Flying Smart : Aviation Speak

Warmer weather brings the promise of good flying days, but it also brings such unlovely atmospheric conditions as thunderstorms and turbulence. You'll know where the weather bullies are hanging out if you get a preflight weather briefing that includes airmets and sigmets.

These aviation weather advisories warn pilots on the ground and in the air of hazardous flight conditions. Airmets (pilot shorthand for airman's meteorological information) describe areas and conditions that are unsafe for light aircraft like those we fly. They indicate where you could encounter moderate icing, moderate turbulence, widespread IFR conditions, strong surface winds, or extensive mountain obscuration.

Sigmets (significant meteorological information) are advisories about weather that would affect all aircraft - tornadoes, lines of thunderstorms, embedded T-storms, large hail, severe turbulence or icing, and dust or sandstorms that could reduce visibility to less than three miles. A convective sigmet means a significant thunderstorm exists or is likely in the region.

Area forecasts will alert you to any airmets that exist for the time period in which you plan to fly: "SEE AIRMET SIERRA FOR IFR CONDS AND MTN OBSCN." The airmet will refer to a list of states and a string of VOR or airport identifiers that make up a geographic area, and it will give you an idea of how bad things are: "OCNL CIG BLW 010/VIS BLW 3SM PCPN/BR" (occasional ceilings below 1,000 feet and visibility less than three statute miles with precipitation and mist).

Sigmets aren't specifically noted in text area forecasts, so if you're getting a weather briefing via computer you must look for them. (If you talk to a Flight Service Station briefer, he or she will give you the bad news up front and in plain English - yet another good reason to get a telephone briefing.) Like airmets, they are valid for a specific period of time. They'll name a geographic area using states, VORs, and airports as the boundaries and specify the conditions (i.e., occasional severe turbulence from 10,000 feet to FL24). Graphic depictions of airmets and segments can be found online (aviationweather.gov/awc/awc-airmets,aviationweather.gov/awc/awc-wsts, and aviationweather.gov/awc/domestic_sigmets).

If you're unsure what an airmet or sigmet says, call Flight Service at 800/WX-BRIEF. Airmets, sigmets, and convective sigmets can keep you from straying onto a weather bully's turf.