September 18-19, 2002: Convective Line ahead of a Cold Front Author: Pam Heinselman, CIMMS/OU Last Updated: 15 April 2003

Forecast/Weather:

A line of convective storms developed over western Oklahoma and moved toward central Oklahoma (Figs. 1-4; 21 UTC 18 September - 06 UTC 19 September). Downdrafts from this line produced an outflow boundary that between 2:20-3:47 UTC (not shown). The precipitation transitioned toward all stratiform once they moved into central Oklahoma. This precipitation formed ahead of a cold front that moved through Norman around 12 UTC on 19 September 2002 (Figs. 5-8). The cold front is observed between 9:40-14:06 UTC. Just behind the cold front, polarimetric variables indicate a group of flying creatures between 13:41-15:08 UTC (Figs. 9-11).

Radar Operations:

Start time: 20:41 9/18/02 UTC (15:41 9/18/02 local time)
Stop time: 15:08 9/19/02 UTC (10:08 9/19/02 local time)

Radar/Operational Status:

Hydrometeor Classification Algorithm: Cold season

Operational Delivery:

Not applicable.

Snapshots:

Figure 1: Radar reflectivity at 2:07 UTC 18 September 2002.	Figure 2: Correlation coefficient shows mixed hydrometeors on the backside cells within the northern end of the line at 2:07 UTC 18 September 2002.
Figure 3: The specific differential phase indicates heavy rain along the leading edge of the line at 2:07 UTC 18 September 2002.	Figure 4: The hydrometeor classification algorithm identifies convective cells embedded within stratiform precipitation at 2:07 UTC 18 September 2002.

Figure 5: Radar reflectivity at 11:57 UTC 19 September 2002 shows stratiform precipitation ahead of the cold front (linear feature just west of KOUN).	Figure 6: The differential reflectivity field at 11:57 UTC 19 September 2002.
Figure 7: The specific differential phase at 11:57 UTC 19 September 2002.	Figure 8: The 12 UTC surface map on 19 September 2002 shows a cold front passing through central Oklahoma.

Figure 9: Interpretation of polarimetric variables reveals flying creatures just west of KOUN and behind the cold front in the reflectivity data at 14:06 UTC 19 September 2002.	Figure 10: The differential reflectivity field at 14:06 UTC 19 September 2002.
Figure 11: The correlation coefficient field at 11:57 UTC 19 September 2002.