Weather

  • Briefings covers receiving weather briefings. It could use a lot of fleshing out.
  • Icing covers icing specifically.

Weather Forecast and Advisories

Airmets, sigmets, convective sigmets, PIREPs (Pilot reports), METARs, TAFs, etc.

Airmets

Airmets are advisories of significant weather that may affect all aircraft, but particularly lighter aircraft - i.e. airlines are less concerned with these. They are valid for 6 hours from time of issue, and have the following subtypes:

  • Airmet T (Tango): Moderate turbulence, sustained surface 30+ kts, and/or non-convective low-level wind shear.
  • Airmet Z (Zulu): Moderate icing and provides freezing level heights.
  • Airmet S (Sierra): Describes IFR conditions and/or mountain obscuration.
  • Airmet G (Graphical): Found at aviationweather.gov

For example, the coastal fog on the west coast usually results in Airmet Sierras being issued.

Sigmets

Sigmets are more significant airmets and are potentially hazardous to all types of aircraft. For what I do, a relevant sigmet means you’re not flying today. They are valid for 4 hours from time of issue, and are issued when the following is expected:

  • Severe icing not associated with thunderstorms
  • Severe or extreme turbulence or clean air turbulence not associated with thunderstorms.
  • Dust storms, sandstorms, and other non-thunderstorm phenomena lowering surface visibility below 3 miles.

For example, the ash spewed from an erupting volcano would cause a sigmet to be issued.

Convective Sigmets

Essentially Sigmets for thunderstorms.

Valid for 2 hours after issue, convective sigmets contain either an observation and a forecast, or only a forecast. All convective sigmets imply severe or greater turbulence, severe icing, and low level wind shear.

They are issued for any of the following:

  • Severe thunderstorms, due to:
    • Surface winds 50+ kts
    • Surface hail greater than 3/4 inch in diameter.
  • Tornadoes
  • Embedded thunderstorms of any intensity level
  • a line of thunderstorms at least 60 miles long with thunderstorms affecting at least 40% of its length
  • Thunderstorms producing heavy or greater precipitation (VIP level 4) affecting at least 40% of an area of at least 3000 square miles.

Last updated: 2021-05-29 23:05:39 -0700