AVIATION 120

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AVIATION 120

• Meteorology

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Todays Agenda

• AIRMET
• Introduction
• Weather conditions for which AIRMETs are issued
• Issuing Procedures
• Format
• Numbering
• Updating/Correcting/Canceling
• Relationship to GFA and SIGMET
• Example AIRMETs
• SIGMET
• Introduction
• Weather conditions for which SIGMETs are issued
• Issuing Procedures
• Format
• Numbering
• Updating/Correcting/Canceling
• Relationship to GFA and AIRMET
• Example SIGMETs

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AIRMET - Introduction

• Refer to AIM 3.4 and MANAIR Chapter 6 for
  detailed information
• An AIRMET is a short-term weather advisory
  intended primarily for aircraft in flight, to
  notify pilots of potentially hazardous weather
  conditions not described in the current GFA and
  not requiring a SIGMET
• Purpose is to ensure dissemination of significant
  meteorological changes to pilots after pre-flight
  briefing or departure and to automatically amend
  the GFA
• Primarily intended to be used for ground-to-air
  communication, so clarity and brevity are
  essential
• Each WMO shall prepare and transmit AIRMETs for
  its area of responsibility

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Weather conditions for which an AIRMET is issued

• IMC conditions (BKN or OVC cloud condition at
  less than 1000 AGL and/or visibility less than 3
  SM
• Freezing precipitation (not requiring a SIGMET)
• Moderate icing (not associated with convective
  clouds)
• Moderate turbulence (not associated with
  convective clouds)
• Thunderstorms (unorganized)
• The surface mean wind over a large area increases
  to 20 KT or more, or an increase in gusts to 30
  KT or more, when lighter winds were originally
  forecast
• The difference between the forecast and observed
  wind direction is greater than 60 degrees
• The difference between the forecast and observed
  wind speed is greater than 20 knots if winds were
  originally forecast

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Issuing Procedures

• Lead time AIRMETs shall be issued as soon as at
  least one of the weather criteria previously
  listed is reported or expected to occur during
  the period of coverage of the current GFA
• Period of Validity An AIRMET is valid until it
  is updated, cancelled or until the next regular
  GFA is issued, whichever comes first
• Language AIRMETs shall be worded in abbreviated
  plain English
• Units Except for height, units must be
  explicitly stated
• Heights are stated in hundreds of feet without
  specifying FT
• Wind Directions are degrees true using 3 digits
• Distance in NM
• Visibility in SM
• Times in UTC
• Speed in knots
• Transmission Issuing centres are responsible for
  inputting AIRMETs to the EC national
  communication system, while NAV CANADA is
  responsible for disseminating them to pilots

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AIRMET Format

• WACN31 CWLW 191815 (Telecommunication Header
  )AIRMET B1 ISSUED AT 1811Z CWLW- (AIRMET Heading
  )AMEND GFACN31 CWUL 191745 ISSUE (GFA Reference)
  WTN AREA BOUNDED BY /5058N11635W/60 E REVELSTOKE
  - /5228N11811W/90 N REVELSTOKE - /5036N11844W/30
  SW REVELSTOKE - /5058N11635W/60 E REVELSTOKE.
  BANDS EMBD TCU 150 LCL 1/2-2SM SHRA BR OBSCD CIG
  5 AGL. BECMG 21Z 60 BKN TCU 150 3-P6SM -SHRA BR
  CIG 10-15 AGL.
  END/KAL (End Line/forecasters
  initials)
• Text
• The fourth and subsequent lines (except the last)
  contain the text of the message
• Order of Content
• Area Coverage (always first in the text section)
• The meteorological phenomenon
• Forecast or observed, if applicable
• Flight levels or layers affected, if applicable
• Type of aircraft reporting the phenomenon, if
  applicable
• Expected movement or duration, if applicable
• Expected development or dissipation, if
  applicable

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Numbering AIRMETs

• AIRMETs shall be alphanumerically numbered (e.g.
  A1)
• AIRMETs issued by the same office for different
  phenomena shall be labeled with a different
  letter (e.g. A1, B1, C1 etc.)
• When two or more criteria for issuing an AIRMET
  are met and they are produced by the same weather
  phenomenon and occurring within the same GFA
  area, then a single AIRMET summarizing the
  situation will be sufficient
• When a single weather phenomenon occurs or is
  expected to occur over two different GFA areas,
  two AIRMETS shall be issued and will be
  identified by different telecommunication
  headers. Each AIRMET will amend its
  corresponding GFA
• If a phenomenon for which an AIRMET was issued
  moves from one GFA area to another, the first
  must be cancelled and a new one issued for the
  new GFA area being affected. In this case the new
  AIRMET must have a new header corresponding to
  the new GFA area and a different alphanumeric
  signature

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Updating/Correcting/Cancelling AIRMETs

• AIRMETs are not updated on a regular basis like
  SIGMETs
• Normally updated by issuance of a new GFA
• May have to be updated when a weather situation
  as described by an AIRMET is no longer valid or
  is expected to change significantly before the
  next regular GFA is issued
• If an error was made in an AIRMET, the correction
  will be issued as an update using the standard
  format and numbering scheme
• Normally, AIRMETs are automatically cancelled and
  no longer broadcast when the next regular GFA is
  issued
• When a weather condition described in an AIRMET
  does not occur, or ends significantly earlier
  than forecast and before the next regular GFA is
  issued, the AIRMET shall be cancelled
• If the phenomenon for which an AIRMET was issued
  was forecast to end prior to the issuance of the
  next regular GFA, then no cancellation is
  necessary
• WACN31 CWLW 191915 AIRMET B1 CNCLD AT 1915Z
  CWLW-
  BANDS EMBD TCU DISPTG
  
  END/KAL
• AIRMET is cancelled if the weather phenomenon for
  which it was issued deteriorates such that a
  SIGMET must be issued

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Relationship with GFA and SIGMET

• An AIRMET is the only tool for amending a GFA
• AIRMETS, as do SIGMETS correspond to ONE GFA area
  only
• SIGMET is a short term weather warning intended
  for aircraft in flight, to notify pilots of
  potentially hazardous weather conditions
• AIRMET on the other hand, is also intended for
  aircraft in flight, but to notify pilots of
  non-forecast potentially hazardous weather
  situations in which the level of danger is not
  great enough to issue a SIGMET, but requires the
  amendment of the GFA if not originally forecast
• AIRMETs may be cancelled and a SIGMET issued to
  replace it
• SIGMETs may be cancelled and an AIRMET issued to
  replace it if the weather phenomenon was not
  forecast in the GFA
• SIGMETs and AIRMETs may be issued for the same
  phenomena of differing intensity and covering
  part of the same area (e.g. AIRMET covers
  widespread MDT turbulence while SIGMET covers an
  area within that of SVR turbulence)

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Example AIRMETs

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Example AIRMETs (cont.)
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SIGMET - Introduction

• Refer to AIM 3.18 and MANAIR Chapter 5 for
  detailed information
• A SIGMET is a short-term weather warning intended
  primarily for aircraft in flight, to notify
  pilots of potentially hazardous weather
  conditions up to and including 60 000
  (70hPa/60000)
• Primarily intended to be used for ground-to-air
  communication, so clarity and brevity are
  essential
• Each MWO shall prepare and transmit SIGMETs for
  its area of responsibility

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Weather conditions for which a SIGMET is issued

• By international agreement, the list of phenomena
  requiring SIGMETs is limited to the most serious
  hazards which are of vital importance to all
  types of aircraft. As a result, the list does
  not include phenomena which are significant only
  to light aircraft or to VFR operations
• The following phenomena require a SIGMET
• Area of active thunderstorms (not issued for SCT,
  unorganized TS)
• Line of thunderstorms
• Severe squall line (poses a hazard to aviation.
  Squalls 40 KT)
• Hurricane/tropical storm
• Moderate or heavy hail
• Severe turbulence (not associated with convective
  cloud)
• Severe icing (not associated with convective
  cloud)
• Marked mountain waves
• Widespread sand or dust storm
• Volcanic Ash cloud
• Low Level wind shear
• Tornado or waterspout

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Issuing Procedures

• Lead time SIGMETs shall be issued whenever at
  least one of the phenomena previously listed is
  reported or is expected to occur within the next
  four hours. However a SIGMET for volcanic ash
  cloud should be issued, whenever possible, up to
  12 hours before the beginning of its period of
  coverage
• Period of Coverage Shall not exceed 4 hours
• International Coordination When volcanic ash
  approaches within 60NM of the Canada-USA border,
  the regional forecast office issuing the SIGMET
  is required to coordinate the content of the
  SIGMET with the Aviation Weather Centre in Kansas
  City or Anchorage
• Language SIGMETs shall be worded in abbreviated
  plain English
• Units Except for height, units must be
  explicitly stated
• Heights are stated in hundreds of feet without
  specifying FT
• Wind Directions are degrees true using 3 digits
• Distance in NM
• Visibility in SM
• Times in UTC
• Speed in knots
• Transmission Issuing centres are responsible for
  inputting SIGMETs to the EC national
  communication system, while NAV CANADA is
  responsible for disseminating them to pilots

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SIGMET Format

• WSCN33 CWTO 191527 (Telecommunication Header
  )SIGMET B3 VALID 191525/191925 CWTO- (SIGMET
  Heading )WTN AREA BOUNDED BY /4539N07540W/20 N
  OTTAWA - /4409N07937W/30 N TORONTO -
  /4216N08258W/WINDSOR - /4256N07844W/BUFFALO -
  /4539N07540W/20 N OTTAWA. AREA OF OCNL SEV MECH
  TURB BLO FL030 ASOCTD WITH LLJ OF 75KT. AREA MOVG
  NWD 10KT. LTL CHG.
  END/1/MAG/YGM/LAK (End
  Line/forecasters initials)
• Text
• The third and subsequent lines (except the last)
  contain the text of the message
• Order of Content
• Area Coverage (always first in the text section)
• The meteorological phenomenon
• Forecast or observed, if applicable
• Flight levels or layers affected, if applicable
• Type of aircraft reporting the phenomenon, if
  applicable
• Expected movement or duration, if applicable
• Expected development, if applicable (INTSFYG,
  WKNG, NO CHNG)
• Tendency beyond period of coverage, if applicable

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Numbering SIGMETs

• SIGMETs shall be alphanumerically numbered (e.g.
  A1)
• SIGMETs issued by the same office for different
  phenomena shall be labeled with a different
  letter (e.g. A1, B1, C1 etc.)
• When a single weather phenomenon meeting SIGMET
  criteria occurs or is expected to occur over two
  different GFA areas, two separate SIGMETS shall
  be issued and will be identified by different
  telecommunication headers. Each SIGMET will
  amend its corresponding GFA and different
  alphanumeric signature. These SIGMETs will also
  be updated and canceled within their
  corresponding GFA areas
• If a phenomenon for which a SIGMET was issued
  moves from one GFA area to another, the first
  must be cancelled and a new one issued for the
  new GFA area being affected. In this case the new
  SIGMET must have a new header corresponding to
  the new GFA area and a different alphanumeric
  signature

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Updating/Correcting/Cancelling SIGMETs

• An updated SIGMET, when issued, shall
  automatically cancel the previous SIGMET in the
  same series (i.e. the previous SIGMET with the
  same letter)
• A SIGMET shall be updated at least one hour
  before the end of its period of coverage, but may
  be updated earlier by a forecaster
• If an error was made in a SIGMET, the correction
  will be issued as an update using the standard
  format and numbering scheme
• If the weather phenomenon covered by a currently
  valid SIGMET does not occur, or has dissipated,
  the SIGMET shall be canceled
• WSCN33 CWTO 191527
• SIGMET B3 CNCLD AT 191815 CWTO-
• TURB DSIPTD EARLIER THEN EXPD.
• END/1/MAG/YGM/LAK
• To avoid any misunderstanding, the last SIGMET of
  any series shall be ended or cancelled by a
  statement. No SIGMET shall be left to expire by
  itself

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Relationship with GFA and AIRMET

• As SIGMETs are intended for aircraft in flight
  who may not have the latest GFA, a SIGMET shall
  be issued even if the responsible phenomenon was
  forecast in the GFA
• During its period of coverage, a SIGMET
  automatically amends the current GFA
• Because the SIGMET may be valid for a greater
  vertical extent then a GFA, it also automatically
  amends the high level SIGWX Prognostic Chart
• AIRMETS, as do SIGMETS correspond to ONE GFA area
  only
• SIGMET is a short term weather warning intended
  for aircraft in flight, to notify pilots of
  potentially hazardous weather conditions
• AIRMET on the other hand, is also intended for
  aircraft in flight, but to notify pilots of
  non-forecast potentially hazardous weather
  situations in which the level of danger is not
  great enough to issue a SIGMET, but requires the
  amendment of the GFA if not originally forecast
• AIRMETs may be cancelled and a SIGMET issued to
  replace it
• SIGMETs may be cancelled and an AIRMET issued to
  replace it if the weather phenomenon was not
  forecast in the GFA
• SIGMETs and AIRMETs may be issued for the same
  phenomena of differing intensity and covering
  part of the same area (e.g. AIRMET covers
  widespread MDT turbulence while SIGMET covers an
  area within that of SVR turbulence)

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Example SIGMETs