AVIATION 120

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AVIATION 120

• Meteorology

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Todays Agenda

• Upper Level Wind and Temperature Forecast (FD)
• Introduction
• Issue times and periods of use
• Format
• Amendments
• Examples

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FD - Introduction

• Refer to MANAIR chapter 3 and your AIP
• FDs are prepared to meet aeronautical needs for
  pre-flight planning purposes
• FD forecasts are based on upper air data received
  from satellites as well as radiosonde and
  rawinsonde soundings which are done at 0000Z and
  1200Z
• Issued by the Canadian Meteorological Centre
  (CMC) in Montreal for 142 locations across Canada
  and the National Weather Service (NWS) in
  Washington, DC for 139 locations across Canada
• CMC issues FDCN01, FDCN02, and FDCN03 CWAO
  messages for the 3000, 6000, 9000, 12000 and
  18000 foot levels (ASL). The 3000 level is
  omitted if the ground elevation is greater than
  1500 ASL
• NWS in Washington, DC issues upper wind and
  temperature forecasts for the same locations
  (with very few exceptions) as the CMC, but for
  the 24000, 30000, 34000, 39000, 45000 and 53000
  foot levels (ASL). These forecasts are issued
  under the headers FDCN1, FDCN2, FDCN3 KWBC

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Issue times and periods of use

• FDs are prepared twice daily and are based on 00Z
  and 12Z upper air data
• When FDs are generated, 6, 12, 18, 24, 30, 36 and
  48 hour forecasts are created
• The 6, 12 and 24 hour forecasts become FDCN01,
  FDCN02 and FDCN03 respectively
• The 18, 24 and 36 hour forecasts are kept as
  backup in case of computer failure during the
  next forecast cycle
• The 30, 36 and 48 hour forecasts are also kept in
  the event of a computer failure during two
  consecutive forecast cycles
• When an FD is based on these backups, the first
  line of the FD will have a remark COMPUTER
  INOPERATIVE ON DDTTTT DATA where DDTTTT
  represents the date and time of the data on which
  the FDCN01, FDCN02 and FDCN03 forecasts would
  have been based under normal circumstances.
• Even though FDs have a specific valid time, it is
  actually for a period of use

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FD Issue Time, Valid Time and Period of Use
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FD - Format

• STN YVR - for use 3000 6000 9000 12000 18000
• FDCN01 CWAO
• FCST BASED ON 240000
• DATA VALID 240600 05-09 9900 350810 311506
  312302 3031-09
• Wind direction is always displayed with two
  digits and is given to the nearest 10 degrees
  true
• Wind speed is always displayed with two digits
  the units are knots
• Wind speed less than 5 knots will be coded 9900
• Wind speeds greater than 99 knots will be coded
  by subtracting 100 from the wind speed and adding
  50 to the direction (e.g. 360 at 120KT would be
  coded 8620)
• Winds greater than 199 knots will be coded as 199
  knots (e.g. 090 at 210 would be coded 5999)
• Temperature is always displayed with two digits
  and is in degrees Celsius
• Temperature is not forecast for the 3000 level
• Negative values for temperature will not be
  included above 24000

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FD - Amendments

• CMC is responsible for FD amendments to FDCN01,
  FDCN02 and FDCN03 CWAO forecasts
• The date/time group of the communication header
  will indicate the time of the amendment, which
  for automatic amendments will normally be 0215,
  0815, 1415 or 2015Z (215 after each synoptic
  hour)
• The communication header will contain AMD
• Each amended forecast will contain wind direction
  and speed, as well as temperature for all levels
  at each of the amended locations
• Automatic amendments are only made to FDCN02 CWAO
  forecasts and are automatically issued by the
  computer for differences meeting amendment
  criteria
• Manual Amendments may be made to an FD

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FD Amendments (cont.)

• Amendment Criteria - WIND
• If the forecast wind speed is less than 25KT
• Direction Difference of 35 degrees or greater
• Speed Difference of 15KT or greater
• If the forecast wind speed is 25KT to lt70KT
• Direction Difference of 25 degrees or greater
• Speed Difference of 20KT or greater
• If the forecast wind speed is greater than 70KT
• Direction Difference of 25 degrees or greater
• Speed Difference of 20KT or greater
• Amendment Criteria Temperature
• Difference of 5 degrees Celsius or greater

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FD Examples