December 3, 2002: Winter Storm Author: Pam Heinselman, CIMMS/OU Contributors: Kevin Scharfenberg, CIMMS/OU Last Updated: 8 April 2003

Forecast/Weather:

On 3-4 December 2002, a winter storm moved across Oklahoma. The storm was responsible for several inches of snow across northwest and north-central Oklahoma, a band of freezing rain west and north of Oklahoma City, and rain elsewhere.

Radar Operations:

Start time: 14:48 12/03/02 UTC (08:48 12/03/02 local time)
Stop time: 23:51 12/03/02 UTC (17:51 12/03/02 local time)

Start time: 00:01 12/04/02 UTC (18:01 12/03/02 local time)
Stop time: 06:53 12/04/02 UTC (24:53 12/04/02 local time)

Start time: 12:16 12/04/02 UTC (06:16 12/04/02 local time)
Stop time: 23:46 12/04/02 UTC (17:46 12/04/02 local time)

Radar/Operational Status:

Hydrometeor Classification Algorithm: Cold season

Operational Delivery:

Not applicable.

Snapshots (taken from case study by Kevin Scharfenberg):

Figure 1: Reflectivity

Figure 2: Differential Reflectivity

Figure 3: Correlation Coefficient

Although a "bright band" of enhanced reflectivity typically marks the melting layer in cold season precipitation events, the reflectivity image (Figure 1) does not clearly show a "bright band". The phase change between rain and snow is much more clearly evident in the differential reflectivity image (Figure 2) where differential reflectivity increases suddenly with range by about 1 dB. This increase is often observed in the melting layer, and is likely caused by aggregation. That is, the falling snow crystals become wet and begin to stick to each other. The correlation coefficient image (Figure 3) shows that while values are above 0.99 in the rain, values range from 0.9 to 0.95 in the mixed phase regime.

Figure 4: Hydrometeor classification algorithm output.

When considering the increasing altitude of the radar beam with range, the hydrometeor classification algorithm (HCA) attempts to mark the level above which mostly snow exists and below which mostly rain exists. For the radar scan corresponding to Figures 1 through 3, the height of that level detected by the HCA (Figure 4) ranges from 1480 meters above radar level to the northwest of the radar to 1850 m above radar level to the southwest. This is consistent with the range where differential reflectivity increased in Figure 2.

Snapshots of winter storm on 4 December 2002:




Figure 1: Reflectivity at 1:24 UTC 4 December 2002.

Figure 2: Differential Reflectivity at 1:24 UTC 4 December 2002.

Figure 3: Correlation Coefficient at 1:24 UTC 4 December 2002.

Figure 4: Hydrometeor classification algorithm at 1:24 UTC 4 December 2002.

Figure 5: Reflectivity at 4:28 UTC 4 December 2002.

Figure 6: Differential Reflectivity at 4:28 UTC 4 December 2002.

Figure 7: Correlation Coefficient at 4:28 UTC 4 December 2002.

Figure 8: Hydrometeor classification algorithm at 4:28 UTC 4 December 2002.