The METAR Remarks Section, the Coded Data Most Students Skip Right Past, and the Weather Intelligence Hiding After That RMK Delimiter

The METAR remarks section - everything after the RMK delimiter - is not fine print. It is the observation system telling you exactly how much to trust the data that came before it. Most student pilots scroll past it. That is a habit worth breaking before it matters.

What Is a METAR and Why Do Remarks Exist?

A METAR (Meteorological Aerodrome Report) is an observation of actual conditions at a specific place and time - not a forecast. Most reporting stations today are automated: either an ASOS (Automated Surface Observing System) or an AWOS (Automated Weather Observing System). Both rely entirely on sensors, and sensors have limitations.

The remarks section is where those limitations get disclosed. The body of the METAR gives you the data. The remarks section tells you how much to trust it.

What Does AO1 vs. AO2 Mean in a METAR?

The first thing you will almost always see after the RMK delimiter is AO1 or AO2. These codes identify what kind of automated station produced the observation, and the difference is critical any time precipitation is involved.

AO2 stations have a precipitation discriminator - a sensor that distinguishes between liquid and frozen precipitation. When an AO2 station reports rain, it has actually identified the type.

AO1 stations lack that sensor. When an AO1 station reports precipitation, it knows something is falling but cannot identify what. If the temperature is below freezing and an AO1 station reports rain, that precipitation could be snow or freezing rain. In any condition where precipitation type matters, AO1 versus AO2 changes how you interpret everything else in the observation.

What Does a Dollar Sign Mean at the End of a METAR?

A $ at the end of a METAR is a maintenance flag. The automated system has detected a fault and is flagging its own data as potentially unreliable.

It sits at the end of the observation, where attention naturally drifts, which makes it easy to miss. If you are making a weather decision based on a METAR that ends with $, treat that observation with real skepticism and seek corroborating data before acting on it.

What Are FZRANO, PWINO, and TSNO?

These three codes are sensor outage disclosures. Each one represents a specific blind spot in the observation.

FZRANO - Freezing rain sensor not operating. If this appears and the temperature is anywhere near 0°C, that station cannot detect freezing rain. If freezing rain were falling at that airport right now, this METAR would not show it. For any flight where icing is possible, FZRANO changes the information environment entirely.

PWINO - Present weather identifier not operating. The sensor that identifies weather type is offline. The station may not report precipitation even if it is actively falling. The METAR body could be completely silent while rain or snow is occurring at the airport.

TSNO - Thunderstorm information not available. No lightning sensor. The station cannot detect or report electrical activity in the vicinity. A clear sky condition paired with TSNO cannot be used to rule out nearby thunderstorms.

Think of these three codes as disclosure codes. The station is telling you: I have a blind spot - here is what it is. If any of them appear in a METAR you are using for a go/no-go decision, find another source to fill that gap before you fly. A pilot report, a SIGMET or AIRMET from the Aviation Weather Center, or a radar picture. Do not just note the code and move on.

The Airman Certification Standards (ACS) requires private pilot applicants to obtain and analyze weather for a cross-country flight. An examiner who understands weather will ask what the remarks showed and what you did with that information. Be ready for that question.

How Do You Read Sea Level Pressure (SLP) in the Remarks?

You will often see SLP followed by three digits in the remarks. The decoding rule:

• If the three digits are 500 or greater, put a 9 in front and a decimal before the last digit. SLP982 = 998.2 hectopascals.
• If the three digits are less than 500, put a 10 in front. SLP023 = 1002.3 hectopascals.

For a VFR cross-country, exact sea level pressure rarely drives a decision on its own. But comparing SLP values across several METARs along your route can reveal a pressure gradient that the altimeter setting alone does not fully capture.

How Do You Read the Temperature and Dewpoint (T Group)?

The METAR body rounds temperature and dewpoint to the nearest whole degree Celsius. The T group in the remarks gives exact values to the nearest tenth of a degree.

The format is the letter T followed by eight digits. Example: T02280178

• The first digit after T is the temperature sign: 0 = positive, 1 = negative
• The next three digits are the temperature in tenths: 022 = 2.2°C → so 0228 = +22.8°C
• The pattern repeats for dewpoint: 0178 = +17.8°C

Why does the extra precision matter? Temperature-dewpoint spread. The closer those two values are, the closer conditions are to saturation - meaning fog risk, or in near-freezing conditions, structural icing. A METAR body might show a one-degree spread; the T group might show a spread of less than half a degree. That difference tells a meaningfully different story, especially for an early-morning departure after a clear night.

How Do You Read Lightning Remarks in a METAR?

When a station with a lightning sensor detects electrical activity, it reports it in the remarks. Key codes:

• OCNL LTG - occasional lightning
• FRQ LTG - frequent lightning
• DSNT - distant (roughly beyond 10 miles)
• VC - vicinity (within approximately 10 miles of the station)
• IC - in-cloud, CC - cloud-to-cloud, CG - cloud-to-ground

LTG CG VC means cloud-to-ground lightning within 10 miles of the airport. That is not a condition to plan around. That is a condition to react to.

Lightning remarks give you real-time sensor data that forecast products cannot always match. They do not replace a radar check, but when you are on the ground pulling up the current METAR, they are the most current snapshot of what the automated system is detecting right now.

What Do Variable Ceiling Codes Mean?

The METAR body gives a single ceiling height, but ceilings are sometimes unstable. The remarks can reflect that with a CIG code followed by a range.

CIG 009013 means the ceiling is varying between 900 and 1,300 feet. That is a meaningfully different picture than a steady 1,000-foot ceiling - particularly when evaluating whether conditions support a visual approach at a destination with rising terrain or close-in obstacles.

How to Read the Remarks Section Systematically

Work through the METAR body as you normally would: wind, visibility, weather, sky condition, temperature/dewpoint, altimeter. Then find the RMK delimiter and keep reading.

1. AO1 or AO2 - note it, especially if precipitation is involved
2. $ at the end - data reliability flag; seek corroborating sources
3. FZRANO, PWINO, TSNO - identify the blind spot; fill the gap before flying
4. Lightning remarks (LTG) - check if convective weather is possible
5. T group - exact temperature/dewpoint spread if fog or freezing conditions are relevant
6. CIG range - check if a variable ceiling affects your approach planning

The entire process takes about 30 seconds once you know what you are looking for.

The Aviation Weather Center at aviationweather.gov includes a METAR decoder that parses any observation line by line into plain language - a solid practice tool while building METAR fluency. The full coding standard lives in the Aeronautical Information Manual, meteorology chapter.

Key Takeaways

• AO1 stations cannot identify precipitation type - in freezing temperatures, reported precipitation could be snow or freezing rain
• FZRANO, PWINO, and TSNO each represent a specific sensor outage; treat affected observations as incomplete and find supplemental sources
• A $ at the end of a METAR flags the station for maintenance - that observation may be unreliable
• The T group provides temperature and dewpoint to the nearest tenth of a degree, which can meaningfully change your fog and icing risk assessment
• LTG CG VC (cloud-to-ground lightning in the vicinity) is an active safety condition, not a background data point