July 24-25, 2000 long-lived supercell over Nebraska

Morning data on July 24, 2000 found a low pressure over northwest Nebraska progged to move slowly east/southeast during the day. Model guidance forecast large values of CAPE as well as shear values that were adequate for supercell development. Based on these conditions GOES-11 science test forecasters decided to place the satellite in super rapid scan operations (SRSO) beginning at 19:15 UTC centered over central Nebraska. The request was made to continue the SRSO over a 24 hour period.

SRSO (1 minute interval imaging) began on schedule. A storm initiated in southern South Dakota at approximately 20:30 UTC. Shortly thereafter the storm appeared to split (see first radar loop). The visible satellite imagery at this time did not show the split but did show what appeared to be storm top rotation (though careful cloud tracking needs to be done before rotation can be confirmed).

LI's were in the -7 to -12 range throughout the risk area. Initially, the storm traveled with the mean flow which was northwesterly according to the the LBF evening sounding. However, the storm turned right shortly after it reached its mature stage (~22:10 UTC) and moved toward due south from then on. As it moved across central Nebraska numerous tornadoes, large hail and damaging winds were reported. The thunderstorm maintained supercell characteristics for over 6 hours.

It is clear that the shear played a key role in maintaining the supercell. The LBF evening sounding shows steep lapse rates as well as winds veering and increasing in speed with height -- an ideal wind profile for supercells. Also, note the 500 mb jet in western Nebraska . This is also indicative of the increasingly favorable shear. The surface dewpoint at the North Platte sounding location (62 °F) results in a CAPE value of 3,796 J/kg. Note that the dewpoints east of there (where the storm actually traveled) were around 70 °F (see surface observations) . The 00:00 UTC theta-e analysis confirms that the instability is greatest just east of North Platte. The supercell moved right through the most unstable area.

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GOES satellite imagery

• GOES-11 Visible imagery 22:00 through 22:53 UTC July 24
  
• GOES-11 Visible imagery 00:35 through 00:55 UTC July 25
  
• GOES-11 IR imagery 24 July 20:15 UTC through 25 July 04:50 UTC (51 frames in the loop)

GOES Derived Product Imagery (DPI)

• GOES-11 Single Field of View (SFOV) CAPE and CIN 22:16 UTC July 24 through 02:16 UTC July 25
  
• GOES-11 Lifted Index 14:46 UTC July 24 through 05:46 UTC July 25
  
• GOES-11 PW 14:46 UTC July 24 through 05:46 UTC July 25
  
• GOES-11 PW minus Eta first guess (mm) 17:46 UTC July 24 through 23:46 UTC July 24
  
• GOES-11 derived soundings at point indicated on previous loop 17:46 UTC July 24 through 23:46 UTC July 24
  
• GOES-10 Lifted Index 19:00 UTC July 24 through 00:00 UTC July 25
  

LNX radar with surface observations

• LNX radar 21:57 UTC through 22:23 UTC July 24
  
• LNX radar 22:28 UTC through 23:14 UTC July 24
  
• LNX radar 23:50 UTC July 24 through 01:54 UTC July 25
  
• 00 UTC July 25 surface Theta-e analysis

Upper air observations

• 00 UTC July 25 Sounding from North Platte, NE (LBF)
  
  
• 500 mb wind speed (knots) analysis valid 00 UTC July 25