TAF Guide: Reading an Aerodrome Forecast End to End

A TAF uses almost the same vocabulary as a METAR and answers a completely different question. A METAR says what the weather is. A TAF says what it will be.

This TAF guide covers the parts that make it a forecast: the valid period, the change groups, and the way those two combine into a timeline you can read against your arrival time.

What a TAF covers

A TAF predicts conditions within about five statute miles of the airport. That is a small circle, and it is worth holding onto.

It is an aerodrome forecast, not an area forecast. Weather along your route belongs to AIRMETs, SIGMETs and the significant weather charts. A TAF has nothing to say about the air twenty miles out.

Most run 24 or 30 hours and are issued four times a day. Larger airports get the longer version.

The header and the valid period

The header is short and every part of it matters.

TAF KDFW 291720Z 2918/3024 reads as a forecast for Dallas Fort Worth, issued at 1720 on the 29th, valid from 1800 on the 29th to 2400 on the 30th.

The valid period uses four digits each side. Two for the day, two for the hour. Minutes never appear.

TAF AMD in the header means this is an amended forecast, replacing the previous one entirely for the rest of its period. An off-cycle amendment is a signal worth reading closely, because somebody rewrote the forecast early for a reason.

The change groups

Four codes build the timeline, and they behave differently from one another. This is the part that makes a TAF harder than a METAR.

FM starts a new steady state at a stated time and cancels everything before it. BECMG describes a gradual change somewhere inside a window. TEMPO marks brief interruptions that do not replace the forecast around them. PROB30 and PROB40 put odds on conditions occurring at all.

The single question that resolves most confusion is whether a group replaces the line above it or sits on top of it. FM and BECMG replace. TEMPO and PROB sit on top.

The full comparison works through each of them with examples.

Finding your arrival time

This is the practical skill, and it is worth doing deliberately rather than reading top to bottom.

Work forward through the FM groups until you reach the one covering your arrival. That block is the prevailing forecast for your time.

Then scan for any TEMPO, BECMG or PROB group whose window overlaps that time. Those modify your answer without replacing it.

The common error is taking the last line on the page as current. The last line is only current if its window covers your time.

Forecast-only codes

Most of a TAF body is shared with METARs. A few codes exist only here.

P6SM means more than six statute miles, and it is very common because forecasters rarely predict an exact visibility above six. NSW means the significant weather has ended, and it only appears inside a change group.

WS marks low-level wind shear that no thunderstorm caused. WS010/27050KT puts a 50 knot wind at 1000 feet while the surface wind is whatever the body says, and that gap is the hazard.

The TAF abbreviations page lists all of them with the codes.

What a TAF leaves out

Knowing what is absent saves you looking for it.

There is no remarks section in a civil TAF. Sea-level pressure, precipitation amounts and peak winds all record measurements, and a forecast measures nothing.

There is no altimeter setting either, and no icing or turbulence group. Those reach civil pilots through the area products instead. A military TAF does carry all three.

How much to trust it

A TAF is one person's best call, made hours before you fly. Two things tell you how much weight it carries.

The first is the issue time. A forecast written six hours ago has had six hours to be overtaken. Check when it was made, not just what it says.

The second is whether the field amends at all. Most civil fields do. Some military and smaller fields carry AMD NOT SKED, which means nobody is rostered to update it.

That second one reads backwards at a glance. It looks like a note about an amendment. It means the opposite: no amendment is coming, whatever the weather does.

Where the forecast is unwatched, lean harder on the observations.

Verdict on this TAF guide

Read the header and the valid period first, then go straight to your arrival time rather than reading the forecast as a story.

Find the FM block covering that hour, then layer on any TEMPO, BECMG or PROB group that overlaps it. Remember the five mile radius, and remember that an amendment replaces the old forecast rather than patching it.

Last updated August 29, 2026