ATIS : Valid Forecast or Not?

[Ear Muffs]

Is the ATIS a valid forecast?

Dubai ATIS has Trend attached (e.g. NOSIG)

Is this Equivalent to a METAR?

Can i use it for in flight fuel requirements?

Thanks for your help. (References Appreciated)

[Intruder]

Dunno 'bout Oz, but in the US there are generally no forecasts on ATIS. "NOSIG" does not substitute for a real TAF.

[FlightDetent]

Some new, fancy automatic, ATIS stations broadcast METAR i.s.o. MET report. Maybe that's how trend got there? AFAIK, trend is as good forecast as any, for planning legal purposes. On the other hand, I've seen TREND forecasts go so unreliable that I'd be reluctant to use them against a non-favourable TAF. See TK A330 Kathmandu thread!

fd.

[CallmeJB]

I think we need to review the meanings of the words trend and forecast.

[ACMS]

In Oz a TTF metar is valid for 3 hours and you can use it in place of a TAF.

[sahni]

I think a TTL (Trend Type Landing) forecast gets only attached to a METAR, and if attached supersedes the TAF for the period specified. So I use it for planning purposes if applicable.

An ATIS is not a forecast at all but a report of actual, reported/observed conditions.

Cheers!

[Duchess_Driver]

As i thought, can't put my hand on the ICAO definitions yet, but Wiki sums up

In addition, a short period forecast called a TREND may be added at the end of the METAR covering likely changes in weather conditions in the two hours following the observation. These are in the same format as a Terminal Aerodrome Forecast (TAF).

[LeadSled]

In Oz a TTF metar is valid for 3 hours and you can use it in place of a TAF.

ACMS,
In AU, not only can you use a TTF in place of a TAF, you must, the TTF supersedes the TAF for the duration of the TTF.
An ATIS that includes a METAR + trend is a valid TTF, and is generally valid for two hours -- the ICAO standard.
A TTF will be based on far more recent data than a TAF -- almost real time.
Check your Jepp. WW Text or equivalent document.
Tootle pip!!

[ACMS]

Every time I plan to Oz I'm 8 hours or more away anyway!! So I have no choice but to use a TAF.....

However thanks for the extra clarification, I'll be sure to look it up soon

[Derfred]

An ATIS that includes a METAR + trend is a valid TTF, and is generally valid for two hours

So where is it written an ATIS that says NOSIG at the end is a TTF?

Genuine question.

[FlightDetent]

Def: NOSIG is one (unique) type of TREND. Effectively meaning, the forecast for 2 hours is "weather unchanged" from the METAR/SPECI observation.

WMO Manual on Codes vol I. http://library.wmo.int/opac/index.ph...splay&id=13617

15.14.15 When none of the elements listed in Regulation 15.14.2 is expected to change significantly as to require a change to be indicated, this shall be indicated by the code
word NOSIG. NOSIG (no significant change) shall be used to indicate meteorological conditions which do not reach or pass specified threshold criteria.

Other references reference in ICAO ANNEX 3 too e.g. here.

6.3 Landing forecasts
6.3.1 A landing forecast shall be prepared by the meteorological office designated by the meteorological authority concerned as determined by regional air navigation agreement; such forecasts are intended to meet the requirements of local users and of aircraft within about one hour’s flying time from the aerodrome.
6.3.2 Landing forecasts shall be prepared in the form of a trend forecast.
6.3.3 A trend forecast shall consist of a concise statement of the expected significant changes in the meteorological conditions at that aerodrome to be appended to a local routine or local special report, or a METAR or SPECI. The period of validity of a trend forecast shall be 2 hours from the time of the report which forms part of the landing forecast.

[roulishollandais]

NOSIG in ATIS ?

[Offchocks]

roulishollandais, Singapore ATIS has a trend on it.

[LeadSled]

Every time I plan to Oz I'm 8 hours or more away anyway!! So I have no choice but to use a TAF.....

ACMS,
Of course you do, but withing AU, and 3 hours of the destination, the TTF supersedes the TAF, the TAF remains valid for the rest of the flight, including an alternate if it is outside of a TTF for the arrival at the alternate.

Put another way, in AU you must get a TTF covering your arrival, you can't ignore it and hope it will go away.

ICAO-wise, the same thing is true, it is not valid to rely on a "favorable" TAF if a TTF indicates a deterioration, because the far more recent TTF will be based on current (as opposed to maybe 20+ hours old TAF data from the time of the original forecast).

The obvious question re. the above comment is: "Why would you", but sadly the aviation business these days is full of "bar room barristers", at the expense of common sense, sometimes referred to as airmanship.

Tootle pip!!

[Microburst2002]

Some METAR, and also ATIS, give a Trend forecast, valid for the next 2 hours.
If there is no significant change within 2 hours, that is a NOSIG. If there is change forecast, a TEMPO or BCMG.

If there is nothing, NOSIG cannot be assumed, it is a trendless report

[roulishollandais]

How do they know the Runway in use will not change during two hours blocked by some crash or incident ? It is not like visibility or height of clouds and other operational parameters. Is that NOSIG for lazy new pilots' generation ?

[FlightDetent]

The ATIS is composed of several sections. Some facilities use METAR in lieu of ATC met-report. Where that is the case, and the METAR is issued by the MET officer with a TREND-type landing forecast, this will be broadcasted.

Assuming the NOSIG meteorological landing forecast (a METAR segment) is somehow applicable to other sections of ATIS is incorrect and a source of potential confusion. The question about the person's ability to read METARs is somewhat hard to avoid.

FD.