In order to run the hydrometer classification algorithm (HCA) and melting layer detection algorithm (MLDA) in w2dualpol, a “first guess” at the melting layer is required. Previously, the same default first guess was used for all radars. Obviously this solution is not ideal, as on any given day, the melting layer is likely to vary wildly across different radar sites (not to mention that at any given radar site, the melting layer is likely to vary wildly across different days).
For a better solution, you can now pull environmental information (specifically, the 0C wet bulb temperature height) into w2dualpol for a more realistic first guess at the melting layer. This first guess is provided through the use of a SoundingTable. The SoundingTable can be created in one of three ways: (1) The WDSS-II program nse can create this from a RUC analysis field. (2) The ingest_sounding.pl script reads and converts sounding data from the U. Wyoming website into WDSS-II’s XML format. (3) You can write your own XML table file.
Once you have your SoundingTable, you will want to be sure that it is included in your RadarIndex. Then, in the command for w2dualpol, set the -S flag, and from there the algorithm will use the SoundingTable information to create a first guess at a melting layer. Additionally, the melting layer found from the SoundingTable will be used in instances when the data is not sufficient for the MLDA to run.
It should be noted that once the SoundingTable is greater than 1 day older than the radar data being processed, the SoundingTable will be aged off and the default melting layer will be used. On a related note, we have altered the algorithm such that if more than two hours pass after the MLDA has run, the algorithm will revert to using the melting layer found in the SoundingTable.
A few final notes; If a SoundingTable is present in the RadarIndex but you do not wish to use it, set -S junk and the default value will be used for the melting layer. Additionally, if no SoundingTable is available, there is no need to set -S.