What is a METAR?
METAR, short for Meteorological Aerodrome Report, is weather data that is used in aviation on a worldwide basis consisting of present weather information of an airport. This report is vital for the safety of aircrew, air traffic officers and every other operator in aviation since it presents timely information that is necessary in making crucial decisions regarding the flight. Now, let us discuss the essential elements of the METAR and how each element of the report should be understood.
2 Types of METARs
There are 2 types of METARs. The standard report that is published every hour is simply called a METAR. If a dangerous condition occurs within the time a METAR can be released and when the next METAR is due, an unscheduled version of a METAR such as a SPECI for “special” will be issued on occasions such as frozen precipitation, low clouds, low visibility, or thunderstorms.
The Structure of a METAR
A METAR typically follows a standardized format which makes use of codes and abbreviations to their fullest for minimizing the length of the report. It may seem difficult at first, but readers will find each part serving the METAR has its own function, making the reading of the report effective and straightforward.
Here is an example of a typical METAR:
METAR KJFK 121651Z 18015KT 10SM FEW020 SCT040 25/13 A2992 RMK AO2
Let’s break down what each component represents.
The Key Components of METAR
Type of Report
METARs can either be routine (METAR) or special (SPECI). Routine METARs are issued every hour, while SPECI reports are issued when significant weather changes occur. The label “METAR” or “SPECI” indicates the report type.
Station Identifier
The airport or aerodrome from where the report was prepared is represented by the four-letter ICAO code. For example, “KJFK” where ‘K’ is the region of the United States and JFK is John F. Kennedy International Airport located in New York.
Date and Time
The date and time of the observation are given in UTC (Coordinated Universal Time). For instance, “121651Z” represents the 12th day of the month at 16:51 UTC. The “Z” suffix indicates Zulu time, the aviation term for UTC.
Modifier
It is advisable to drop the modifier element which comes after the date and time, since it is not compulsory. When present, the modifier code will read either ‘AUTO’ or ‘COR’ which will be placed after the date and time block. The word “AUTO” means the weather report in question was produced by an automated station and not a weather forecaster. In the situation where a report is auto generated, the type of sensor equipment used to collect the data will be relayed in the remarks section of the METAR. The word “COR” shows that the report was corrected by a meteorologist. If there is no modifier then it means that the report was completely and exclusively completed by a human or a supervisor of the automated system was logged at that time.
Wind Information
The next detail adds the wind speed and direction which is significant in controlling the plane while taking off and landing. For instance, in “18015KT”, “180” implies that the wind is from 180 degrees (down south) and “15KT” indicates a wind speed of 15 knots. If the wind were gusty, it would, for instance, be shown as “G20KT” for 20 knot gusts. When direction is not constant there may be variable wind directions marked by “VRB” as well.
Visibility
Visibility is expressed in statute miles (SM) which helps in appreciating the flight visibility constraints. For instance, “10SM” in our case means 10 statute miles of visibility, which is considered optimal, desired in most situations. Some visibility conditions such as 1-2 SM would be of such low visibility that they could mean fog, heavy rain, and snow where added measures would be needed to enable safe operations.
Present weather
If there are any weather conditions, these are indicated with the help of standard abbreviations. In METAR, rain (RA), fog (FG), thunderstorm (TS) and other phenomena are indicated with two-letter symbols and modifiers – for instance, “+” indicates heavy, while “-” – light precipitation. For example, heavy rain is denoted by “+RA” while mist which reduces standard visibility but no precipitation is “BR”. No symbols for weather conditions means clear weather.
Sky Condition
Cloud coverage and height are significant for flight operations, especially during approach and departure. In METAR, cloud cover is indicated by oktas.
The major sky conditions you might encounter:
VV – Vertical visibility
SKC – Clear (manual report)
CLR – Clear (automated report)
FEW – Few (⅛ to ¼ of sky covered)
SCT – Scattered (⅜ to ½ of sky covered)
BKN – Broken (⅝ to ⅞ of sky overed)
OVC – Overcast (complete sky coverage)
Each code is followed by a three-digit altitude in hundreds of feet above ground level. For instance, “FEW020” denotes few clouds at 2,000 feet, and “SCT040” indicates scattered clouds at 4,000 feet.
Temperature and Dew Point
The temperature and the dew point indicated in Celsius are separated by a slash. For example, “25/13” means the temperature is 25 degrees celsius and the dew point is 13 degrees celsius. The dew point will aid in the evaluating of moisture as well as the potential for condensation, which is important in predicting conditions like fog or frost.
Altimeter and Pressure
The altimeter setting follows the temperature and dew point and it shows the atmospheric pressure in inches of mercury (Hg) in the U.S. or in hectopascals (hPa) outside the U.S. taken internationally. In the example, “A2992,” the letter “A” denotes inches of mercury, while “2992” means that the value is 29.92 which is the standard sea-level pressure. Currently it is most useful since it enables pilots to calibrate their altimeter during the flight and therefore obtain trustworthy altitude values.
Remarks Section
The remarks (RMK) section provides additional information, often specific to local conditions. For example, “AO2” indicates that the station has an automated precipitation sensor, while “SLP” could represent sea-level pressure, with additional data such as temperature trends or recent weather changes. The details of the remarks section vary as well in content and extent in providing some lesser climatic changes or point out the observations made in one or more characteristics of a station.
Understanding and Using METAR Data
METARs serve a significant purpose in aviation operations as they give a report of the weather at an airport at a given instant. Such information matters to the pilots as it aids in making decisions such as fuel needs, other landing spots, and delay or re-routing situations.
Pre-Flight Planning: METARs give a good overview of the weather at the departure and destination airports, allowing the pilot to be aware of the hazards he might face.
In-Flight Adjustments: While in flight, the METARs are comprehensively updated providing pilots with information on the conditions of their intended destination and allowing them to make changes to speed, altitude or direction as appropriate.
Safety Measures: Understanding the perspective of the visibility and the factors of cloud coverage and temperature can assist in executing safer takeoff and landing operations. For instance, information pertaining to crosswind can assist in avoiding difficult landings when high winds are an issue and visibility data is necessary in enabling the pilot to avoid difficult approach conditions.
Conclusion
METARs are an invaluable aid to any pilot, as it provides crucial weather updates in real-time that allow for smooth flying operations. Aviation employees who comprehend the specifics of METAR data can receive a detailed picture of the present weather at any given airport and prepare to deal with difficulties associated with bad weather.
Apart from the need by pilots to be able to understand METAR, they also have potential value to others working in the aviation field since it enhances one’s situational awareness and ensures flights are conducted in a safe and efficient manner in an unpredictable environment.