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I was asked what is the worst visibility forcast for 1800 UTC. The answer I was given is 10km. I thought FM refers to a quick (in less than 60 min) change in weather occurring at hh hours and mm minutes. If this is the case, wouldn't the change starts to take place anytime from 1800 and visibility at the very worst be at 3000m still?
Dont spread your own confusion onto the lad Jamie23
sorry mate but i don't agree & neither do any of the other instructors at the flight school, I seriously think you are misunderstanding what a TAF & METAR are.
I agree that in the trend section of a METAR the term from will indicate a change that may occur from a specific time however my understanding of the term FM in a TAF indicates a change from that time hence as the clock strikes 1800 the worst case scenario will be 3000m vis.
The notes I have says in a TAF, FM is used to show the beginning of a self-contained part in the forecast. All conditions before this group are superseded. So I took it as the weather will change to replace the previous weather complete from this 1800 so the worst case is 3000m visi at 1800. If the weather will change before 1800 (to give 9999) at 1800, I'm sure they would stated BCMG 1719 or something like this?
So from 8pm to 9pm you went and asked all your instructors? Sure you did. I think they'd be embarrassed to see you claim their opinion supports yours. Which magical FTO are you at that believes this?
seriously i'm not going to get petty but I start work at 8am in my FTO, I asked 4 instructors that have more experience than I do (two of which are PPL examinars) what their understanding of FM meant to check that what I believed was correct & all aggreed with my comments. I also got one of them to check in a met textbook for a definitive answer which was;
"The FM indication in a TAF denotes a change in the forecast conditions begining to occur after the time designator"
baring in mind that one of the four instructors I checked with has been teaching groundschool for over 20 years & another has a degree in Met as well as the fact that the PPL textbook states the same as what I thought to be true I think this is conclusive.
& for the record, if the TAF had stated AT 1800 then I would have agreed that the vis would have been 10km+ however FM & AT are two very different things.
Surprising how hard it is to find definitive answers on this, but the DK met office has a (seemingly authoritative, as from WMO) scanned copy of the METAR AND TAF codes here: http://www.dmi.dk/dmi/koder.pdf
Page 2: FM: "...all forecast conditions before this group are superseeded by conditions indicated after this group."
OK, Just a quick question on the TAF? After the FM 18 what is the 25025? Is it just the fact there should be KT after it to indicate the wind? Also, I would have though the FM 18 would be written as FM1800?
I take it this is a TAF for an exam, not a real life one?
Inbetween evening posts you claimed that all your instructors had agreed with you. You are lying to create support for yourself, further confusing the original poster. It is unethical. Please name your FTO if you are so convinced. Nothing to be worried about surely?
Once again you quote a textbook answer, but somehow ignore the meaning of the words.
If you are going to be blindly stubborn in the face of all logic, definition, and explanation then that's your problem. I realise you want to save face, but if the question comes up, Dream747 tick 10k. That's all I worry about.
Shouldn't be answering peoples questions so confidently when you dont know yourself.
Maybe this will help clear things up:
BCMG is used in a TAF for the gradual change you are talking about. FM is used in a TAF for an immediate change.
ICAO terminology. How can you argue with that?
For anyone else reading, please use ICAO instead of jamies mystery PPL examiner.
Have to say I totally agree with cc2180 on this one. I'd tick the 10k answer if in an exam. FM 18:- 9999.
What would I know, it's nearly always less than 10k over the North Sea.
Not entirely sure you would have a good case, in the event of getting it wrong, that you could argue the TAF was incorrectly written and not what you would expect to find in everyday use, with the missing letters here and there. Correct terminology.????