Terms Describing Cumulonimbus (CBs): (ICAO Annex 3, Attachmetn F, 1998)
| Term | Contraction | Duration |
| isolated | ISOL | indicates an area of individual cumulonimbus and/or thunderstorms with a maximum spacial coverage less than 50 percent of the area affected, or forecast to be affected, by the phenomena (at a fixed time or during the period of validity) |
| occasional | OCNL | indicates an area of well-separated cumulonimbus and/or thunderstorms with a maximum spatial coverage between 50 and 75 percent of the area affected, or forecast to be affected, by the phenomena (at the fixed time or during the period of validity) |
| frequent | FRQ | indicates an area of thunderstorms within which there is little or no separation between adjacent thunderstorms with a maximum spatial coverage greater than 75 percent of the area affected, or forecast to be affected, by the phenomena (at a fixed time or during the period of validity) |
| embedded | EMBD | indicates that the thunderstorms (including cumulonimbus cloud which is not accompanied by a thunderstorm) is embedded within cloud layers and cannot be readily recognized |
Flight Categories: (NWS WSOM Chapter D-31)
| Flight Rules | Contraction | Ceiling | Visibility |
| very low instrument flight rules | VLIFR | < 200 feet | < 0.5 mile |
| low instrument flight rules | LIFR | > 200 feet and < 500 feet | > 0.5 mile and < 1 mile |
| instrument flight rules | IFR | > 500 and < 1000 feet | > 1 and < 3 miles |
| marginal visual flight rules | MVFR | > 1000 and < 3000 feet | > 3 and <5 miles |
| visual flight rules | VFR | > 3000 feet | > 5 miles |
Conditional Terms for Clouds and Visibility (in Aviation Area Forecast Products): (NWS WSOM Chapter D-20)
| Term | Contraction | Duration |
| isolated | ISOL (int'l) ISOLD (U.S.) |
used when clouds or visibility is expected to affect less than 3,000 square miles or to be widely dispersed |
| occasional | OCNL | greater than 50 percent probability of the phenomena occurring but for less than one-half of the forecast period or a prescribed time span within the period |
Convective Areal Coverage Terms (in Aviation Area Forecast Products): (NWS WSOM Chapter D-20)
| Term | Contraction | Areal Coverage |
| isolated | ISOL (int'l) ISOLD (U.S.) |
phenomena affects area less than 3,000 square miles and/or events are widely separated in time |
| widely scattered | WDLY SCT | less than 25 percent of area affected |
| scattered | SCT | 25 to 50 percent of area affected |
| numerous (or widespread) | NMRS | more than 50 percent of area affected |
Convective Areal Coverage Terms (in Public Forecast Products): (NWS WSOM Chapter C-11)
| Term | Areal Coverage |
| isolated | 10 percent |
| widely scattered | 20 percent |
| scattered | 30 to 50 percent |
| numerous | 60 to 70 percent |