TAF Question??
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TAF Question??
Gen 3.5 - 31
Temperature
-------------
"Up to four forecasts are given for the times HH, HH + 3, HH + 6, HH + 9 where HH is the time of commencement of TAF validity period........these times are valid for in the case of the first value, ninety minutes after time point HH.
Subsequent values, ninety minutes each side of the time point."
OK so I have this temp forecast from a TAF:
062008
.......
.......
.........
T16, T18, T20, T22
To break it down:
HH (2000) = 2000 - 2130 -> 16 degrees
HH + 3 (2300) = 2130 - 0030 -> 18 degrees
HH + 6 (0200) = 0030 - 0330 -> 20 degrees
HH + 9 (0500) = 0330 - 0630 -> 22 degrees
??What about after 0630? - do we still use 22 degrees?? or do we have to get a new TAF?? - I'm confused?!!?
Thanks guys and gals......
Temperature
-------------
"Up to four forecasts are given for the times HH, HH + 3, HH + 6, HH + 9 where HH is the time of commencement of TAF validity period........these times are valid for in the case of the first value, ninety minutes after time point HH.
Subsequent values, ninety minutes each side of the time point."
OK so I have this temp forecast from a TAF:
062008
.......
.......
.........
T16, T18, T20, T22
To break it down:
HH (2000) = 2000 - 2130 -> 16 degrees
HH + 3 (2300) = 2130 - 0030 -> 18 degrees
HH + 6 (0200) = 0030 - 0330 -> 20 degrees
HH + 9 (0500) = 0330 - 0630 -> 22 degrees
??What about after 0630? - do we still use 22 degrees?? or do we have to get a new TAF?? - I'm confused?!!?
Thanks guys and gals......
Nunc est bibendum
Why do you care? What are you using the forecast temp for?
The only thing I use them for is to tell the punters what the forecast max is for the day and to work out how quickly I'm going to need to walk from the terminal to the car park at MEL to avoid freezing.
(Sorry Sunfish, Buster et al but it's a cold miserable place most of the time. When it's not it's often hot and miserable).
The only thing I use them for is to tell the punters what the forecast max is for the day and to work out how quickly I'm going to need to walk from the terminal to the car park at MEL to avoid freezing.
(Sorry Sunfish, Buster et al but it's a cold miserable place most of the time. When it's not it's often hot and miserable).
What are you using the forecast temp for
2. Estimate the potential cloud base.
3. Estimate runway performance and climb gradients.
4. Estimate local freezing level.
1. Estimate time of onset of fog.
2. Estimate the potential cloud base.
2. Estimate the potential cloud base.
The TAF doesn't provide a dewpoint. Therefore, those temperatures would be totally useless for calculating the onset of fog or the cloud base.
Creampuff,
METARs and AWIS are reports at a historical point in time therefore they dont have a period of validity as such.
TAFs and TTFs are forecast conditions over a period of time.
A historical report is not much use if your ETA or ETD is say in 6 hours.
Edit to say if conditions are conducive to fog then its a safe bet that the dew point is not going to change much, where as the viz due to fog can change rapidly.
METARs and AWIS are reports at a historical point in time therefore they dont have a period of validity as such.
TAFs and TTFs are forecast conditions over a period of time.
A historical report is not much use if your ETA or ETD is say in 6 hours.
Edit to say if conditions are conducive to fog then its a safe bet that the dew point is not going to change much, where as the viz due to fog can change rapidly.
Last edited by desmotronic; 9th Jul 2008 at 02:56.
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Holy crap guys ....
You're telling me that despite the fact that you should obtain a forecast update no more than 60 mins prior to departure, the 9hrs 30mins worth of coverage for temp and QNH is not going to be good enough for you? If you're that long haul you probably won't be asking these questions.
I admire your commitment to accuracy and in-depth analysis of everything you can glean from a TAF, but the guys who produce TAFs are probably going to be using much better information than is published to you, and if fog is an issue - you'll see PROBs starting to appear.
You're telling me that despite the fact that you should obtain a forecast update no more than 60 mins prior to departure, the 9hrs 30mins worth of coverage for temp and QNH is not going to be good enough for you? If you're that long haul you probably won't be asking these questions.
I admire your commitment to accuracy and in-depth analysis of everything you can glean from a TAF, but the guys who produce TAFs are probably going to be using much better information than is published to you, and if fog is an issue - you'll see PROBs starting to appear.
yup usually i get prob 40 covering a 12 hour period. which is fine and dandy for conservative alternate purposes but it is handy to actually arrive at the intended destination.
Nunc est bibendum
Desmo, when someone shines the light on you it's generally considered wise to stop digging the hole you've found yourself in.
My question still stands. Why does anyone care what the forecast temp is in 9 1/2 hours time? What use is it that 10 hours before. If the performance is that marginal that the temperature is going to make a significant difference from a previously identified trend on the TAF then conservatism is the key and you'd update your weather close to the time.
Cloud base? Fog? Freezing level? Seriously?
.
My question still stands. Why does anyone care what the forecast temp is in 9 1/2 hours time? What use is it that 10 hours before. If the performance is that marginal that the temperature is going to make a significant difference from a previously identified trend on the TAF then conservatism is the key and you'd update your weather close to the time.
Cloud base? Fog? Freezing level? Seriously?
.
I don't think any one cares in reality.
Maybe the guy asking the initial question was studying for an exam and simply wanted to know.
I hope so.
As for fog and cloud base, hhhhhhmmmmmmmmmm. I think not.
Maybe the guy asking the initial question was studying for an exam and simply wanted to know.
I hope so.
As for fog and cloud base, hhhhhhmmmmmmmmmm. I think not.
ok keg here is a scenario for you:the time is 1145UTC.
The 1022 Taf says amongst other things
FM 11 prob 40 fog 500m temps 10 8 6 5
The 1130 metar and current AWIS say viz 8000m temp 9 dew point 9
You want to depart a runway with runway edge lighting spaced 75m:
1. What are your chances at 1300?
2. What are your chances at 1200?
I'll give you a hint captain, neither answer is 40%.
The 1022 Taf says amongst other things
FM 11 prob 40 fog 500m temps 10 8 6 5
The 1130 metar and current AWIS say viz 8000m temp 9 dew point 9
You want to depart a runway with runway edge lighting spaced 75m:
1. What are your chances at 1300?
2. What are your chances at 1200?
I'll give you a hint captain, neither answer is 40%.
8Km vis, you could even depart VFR in that, .
I've seen the dewpoint and temperature the same plenty of times, and yet fog doesn't always form.
How do you know the dew point is still going to be the same at 1300?
In answer to your questions; 1. Likely, 2. Highly likely
morno
.I've seen the dewpoint and temperature the same plenty of times, and yet fog doesn't always form.
How do you know the dew point is still going to be the same at 1300?
In answer to your questions; 1. Likely, 2. Highly likely
morno
Nunc est bibendum
Ok, so to make sure we're very clear about this. The question that you are asking is completely unrelated to the one that was asked by Mamakim at the very beginning. Just to re-hash though:
As to your different and new question Des regarding departure in a little while as opposed to a departure in a bunch of hours time, I'll get back to that when I get home from a session in the lurching cave.
What about after 0630? - do we still use 22 degrees?? or do we have to get a new TAF?? - I'm confused?!!?