Just a few points to make about fog at YPPH (from a BoM forecaster). I wasn't involved in the ASI disussed in this thread by the way.

1. What is now known as FDSS has essentially been operating at Perth since about 2001, where it was developed in-house and has been generalized to other Aus capitals this year (I believe this became a
matter of urgency after an unforecast fog at Sydney last year,
which caused a large a number of diversions and a lot of lost money to Qantas). FDSS integrates a range of model predictions about the likelihood of fog formation, and allows forecaster 'subjective' input. FDSS' main advantage is that it delivers consistency, instead of the old system of forecasters pretty much doing their own thing. I didn't have to experience that myself, but by all accounts it was pretty harrowing coming onto night shift and having to nurse a CAVOK TAF when you would have been much more comfortable with a PROB30 for around dawn.

Since 2001 unforecast fogs at YPPH have generally averaged about 1 per year, with a few zeroes. For obvious reasons we are pretty conservative about fog forecasting at YPPH. If an unforecast fog occurs believe me, it's not because we don't give a damn!

The trouble with unforecast fogs is that there seems to be a different meteorological cause for each one that occurs! While there are rules of thumb we use to rule out fog forming (these rules tend to be implicitly find their way into FDSS), none of these are absolutely fool-proof.

Pilots should beware of rain falling during the day before, and especially close to sunset. I've been stung by this once - it causes the dew point depression to drop alarmingly in the evening (esp. if the sky clears behind the rain and the wind drops out), and is a major cause of short-notice amendments of the TAF from PROB30 1624 0300 FG to (say) 1324. I'm not sure if this situation is related to the ASI under discussion here.

If you know your synoptic met. then always look out for strong ridging directly over Perth behind a cold front. If the wind is expected to tend E/SE'ly overnight then you're nearly always OK. Wet winters (such as this year) also promote more fogs, and you have to be careful during autumn, when the sea temperature is warmest, there are offshore troughs (i.e. light winds) and the land starts to become cooler overnight - the April 7 2005 fog is still burned into my mind (I did the 0606 TAF). Wind doesn't necessarily kill fog at YPPH - I've experienced fogs advecting down the Swan Valley in a 5-7 knot wind. Likewise fog has occurred at YPPH while there has been a 15-20kt S'ly at Rotto, so the boundary layer conditions can change markedly over a short distance.

As forecasters we are bit annoyed that the SLAM minima are still at 2500m/750ft (used to be 2000m/400ft), and mystified that such an isolated yet important airport (and getting more important -- isn't the
A380 scheduled to start using YPPH?) isn't upgraded to permit landing
in more adverse weather conditions. 'Tis the curse of the service I guess ... All in all, I think we deserve your trust,
but not your blind faith :O

Sometimes I dont get it at all - approx 2 weeks ago coming into Perth from Bali - during transit at Bali - we look at forecast for Perth (our ETA YPPH approax 430am) - it was along the lines of (Latest TAF, not old)

CAVOK 030/5 4/3 1023.

The TTF was along the lines of CAVOk 030/3 3/3 WBD 0.3 1024

No indication of fog at all.

WE sat there and discussed it, and the comment was made - "everything about that forecast would suggest fog - how can they not even put a PROB30 fog on.....". So we carried extra fuel for an alternate.

Monitoring the weather on the way down, the TTFs Continued the theme approx CAVOK 040/4 3/3 WBD 0.2 1024 etc..

Thinking that MET had taken a bit of a gamble and it payed off - until about an hour out the forecast was TTF SPECI 030/4 3/3 WBD 0.1 FOG PATCHES

The FOG didnt get any worse - but it seemed incredible that FOG hadnt been added to the TAF.

I say this with a lack of expertise in the MET area, and I have no idea what modelling is used - but there have been a few nights like this, where the basic MET ATPL we study suggests ideal conditions for fog, yet MET says otherwise. Obviously there are some key ingredients in the mix, which we dont see on these nights that gives the forecasters the confidence not to put it on the TAF.




AS an aside, I realise in the early hours in Perth that traffic is limited or non-existant, but why is the ATIS never updated - on nearly every occasion I have been in that early it is nearly 3 hours old, even when we get to top of descent the ATIS is still old, to the point where for briefing/planning the approach it appears more prudent to use the METAR for QNH etc. 90% the ATIS is updated half way down descent - usually to reflect the METAR, (which is often significantly different from the 3 hour old ATIS).

On nights where we suspect fog, the METAR reflects fog patches, it can be helpful to look at the ATIS early to plan and monitor the trend.

Wizofoz
 

"Anywhere else in the world, the aircraft would have dispatched with enough fuel to go somewhere else if the destination went down for weather or any other reason."

Ummmm, I don't think so mate. Aussie aviation isn't a lone soldier in that department.... :sad:

Withoth getting into the alternate fuel debate, one would think that even a manual landing from an ILS in low vis would be preferable to a ditching. Surely even lacking an ILS you could set up some sort of FMS approach for guidence. I'm suprised a ditching was even on the list of alternatives.

Titty Bob Dude
 

The "3/3" obviously means the ambient temp, in this case 3 deg, equals the dew point temp ie a high relative humidity. This condition when combined with 5-7 knots of wind creates ideal conditions for the mixing of air and thus the formation of fog.

I am no meteorologist either but perhaps they were willing to take the gamble with the ttf predicting only 3 knots of wind.

Any Met people up for comment?

Smoking, those were the conditions when Bob went in, not necessarily what they were for the QF crew. I haven't seen reference to that yet. Perhaps they're the same numbers but don't let Bob's example make you think that these were the exact same conditions confronting the QF crew.

1000ft wind
 

Some years ago a colleague who'd spent many a year in Perth, told me of his "local knowledge".

Whenever he felt that a forecast suggested fog but it wasn't written, he would get on the phone or radio and ask for a recent 1000 or 1500ft wind. If it was 15kts or more he'd feel confident that fog was unlikely. Less than 10kts he'd put the gas on for an alternate or begin refining a PNR/alternate if enroute.

He'd been doing this since his GA days and still does it now with his current airline, as do I.

c441;

i've shot an (unsuccessful) approach into PER on a foggy morning with 30kts at 1000'... didn't clear for a while either- nor was it accurately forecast.

Musta been a westerly!

Perth only has 1 or 2 low vis days a year! no need for CAT111 & FYI is YPPH is CAT1 ILS.

This really scares me!!! & makes me wonder why pilots who take such risks even have their wings! I thought only formula 1 run to minimum fuel loads!!!!! I tell ya its only a matter of time before one of you & 300 pax fall silently out of the sky!!!! STUPID STUPID STUPID..........
Whats it all for? to save a few $$$ for the company hmmmmmmmm