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TAF EBOS - Why this order

Hello, I was puzzled by yesterday’s EBOS TAF:

TAF EBOS 010507Z 0106/0212 28002KT 0800 BCFG FEW025 BECMG 0106/0108 9999 NSW BECMG 0113/0115 36010KT

As I read it the TAF foresees patches of fog all morning (from 6z to 12z) but it will improve between 8z and 10z.
Why not do the contrary ? NSW all day with risks of fog in the morning ?
Or maybe I am missing something… Thanks in advance for your insight.

jfw
Belgium: EBGB (Grimbergen, Brussels) - EBAW (Antwerp) - EBNM (Namur), Belgium

Do mean that fog banks imply temporary fog so that the TAF should read TAF EBOS 010507Z 0106/0212 28002KT CAVOK TEMPO 0106/0108 0800 FG FEW025 BECMG 0113/0115 36010KT?

The difference is that the FEW025 are not temporary and also TEMPO weather must be at most half the time and not more than 30 minutes at a time. There’s no guarantee for that with fog banks. Also, with fog banks it is unlikely that the entire airport is free of fog at any one time which would be a requirement for NSW.

Last Edited by Airborne_Again at 04 May 09:03
ESKC (Uppsala/Sundbro), Sweden

I’d also argue, that the original TAF is a better representation of the actual weather: It is already foggy at the beginning of the TAF and the fog will go away at some point in time.

0106/0212 FEW025 TEMPO 0106/0108 BCFG would more read like “it is not foggy at the beginning but there will be patches of fog moving through”.

Germany

Let’s analyze this.

TAF EBOS is issued day 1 of a month on 0507Z. It is valid from day 1, 0600Z until day 2, 1200Z, so 30 hours of validity.

It starts with the conditions: Wind 280° 02kts, visibility 800 meters, fog patches, few in 2500.

Conditions are changing all over between 0600Z and 0800Z of day 1. Visibility will become 10km or more, with no significant weather expected.

Conditions are expected to change [all over, not only temporarily] again between 1300Z and 1500Z of day 1, where wind will be 360°10kts.

So to the question: Patches of fog are forecast on the morning of day 1, and will perish between 0600Z and 0800Z of day 1.

Last Edited by UdoR at 04 May 09:22
Germany

Malibuflyer wrote:

would more read like “it is not foggy at the beginning but there will be patches of fog moving through

As we do not have the METAR, but only the TAF, we do not know whether actually there are patches of fog already present upon issuance of the TAF. So I assume, that the fog was already present and due to this made its way into the TAF. But this is speculation.

Germany

@jwf

adding to what UdoR wrote:

As I read it the TAF foresees patches of fog all morning (from 6z to 12z)

Your seem to interpret it as
TAF EBOS 010507Z
[From] 0106 [To] 0212 28002KT 0800 BCFG FEW025
BECMG 0106/0108 9999 NSW
BECMG 0113/0115 36010KT

which is not what it means.

This TAF is read
TAF EBOS 010507Z [Valid From] 0106 [To] 0212
[Initially] 28002KT 0800 BCFG FEW025
BECMG 0106/0108 9999 NSW
BECMG 0113/0115 36010KT

Last Edited by Cobalt at 04 May 14:14
Biggin Hill

@Cobalt has got it right.

A TAF always starts with the initial condition expected and develops from there. In this case, the forecaster expects the fog to be gone earliest at 6z and latest by 8z.

LSZH, Switzerland
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