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|A SIGMET (SIGnificant METeorological
Information) advises of weather potentially hazardous to all aircraft
other than convective activity.
SIGMETs are issued (for the lower 48 states and
adjacent coastal waters) for the following weather-impacted reasons:
These SIGMET items are considered to be widespread
because they must be affecting or be forecast to affect an area of at
least 3000 square miles at any one time. However, if the total area to
be affected during the forecast period is very large, it could be that
only a small portion of this total area would be affected at any one
time. SIGMETs are issued for 6 hour periods for
conditions associated with hurricanes and 4 hours for all other
events. If conditions persist beyond the forecast period, the SIGMET
is updated and reissued. Convective
SIGMETS are issued hourly for thunderstorm-related aviation
- Severe Icing
- Severe or Extreme Turbulence
- Duststorms and sandstorms lowering visibilities to less than
three (3) miles
- Volcanic Ash
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