1. What is a TAF?
A TAF (Terminal Aerodrome Forecast) is a weather forecast for the area within approximately 5 nautical miles of an airport. While METARs tell you current conditions, TAFs tell you what conditions are expected over the next 24-30 hours.
TAFs are essential for flight planning because they help you:
- Determine if your destination will have suitable weather
- Plan your departure time to avoid bad weather
- Select appropriate alternate airports
- Decide whether to file VFR or IFR
- Calculate fuel requirements based on expected conditions
METAR vs TAF
METAR = "What IS the weather?" (observation)
TAF = "What WILL the weather be?" (forecast)
TAFs are issued four times daily at major airports:
- 0000Z (midnight UTC)
- 0600Z (6 AM UTC)
- 1200Z (noon UTC)
- 1800Z (6 PM UTC)
2. TAF Format Overview
TAFs use the same weather codes as METARs but add forecast-specific elements. Here's a complete TAF example:
TAF KJFK 251130Z 2512/2612 31012KT P6SM FEW040 BKN250
FM251800 27015G25KT P6SM SCT030 BKN060
TEMPO 2520/2524 4SM -SHRA BKN025
FM260200 33010KT P6SM FEW050
This TAF contains:
- Header line - Type, station, issue time, validity period
- Base forecast - Initial expected conditions
- FM group - Significant change at 1800Z
- TEMPO group - Temporary conditions 2000-0000Z
- FM group - Another change at 0200Z
3. Header and Validity Period
TAF KJFK 251130Z 2512/2612
- TAF - Report type (or TAF AMD for amended)
- KJFK - ICAO station identifier
- 251130Z - Issue time: 25th day at 1130 Zulu
- 2512/2612 - Valid period: 25th at 1200Z to 26th at 1200Z
Understanding Validity Periods
The validity period format is DDHH/DDHH:
- 2512/2612 = Valid from 25th at 1200Z to 26th at 1200Z (24 hours)
- 2518/2624 = Valid from 25th at 1800Z to 26th at 2400Z (30 hours)
Important
Always check that the TAF is still valid for your planned flight time. An old TAF may have been superseded by an amended (TAF AMD) or corrected (TAF COR) forecast.
4. Base Forecast
The base forecast follows immediately after the validity period and uses the same format as METAR:
31012KT P6SM FEW040 BKN250
- 31012KT - Wind from 310° at 12 knots
- P6SM - Visibility plus 6 statute miles (greater than 6)
- FEW040 - Few clouds at 4,000 feet
- BKN250 - Broken clouds at 25,000 feet
Notable differences from METAR:
- No temperature/dewpoint - TAFs don't include temp/dewpoint
- No altimeter setting - Pressure not forecast in TAFs
- P6SM - "Plus 6 SM" indicates visibility > 6 miles
5. Understanding Change Groups
TAFs use several types of change indicators to show how conditions will evolve:
| Group | Meaning | Duration |
|---|---|---|
| FM | From - Rapid, permanent change | Conditions stay until next change |
| TEMPO | Temporary fluctuations | < 1 hour each, < half the period |
| BECMG | Becoming - Gradual permanent change | Occurs during the specified period |
| PROB | Probability of conditions | 30% or 40% chance |
6. FM (From) Groups
FM indicates a rapid and significant change expected at a specific time. Everything after FM completely replaces the previous forecast.
FM251800 27015G25KT P6SM SCT030 BKN060
This means: Starting at 1800Z on the 25th, expect:
- Wind from 270° at 15 knots, gusting 25
- Visibility greater than 6 miles
- Scattered clouds at 3,000 feet
- Broken clouds at 6,000 feet
Key Point
FM groups are self-contained. They include ALL expected conditions - wind, visibility, and clouds. Previous conditions no longer apply after FM.
The FM time format is FMDDHHmm:
- FM251800 = From the 25th at 1800Z
- FM260200 = From the 26th at 0200Z
7. TEMPO Groups
TEMPO indicates temporary fluctuations that are expected to:
- Last less than one hour at a time
- Occur during less than half of the total period
TEMPO 2520/2524 4SM -SHRA BKN025
This means: Between 2000Z and 2400Z on the 25th, temporarily expect:
- Visibility 4 statute miles
- Light rain showers (-SHRA)
- Broken clouds at 2,500 feet
The base conditions (or previous FM conditions) apply most of the time, with TEMPO conditions occurring occasionally.
Planning Tip
When TEMPO conditions affect your minimums, assume they WILL occur during your arrival time and plan accordingly. Have an alternate ready.
8. BECMG Groups
BECMG (Becoming) indicates a gradual, permanent change expected to occur during the specified period.
BECMG 2514/2516 BKN015
This means: Between 1400Z and 1600Z on the 25th, conditions will gradually change to broken clouds at 1,500 feet, and will remain that way.
Key differences from FM and TEMPO:
- BECMG is gradual - change happens over the time period
- BECMG is permanent - new conditions persist after the period
- BECMG only shows changes - other conditions remain from base forecast
FM
Rapid change
At specific time
Complete new forecast
TEMPO
Temporary change
During period
Returns to base
BECMG
Gradual change
Over period
Stays changed
9. Probability Groups (PROB)
PROB indicates conditions that might occur but aren't certain enough for a definitive forecast.
PROB40 2502/2506 1SM +TSRA BKN010CB
This means: 40% probability between 0200Z and 0600Z on the 25th of:
- Visibility 1 statute mile
- Heavy thunderstorm with rain (+TSRA)
- Broken cumulonimbus at 1,000 feet
US TAF Note
In US TAFs, only PROB40 is used. PROB30 is considered too uncertain. International TAFs may use PROB30. When you see PROB40, take it seriously - there's a significant chance of those conditions.
PROB can be combined with TEMPO:
PROB40 TEMPO 2520/2524 2SM TSRA
40% chance of temporary conditions with 2SM visibility and thunderstorms/rain.
10. Complete TAF Examples
Example 1: Simple TAF
TAF KORD 251130Z 2512/2612 27010KT P6SM SCT040 BKN100
FM252000 31015KT P6SM FEW050
Translation: Chicago O'Hare, valid 25th 1200Z to 26th 1200Z. Initially wind from 270° at 10kt, visibility >6 miles, scattered clouds at 4,000ft, broken at 10,000ft. From 2000Z, wind shifts to 310° at 15kt with few clouds at 5,000ft.
Example 2: Complex Weather
TAF KSFO 251130Z 2512/2612 28008KT 6SM BR SCT004 BKN012
TEMPO 2512/2516 2SM BR BKN004
FM251600 29012KT P6SM FEW020
BECMG 2520/2522 VRB03KT
FM260000 25005KT 3SM BR SCT003 BKN008
TEMPO 2604/2610 1SM FG VV002
Translation: San Francisco, typical marine layer pattern:
- Morning mist and low clouds (6SM visibility, ceiling 1,200ft)
- Temporarily worse 1200-1600Z (2SM, ceiling 400ft)
- Burns off by 1600Z (>6SM, few clouds 2,000ft)
- Winds becoming light and variable 2000-2200Z
- Marine layer returns after midnight (3SM mist, ceiling 800ft)
- Temporarily fog early morning (1SM, vertical visibility 200ft)
Example 3: Convective Weather
TAF KDFW 251130Z 2512/2612 17010KT P6SM SCT045 BKN200
PROB40 2518/2524 4SM TSRA BKN030CB
FM260000 36012G20KT P6SM SCT040
Translation: Dallas-Fort Worth:
- Initially good VFR from the south
- 40% chance of thunderstorms 1800-0000Z
- Wind shift to north with gusty conditions after midnight
Convective SIGMET
When thunderstorms are forecast in TAFs, always check for Convective SIGMETs and AIRMETs for the bigger picture of convective activity.
Check Current TAFs
Ready to read real TAFs? Search any airport to view current forecasts:
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