The following paragraphs present observing and reporting procedures for various types of obscurations. When reference is made to phenomena not occurring at the station location, the rules given in paragraph 11-7, Rules for Phenomena Not Occurring at the Point of Observation, shall apply.

11-37.   OBSERVING OBSCURATIONS

Obscurations shall be determined by observing the prevailing conditions at the station (usual point of observation) in accordance with the definitions of the various types of obscurations given in paragraph 11-3, Obscurations.

11-38.   REPORTING OBSCURATIONS

With the exception of volcanic ash, low drifting dust, low drifting sand and low drifting snow, an obscuration shall be coded in the body of the report if the surface visibility is less than 7 miles or considered operationally significant. Volcanic ash shall always be coded when observed. MIFG, BCFG and PRFG may be reported when visibility is equal to or greater than 7 miles. The reporting format is given in paragraphs 15-14, Present Weather Group, and 16-19, Present Weather (column 9). If these conditions are not met, but an obscuration is observed that is considered operationally significant, it shall be reported in the remarks section as not at the station. If more than one type of obscuration is occurring at the same time, they shall be reported in order of decreasing estimated predominance.

11-39.   SPECIAL PROCEDURES FOR VOLCANIC ASH

Volcanic ash (VA) shall be reported in the body of the report whenever it is observed. Reporting volcanic ash is different from other obscurations because volcanic ash is reported even if the visibility is greater than 7 miles.

11-40.   OPERATIONALLY SIGNIFICANT REMARKS FOR OBSCURATIONS

Any occurrence of an obscuration which the observer judges to be operationally significant and not reported elsewhere in the observation should be reported in the remarks section. Some examples of desirable items to be entered in the remarks section are fog dissipating or increasing, smoke drifting over the field, drifting snow, obscurations at a distance from, but not at the station.