A Deeper Look At TAFs

| January 26, 2021 | By: Severe VFR
Cessna Skyhawk Flying Through Building Storm Clouds
A Terminal Aerodrome Forecast (TAF) is a concise statement of the expected meteorological conditions at an airport during a specified period.

Weather Types

TAFs are similar to weather forecasts shown on tv. However, the information is presented in a textual format and generally requires a higher skill level to comprehend. The weather information that TAFs provide is tailored to the needs of the aviation and can include forecasted:

  • Wind direction and speed
  • Surface Visibility
  • Precipitation Types (Rain, Snow, Ice, Hail)
  • Obstructions To Vision
  • Vertical Visibility
  • Low-Level Wind Shear
  • Weather Phenomenon (Dust Storms, Thunderstorms, Tornadoes, Squall Lines)
  • Sky Condition

The weather information is only officially accurate for the area within a five statute mile radius from the issuing airport center. However, if forecasters believe a significant weather event will occur within the area between 5 and 10 statute miles, they can list the weather event as "in the vicinity." Weather in the vicinity will be proceeded by the text code "VC" before the type of weather, i.e., VCFG, VCSH, VCTS.

Forecasters will list weather phenomena within the 5-10 statute mile range if the weather has an equal to or greater than 50% probability of occurring for at least half of the forecasted period.

TAFs will also typically include more detail about expected weather conditions within the first 12 hours of the forecast. Times beyond the first 12 hours may contain less detail. However, they will still highlight significant weather changes for airline dispatchers and other aviation groups' strategic planning.

Types Of TAFs

TAFs are typically grouped as either "Routine" or "Amended." However, a better way of grouping TAFs is as either "Routine" or "Unscheduled."

The difference between a "Routine" and "Unscheduled" TAF is that routine TAFs are issued routinely at set time periods. Unscheduled TAFs are issued on an as-needed basis. 

When an unscheduled TAF is issued, it will be issued as either an amended, delayed, or corrected TAF.  

Amended TAFs are issued when the current TAF and its forecasted weather do not match the actual weather. The benefit of issuing the amendment to the TAF is that the quality of the TAF will improve. The whole purpose of the TAF is to allow the end-user: airlines, dispatchers, airports, and you, to plan for the future. A TAF that deviates from the actual weather conditions creates a rippling effect that increases delays and creates a rippling effect across the entire country. Therefore, the sooner forecasters can amend TAFs, the better.  

For an Amended TAF to be issued, the forecasters' assessment of existing conditions and expectations must differ from the current conditions. However, small differences in the forecast to current observed conditions do not call for minor adjustments to the TAF. Changing a TAF for small differences to the observed weather currently occurring is referred to as "Chasing the observation" and is not beneficial to end-users. 

Instead, Amended TAFs will be issued when significant operational criteria are met. Such as:

  • A change between predicted and actual flight category (VFR, IFR, MVFR, LIFR).
  • New information indicates future conditions are expected to be in a different flight category, especially in the 1-6 hour time period after TAF issuance. 
  • If thunderstorms, freezing precipitation, or ice pellets occur and are not forecast, or if forecasted does not occur. 
  • The mean wind speed differed by greater than or equal to 10 knots, while the original or newly expected mean wind speed is greater than or equal to 12 knots. 
  • Forecasted wind gusts, or non-forecasted gusts, differs from observed wind gust by greater than 10 knots. 
  • Non-convective low-level wind shear up to 2,000ft is forecasted and does not occur, or does occur and is not forecasted. 

These criteria are considered significant because a change from one to the other requires different operating and regulatory requirements. Such as Fuel requirements between VFR and IFR, requirements for alternates, flight cancellations, delays, and traffic flow, to name a few. 

Delayed TAFs are issued when a problem occurs. Potential causes of delayed TAF might include power outages, equipment failures, and mechanical errors. Delayed TAFs are issued as soon as possible after the cause of the problem is fixed. 

Corrected TAFs are issued when a typographical error or other mistake is discovered. Once discovered, a corrected TAF is issued as soon as possible. 

Issued And Valid Times

A Routine TAFs is issued every 6 hours. Therefore, a routine TAF will be issued four times daily.

Routine TAFs are issued at: 

  1. 00z
  2. 06z
  3. 12z
  4. 18z

Even though Amended TAFs are considered an "unscheduled" TAF, amended TAFs can be routinely issued at set times after the initial TAF issuance. 

Routinely scheduled amended TAFs are issued at:

  1. 03z
  2. 09z
  3. 15z
  4. 21z

Generally, routinely scheduled amended TAFs will be found at the FAA's core airports. 

For each 6 hour period is a scheduled issuance window for when the TAF for that period must be issued.

The issuance window for every time period starts 40 minutes before issuance and ends 20 minutes before issuance. 

For example:

Issuance Time: 00z. Issuance window: 2320z - 2340z. 

Issuance Time: 06z. Issuance window: 0520z - 0540z.

Issuance Time: 12z. Issuance window: 1120z - 1140z.

Issuance Time: 18z. Issuance window: 1720z - 1740z. 

On top of these scheduled times, weather forecasts can choose to issue a TAF more frequently than every 6 hours as a method of keeping the TAF as most representative of current conditions as previously described. 

The issuance of a new TAF cancels any previous TAF for the same time and location. 

Routine TAFs may also be amended before the top of the hour without being marked as an Amended TAF. Therefore, an 18z TAF may be amended between 1720z to 1759z.

Generally, each TAF is valid for 24 hours. However, high-impact airports (those with large amounts of domestic and international traffic) are valid for 30 hours. 

As of this writing, 30 hour TAFs can be found at the following locations:

  1. KAUS: Bergstrom International Airport
  2. KATL: Atlanta Intl 
  3. KBDL: Bradley Intl 
  4. KBOS: Logan Intl
  5. KBWI: Baltimore-Washington Intl
  6. KBZN: Bozeman
  7. KCLE: Cleveland Hopkins Intl
  8. KCLT: Charlotte Douglas Intl
  9. KCVG: Covington/Cincinnati
  10. KDCA: Ronald Reagan Washington National
  11. KDEN: Denver Intl
  12. KDFW: Dallas/Fort Worth Intl
  13. KDTW: Detroit
  14. KEWR: Newark Liberty Intl
  15. KFLL: Fort Lauderdale/Hollywood Intl
  16. KIAD: Washington Dulles Intl
  17. KIAH: Houston – George Bush Intl
  18. KIND: Indianapolis Intl
  19. KJFK: John F. Kennedy Intl
  20. KLAS: Las Vegas McCarran Intl
  21. KLAX: Los Angeles Intl
  22. KLGA: New York LaGuardia
  23. KMCO: Orlando Intl
  24. KMDW: Chicago Midway
  1. KMEM: Memphis Int
  2. KMIA: Miami Intl
  3. KMKE: General Mitchell Intl
  4. KMSP: Minneapolis-St Paul Intl
  5. KMSY: New Orleans Intl
  6. KOAK: Oakland Intl
  7. KONT: Ontario Intl
  8. KORD: Chicago-O'Hare Intl
  9. KPHL: Philadelphia Intl
  10. KPHX: Phoenix Sky Harbor Intl
  11. KPIT: Pittsburgh Intl
  12. KSAN: San Diego Intl
  13. KSDF: Louisville Intl
  14. KSEA: Seattle-Tacoma Intl
  15. KSFO: San Francisco Intl
  16. KSLC: Salt Lake City Intl
  17. KSTL: Lambert-St Louis Intl
  18. KSWF: Stewart Intl
  19. KSAT: San Antonio International Airport
  20. KTPA: Tampa Intl
  21. KTEB: Teterboro
  22. PANC: Anchorage Intl
  23. PAFA: Fairbanks Intl
  24. PGUM: Guam Intl
  25. PHNL: Honolulu Intl
  1. KAUS: Bergstrom International Airport
  2. KATL: Atlanta Intl 
  3. KBDL: Bradley Intl 
  4. KBOS: Logan Intl
  5. KBWI: Baltimore-Washington Intl
  6. KBZN: Bozeman
  7. KCLE: Cleveland Hopkins Intl
  8. KCLT: Charlotte Douglas Intl
  9. KCVG: Covington/Cincinnati
  10. KDCA: Ronald Reagan Washington National
  11. KDEN: Denver Intl
  12. KDFW: Dallas/Fort Worth Intl
  13. KDTW: Detroit
  14. KEWR: Newark Liberty Intl
  15. KFLL: Fort Lauderdale/Hollywood Intl
  16. KIAD: Washington Dulles Intl
  17. KIAH: Houston – George Bush Intl
  18. KIND: Indianapolis Intl
  19. KJFK: John F. Kennedy Intl
  20. KLAS: Las Vegas McCarran Intl
  21. KLAX: Los Angeles Intl
  22. KLGA: New York LaGuardia
  23. KMCO: Orlando Intl
  24. KMDW: Chicago Midway
  25. KMEM: Memphis Int
  26. KMIA: Miami Intl
  27. KMKE: General Mitchell Intl
  28. KMSP: Minneapolis-St Paul Intl
  29. KMSY: New Orleans Intl
  30. KOAK: Oakland Intl
  31. KONT: Ontario Intl
  32. KORD: Chicago-O'Hare Intl
  33. KPHL: Philadelphia Intl
  34. KPHX: Phoenix Sky Harbor Intl
  35. KPIT: Pittsburgh Intl
  36. KSAN: San Diego Intl
  37. KSDF: Louisville Intl
  38. KSEA: Seattle-Tacoma Intl
  39. KSFO: San Francisco Intl
  40. KSLC: Salt Lake City Intl
  41. KSTL: Lambert-St Louis Intl
  42. KSWF: Stewart Intl
  43. KSAT: San Antonio International Airport
  44. KTPA: Tampa Intl
  45. KTEB: Teterboro
  46. PANC: Anchorage Intl
  47. PAFA: Fairbanks Intl
  48. PGUM: Guam Intl
  49. PHNL: Honolulu Intl
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