KOUN Case Study
Detecting the melting layer in a winter storm
Author: Kevin Scharfenberg, CIMMS/OU
Last Updated: 15 January 2003
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. The hydrometeor classification algorithm output from this event, and a verifying
sounding, are studied.
Indentifing the melting layer
A special sounding was released at the Norman, OK office of the National Weather Service at the time of the radar images in
Figures 1-4. This sounding was used to verify the actual melting level altitude. The sounding (Figure 5) found the melting level
to be about 2350 m ARL. At first glance, this may appear inconsistent with the KOUN measurement of the rain-snow line between
1480 and 1850 m ARL. However, note the sounding indicates the layer of air just below the melting level is subsaturated.
Observational studies indicate snow falling below the melting level into subsaturated area may fall more than 500 meters before
melting. Therefore, the KOUN measurement is reasonable, and is also consistent with reports in northwestern Oklahoma of snow
falling with surface temperatures of 2° C to 3° C.
Also note in the HCA image (Figure 4) that the detected melting level is higher to the south (1850 m ARL) than to the north
(1480 m ARL). This is consistent with the weather situation on 3 December 2002, when the cold air mass was cooling and deepening
from the north.
Figure 5: Norman, OK sounding corresponding to the radar image in Figure 4.
Since a bright band was difficult to identify, the polarimetric products were valuable in determining the location of the
melting layer in this case. The differential reflectivity field could be used to mark the location of ice aggregates, which
was also marked by a decrease in the correlation coefficient. The hydrometeor classification algorithm correctly indicated
a lower altitude of melting to the northwest of the radar than to the south, associated with the deeper and colder air mass to the
northwest. While the sounding suggested the freezing level was at least 500 m higher, the KOUN observation is consistent with
previous observations of a deep layer of melting below the melting level in subsaturated environments.
This case study would not have been possible without the dedicated work of the scientists who maintain,
operate, and collect data from KOUN radar. Thank you!