 pm CDT)
    28. 0415Z (11:15 pm CDT)
    29. 0445Z (11:45 pm CDT)
    30. 0545Z (12:45 am CDT) -- Damaging convective windstorm under cloud canopy over MN

    Javascript loop of all the above IR images. This is a 30-frame, 2 MB loop which may take several minutes to load even on a fast connection.

OTHER

    Regional 24-hour rainfall map preceding Spencer storm [17K GIF], with interpretation

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