Question 1

What is aviation weather decoding?

Accepted Answer

Aviation weather decoding is the process of converting standardized ICAO weather reports and forecasts into plain English operational information. METAR, TAF, SNOWTAM, and NOTAM reports use coded formats designed for brevity and global consistency. Decoding these reports helps pilots determine flight category, assess weather conditions, and make preflight go or no-go decisions.

Question 2

What aviation weather reports do pilots decode before a flight?

Accepted Answer

Pilots typically decode METAR reports for current conditions at departure and destination airports, TAF forecasts for expected conditions during the flight, NOTAM notices for airspace and runway restrictions, and SNOWTAM reports for runway contamination during winter operations. Cloud base calculations supplement METAR ceiling data when additional verification is needed.

Question 3

What are the four aviation flight categories?

Accepted Answer

The four aviation flight categories are VFR, MVFR, IFR, and LIFR. VFR applies when ceiling is above 3,000 feet AGL and visibility exceeds 5 statute miles. MVFR applies when ceiling is 1,000 to 3,000 feet AGL or visibility is 3 to 5 statute miles. IFR applies when ceiling is 500 to 999 feet AGL or visibility is 1 to less than 3 statute miles. LIFR applies when ceiling is below 500 feet AGL or visibility is below 1 statute mile.

Question 4

How is flight category determined from a METAR?

Accepted Answer

Flight category is determined by the lowest broken or overcast cloud layer and the prevailing visibility in the METAR. The most restrictive of the two values governs the category. Scattered and few cloud layers are not ceilings and do not affect the flight category determination. When the sky is obscured, vertical visibility replaces ceiling for category purposes.

Question 5

What is the difference between a METAR and a TAF?

Accepted Answer

A METAR is a weather observation that reports actual conditions at a specific airport at a specific time. A TAF is a weather forecast that predicts expected conditions at the same airport over the next 9 to 30 hours. METARs are issued hourly or when conditions change significantly. TAFs are issued four times daily and include change groups such as TEMPO, BECMG, FM, and PROB to describe forecast transitions.

Question 6

What does CAVOK mean in a METAR?

Accepted Answer

CAVOK stands for Ceiling And Visibility OK. It is used when visibility is 10 kilometres or more, there are no clouds below 5,000 feet or below the minimum sector altitude, there are no cumulonimbus clouds at any level, and there are no significant weather phenomena. CAVOK replaces the visibility, weather, and cloud groups in the report and always indicates VFR conditions.

Question 7

How is cloud base estimated from temperature and dew point?

Accepted Answer

Cloud base is estimated using the surface temperature and dew point spread. For every 1 degree Celsius of spread between the temperature and dew point, the cloud base rises approximately 400 feet above ground level. A temperature of 20 degrees Celsius and a dew point of 12 degrees Celsius gives a spread of 8 degrees, producing an estimated cloud base of 3,200 feet AGL.

Question 8

What is a SNOWTAM and when do pilots use it?

Accepted Answer

A SNOWTAM is a special NOTAM that reports runway surface conditions during winter operations. It includes information on contamination type such as snow, slush, or ice, contamination coverage, depth, and runway condition codes that correspond to braking action levels. Pilots use SNOWTAM information to assess landing and takeoff distance corrections required for contaminated runway surfaces.

Aviation Weather Decoding Tools

METAR Decoder

TAF Decoder

SNOWTAM Decoder

NOTAM Decoder

Cloud Base Calculator