ARFOR question

[Ambitious]

I have a question in regards to visibility information in ARFOR and I am hoping for your expert advice!

Example: (extracted from ARFOR)

VISIBILITY:
4000M SH/DZ/TS

The question asks what the forecast visibility is. The possible answers are:

a) 4000 meters with SH/DZ/TS
b) 10km or more
c) 10km reducing to 4000 meters in SH/DZ/TS
d) 4000 meters reducing in SH/DZ/TS

Now, I know that a is incorrect. b is complete rubbish. d doesn't state what the visibility is actually reducing to. The only answer left is c. However, 10km is not referred to anywhere on the forecast, so I am wondering if for ARFOR 10km visibility is implied with limitations expressly stated under the VISIBILITY section? :confused:

Your help will be much appreciated :O

[Ex FSO GRIFFO]

Its been a 'while' now....but, from the limited info given,

Usually the VIS is f'cast as 10km (9999) or better, except where reduced by the associated phenomena - whatever it may be - e.g. dust, rain, showers etc. AS it occurs.

T'would be rare for the VIS to be 4000M for the WHOLE period of the FCST.

So, (c)....For the f'cast period of the Showers.

:ok:

[bentleg]

4000 m viz forecast at the same time as showers/drizzle/thunderstorm

If there are no showers etc the viz might be better than 4000 m but for flight planning purposes use the worst case forecast. I go for (a).

[Ambitious]

Yeap, that’s exactly what I thought and answered (a) but this was incorrect :ooh:

If there was an answer along the lines of: “Visibility reducing to 4000 meters in SH/DZ/TS”, I would go for that. However, I think the correct answer as per the exam answers is (c) … which makes me wonder where they get 10km from? The only possible explanation is that 10km visibility is implied with ARFOR unless stated otherwise under VISIBILITY section, but I could not find confirmation of this theory in any book… Does anyone know if 10km visibility is ok to assume with ARFOR? :suspect:

[UnderneathTheRadar]

Sorry bentleg - it's got to be (c).

By your reasoning, you wouldn't go flying on a day with forecast isolated showers and the above comment - which is pretty silly given that it will be >9999 everywhere else.

UTR

[Ambitious]

Here is the complete forecast:

AREA22 (22)

AREA FORECAST 112300 TO 121100 AREA 22
OVERVIEW:
THUNDERSTORMS WITH HAIL (SMALL) DEVELOPING IN W AREA 22 EXTENDING E
SCATTERED SHOWERS/DRIZZLE
WIDESPREAD LOW CLOUD. BECOMING SCATTERED NW
ISOLATED SEVERE TURBULENCE BELOW 8000
REFER SIGMET FOR LATEST DETAILS OF SEVERE ICING
WIND:
2000 5000 7000 10000 14000 18500
270/40 270/35 260/40 270/45MS10 270/50MS18 260/60MS28

CLOUD:
OCNL CB 2500/28000 W AREA 22 EXTENDING E
BKN ST 800/3000. BECOMING SCT NW
BKN CU 2500/15000
WEATHER
TS (HAIL) SH/DZ
VISIBILITY:
4000M SH/DZ/TS
FREEZING LEVEL:
4000S/5000N
ICING:
REFER SIGMET
TURBULENCE:
ISOL SEV BELOW 8000

[DanArcher]

I go with (C) although cant find anything to back it up in aip or other wise :ugh:

AS you can see from the overview SH & DZ are scattered, so 4000m is the worst forcast visibility for the area & when not in SH or DZ vis expected greater than 9999

[Ambitious]

Dan,

That's exactly my point - nothing in the ARFOR to back it up :suspect:

[The PM]

guys, have a look at AIP on page GEN 3.5 - 6 paragraph 3.6.4. The answer would be C.

Going slightly off on a tangent, I'm starting to come back into flying after a verrrrrrrrrrrrrrrrrrrrrrryyy long break, and the LACK of info on decoding a low level ARFOR in the AIP is staggering.There is reams of info on high level forecasts, but barely a page in total for low level.If you go to the BoM website, there is a really comprehensive page that looks a hell of a lot like what used to be in AIP many many years ago.

[Masif Eego]

Yep 'C' is the correct answer.

A detailed decode can be found here - http://www.bom.gov.au/general/reg/ash/ASH.pdf

[Ambitious]

Thanx for the link, but it's prompting for a username and password whan you click on it.

p.s. great nick name! :ok: lol

[The PM]

Ambitious, use:

Username: bomw0007
password: aviation

They are the generic codes for aviation weather on the BoM website.
Also have a look at:

http://www.bom.gov.au/general/reg/aviation_ehelp/

[Ambitious]

Username: bomw0007
password: aviation

doesn't seem to work for me ... :(

[The PM]

yeah, I get that as well from that link as well as the link I put in.I kn ow it works was just using it! Must be some block on linking back to the BoM website.Check your PMs!

:ok:

[DanArcher]

http://www.bom.gov.au/general/reg/aviation_ehelp/explanarfor.shtml

seems to answer the question pretty well

[Ambitious]

Ok, ok I must be completely blind, but the only piece of info I seem to find on the 10km part is this:

Visibility

Visibility is given following the word 'VISIBILITY' and is expressed in metres.
Visibility is given to the nearest 100 metres up to and including 5000 metres and whole kilometers above that value.
Forecast visibilities of 50 metres or less are given as 'ZERO'.
The forecast value is followed by the units used e.g. '8KM' or '1000M'.
Significant variations of visibility are included.
If the visibility is forecast to be above 10 kilometres throughout the area, the words 'UNRESTRICTED' or 'GOOD' are used.
Vertical variations of horizontal visibility, which might prevent flight under VMC conditions, are significant. For example, information is supplied on the depth of layers affected by drizzle, haze and duststorms, and the levels of haze layers under inversions. Visibility variations with these phenomena is given.I just don't see where exactly in that ARFOR above is it written "unrestricted" or "good"? :ugh:

[The PM]

Thats because it isn't!

Have a look at AIP on page GEN 3.5 - 6 paragraph 3.6.4.

"GOOD is used in the visibility section of low level area forecasts to indicate a visibility greater than 10 km over the entire area.When weather elements are forecast to reuce the visibility below 10km, GOOD is replaced by those elements and their associated visibilities.Note that the visibility remains greater than 10km in parts of the area unaffected by those elements."
My bolding.

[Ambitious]

Thanx mate! I don't have AIP at hand, but that quote made it all clear now. :O

On another note - I just can't help but feel so frustrated by having to chase this kinda info all over the place. CASA exams frequently refer to some small detail that you gota spend hours researching... grr... but then again, it's Sunday night and I gota go to work tomorrow, so I'm whinging :(

[AussieNick]

i got a question like that in the CPL met exam, and they are looking for C, 10km reducing to 4000m in SH/DZ/TS