TAF

[Melvyn82]

Hi all, I am pretty new at flying, only recently obtained my ppl, and planning on training/hour building for my CPL in due time.

My question is about reading a TAF properly:

Example:

240457Z 2406/2506 VRB04KT 0200 FG PROB40 TEMPO 2406/2418 3000 BR BKN005 BECMG 2408/2411 08010KT 7000 NSW SCT007 PROB40 TEMPO 2418/2506 1200 RADZ BR BKN002

Question: the period of BECMG 2408/2411 is a nice improvement compared with the rest of this TAF, when this time period has elapsed, do I then revert back to the main body of the TAF, or do I use the TEMPO 2406/2418 until 18hrs, although after 18hrs it is starting to get worse again...

Sorry If these kinda questions have been asked before, but I would appreciate any inputs!!!

Thanks in advance.

Melvyn82

[SteveTonks]

In short yes. The tempo means that for at least 50% of the time period stated the weather is forecast to be like that. Once a tempo has expired you would the either revert back to the baseline TAF or onto the next or current tempo/bcmg/frm or full change.

[Cylinder Head]

Melvyn
TEMPO can be defined as "temporary fluctuations in conditions during the period, each change lasting not more than 1 hour and existing for less than 50% of the time period stated." This means that conditions should revert to the base forecast when the TEMPO conditions do not prevail and when the defined TEMPO period ends.
It's a common trap to read a TAF with a generally good base forecast and think "it'll be alright as long as I avoid the poorer conditions in the tempos."
- especially if you have multiple poor tempos! Hope this helps>

[SARWannabe]

Hi Melvyn.

You have picked an interesting TAF to decode, and what CH says is absolutely correct. To offer something that might perhaps add clarity to your question about the BECMG.

Question: the period of BECMG 2408/2411 is a nice improvement compared with the rest of this TAF, when this time period has elapsed, do I then revert back to the main body of the TAF, or do I use the TEMPO 2406/2418 until 18hrs, although after 18hrs it is starting to get worse again...

Just as an exercise read the TAF without the Tempos (don't misinterpret this as me saying they don't matter or can be ignored).

240457Z 2406/2506 VRB04KT 0200 FG BECMG 2408/2411 08010KT 7000 NSW SCT007

The BECMG indicates an overall change in the baseline forecast until the end of the TAF or next BECMG or FRM, before taking the TEMPOS into account. In this case, between 0800Z and 1100Z the base forecast wind strength is due to increase, visibility to lift from 200m to 7km, and cloud to lift from fog to scattered at 700 feet. The time of the BECMG just indicates the times between which that change is due to first occur.

On top of this, overlay your tempos for their stated time periods. So in answer to your question "when this (BECMG) time period has elapsed, do I then revert back to the main body of the TAF?" No, a BECMG doesn't revert back. It indicates an overall change moving forwards (this could be solely a change in wind, viz, cloudbase etc or a combination), BUT in this case there are still TEMPOS (PROB40 TEMPO 2406/2418 & PROB40 TEMPO 2418/2506) that are forecast to happen during the period of the nicer weather, and which cannot be ignored. These are the traps Cylinder Head alludes to.

[Arm out the window]

I'd prefer to see it written with the full lot of base weather first (eg the initial conditions and the BECMG), followed by the TEMPOs.

This would allow an overview of the base weather for the full period first and then, as you said SARWannabe, the predicted fluctuations in those with the TEMPOs. Seems a clearer way to do it.

[Melvyn82]

Thank you for the replies!!
Much appreciated.

Makes more sense now :ok: