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#1799113
Probably a very stupid question, but can someone help me:

TAF: EGKA 290801Z 2909/2918 26008KT 6000 FEW006 BKN010 PROB30 TEMPO 2909/2910 4000 BR BKN006 BECMG 2910/2913 9999 SCT020

Today's forecast from Shoreham, on what is a fairly murky start to the day. The forecast looks like it's clearing up a bit later, but the question I've got is: is 'becoming' also a 'tempo' state, or is it a 'permanent' condition after which the weather remains the same?

Better phrased as:

The forecast suggest the day starts Carp, but between 10 and 1pm it gets better - 10k vis and scattered at 2k feet.

After 1pm, does 'becoming' persist (e.g. it's going to say that way for the rest of the day), or does the time period for 'becoming' imply that it reverts back to the general forecast, e.g:

The forecast suggests that day IS Carp between 9am and 6pm, but it gets better between 10 and 1pm before reverting back to Carp between 1pm and 6pm.

If the weather remains decent after 1pm, why does the TAF cover the period up to 18:00 - why not cap the taf at 1pm?

Sorry if this is a really stupid, basic question...
#1799116
'Becoming' means it stays like that after the 'becoming' period, so in this case it should be 10k vis (or better) and scattered cloud at 2000'. The wind should still be 260/08 kts as there is no forecast change to it.

This is a standard 9 hour 'short' TAF, so it covers a wider period than just what happens once something has 'become'. You can expect the 'become' conditions to remain until the end TAF period, assuming it doesn't say otherwise.
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By JAFO
#1799137
flyingearly wrote:Of course, I then speak too soon:

EGKA 290908Z 2909/2918 29008KT 9999 SCT012 PROB30 TEMPO 2909/2912 7000 -RADZ BKN007


Not suggesting that you should push into weather that you may be unqualified and/or unprepared for but do bear in mind that if that's going to happen TEMPO then most of the time it's not going to happen and if it's PROB30 that it will happen temporarily then it's PROB70 that it won't happen at all.

Of course, when you start seeing things like that, it needs a lot more consideration than when the weather is clearly better. There is also the old adage that when there is doubt, there is no doubt and it's always better to be down here wishing you were up there rather than up there wishing you were down here.
#1799139
I'm using the Mk 1 eyeballs at the moment and it looks a bit miserable out there, but I'll still head to the airfield as even if not good enough for a trip further afield, I'll hopefully still be able to get up and do a few circuits to keep fresh.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1799151
Blue skies and sunshine here in Wales.

"BECMG 2910/2913 9999 SCT020"

Forecasting when fog will "burn off" is a very inexact science, so they make a guess at some time between 11am and 2pm (local time). In fact, it may never "burn off" and they'll usually update that later. I don't know if there are any new formulae for calculating when fog will disappear (rather than lift) but the old ones they used were wrong, and they knew they were wrong but didn't have anything better to go on.
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By skydriller
FLYER Club Member  FLYER Club Member
#1804809
Paul_Sengupta wrote:Forecasting when fog will "burn off" is a very inexact science, so they make a guess at some time between 11am and 2pm (local time). In fact, it may never "burn off" and they'll usually update that later. I don't know if there are any new formulae for calculating when fog will disappear (rather than lift) but the old ones they used were wrong, and they knew they were wrong but didn't have anything better to go on.


This type of fog is invariably local and will either burn off or "lift" very much dependant upon where you are and local knowledge is invaluable. Where I am on a peninsular between river and sea, the weather can be superblue and zero viz fog 1km apart - the same can happen wrt low cloud too, but with the locations reversed at other times of the year.

Oddly alot of "new" airports are built where there is always lingering fog - Munich Airport is a prime example of this - You fly around their hold in bright sunshine looking down on a small patch of fog in a gorgeous landscape - that patch is where the airport is...

Regards, SD..
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By Human Factor
FLYER Club Member  FLYER Club Member
#1805464
... if that's going to happen TEMPO then most of the time it's not going to happen and if it's PROB30 that it will happen temporarily then it's PROB70 that it won't happen at all.


Hopefully.

It’s PROB30 that it will happen where they say it’s going to happen. It may be more than PROB30 when you’re away from that place. It could even be PROB100. :shock:

Caveat emptor. :wink:
#1805559
flyingearly wrote:Probably a very stupid question, but can someone help me:......<snip>..........

Sorry if this is a really stupid, basic question...


There are no stupid questions in aviation, because the consequences of not learning can be serious! No one can know everything, so asking is a "good thing".

Ask away and learn away, please :thumleft: