Conditions that indicate the presence of a specific SIGMET phenomenon such as volcanic ash or a thunderstorm, along with expected changes to the phenomenon such as intensity, speed, and direction.  These conditions are reported with OBS/FCST conditions on all SIGMET types.<br /></p><p><br /></p><p>TC TOP (ABV and BLW) conditions are represented by the vertical component of the geometry.  For example: CB TOP FL500 is represented as a missing lowerLimit and an upperLimit of 500FL.  <br /></p><p><br /></p><p>Design note:<br /></p><p>This class is no longer a subclass of MeteorologicalPosition. This change was made to ensure that there is no confusion between the two classes when results from different OM_Observation types are populated.  Constraints could be used to ensure a specific superclass but not its subclasses are valid, but this would disallow the use of sub-classes of this type for other purposes such as regional extension<br /></p>