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METAR, TTF, TAF, SPECI questions
Spinrecovery created the topic: METAR, TTF, TAF, SPECI questions
I would like to ensure that I have a complete understanding of all the forecast terminologies. Please correct if I am wrong.
METAR = a report issued hourly or half hourly and the cloud base is given about ground level, wind is given in degree true.
TTF = a forecast for a specified aerodrome valid for three hours and supersede the TAF, cloud base is AGL and wind is degree true.
TAF = aerodrome forecast valid for 24 hour, cloud is AGL and wind is degree true.
SPECI = special report when conditions at an aerodrome fluctuate or below specified criteria, cloud is AGL and wind is degree true. (dont know the validity period)
PIREP = pilot report.
Is PIREP more accurate than the TTF?
Is the term above ground level the same is above aerodrome elevation?
The only forecast that gives the wind in degree magnetic is ATIS?
Only the Area forecast gives the cloud base above mean sea level?
Richard replied the topic: METAR, TTF, TAF, SPECI questions
METARs are issued at fixed times, hourly or half hourly and cloud base is given above aerodrome elevation. Wind in degrees true.
SPECI is a special report issued when certain changes in the conditions have occurred. Cloud heights above aerodrome level and wind in degrees true. A SPECI has no validity period because it is a report. It "expires" as soon as it is issued since it is simply a statement of the conditions at the time the report was made.
TTFs are "mini-forecasts", highly accurate and valid only for 3 hours from the time of the report to which they are attached. TTF's will be attached to a METAR or a SPECI. Cloud heights given above aerodrome level. Wind in degrees true.
PIREPs are not more accurate than a TTF since the two are completely different. The PIREP is a report, the TTF is a forecast of expected conditions for a 3 hour period.
AGL is not the same as above aerodrome level (AAL) since the AAL is measured at the aerodrome reference point whereas AGL is simply height above ground level. AGL and AAL will only be the same at the aerodrome reference point unless the terrain is perfectly flat.
The ARFOR is the only one that gives cloud bases and tops and these are given in feet AMSL. After all, which elevation could an ARFOR use as a reference for heights? The elevations will vary wildly in the area covered by the ARFOR so using sea level as the zero-point for height measurements is the only thing that would work.
As a rule of thumb, if the Met message is written, wind will be given in degrees True, if it is spoken, it will be in degrees Magnetic. Therefore ATIS uses degrees magnetic and even recorded MET messages (e.g. AWIS) will give the wind in degrees magnetic. By the way, the ATIS is not a forecast. It is a report.
Also, if the met message references an aerodrome directly (e.g. TAF, SPECI, METAR, TTF), the cloud heights will be given in feet AAL.
Mister W replied the topic: METAR, TTF, TAF, SPECI questions
Not really. The TAF is the forecasters prediction of what will happen over the airport's category time period (see GEN 3.5-3). The METAR is basically the forecaster sticking their head out the window seeing what's going on.
From that, you can compare the information between the two to get an idea of accuracy.
The information on METARs are also good for tracking the passage of a front and comparing the information to your ARFOR.
Carello replied the topic: METAR, TTF, TAF, SPECI questions
Yes, a TAF and TTF are both forecasts.
That being said, the TTF is also an "aerodrome weather report" (Metar or Speci) to which a BoM forecaster adds a 3 hr "trend forecast". If there is no trend attached you are left with an aerodrome weather report, not a TTF.
The first part of the TTF is the aerodrome report and everything following "RMK RF" is the 3 hr trend forecast - see image below.