What BOM TAF's don't tell you.

[Blip]

Hello fellow ppruners.

I would like to raise the issue of aviation weather forecasts and what they DON'T tell you.

Here are today's forecast for Brisbane and surrounding areas issued by the Australian Bureau of Meteorology. I have copied both the Aviation forecasts and also those forecasts issued to the general public.



TAF AMD YBBN 072227Z 0024 02014KT 9999 FEW035
FM11 17012KT 9999 -SHRA SCT020 BKN040
INTER 1024 3000 SHRA BKN010
RMK
T 29 30 29 26 Q 1008 1006 1005 1007


TAF AMD YBCG 072228Z 0018 01014KT 9999 SCT035
FM08 17015KT 9999 -SHRA SCT020 BKN040
INTER 0718 3000 SHRA BKN010
RMK
T 29 29 28 26 Q 1007 1005 1005 1006


TAF YBMC 072231Z 0012 02013KT 9999 FEW030
RMK
T 29 30 30 27 Q 1008 1006 1005 1006


Brisbane Forecast
Issued at 11:10 am EST on Monday 8 January 2007

Warning Summary
Nil.

Forecast for Monday
Chance of a shower or thunderstorm late afternoon or evening. A few showers
overnight. Moderate NW to NE winds.

Precis: Late storm
City: Max 32
Bayside: Max 30
UV Index: 12 [Extreme]


Gold Coast
Forecast for Monday
Chance of a thunderstorm late afternoon or evening, followed by showers
overnight. Moderate to fresh NW to NE winds changing fresh southerly tonight.

Precis: Late storm. Max 29
UV Index: 12 [Extreme]


Sunshine Coast
Forecast for Monday
Mostly fine. Chance of a thunderstorm tonight. Moderate to fresh NW to NE winds.

Precis: Late storm. Max 30
UV Index: 12 [Extreme]



I've just read the Australian AIP and it says:

When reduced visibility due to fog, mist, dust, smoke or sand is
forecast, but the probability is assessed at between 30% and 40%,
the terms PROB30 or PROB40 are used. The term may also be
added before a TEMPO or INTER statement to express probability
assessments of thunderstorms. If greater than, or equal to, 50%
probability is forecast, reference is made to the phenomena in the
forecast itself and not by the addition of the statements PROB30 or
PROB40.

So if there is only a 5%, 10%, 20%, or 25% chance of there being thunderstorms, the powers that be deem that information superfluous when it comes to aviation. Does anyone else think this is rather odd? As important as this information is to someone wanting to put the washing out to dry, or a family organising a day at the beach, surely it is even more important to a pilot operating an aircraft, especially one flying IFR with no radar!

Perhaps the requirements for holding fuel could be such that if there is less than a 30% chance of thunderstorms (eg PROB10 TEMPO TS) that holding fuel is discretionary, but please do not filter this information out of the TAF. Allow the pilot to make their own assessment!

[gliderboy]

Mate

A TAF is a valid forecast for 5nm ONLY around an aerodrome.

Your general weather forecast for Brisbane (you showed later) is a general non aviation forecast for the greater Brisbane area. ie a lot bigger area than the 5nm around the airport.

So if the Met forecasters don't think the storm will get within 5nm, the TAF won't even mention it.

So in theory there could be stationary TS all around the airfield and in theory the TAF does not have to mention it.

That is why an AREA forecast goes hand in hand with a TAF, so you can get the big picture. A SIGWX chart completes the forecast.

Gliderboy

[SM4 Pirate]

Also TAFs get amended; usually a daily generic city forecast is good enough for the whole day.

If the prob of a TS within the 'TAF area' goes up then it would get mentioned in the amended TAF or next TAF, would it not?

[illusion]

What we do not want is for the forecasters to put on 30/60 holding due TS to cover themselves when it is highly unlikely, but possible that it may occur. This can have a big impact on payloads for contract flying.

A forecast is a best guess of what nature will bring. Sometimes on a clean forecast it may be prudent to put on some for Mum and the kids. For example if the temp/dew point is getting a bit close then alternate fuel may be advisable. Forecasts are not ironclad. Perth would average 3-5 days per year when fog unforecast or formimg a number of hours earlier than forecast occurs. When it does you can tell by the pitch of da' voice on the radio who has not picked it!

[Howard Hughes]

Chance of a shower or thunderstorm late afternoon or evening.
This could be the forecast for Brisbane almost everyday through summer!!:ok:

[king oath]

Aviation is an art not a science. Nobody writes it all down on paper for you to follow, chapter and verse. If you need that ,you should have become a lawyer.

You use common sense, animal cunning and past experience along with the forecast to work out what might happen. With weather the word "might" is the operative word. Then you err on the side of caution.

It makes things a lot less stressful.

[BrazDriver]

Ever seen the Perth TAF during the winter?
If there is even the slightest chance of fog it gets a prob 30.
A fair few have been caught out previously so I think it does boil down to risk management!

[BrazDriver]

I went on a tour of the BoM in PH some time years ago, and one of the guys there was mentioning they were working on improving the accuracy of their fog forcasting due to a few serious unexpected fog incidents.
Further in the conversation he mentioned that whenever there is a chance of fog it will be in the TAF.
Just a Perth SOP i take it.

There was a thread a few months back regarding unexpected fog at Perth.


I must add the lower level area briefing is a great product compared to other countries.

[layman]

Apologies for the thread divergence but … how readable are BoM aviation forecasts? I assume trainee pilots may take a bit of time to become familiar with them, but is the arcane terminology something that can cause an occasional misunderstanding among experienced pilots?
I’m not a pilot (RAAF pilot son and commercial pilot brother) but have read a few forecasts over the phone to them.
I 'teach' usability and use these forecasts as examples of how the initiated can understand something but the uninitiated just see ‘gibberish’.
just interested
thanks
layman

[ITCZ]

I think you have answered your own question, Layman.

A private pilot license holder is "initiated." They do a course on meteorology which not only includes an understanding of weather (such as one might gain in high school geography), but also its impact on aircraft operations, and weather services available. That is, how why and where forecasts are produced, how to read them, what they do and don't tell you.

Last time I looked there were exams on met at PPL, CPL and ATPL level. Don't get to exercise the privileges of those licenses if you don't pass those exams!

Take the basic met, read the AIP section on Met, apply experience.... those arcane forecasts tell you a lot. The better you know your met and AIP, the more they tell you.

I've done the study and read the books. I don't think its broke, so please... no fixing it!!

Tip - do yourself a favour and ring the officer in charge of your local BoM office. Tell them you are a pilot and would like to come and meet an aviation forecaster. You will be welcomed with open arms. They are a very professional group of people and you will be most likely impressed with their interest in aviation and the questions they will have for you. We still get the same quality of met info they gave in the old days of face to face briefings. The thing you don't get anymore is the 'feel' for the men and women that put them together. Do yourself a favour. Get on in there!

[megle2]

This forecast variation is quite common in Brisbane. All day today there has been mention of a chance of a late storm by the radio jocks.
No mention on our forecasts.

I see it more as a " cover " for the met guys so if by remote chance a storm does come the public can't winge about not being warned.

[BrazDriver]

I agree with ITCZ, Ring up the BoM. They are a fantastic bunch of people and more than happy to help!

On the ARFOR product if you are unsure of anything, ring the aviation desk number. Most times you actually speak to the bloke who put the forcast together. He can go into any depth you want and will be a wealth of knowledge. I have learnt many things from ringing them up!!

:ok: ITS A FANTASTIC SERVICE!! :ok:

They just get annoyed when people ring up and say ''whats the weather?":ugh:

If you ring up and say ''I have the area xx ARFOR, I have a question about xx" they will bend over backwards! :D

As for the media, many get their weather from 3rd party sources and are not as accurate.

I know here in Perth the ch10 weatherman will go to the BoM and sit and chat to them whats going on. Good Stuff :ok:

Channel 9 on the other hand cannot even draw a synoptic properly. They draw a trough as a cold front! According to them theres been a cold front over the N.T for the last few days thats moving east to west!! :ugh:

[The Voice]

theres been a cold front over the N.T for the last few days thats moving east to west really? I wish! :p

[Desert Duck]

A little off the thread but many years ago ( when Flight Service was operating )the Met man in Alice Springs had a sign on his desk -

Bureau of Meteorology - this is a non prophet organization

[Bleve]

You might be interested to know that QF has so much faith in the official BOM forecasts that they have hired their own met guys/gals to make their own assessment of the weather and if the BOM forecasts are deemed inadequate QF will issue additional 'OPRISK' requirements to its crews.

The situation in BNE could well result in QF issuing an OPRISK requirement to carry Tempo holding fuel due to 'unforecast TS'.

[layman]

ITCZ, BrazDriver
thanks for the responses / hints - I'll give BoM a ring
regards
layman

[Blip]

A little off the thread but many years ago ( when Flight Service was operating )the Met man in Alice Springs had a sign on his desk -
Bureau of Meteorology - this is a non prophet organization

That's quite funny. Thanks for that. :)

Glider boy. Yes I know TAF's only cover 5 nm radius around an aerodrome. You said: So if the Met forecasters don't think the storm will get within 5nm, the TAF won't even mention it.

So in theory there could be stationary TS all around the airfield and in theory the TAF does not have to mention it.

Do you really believe a meteorologist has the ability to make that call? Remember we are talking about a FORECAST with a validity period of 6,12, or 24 hour period not a weather REPORT.

And don't you remember them teaching you during your pilot licence theory about thunderstorms and the three things that are required to make them happen. Humidity, Unstable/Conditionally Stable atmosphere, and a trigger that initially pushes up the parcel of air that gets the process started. In this case the trigger was a low level trough. This trough covered a wide area across the state, let alone the Brisbane metropolitan area! A nascent storm could appear anywhere within the trough and then travel a significant distance during its life span of several hours.

With these facts in mind, your statement: So in theory there could be stationary TS all around the airfield and in theory the TAF does not have to mention it. although being made to illustrate your point about the 5 nm radius, is rather silly don't you think?

SM4 Pirate said: Also TAFs get amended; usually a daily generic city forecast is good enough for the whole day.

If the prob of a TS within the 'TAF area' goes up then it would get mentioned in the amended TAF or next TAF, would it not?

Sure it would but you are missing the point for a couple of reasons.

1. What if the chances don't increase? What if they remain at 20%? That is a very significant probability. One in five. Even 10% or one in ten is significant!

2. So an increase of only 10% from PROB20 to PROB30 will cause a requirement for TS to suddenly appear on an amended TAF with all the associated operational implications. What about a flight that has already departed and is mid-flight either from a domestic port or from overseas? Surely it would be better for them to have known that there was always a risk of there being a thunderstorm during the given period so that they could have allowed for it if they wanted to.

illusion said: What we do not want is for the forecasters to put on 30/60 holding due TS to cover themselves when it is highly unlikely, but possible that it may occur. This can have a big impact on payloads for contract flying.

Pass-A-Frozo said: I asked a met man about this some 8 years or so ago and he was of the belief the <30% omission was made due to the cost of holding fuel. Risk vs. Return type arrangement.

BrazDriver said:Ever seen the Perth TAF during the winter?
If there is even the slightest chance of fog it gets a prob 30.
A fair few have been caught out previously so I think it does boil down to risk management!

Pass-A-Frozo then said: Funny you mention that. The other thing the met man said was that because of the 30% rule, some met guys wanted to cover their arse and just up a 5% prob to PROB30.

I made the point in my original post that there is no reason why the mention of TS or FOG or anything else for that matter that has a probability of less than 30% should automatically mean that there is a requirement for holding/diversion fuel! Would you please read my post again. If the Bureau of Meteorology determines that there is a 20% chance of thunderstorms, well then there is a 20% chance of thunderstorms regardless of whether or not that is included in the TAF!! There is absolutely no reason why a 20% percent chance of thunderstorms if mentioned on the TAF should automatically require holding/diversion fuel be carried.

Meteorologists should not be forced to make decisions on whether or not there should be a requirement for holding/diversion fuel at an aerodrome. They should simply be telling it how it is. If there is a 20% chance of thunderstorms in Brisbane, or a 10% chance of fog in Perth, well then let them state that in the TAF. It is then up to the aviation industry to determine what the fuel requirements are. If there is less than a 30% chance of some meteorological phenomenon happening, well then the regulations could be written such that the information can be considered as advisory only and that holding/diversion fuel is optional.

It is completely unfair to blame a meteorologist for there being mass diversions and forced autolands below landing minimas at a destination such as Perth because there was only a 5% or 10% chance of there being fog that doesn't rate a mention on the TAF simply because that is the way things are done! Why should a meteorologist be forced to say there is a 30% chance of fog when there is really is only a 5% chance, simply because they don't want there to be no mention of a chance of fog on the TAF and cop the abuse when the fog does roll in that one time in twenty.

Can no-one see the point I am making??

gliderboy said:That is why an AREA forecast goes hand in hand with a TAF, so you can get the big picture. A SIGWX chart completes the forecast.

You will find that overseas carriers and the major domestic ones do not include ARFOR's in the pilot briefing, and the pilots certainly do not have the time and rarely the facilities to seek them themselves.

Bleve said: You might be interested to know that QF has so much faith in the official BOM forecasts that they have hired their own met guys/gals to make their own assessment of the weather and if the BOM forecasts are deemed inadequate QF will issue additional 'OPRISK' requirements to its crews.

The situation in BNE could well result in QF issuing an OPRISK requirement to carry Tempo holding fuel due to 'unforecast TS'.

That is not quite true. My understanding is that they are actually BoM employees seconded to Qantas and imbedded within flight dispatch (the sections that produce the flight plans) and operations control (the section that keeps the world wide operation together).

These OPRISKs you mention can often be the result of these 5%, 10%, 20% PROB's that never get a mention on any TAF. They're not "unforcast TS" but rather "unmentionable TS"!

[illusion]

It can work the other way as well. If you have a long flight that won't allow you to carry the 30/60 holding due TS, a phonecall to met asking them nicely to review the TAF prior to an unwanted fuel stop works wonders. ATC call up with an amended TAF and the calculator is replaced with the newspaper!

[Bleve]

Blip yes I think you are correct. However from previous experience the BoM (being a government dept) would have insisted that QF pay for their wages. So the fundamental point remains that QF don't trust the 'vanilla' head office TAFs/TTFs and paying for on site BoM personnel is deemed a sound investment.

[SM4 Pirate]

What if the chances don't increase? then there will be no TS... The point of an amended TAF is to show the changes; there are various requirements (usually alternate management and extra fuel) that puting TS probs on TAFs in terms of complience. If you willy nilly post every % say 10 and above on a TAF then for the 8 times a year a TS hits an aerodrome, it's forecast 250 times...

2. So an increase of only 10% from PROB20 to PROB30 will cause a requirement for TS to suddenly appear on an amended TAF with all the associated operational implications. What about a flight that has already departed and is mid-flight either from a domestic port or from overseas? Surely it would be better for them to have known that there was always a risk of there being a thunderstorm during the given period so that they could have allowed for it if they wanted to. It's called hazard alerting, if you are within 1 hours flight time as an IFR you gt tld about the amended conditions, if VFR it will be braodcasy on area freq's; and flightwatch have all the info available at the click of a mouse; call them.

Are you suggesting a flight departing WSSS will have the latest on BN on departure and take that as the only time the WX is checked?

We (ATC) assume your wx brief was accurate 1 hour before ATD; after that we are considering the ramifications of change on your operations. Airlines have various operations people assessing these things for their pilots.

If you are on your own, single pilot etc., call flightwatch within a hour of dest and get an update; all sig changes (hazardous) there after will be braodcast on the area freq, or directed to you if you are IFR.

It's not perfect, agreed, but at least it isn't "chick'n little" stuff either.

[gliderboy]

Blip
I live and work overseas mate so I don't need the lecture about what you do and don't get weather wise when overseas.
In Hong Kong it is COMMON and a daily event in Summer that TS are all around the Hong Kong Airport and it is NOT mentioned in the TAF. So my "silly" point is not so silly after all.
Your point was related to Brissy (where I was raised) so that's why I mentioned the ARFOR. You CAN get them in Australia last time I checked.
Gliderboy
ps At the end of the day use all available aids; common sense, experience and local knowledge (if available). Oh and those things on the wings are fuel tanks not airtanks;)
pps mate you like the quote button don't you:8

[BrazDriver]

Sorry to diverge the thread again.
One thing on the ARFOR over here in the west (not too sure bout you guys over the other side) that they have started doing that is annoying is replacing place names with thir designator.

This has been going on for roughly 6 months, I feel it is a loss of situational awareness and they always seem to pick places with a funny designator that you have no idea where it is! My PCA is getting a seriously abnormal workout!

The funny thing is other fields on the forcast, like Turbulence and to some extent the cloud it is being written out longhand.

Nil Sig now is Nil Significant
CUF now is Cumloform cloud etc.

At least with the places put the name like '' showers west of Perth(YPPH) after 06z'' for example

[Dick N. Cider]

The cover your @rse component does apply in some instances. Met has been known to advertise possible severe hail on the general forecast after several million dollars worth car damage that wasn't forecast.

Met doesn't ever put 30 or 60 minutes holding fuel on. They just forecast the conditions. Since the demise of OPS in the CAA days the only person responsible for fuel is the pilot in command. As for TAFs, they are regulary amended and to assume that they'll only be amended on the 6 hourly schedule is ridiculous. We deal with amended TAFs all day every day. Major locations also receive a TTF service updated half hourly valid for 3 hours.

Obviously people will get caught out but then as already advertised there's a fair bit of PROBability involved.

[CFPlnr]

..................................................

[Capt Basil Brush]

CFPlnr,

Yes I always read the Airport Weather Briefs, they are very good reading.

Some good tips. :ok:

[GearOff]

Are these airport weather briefs available to non-airline users? Looks like good info

[Blip]

I'm sorry SM4 Pirate but with respect, some of the things you said really don't make sense at all and indicate that you continue to miss the points I am making.

Firstly you said: What if the chances don't increase?
then there will be no TS...
So you consider a 20% chance of something happening as really a zero chance do you?:confused:

If you willy nilly post every % say 10 and above on a TAF then for the 8 times a year a TS hits an aerodrome, it's forecast 250 times...

I'm sure the meteorologists don't consider their probability estimates to be made "willy nilly".:rolleyes: I don't care how many times a PROB10, PROB20, PROB30, or PROB40 appears on a TAF. And why should anyone else care? If it is the honest estimate of the meteorologist, so be it.

It's called hazard alerting, if you are within 1 hours flight time as an IFR you gt tld about the amended conditions, if VFR it will be braodcasy on area freq's; and flightwatch have all the info available at the click of a mouse; call them.

Are you suggesting a flight departing WSSS will have the latest on BN on departure and take that as the only time the WX is checked?

No. Of course not. You are missing the point again. I am not suggesting that the flight crew will not receive weather updates along the way. Of course they will. But once they depart, they are stuck with the fuel they have in the tanks. For a commercial operation such as a major airline, there is often the commercial pressure to carry the least amount of fuel, especially if that fuel will offload revenue freight or pax.

Now if the crew at flight planning see 10PROB INTER TS, they can at least determine weather or not they will carry 30 mins holding fuel or not. They may decide to negotiate with the weight and balance people as to what can be left behind for the next flight (that does not have to deal with the PROB10 INTER TS or simply has a better load capacity such as a B767 vs B737) and what must be carried on that particular flight. The INFORMED decision can be made as to the cost of carrying holding fuel or diversion fuel verses not carrying the fuel and risking a PROB10, or PROB20.

If a PROB10 or PROB20 is increased in an TAF AMD to PROB30, PROB40, or PROB 50 (which is simply included in the TAF without the "PROB50") then that would come as no surprise to anyone. Those that are forced to divert due insufficient fuel would have taken the INFORMED risk of not carrying the fuel and lost. But if the PROB10 or PROB20 is not included, well then it does come down to "experience" or more likely luck.

CFPlnr's post includes exactly the kind of information I am talking about.
10% chance of thunderstorm activity within 5nm of the airport 14/22Z.

I honestly don't understand why anyone would argue against including this information in a TAF.:ugh:

Gliderboy also said: pps mate you like the quote button don't you
Just trying to keep the conversation legible. :ok:

[SM4 Pirate]

Blip, I don't want to get into a raging debate; a 20% chance is a 20% chance, not 100%... If it remains a 20% chance then it will not happen (it's reviewed constantly)... The forecast in a TAF is a living event; if the chance goes up; ie it becomes more likely that a storm will actually hit within the 5NM of the aerodrome reference point then the chance goes up and the TAF is amended to include the prob/inter period; mentioning a PROB 30% has the same effect as saying 100% possibility; but a 20% chance has the same effect as saying 0%; you have to draw the line somewhere; I believe it is in the right place.

You will never see a TS hit an aerodrome that is not forecast in a TAF; fact. It might be forecast only moments before, but it will happen.

I do see what you are saying; I just disagree with your point. I see no value in having a 10% chance being considered for fuel/alternate planning; that is 90% chance of not happening; the industry standards currently revolve around 30%; it seems to work, so what is the problem exactly? You seem to believe that we should be considering the chance, but why stop at 10% under your logic, why not 2%?

Having done some met stuff in my time; it's a science, not a science... It's a guess more often than not, educated yes, but still a guess; the change of a 20% chance, to a 30% chance maybe be just nothing more than a gut feeling of an individual based on previous experience, computer modelling be damned.

I guess my final point is, is it broken? if not, then don't mess with it.

[Bleve]

You will never see a TS hit an aerodrome that is not forecast in a TAF; fact. It might be forecast only moments before, but it will happen.
NOT TRUE

I'm sorry but I have seen a TS hit SYD that was unforecast. Watched a huge line of CBs out out the window and on Wx radar as we flew into SYD. Nothing on the TAF or TTF. Acft dodging left right and centre as they arrived and departed SYD. Nothing on the TAF or TTF. Safely parked at the terminal when the TS hit. Lighnting strikes, heavy rain, black as midnight at 4 in the afternoon. Airport closed to all activities. Nothing on the TAF or TTF. The first forecast to mention TS was a TTF SPECI issued seven minutes after the storm hit the airfield.

[SM4 Pirate]

Bleve, ok yes one slipped through the net (and there are probably more examples too)... Perhaps there was a difference in forecast issued and forecast published... The point is it did get changed when the probability went over 30%; even in the case you mention, although it was late...

[Bleve]

That experience and your comments highlight to me a fundamental problem with modern Australian aviation forecasts - and that problem is the over reliance on computer modelling. On the day in question it was obvious (for at least an hour beforehand) to anybody that bothered to look out the window or at a weather radar that SYD was going to be affected by TS. ie the human assesment was that the probabilty of TS was close to 100%. Yet nothing on any forecast. I suspect that the BOM was blindly issuing the computer model generated forecasts and the models had the prob at less than 30%. But the models were simply wrong and there was no human input into the accuracy of the forecast, ie using the Mark I eyeball to have a look out the window. I also suspect that ATC at SYD rang up the BOM after the airfield was closed and asked why the TTFs didn't have TS on them and then there was a mad scramble to catch up with reality.

Not too long ago TTFs were issued by real forecasters that used a blend of modelling and local knowledge and experience. That's what is missing these days - the human input. And that's why QF are paying for BOM forecasters to keep an eye on things and if the computer modelled forecasts aren't up to scratch it imposes it's own operational requirements in the form of OPRISK notices to it's crews.

[Ratshit]

You guys who fly all the time must see lots of this, cause I only fly 200 hr a year (mostly IFR) and I see enough examples of poor forcasts to make me very wary, but I generally have the luxury of carrying full fuel.

1) Before Xmas I dodged a big Cu/gestating CB north of YBOK that went on to belt the crap out of the Sunshine Coast. No mention of the possibility of CBs on any forcast!

2) Similar thing with a line of CBs between Alice and Ayers Rock middle of last year.

3) My personal favourite - having to fly an intrument appr into an aerodrome that has a CAVOK forcast!

R:cool: