KOUN Convective Cells w/ Hail: April 29, 2003

April 29-30, 2003: Convective Cells in Southwest OK w/ hail

Last Updated: 30 April 2003

Forecast/Weather:

On 29 April 2003, convective cells initially developed over the west Texas Panhandle during the late afternoon. By early evening, these cells began to move into western Oklahoma. The strongest storms occurred over the southernmost counties w/in the Norman NWS CWA, where the WCM issued several severe storm warnings. Storms in Tillman Co. were close enough to KOUN to provide useful polarimetric signatures that aided the warning process. Later (3:39 UTC), a cell initiated northwest of KOUN w/ a good hail signature (see Figs. 9-12).

Radar Operations:

Radar Data Quality:

The correlation coefficient field was noisy, making it difficult to use during operations. Other polarimetric fields looked fine.

Performance of HCA and Precipitation Estimation Algorithm:

Thunderstorm Updraft/Downdraft:
The differential reflectivity field in far southwestern Oklahoma showed larger droplets within the echo closest to KOUN , with smaller droplets behind it (Fig. 2). The HCA identified these droplets as big droplets. These larger droplets were growing within mid-levels of the convective cells, whereas the smaller droplets and/or ice particles were within upper-levels of the storms (Fig. 4).

Hail:
The HCA identified hail within the convective cell over southern Tillman County between 01-01:30 UTC. The far distance of these storms from KOUN made the polarimetric signatures weak, adding uncertainty to their interpretation (e.g., see Figs. 1,2,4 for example of hail signatures). An hour and a half after JPOLE operations at the NWS were completed (3:30 UTC), a storm just northwest of KOUN had a good polarimetric hail signature (see Figs. 9-12).

Supercells or TVS:
None.

Non-meteorological Scatterers:
By 02:00 UTC, polarimetric signatures indicated that biological scatterers were prevalent around KOUN (Figs. 5-8).

Operational Use & Benefits:

The NSSL meteorologists (Kevin and Pam) worked part of the time in the operations area with WCM during this event (23-03UTC). The WCM was alerted of polarimetric hail signatures, and the WCM occasionally inquired about the status of such signatures as warnings approached expiration.

Snapshots:

Figure 1: Reflectivity at 1:28 UTC 30 April 2003.

Differential Reflectivity

Figure 2: Differential reflectivity at 1:28 UTC 30 April 2003.

Correlation coefficient

Figure 3: Correlation coefficient at 1:28 UTC 30 April 2003.

Hydrometeor Classification

Figure 4: Hydrometeor classification algorithm output at 1:28 UTC 30 April 2003.

Figure 5: Reflectivity at 2:14 UTC 30 April 2003.

Differential Reflectivity

Figure 6: Differential reflectivity at 1:28 UTC 30 April 2003.

Correlation coefficient

Figure 7: Correlation coefficient at 2:14 UTC 30 April 2003.

Hydrometeor Classification

Figure 8: Hydrometeor classification algorithm output at 2:14 UTC 30 April 2003.

Figure 9: Reflectivity at 3:39 UTC 30 April 2003.

Differential Reflectivity

Figure 10: Differential reflectivity at 1:28 UTC 30 April 2003.

Correlation coefficient

Figure 11: Correlation coefficient at 3:39 UTC 30 April 2003.

Hydrometeor Classification

Figure 12: Hydrometeor classification algorithm output at 3:39 UTC 30 April 2003.