Table 1-25 -- NWS in-flight weather advisories

Table 1-24 -- Four TAF change groups

Pilot Reports

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Advisory

Remarks

Convective Convective SIGMETs are issued for any of the following

SIGMET

SIGMET phenomena:

 Severe thunderstorms due to:

-- surface winds greater than or equal to 50 knots

-- hail at the surface greater than or equal to 3/4 inches in diameter

-- tornadoes

 Embedded thunderstorms

 A line of thunderstorms

 Thunderstorms greater than or equal to VIP level 4 affecting 40

percent or more of an area at least 3,000 square miles

NOTE:

Radar weather echo intensity levels are

sometimes expressed during communications

as VIP levels. VIP is derived from the

component of the radar that produces the

information, the video integrator and processor.

Since thunderstorms are the reason for issuance, severe or greater

turbulence, severe icing, and low-level wind shear are implied and will not

be specified in the advisory.

SIGMET

Weather advisory issued concerning weather significant to the safety of all

aircraft. SIGMET advisories cover:

 Severe and extreme turbulence or clear air turbulence not

associated with thunderstorms

 Severe icing not associated with thunderstorms

 Dust storms, sandstorms, or volcanic ash that lower surface or

inflight visibilities to below 3 miles

 Volcanic eruption

AIRMET

AIRMETs are issued for all aircraft and specifically light aircraft having

limited capability because of lack of equipment, instrumentation, or pilot

qualifications. AIRMETs are issued for:

 Moderate icing

 Moderate turbulence

 Sustained winds of 30 knots or more at the surface

 Widespread area of ceilings less than 1,000 feet or visibility less

than 3 miles

 Extensive mountain obscurement

AIRMETs are issued on a schedule basis every 6 hours with unscheduled

amendments issued as required.

Table 1-25 -- NWS in-flight weather advisories

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