Reading the TAF and the twenty-four hour forecast that tells you what the weather will do before you get there

A Terminal Aerodrome Forecast (TAF) is a 24- to 30-hour weather prediction for a specific airport, and learning to read one is essential for any cross-country flight. While METARs tell you what the weather is, the TAF tells you what it’s going to do—covering winds, visibility, clouds, and precipitation in a structured timeline. The key to using a TAF effectively is reading the entire forecast, not just the first line, and matching conditions to your planned arrival time.

What Is a TAF and How Often Is It Updated?

TAF stands for Terminal Aerodrome Forecast. It’s issued by the National Weather Service and covers expected weather within a five statute mile radius of an airport.

TAFs are issued four times daily—approximately at 0000Z, 0600Z, 1200Z, and 1800Z. Each forecast covers either a 24- or 30-hour period, depending on the airport.

Not every airport receives a TAF. Smaller uncontrolled fields typically don’t have one. In those cases, use the TAF from the nearest larger airport and adjust for local differences. It’s not perfect, but it gives you a working baseline.

How Do I Decode the Header and Prevailing Forecast?

Consider this example TAF:

TAF KORD 071741Z 0718/0818 27012KT 6SM BKN025 OVC050

The header tells you three things: the airport identifier (KORD—Chicago O’Hare), the issuance time (071741Z), and the valid period (0718/0818—from the 7th at 1800Z to the 8th at 1800Z). Always check the valid period first. If the TAF doesn’t cover your arrival time, it’s useless—find a current one or call Flight Service.

The first weather group after the valid period is the prevailing forecast. This is your baseline. In this example: winds from 270° at 12 knots, 6 statute miles visibility, broken clouds at 2,500 feet AGL, overcast at 5,000 feet. Solid VFR conditions.

What Does FM (From) Mean in a TAF?

FM is the most important change indicator in a TAF. When you see FM followed by a time, the weather is expected to make a significant, lasting change at that time.

Example: FM0800 31015G25KT 3SM -RA BKN012 OVC025

Starting at 0800Z, winds shift to 310° at 15 gusting 25 knots, visibility drops to 3 miles in light rain, and the ceiling falls to broken at 1,200 feet. That’s a completely different airport than the prevailing forecast described.

The critical concept: FM groups replace everything before them. Once that FM time arrives, the previous forecast is gone. Think of each FM group as a new chapter. If your arrival falls after 0800Z in this example, the prevailing forecast at the top of the TAF is irrelevant to you.

What Does TEMPO Mean and Why Does It Matter?

TEMPO stands for temporary. Conditions listed after TEMPO are expected to last less than one hour at a time but may occur repeatedly throughout the time window.

Example: TEMPO 0812 1SM +TSRA OVC008

Between 0800Z and 1200Z, there may be temporary periods of 1 mile visibility in thunderstorms and heavy rain with an 800-foot overcast ceiling. That’s IFR. That’s below minimums for any VFR pilot.

TEMPO doesn’t guarantee the conditions will occur. But if you’re 20 miles out and one of those TEMPO drops rolls through at your arrival time, you’re out of options. On a checkride, if the TAF shows a TEMPO group with IFR conditions during your arrival window, the correct response is to adjust your timing or pick an alternate airport.

What Is the Difference Between FM and BECMG?

BECMG stands for becoming, and it describes a gradual transition rather than an abrupt change.

Example: BECMG 1416 27008KT 6SM SCT025

Between 1400Z and 1600Z, conditions gradually improve—winds ease to 8 knots, visibility returns to 6 miles, scattered clouds at 2,500 feet.

The distinction matters for planning:

• FM is a switch. Conditions change at that time.
• BECMG is a transition. Conditions shift gradually over the listed window. During that period, you might see visibility bouncing between the old and new values.

How Should I Interpret PROB Groups?

PROB indicates a probability of conditions occurring. You’ll see PROB30 or PROB40 followed by a set of conditions.

The FAA doesn’t issue PROB groups below 30%. Treat PROB40 as a real possibility, not a maybe. If a PROB40 group shows thunderstorms during your flight window, have a backup plan ready.

What Is the Best Way to Read a TAF Quickly?

Use this three-question method:

1. Does the TAF cover my departure and arrival times? Check the valid period. If your flight falls outside the forecast window, find the right TAF.

2. What are the conditions at my expected arrival time? Walk through the FM, TEMPO, and BECMG groups in sequence. Identify which group applies to your arrival. That’s the forecast that matters.

3. Is there anything in the TEMPO or PROB groups that exceeds my personal minimums? Not the legal minimums—your personal minimums. A 60-hour student pilot should think twice about a TEMPO group showing 3 miles and a 1,000-foot ceiling, even though that’s technically VFR.

What Details Do TAFs Leave Out?

A few practical points that catch pilots off guard:

• TAF winds use true north. Apply magnetic variation when comparing to runway headings for crosswind calculations.
• Cloud heights are AGL, the same as METARs. No math needed with field elevation.
• TAFs do not include temperature or altimeter settings. Those change constantly and belong in the METAR. For forecast temperatures (density altitude planning on hot days), check the forecast discussion or other planning tools.

How Should I Use TAFs for Cross-Country Planning?

Pull up TAFs for your departure airport, destination, and at least one airport along your route. Read each one completely—don’t stop at the prevailing forecast.

A common trap: departure weather is perfect, the top line of the destination TAF looks great, but an FM group buried in the middle kicks in one hour before your arrival. The ceiling drops, wind picks up, and a TEMPO group shows marginal VFR. Pilots who only glanced at the first line never saw it coming.

The prevailing forecast is only valid until the first FM group replaces it. You have to read the whole TAF and ask yourself: am I comfortable with the worst-case TEMPO group? Do I have an alternate if conditions drop below my minimums?

Key Takeaways

• A TAF is a 24-30 hour forecast for a specific airport, issued four times daily, covering a five-mile radius
• FM groups replace all previous conditions—always identify which FM group applies to your arrival time
• TEMPO conditions are real threats even though they’re temporary; plan for them, especially if they show IFR weather
• BECMG describes gradual change; FM describes abrupt change—know the difference for accurate planning
• Read the entire TAF, not just the first line; the prevailing forecast becomes irrelevant once an FM group takes effect