Conditions that indicate the presence of a specific SIGMET phenomenon such as volcanic ash or a thunderstorm.  Used to represent the forecast positions of SIGMET phenomena.<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>In cases where the position covers an entire FIR or CTA, ("ENTIRE CTA or ENTIRE FIR" from ICAO Annex 3 / WMO No. 49-2) the geometry should be an xlink to the sampled feature for this SIGMET.<br /></p>