What does CLR mean on a METAR and is it the same as SKC?

CLR (Clear) is used by automated stations (ASOS/AWOS) and means no clouds were detected below 12,000 feet AGL. SKC (Sky Clear) is used by human observers and means the entire sky is clear with no clouds at any altitude. They are functionally similar for most purposes, but CLR does not rule out clouds above 12,000 ft that the automated sensor cannot detect.

Is METAR wind direction in true or magnetic degrees?

METAR wind direction distributed on national networks — including the internet, FIS-B, and FSS — is in true degrees. However, when ASOS or AWOS broadcasts wind over local radio or telephone, it uses magnetic degrees. Always confirm which reference you are using when comparing METAR winds to runway headings or compass courses.

What is the difference between ASOS and AWOS for METAR reporting?

ASOS is the primary national network and issues both routine METARs (hourly) and special METARs (SPECIs) when significant condition changes occur, such as visibility dropping below 3 statute miles. AWOS issues METARs every 20 minutes but does not issue SPECIs, and generally reports fewer weather elements depending on the specific AWOS type installed at that airport.

Decoding a METAR: Wind, Visibility, Weather, Sky, and Altimeter

The Aviation Routine Weather Report (METAR) is the worldwide standard format for reporting surface weather conditions at airports. Issued hourly (or more frequently as a Special observation, SPECI), the METAR distills wind, visibility, present weather, sky condition, temperature, dewpoint, and altimeter setting into a compact coded string. While many preflight apps now display a plain-language translation alongside the raw code, every pilot must be able to decode a raw METAR independently — the decoded version is not always available, and a misread METAR has led to flights that departed into conditions far below minimums.

This article walks through each major group of the METAR in sequence, explaining what every code means, where the numbers come from, and how to apply the information operationally. The source authority is FAA Aviation Weather Handbook FAA-H-8083-28B, Chapter 24 (Observations).

The METAR Header: Type, Station, and Time

Every METAR begins with an optional type designator. METAR signals a routine hourly observation; SPECI signals a special (non-routine) report issued when conditions cross a significant threshold — for example, when visibility drops below 3 statute miles. Following the type is the four-letter ICAO station identifier (e.g., KORD for Chicago O'Hare). The six-digit time group ends in Z for Zulu (UTC); the first two digits are the day of the month and the last four are the hour and minute (e.g., 030053Z = the 3rd day of the month at 0053 UTC).

After the time, automated stations include AUTO to indicate no human observer is present. If the report has been augmented by a certified observer, AUTO is dropped. The distinction matters because automated systems have sensor limitations — they cannot observe phenomena like tornadoes, waterspouts, or certain types of precipitation that a human would note.

Wind Group

Wind is reported as a five- or seven-character group immediately following the time/modifier. The first three digits are the direction the wind is blowing from, in degrees true (on national distribution networks such as FSS, internet, and FIS-B). The next two digits are the speed in knots, followed by KT. If gusts are present, a G separates the sustained speed from the gust speed (e.g., 18015G28KT = wind from 180° at 15 knots, gusting to 28 knots).

When the wind direction is variable and the speed is 6 knots or less, the direction group is coded VRB (e.g., VRB04KT). When the wind varies more than 60° and the speed exceeds 6 knots, a variable direction range is appended immediately after the wind group in the body of the METAR (e.g., 350V070). Calm wind is coded 00000KT. An important operational note: while METAR wind direction on digital networks is in true degrees, local voice broadcasts (ASOS/AWOS radio and telephone) report wind direction in magnetic degrees — a critical difference when comparing the written METAR to what you heard on the ATIS.

Visibility Group

Prevailing visibility is reported in statute miles and fractions in the United States (e.g., 10SM, 1 1/2SM, 1/4SM). The maximum reported value is 10SM, which means visibility is 10 statute miles or greater — it does not distinguish between 10 and 50 miles. When visibility is below one statute mile, the fraction appears without a leading whole number (e.g., 1/4SM). Variable visibility and sector visibility may appear in the remarks.

ASOS and AWOS sensors time-average visibility data over a 10-minute window. This averaging is asymmetric: the algorithm is designed to report deteriorating conditions much faster than improving conditions. If dense fog suddenly lifts, the OMO (One-Minute Observation) may continue to report low visibility for up to 10 minutes before fully reflecting the improvement. Pilots should keep this lag in mind when evaluating rapidly changing conditions.

Present Weather Group

Present weather is coded using a structured combination of qualifiers and phenomena descriptors. A two-letter intensity prefix may precede the descriptor: a minus sign (−) for light, no sign for moderate, and a plus sign (+) for heavy. A VC prefix indicates a phenomenon in the vicinity of the airport (roughly 5 to 10 statute miles), such as VCTS (thunderstorm in the vicinity).

ASOS reports the following present weather types: rain (RA), snow (SN), freezing rain (FZRA), and unknown precipitation (UP). Obstructions to visibility reported by ASOS include:

FG (Fog) — reported when visibility is less than 5/8 statute mile.
BR (Mist) — reported when visibility is 5/8 SM to less than 7 SM and the temperature-dewpoint spread is 4 °F (≈2 °C) or less.
HZ (Haze) — reported when visibility is 5/8 SM to less than 7 SM and the temperature-dewpoint spread exceeds 4 °F (≈2 °C).
FZFG (Freezing Fog) — reported when fog is present and temperature is below 0 °C.

A common pilot confusion: BR and HZ occupy the same visibility range but are differentiated by the temperature-dewpoint spread, which reflects whether the obscuration is moisture-based or particulate-based.

Sky Condition Group

Sky condition reports cloud layers from the lowest to the highest, using three-letter coverage codes and height in hundreds of feet AGL:

SKC — Sky Clear (used by human observers; no clouds)
CLR — Clear below 12,000 ft AGL (used by automated stations)
FEW — 1/8 to 2/8 sky coverage
SCT (Scattered) — 3/8 to 4/8 sky coverage
BKN (Broken) — 5/8 to 7/8 sky coverage — operationally defines the ceiling
OVC (Overcast) — 8/8 sky coverage — also defines the ceiling

The ceiling is defined as the lowest broken or overcast layer (or vertical visibility into obscuration). A layer coded FEW or SCT is not a ceiling. Heights are three digits representing hundreds of feet: BKN025 = broken ceiling at 2,500 ft AGL. Cumulonimbus (CB) or towering cumulus (TCU) suffixes may follow the coverage code when those cloud types are observed.

ASOS evaluates sky condition using a 30-minute time-averaging window ending at the observation time. Human observers use spatial averaging — scanning the entire sky — which can yield slightly different results, particularly when cloud cover is variable. ASOS sky condition reporting is limited to clouds at or below 12,000 ft AGL; clouds above that altitude are not detected and will not appear in the coded sky group.

Temperature and Dewpoint

Temperature and dewpoint are reported in whole degrees Celsius, separated by a slash (e.g., 30/23 = temperature 30 °C, dewpoint 23 °C). Sub-zero values are preceded by M for minus (e.g., M05/M10). A narrow temperature-dewpoint spread signals high relative humidity and the potential for fog, low ceilings, or icing. The METAR remarks may include a more precise temperature to the nearest tenth of a degree Celsius in the T-group (e.g., T03000233 = 30.0 °C / 23.3 °C).

Altimeter Setting

The altimeter setting is the last element before the remarks section and is prefixed with A in U.S. METARs (e.g., A2992 = 29.92 inHg). This is the value you dial into your altimeter's Kollsman window to make the instrument read field elevation when on the ground — and to maintain accurate altitude readings in flight. The sea-level pressure in millibars may also appear in remarks as SLP followed by three digits (e.g., SLP132 = 1013.2 mb). Note that A2992 and SLP132 in the example METAR for KPNS are very nearly equivalent values expressed in different units.

ASOS vs. AWOS: What Each System Reports

The ASOS (Automated Surface Observing System) is the nation's primary surface weather observing network, operated jointly by the NWS, FAA, and DOD. It issues hourly METARs and SPECIs, and also broadcasts One-Minute Observations (OMOs) directly to aircraft via FAA ground-to-air radio. The OMO broadcast may differ slightly from the METAR you see online because the broadcast uses the most recent one-minute data rather than the archived hourly observation.

The AWOS (Automated Weather Observing System) is similar but generally reports fewer elements and may lack backup sensors. AWOS generates a METAR at 20-minute intervals and does not issue SPECIs. There are six AWOS types, ranging from altimeter-only (AWOS-A) to full-featured systems:

AWOS-A: Altimeter only.
AWOS-AV: Altimeter + visibility.
AWOS-1: Wind, temperature, dewpoint, altimeter, density altitude.
AWOS-2: All AWOS-1 parameters + visibility.
AWOS-3: All AWOS-2 parameters + precipitation accumulation + cloud height. Optional sensors for precipitation type (AWOS-3P) and/or thunderstorm/lightning (AWOS-3PT).
AWOS-4: All AWOS-3PT parameters + freezing rain.

Understanding which AWOS type is installed at an airport tells you exactly which elements will — and will not — be reported. An AWOS-1 at a remote strip, for instance, will not give you ceiling information.

Why It Matters Operationally

A single METAR read correctly can be the difference between a safe departure and a violation of instrument flight minimums. The ceiling and visibility values determine whether VFR or IFR flight rules apply, and whether an instrument approach is legal given the published minimums. The altimeter setting ensures terrain and traffic separation is based on accurate altitude. The wind group drives crosswind calculations and runway selection. Present weather codes — especially FZRA, TS, or +SN — are immediate red flags for hazardous conditions.

Key Numbers and Rules

ASOS sky condition: time-averaged over the last 30 minutes; clouds reported up to 12,000 ft AGL.
ASOS/AWOS visibility: time-averaged over the last 10 minutes.
Fog (FG) threshold: visibility less than 5/8 SM.
Mist (BR) vs. Haze (HZ): both in the 5/8 SM–7 SM range; BR when temp-dewpoint spread ≤ 4 °F (≈2 °C), HZ when spread > 4 °F.
AWOS issues METARs every 20 minutes; AWOS does not issue SPECIs.
ASOS issues a SPECI when visibility drops below 3 statute miles (among other thresholds).
Wind direction on national networks (internet, FIS-B, FSS) is in true degrees; local radio/phone is magnetic degrees.
Ceiling = lowest BKN or OVC layer; FEW and SCT are not ceilings.

Common Test Traps

CLR ≠ no clouds anywhere. CLR only means no clouds detected below 12,000 ft AGL by the automated station. There could be a solid overcast at 15,000 ft that the ASOS simply cannot see.
10SM does not mean exactly 10 miles. It means 10 statute miles or greater — the METAR does not distinguish between 10 and unlimited visibility.
Wind direction in METARs is TRUE, not magnetic. Confusing these when planning crosswind calculations or comparing to a VOR radial is a common error.
AWOS does not issue SPECIs. If you are relying on an AWOS for rapidly changing conditions, you will not receive an automatic special report when conditions deteriorate — you must check OMOs or contact FSS.
BR vs. FG depends on visibility, not just moisture. Many students default to fog whenever it is humid. Remember: visibility must be below 5/8 SM for FG; above that threshold with a tight spread, it is BR.