May 20, 2003: Line of Convective Cells East and South of KOUN w/ long-lived Hail signatures associated with storm in Stephens Co. Author: Pam Heinselman, CIMMS/OU Last Updated: 22 May 2003

Forecast/Weather:

On 20 May 2003, a cold front moved slowly across central and into eastern Oklahoma during the evening and night-time hours. A line of convective cells developed in association w/ this front by 23:00 UTC, just east and south of KOUN. During the early evening, the strongest storms developed over Stephens and Pottawatomie Counties. The Stephen's County storm has polarimetric hail signatures at the 0.5 deg tilt from 23:10-1 UTC. Hail signatures are also observed on several other storms between 2-5 UTC. Interestingly, storms developed behind the cold front also, possibly due, in part, to frontogensis (~1:30 UTC). By 6 UTC, this storm system developed into an MCS over the eastern half of Oklahoma, continuing through 10:29 UTC. Between 9:44-13 UTC a large area of stratiform precipitation developed along and south of the OK/TX border. This precipitation dissipated by 19 UTC.

Radar Operations:

Start time: 23:10 5/19/03 UTC (18:10 5/19/03 local time)
Stop time: 19:14 5/20/03 UTC (14:14 5/20/03 local time)

Radar/Operational Status:

Hydrometeor Classification Algorithm: Warm season

Operational Delivery:

Pam Heinselman worked this event with the WCMs at the Norman NWS. The differential reflectivity and reflectivity products were useful for identifying storms with a high liklihood of producing hail at the surface. A ZDR column would form aloft prior to a ZDR occur appearing in the 0.5 degree tilt. Soon after the ZDR hole was found at the lowest tilt, hail reports were received from spotters. WCMs were kept up-to-date concerning the evolution of ZDR columns and new updrafts. WCMs asked for storm status near the time when a warning would expire to help decide whether to re-issue the warning.

Snapshots:

Figure 1: Reflectivity at 23:24 UTC on 19 May 2002 associated with hail-producing storm in Stephen's Co.	Figure 2: Differential reflectivity at 23:24 UTC on 19 May 2002 associated with hail-producing storm in Stephen's Co.
Figure 3: Reflectivity at 2:13 UTC on 20 May 2002 associated with storm located 45 deg and 164 km from KOUN.	Figure 4: Differential reflectivity at 2:13 UTC on 20 May 2002 associated with storm located 45 deg and 164 km from KOUN.

Figure 5: Reflectivity at 3:19 UTC on 20 May 2002 associated with storm in Love Co. (223 deg 133 km from KOUN).	Figure 6: Differential reflectivity at 3:19 UTC on 19 May 2002 associated with storm in Love Co. (223 deg 133 km from KOUN).
Figure 7: Reflectivity at 6:28 UTC on 20 May 2002 associated with MCS.	Figure 8: Specific differential phase at 6:28 UTC on 20 May 2002 associated with MCS.