TAF is a forecast
A TAF is an aerodrome forecast, not an observation. Read its issue time, validity period and initial forecast before interpreting a change group. Joshi adds that domestic and international issue arrangements may differ, so always use the product validity shown in the message.
Report order and use
The TAF gives forecast wind, visibility, weather and cloud for an aerodrome. It is used with METAR, SPECI, warnings and route products, not in place of them. The forecast must be matched to the planned arrival or alternate time.
Date-time groups and validity
A validity group has a start and end day and UTC hour. It defines the period during which the forecast applies. The issue time shows when the forecast was prepared and may be earlier than the flight decision.
Forecast weather groups
The wind, visibility, present weather and cloud groups use familiar coding logic, but their meaning is forecast. Treat each group as the expected condition for the relevant period, then use change indicators to understand when the baseline is replaced or modified.
Wind and cloud
Forecast wind supports runway and fuel planning. Forecast cloud must be compared with approach, terrain and alternate requirements. CB and significant weather groups can change an otherwise acceptable route into a diversion or holding problem.
Visibility and weather
Forecast visibility, fog, showers, thunderstorms or snow must be tied to its change period. A low visibility value under TEMPO is not the same risk as a low value that forms the baseline forecast.
FM and BECMG
FM introduces a new forecast from a stated time. BECMG describes a change expected within its stated period. The difference matters because one replaces the previous condition from its effective time, while the other gives a window for the transition.
FM replacement
When FM appears, read the following groups as the new prevailing forecast. Do not retain an earlier wind or cloud group beyond the FM time unless it is repeated.
BECMG window
BECMG requires a planning margin because the change may occur at any point within the given window. Its operational consequence depends on whether the change is improvement or deterioration.
TEMPO, PROB, NSW and AMD
TEMPO indicates temporary fluctuations. PROB 30 or PROB 40 expresses probability when permitted in the code. NSW means no significant weather. AMD identifies an amended TAF. Read these modifiers as part of a forecast structure rather than as isolated abbreviations.
Temporary versus prevailing
A TEMPO event has a limited duration and is not a new prevailing forecast. It can still be operationally decisive if it overlaps the approach or departure window.
Full decode discipline
Start with validity and baseline, then process FM, BECMG, TEMPO and PROB in time order. Check the amendment status and the end marker.
ARFOR: the route-area forecast
ARFOR is a forecast for a specified area or route. It adds en-route fields which an aerodrome TAF does not contain. Joshi includes cloud, weather, icing, turbulence, upper wind and temperature, tropopause and significant weather as route-planning information.
Read the area first
Confirm the area or route, validity and height reference. A cloud or turbulence layer has no meaning until its horizontal extent and vertical limits are located against the planned track.
Do not substitute products
A TAF is aerodrome-focused. ARFOR gives the en-route picture. Use both, then compare them with SIGWX and wind-temperature charts.
ROFOR and integrated briefing
ROFOR arranges route forecast information in sections. It supports the climb, cruise and descent picture by placing wind, temperature, cloud and significant weather along the route. The right level is selected by comparing several forecast products, not by one value.
Cross-check sequence
Use TAFs for departure, destination and alternates. Use ARFOR or ROFOR for the route. Compare both with SIGWX and wind-temperature charts. Update the plan with METAR, SPECI and warnings before departure.
Reasoning from conflict
If a route chart and an aerodrome forecast appear inconsistent, first check validity, height and geographic extent. They may both be correct for different conditions.
Worked TAF and change groups
TAF VECC 102100Z 1100/1109 09012KT 2500 BR FEW040 SCT150 BECMG 0204 16015KT 6000 TEMPO 1107/1109 FEW030CB=
- 102100Z is issue time on day 10 at 2100 UTC; 1100/1109 is valid from day 11 0000 to 0900 UTC.
- 09012KT 2500 BR is the opening forecast wind and mist visibility.
- BECMG 0204 means the forecast becomes 160 degrees at 15 kt and 6000 m at some time from 0200 to 0400 UTC.
- TEMPO 1107/1109 FEW030CB forecasts temporary CB cloud at 3000 ft during that final period.
NSW cancels significant weather in the relevant forecast section. AMD marks an amended TAF. ARFOR is route-area information: cloud, weather, icing, turbulence, upper wind and temperature, tropopause and significant weather. ROFOR arranges route weather in four sections and adds planning detail such as jet maximum wind and wind shear. Use TAF for aerodromes and ARFOR or ROFOR for the route.
Forecast-code distinctions
Unlike a METAR, a TAF does not report what is occurring at the moment. Its initial group is the expected prevailing condition from the start of validity until changed. FM starts a replacement forecast at the stated time. BECMG permits the change at any time inside its stated window. TEMPO describes temporary conditions, so its duration and overlap with ETA are operationally important.
PROB30 and PROB40 express the permitted probability values. A probability group must be read with its associated time and weather. NSW means no significant weather, not no cloud or no wind. The equals sign is the end marker. These distinctions are why a forecast can be correctly decoded yet still require an alternate margin.
ARFOR and ROFOR fields
For ARFOR, read the area name and validity first, followed by cloud and weather, icing, turbulence, upper wind and temperature, tropopause and significant weather. ROFOR divides the route into forecast sections. Its wind, maximum-wind, jet and shear information must be plotted by section and level. A destination TAF cannot answer a route icing or cruise-wind question; that is why the route products remain essential.
TAF planning questions
- Which condition prevails at ETA? Follow the baseline and each FM or BECMG in time order.
- Which condition is temporary? Read TEMPO limits and compare them with the approach window.
- What is uncertain? Read PROB30 or PROB40 with the affected weather.
- What has changed? If the TAF is AMD, discard the superseded planning assumption.
Cloud, visibility and weather groups in a TAF are forecast groups. A cloud amount and base may change within BECMG while wind remains unchanged, or an FM group may replace both. Decode every group following a change indicator, not merely the first value after it.