Decode TAF Forecast Validity Periods
Live Zulu
UTC +00:00
16:27:12Z
May 25, 2026
Useful for pre-departure forecast window interpretation.
Forecast Window (UTC)
Enter DDHH/DDHH token
Forecast Duration
Calculated after parsing
Local Airport Window
Select airport timezone
UTC Offset
Offset appears after timezone selection
Forecast Timeline Progress
Waiting for TAF validity token.
TAFs outline weather forecasts over prolonged windows (typically 24 to 30 hours) for flight dispatch planning. Interpreting the DDHH/DDHH validity group correctly ensures airport arrival weather matches legally required safety margins.
| TAF Indicator | Meaning & Purpose | Zulu Validity Constraints | Planning Consideration |
|---|---|---|---|
| FM (From) | Rapid, significant change. | FM171200 - Starts exactly at 12:00 Zulu. Preceding conditions expire. | Strict cutoff for weather conditions. |
| BECMG (Becoming) | Gradual transition over a period. | BECMG 1712/1714 - Transitions between 12:00 and 14:00 Zulu. | Apply worst-case limits during transition window. |
| TEMPO (Temporary) | Fluctuations lasting < 1 hour. | TEMPO 1718/1722 - Occasional fluctuations within the 4h window. | Alternative fuel planning required. |
| PROB30 / PROB40 | 30% or 40% probability of hazard. | PROB30 1802/1806 - Expected window of occurrence in Zulu. | Often triggers alternate airport requirements. |
TAF forecasts use 24 (e.g. 1724) to represent midnight of the current day, and 00 (e.g. 1800) to represent midnight as the start of the next day. In calculation, 1724Z is identical to 1800Z. Confusing this rollover representation can lead dispatch software or crew calculators to skip or double-count a full calendar day, resulting in a blank weather planning segment.
TAF timing is about forecast coverage. This tool helps align a route ETA with the correct forecast period, plus any TEMPO or BECMG sub-window.
Forecast anatomy
A complete TAF briefing separates when the forecast was issued from when its conditions are valid.
When the forecast bulletin was published.
Beginning of the forecast validity period.
End of validity, with 24 meaning midnight at day end.
Shorter change windows inside the main validity period.
TAF notation
These compact groups can change how a pilot interprets arrival weather.
| Pattern | Decoded timing | Planning use |
|---|---|---|
| 1718/1824 | Day 17 1800Z to day 19 0000Z | A long validity window that crosses a date boundary. |
| TEMPO 1806/1810 | Day 18 0600Z to 1000Z | Temporary conditions inside a defined sub-window. |
| BECMG 1812/1814 | Changing between 1200Z and 1400Z | Transition expected over the specified period. |
| FM181500 | From day 18 at 1500Z | A more exact forecast change start. |
Dispatch check
The forecast only helps if its valid period covers the operational phase you care about.
Forecast starts day 17 at 18:00 UTC and runs through day 18 at 24:00 UTC, which is day 19 at 00:00 UTC.
Related link: Military Time to Zulu Converter .
It prevents timing mistakes when matching forecast periods to takeoff, cruise, and arrival phases.
Related link: Zulu To Est .
Yes. The parser returns full validity duration in hours and minutes.
Yes. Select airport timezone to view validity period in local clock terms.
Large international airports issue 30-hour TAFs to cover long-haul routes. The DDHH/DDHH format naturally captures the day roll.
24:00 Zulu represents midnight of that forecast day. Operationally, it is identical to 00:00 Zulu of the following calendar day.
These are sub-intervals within a TAF, written as DDHH/DDHH, specifying when a weather transition or temporary condition is expected.
No, the forecast remains strictly locked to Zulu. Converted local flight briefing schedules must account for station DST shifts manually or via this tool.
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