Considering the Weather

The main source of meteorological information in VATSIM is meteorological coded information also known as METAR. This kind of information published every 30 minutes for most of the world’s airports and can be easily found in the internet. It consists of a few major types of information for every specific airport – they are wind, visibility, weather phenomena, air pressure, runway surface condition and predictable changes. Therefore, you would understand how to decode this kind of information. We provide you with the diagram as shown below.

Let us decode this code.

• METAR - is an identifier of a meteorological code, it means that this is weather observation, not forecast.
• OIII - station of observation.
• 030800Z - date (03) and time (0800Z) [Z=GMT] of observation.
• VRB02KT - first three symbols - wind direction in degrees (VRB – means it has no specific direction) and the next 2 indicates the speed (02 Knots).
• 9999 – visibility near the ground in meters, if 9999 – visibility more than 10 kilometers. If stated CAVOK – it would mean that the visibility is more than 10 kilometers and there are no significant weather phenomena. If there is no way to determine visibility, the runway visual range will be stated with the code RVR as shown as R29R/5000, which means that on runway 29R the visibility is 5000 meters.
• BKN050 – cloud base in hundreds of feet, so this are broken clouds with ceiling of 5000 feet. Type of clouds you can encounter: FEW – fewer, SCT – scattered, BKN – broken and OVC – overcast. After the ceiling altitude, the abbreviation CB could be stated which indicates cumulonimbus clouds are present.
• 24/M10 – temperature and dew point in degrees of Celsius (24° and -10°), symbol M indicates that the temperature is below zero.
• Q1024 - air pressure in hectopascals 1024hPa.
• NOSIG – "NOSIG" is used to indicate that no significant changes to the elements in wind, visibility, weather or cloud, as reported in the METAR/SPECI, are expected to occur during the validity period of the forecast.

To get more information about how to decode METAR you can use our special manual.

Download Manual

What weather can we actually fly in?

First, we have to decide whether the current weather conditions allow us to perform a flight at all. There are many visibility restrictions, especially for visual flights, and if the current visibility and cloud ceiling are below the minimum, we should not fly and wait for weather to get better. Despite we fly virtually, we strongly suggest you to consider this factors and evaluate your personal skills in marginal weather conditions. Here are some numbers to start with:

	VFR	CAT I	CAT II	CAT IIIA	CAT IIIB	CAT IIIC
CLOUD BASE	1000 ft	< 200ft	200-100 ft	100-50 ft	50 ft	0 ft
VISIBILITY	5000 m	< 550m	550-350 m	350-200 m	200-50 m	0 m

If current weather conditions are below them, it is better to postpone the flight.

What runway should we use?

If there were a controller providing service for the airport of your desire, you would not be asking yourself the question about the runway in use – the controller will tell you, but if there is not a single controller available, you have to decide which runway to pick for your operations. To determine this, we need the direction of the wind. You may already know that airplanes should take off and land in a headwind. We already got the direction from which wind is blowing from METAR and runway heading we can get either from map or simply by multiplying the number of the runway by number 10. Therefore, the formula is - the closer wind direction to the runway heading – the better. For example, for wind 330 degrees will suit the runway 29, but if the wind is 160 – it definitely should be runway 11.

For what do we need pressure?

You may already know that airplanes should take off and land in a headwind. We already got the direction from which wind is blowing from METAR and runway heading we can get either from map or simply by multiplying the number of the runway by number 10. Therefore, the formula is - the closer wind direction to the runway heading – the better. For example, for wind 330 degrees will suit the runway 29, but if the wind is 160 – it definitely should be runway 11.