How to interpret METARs and TAFs
TAF refers to: a Terminal Aerodrome Forecast (TAF), a weather forecast for an airport. Many conflict situations originate from a misinterpretation of the weather situation, either at the point of origin or destination, and of its foreseeable evolution.
The TAF is somewhat more complex, as its information refers to weather evolution, the prevailing meteorological conditions expected at the aerodrome throughout the forecast period, including changes considered significant for aircraft operations. The forecast period covers 9 hours (short TAF), or 24 or 30 hours (long TAF).
The definition is crystal clear. We have a forecast, but like all forecasts, it may come true…or not. It follows that the two key points we must interpret correctly are: TEMPO and BECMG. The information they provide is very valuable, as it warns us of possible changes, but it requires a detailed reading and in-depth analysis to extract all its benefit.
BECMG, The acronym TEMPO, short for "becoming," is used to describe expected changes in weather conditions that reach or exceed certain values at a regular or irregular rate. TEMPO, as its name suggests, is used to describe predicted temporary fluctuations in weather conditions that reach or exceed specified values and last less than one hour in each instance, and collectively less than half the forecast period during which the fluctuations are expected to occur.
The groups BECMG These indicate a regular or irregular change in the forecasted weather conditions at an unspecified time within the indicated period (GG to GeGe). This period will generally not exceed two hours, but will never exceed four hours.
The groups TEMPO They indicate temporary fluctuations in the forecasted weather conditions that may occur at any time during the period GG to GeGe.
Understanding and assimilating the information obtained from METARS and TAFORS is essential. Familiarizing yourself with this information will help you have more pleasant and safer flights.
One of the best ways to mitigate these situations is through the correct interpretation of the aeronautical reports that the various meteorological services make available to pilots. These include METAR and TAF reports.
HOW TO INTERPRET THE DATA:
TAF (Tafor): It is a forecast or prediction for a specific airfield and there are 2 types.
Short Taf, valid for the next 9 hours and is issued every 3 hours.
Long Taf, (the most common) 18 or 24 hours of validity and is issued every 6 hours.
AIRPORT CODES:
MROC. Juan Santamaría
MRPV. Tobias Bolaños
MRLM. Lemon
MRLB. Daniel Oduber
Example: MROC 210500Z 2106/2206 02012KT 9999 BKN015 TX10/2116Z TN05/2206Z
TEMPO 2106/2108 2000 SN BKN010 OVC020
TEMPO 2108/2112 2000 RA OVC005
BECMG 2110/2112 23012KT
TEMPO 2116/2202 24015G25KT
*Normally it all goes together, I have separated it to clarify things better and understanding how to read metadata, since if we know that we almost know how to read a tafor, the following is added.
-MROC 210500Z= that with the Juan Santamaría meta on the 21st, and prediction issued at 05:00 Z (GMT)
-2106/2206 : Validity Period (It also helps us to know that it is the Taf and not the metar), valid from the 21st at 06:00Z until 06:00Z on the 22nd.
– 02012KT 9999 BKN015: Same as before but this is what is expected in that period, wind of 020 degrees and 12 knots, visibility of 10 km or more and 5-7 Octas of the sky overcast at 1500 feet above the ground.
-TX10/2116Z TN05/2206Z Temperature forecast: a maximum of 10 degrees Celsius at 16:00Z on the 21st and a minimum of 5 degrees Celsius at 06:00Z on the 22nd. (If negative, add an M before the temperature value)
-TEMPO 2106/2108 2000 SN BKN010 OVC020: Temporary weather type change group, (The weather would change to these conditions with a probability greater than 50% between these hours), in this case temporarily between 06:00Z and 08:00Z on the 21st, visibility of 2000 meters is expected, Moderate Snow, 5-7 octas of the sky covered at 1000 feet and 8 octas completely covered at 2000 feet from the ground.
It includes the variables PROB 40 and PROB30 which would go before (TEMPO), to tell us something less about probability although in practice 40 tells us that it is quite likely to fall, and 30 very unlikely.
-BECMG 2110/2112 23012KT: Permanent Change Group, the weather will start to be (With a probability higher than 50% who tells us), Wind of 230 degrees and 12 knots.
-NSW: It would indicate the end of some significant time phenomenon, which would come at the end of these similar tafs.
