Guidelines for Writing Effective TAFS
Cammye Sims, WFO SAT
Brad Sipperly, WFO FAI
NOTE: See additional presentations for this subject in the Training and Presentations section of this website
TAF LENGTH - 6 LINES MAXIMUM, Includes 5 lines of FM groups, plus 1 line TEMPO group.
TEMPO - MAXIMUM 1 PER TAF confined to the first 6 hours of the TAF
BEYOND 6 HOUR POINT – FM groups should indicate trends showing categorical changes (VFR, MVFR, IFR, LIFR)
CHANGE GROUPS – use to indicate ceiling/visibility changes by category
ELIMINATE NON-OPERATIONAL CHANGE GROUPS – Examples: SCT250 changing to BKN250 or winds 03006KT to 02003KT
TAF CONSTRUCTION – First 6 hours use perishable data (Radar, Satellite, Obs), 6 to 24 hours use climatology/model data. Persistence should be considered as the first line of every TAF with any TEMPO group used here only to show variability already occurring or expected to occur, based on perishable data.
THUNDERSTORMS & SHOWERS - If not expected to be within 5 miles of airfield, use VCTS/VCSH. Do not include hail in TAFs unless certain will occur OVER the airfield.
LAST LINE OF THE TAF – Should represent expected conditions for the last 6 hours of the TAF valid period.
ADDITIONAL TIPS FOR WRITING MORE EFFECTIVE TAFS
TEMPO GROUPS During conditions of observed high variability of ceiling and/or visibility, only 1 TEMPO group should be used to describe, as closely as possible, those conditions. Verification indicates forecast accuracy for high probability events beyond the first 6 hours is extremely difficult to define. Verification also indicates the use of TEMPO groups beyond the first 6 hours generally hurts the TAF rather than helps it.
REMOVE TEMPO groups if they have not occurred for half of the time allowed, and if not expected to occur. AvnFPS is configured to alert you of these instances.
AVOID major changes to the previously written TAF whenever possible. Adjust timing and severity of previously forecasted changes as conditions warrant. Add new change groups for categorical changes whenever data indicates such changes are likely to occur.
CHANGE GROUPS beyond the 6 hour point should show categorical change trends most likely to occur during the forecast period. When conditions exist that make it difficult to positively identify any given categorical change in ceiling conditions, use hints to indicate possibly changing trends. For example, using SCT005 versus BKN005 indicates to pilots that a lowering trend is expected, but confidence is not high enough at forecast time to define this condition as a ceiling. When a disparity exists in deciding visibility conditions, choose a mid point to show a trend up or down accordingly. Subsequent forecasts will further define indicated changes as new data becomes available.
INCLUDE FORECAST OF THUNDERSTORMS in the first 6 hours of a TAF when perishable data indicates a high likelihood of occurrence within 5 statue miles of the center of the runway complex. The use of VCTS in many cases is a better forecast and does not affect airline operations. Remember VCTS is a donut-shaped area 5 to 10 statute miles from the center of the runway. If data does not indicate thunderstorms are likely within 5 statute miles of the center of the runway, forecast accordingly. If forecasting in the latter periods of the TAFs, use of CB will give the pilots a heads up for thunderstorm development.
BE PRO-ACTIVE Workload permitting amend TAFs that indicate a significant change within the first few hours of the next TAFs starting point. Use persistence alerts received on AvnFPS to issue, before the fact conditions warrant an amendment.
EXAMPLES TO FOLLOW FOR WRITING MORE EFFECTIVE TAFS
EXAMPLES FOR FOG EVENTS:
TAF
KSAT 030530Z 030606 16005KT P6SM SCT015 OVC050
FM0800 VRB03KT 6SM BR BKN015
TEMPO 0811 1/2SM FG BKN009
FM1100 17010KT P6SM BKN020
FM1800 18012KT P6SM SCT040
FM0300 32010KT P6SM SCT250=
TAF
KSAT
031130Z 031212 VRB03KT 1/4SM FG OVC002
FM1500
18010KT 2 1/2SM BR OVC005
FM1800 32015G25KT P6SM SCT040
BKN250
FM0300
32010KT P6SM SKC=
EXAMPLES FOR SHOWER & THUNDERSTORM EVENTS
TAF
KSAT
031730Z 031818 17010G15KT 4SM -SHRA BR OVC007
FM1900
17015G30KT 2 1/2SM -SHRA BR OVC009
TEMPO
1922 4SM BR OVC012
FM2200
18010KT P6SM OVC010
FM0800
18010KT 1/4SM FG OVC001
FM1500
32010KT P6SM OVC040=
TAF
KSAT
032330Z 030024 17015G22KT 4SM -TSRA BR OVC015CB
TEMPO 0002 2SM
–TSRA OVC010CB
FM0200
17010G15KT P6SM VCTS OVC015CB
FM0600
16010KT P6SM BKN035
FM1500 16012KT P6SM SCT250=
THE NUMBER 1 RULE AND MOST IMPORTANT THING TO REMEMBER IS…
KEEP IT SIMPLE!
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