What is a METAR and how does it differ from a METAR received via ASOS versus AWOS?

A METAR (Meteorological Aerodrome Report) is a standardized aviation weather observation that includes wind, visibility, sky condition, temperature, dewpoint, and altimeter setting. ASOS (Automated Surface Observing System) is an FAA/NWS-operated network that generally provides more comprehensive and frequent observations, while AWOS (Automated Weather Observing System) stations vary by equipment tier and may report fewer weather elements. Both broadcast their observations over discrete radio frequencies that pilots can monitor directly, and both generate METARs formatted identically per FAA and WMO standards. Understanding the source helps you recognize potential gaps, such as an AWOS-1 reporting only altimeter and wind but not sky condition.

How do you decode the sky condition field in a METAR from an ASOS or AWOS broadcast?

Sky condition is reported using three-letter contractions followed by a height in hundreds of feet AGL: FEW (1–2 oktas), SCT (3–4 oktas), BKN (5–7 oktas), and OVC (8 oktas, or totally overcast). A reading of BKN015, for example, means a broken ceiling at 1,500 feet AGL. CLR or SKC indicates no clouds below 12,000 feet for automated stations, and VV followed by a number indicates an obscured sky with a vertical visibility value. According to the Aviation Weather Handbook (FAA-H-8083-28), understanding these fields is critical for determining whether visual flight conditions exist before any sUAS operation under 14 CFR Part 107.

Why does the altimeter setting in a METAR matter for a Part 107 remote pilot even though drones don't have traditional altimeters?

The altimeter setting in a METAR, reported in inches of mercury (e.g., A2992), reflects the current local pressure and is essential for understanding atmospheric density and for coordinating with manned aircraft operating in the same airspace. Many GPS-based ground control stations and sUAS flight apps use barometric pressure data to improve altitude accuracy, making the reported altimeter setting directly relevant to flight planning. Additionally, when a remote pilot communicates with ATC or files operational data, understanding altimeter settings ensures consistent altitude references with manned traffic. The FAA's Aeronautical Information Manual (AIM) and Part 107 guidance both emphasize situational awareness of real-time weather data, including pressure, as part of safe remote pilot operations.

Reading and Interpreting METARs Received via ASOS/AWOS Broadcasts

Before a Part 107 remote pilot ever launches a small unmanned aircraft system (sUAS), they must have a clear picture of current weather conditions at and near the operating site. The METAR — Meteorological Aerodrome Report — is the standardized observation that provides exactly that picture. Automated Surface Observing System (ASOS) and Automated Weather Observing System (AWOS) stations generate these reports continuously, broadcasting them over dedicated radio frequencies and making them available through flight service and digital weather sources. For Part 107 operations, understanding how to access, read, and correctly interpret a METAR is not just a knowledge test requirement — it is a fundamental safety skill.

This article walks through every major field of a METAR in the order it appears, explains the FAA-defined conventions behind each element, and highlights the practical judgment calls a remote pilot must make based on what the report says. By the end, you will be able to pick up a raw METAR and extract actionable weather intelligence in seconds.

What ASOS and AWOS Stations Actually Report

ASOS and AWOS are ground-based automated sensor arrays typically located at airports. They measure wind speed and direction, visibility, sky condition (cloud height and coverage), temperature, dew point, and altimeter setting — all without a human observer. ASOS stations are the FAA/National Weather Service standard and generally provide the most complete data set, including precipitation type identification and thunderstorm detection. AWOS stations come in several tiers (AWOS-1 through AWOS-3P+) that vary in the parameters reported; some only report wind and altimeter, while others approach ASOS capability. As a Part 107 pilot, note which tier serves your area so you know what data is and is not being automatically generated.

These stations issue routine METAR observations every hour, typically at the top of the hour, and special observations (SPECI) whenever conditions change rapidly — for example, when visibility drops below certain thresholds or when the ceiling falls. SPECIs are formatted identically to routine METARs but are labeled SPECI at the start.

Decoding the METAR Field by Field

Type, Station, and Date/Time

A METAR begins with the report type (METAR or SPECI), followed by the four-letter ICAO station identifier. U.S. stations begin with the letter K (e.g., KORD for Chicago O'Hare). Next is the date and time group: a six-digit code where the first two digits are the day of the month, and the last four digits are UTC time (always expressed in Zulu). For example, 151755Z means the 15th day of the month at 1755 UTC. Remote pilots operating visually must convert this to local time to confirm the observation is recent — a METAR more than an hour old may not reflect rapidly changing conditions.

Wind

Wind is reported as a five- or six-digit group followed by KT (knots). The first three digits give the true direction from which the wind is blowing, rounded to the nearest 10 degrees. The next two (or three) digits give the speed in knots. Gusts are indicated by a G and then the gust speed: 27015G28KT means wind from 270° at 15 knots gusting to 28 knots. A variable wind direction below 6 knots is coded VRB03KT. If the wind direction varies significantly, a variable group such as 210V280 appears after the main wind group, showing the range of directions. For sUAS operations, high winds and gusts relative to your aircraft's performance envelope directly impact safe control, so this is often the first field to evaluate.

Visibility

Prevailing visibility is reported in statute miles in U.S. METARs. A reading of 10SM means 10 statute miles — the maximum routinely reported. Fractions such as 1/2SM or 1 3/4SM indicate reduced visibility. The critical Part 107 visibility threshold is 3 statute miles: remote pilots must have at least 3 SM of flight visibility to operate without a waiver. If the METAR shows visibility below 3 SM, flight is not permitted under standard Part 107 rules.

Weather Phenomena

Present weather codes appear between visibility and sky condition. These use standard qualifiers and descriptors. Common examples include -RA (light rain), RA (moderate rain), +RA (heavy rain), TS (thunderstorm), FG (fog), BR (mist), HZ (haze), SN (snow), and DZ (drizzle). Fog (FG) is reported when visibility is below 5/8 SM; mist (BR) applies from 5/8 SM up to 6 SM with high relative humidity. Thunderstorms (TS) are an immediate stop-flight indicator for sUAS — the associated turbulence, wind shear, and lightning create conditions far beyond safe small UAS operation.

Sky Condition

Sky condition is one of the most operationally important fields for Part 107. Cloud layers are reported using three-letter coverage codes followed by height in hundreds of feet AGL:

FEW — 1 to 2 oktas (eighths) of sky coverage
SCT (Scattered) — 3 to 4 oktas
BKN (Broken) — 5 to 7 oktas; constitutes a ceiling
OVC (Overcast) — 8 oktas; constitutes a ceiling

For example, BKN025 means a broken ceiling at 2,500 feet AGL. The Part 107 requirement is that sUAS must remain at least 500 feet below clouds and 2,000 feet horizontally from clouds. A ceiling of BKN025 (2,500 ft AGL) means the maximum allowed altitude is 2,000 ft AGL — but since Part 107 already caps altitude at 400 ft AGL above ground level (or within 400 ft of a structure), the practical cloud clearance constraint most often comes into play with low ceilings. If the ceiling is at or below approximately 900 feet AGL, the 500-foot below-cloud requirement combined with the 400-foot altitude limit begins to create a very narrow or nonexistent operating window. SKC (sky clear) or CLR (clear below 12,000 ft, used by automated stations) indicate no significant clouds.

Temperature and Dew Point

Temperature and dew point are reported in degrees Celsius, separated by a slash: 22/14 means temperature 22°C, dew point 14°C. A minus sign prefix (M) indicates below zero: M03/M08. The temperature-dew point spread matters: when the two values are within about 2-3°C of each other, relative humidity is near 100% and fog or low clouds are likely to form or persist. Battery performance in your sUAS degrades noticeably in cold temperatures, making the temperature reading operationally relevant beyond just weather judgment.

Altimeter Setting

The altimeter setting is prefixed with an A and given in inches of mercury to the nearest hundredth: A2992 means 29.92 in. Hg. While altitude control for most small UAS relies on GPS or barometric sensors, understanding the pressure environment matters for flight planning and any airspace coordination. Low pressure systems are associated with deteriorating weather; cross-referencing the altimeter with standard (29.92) tells you whether you are in relatively high or low pressure air.

Remarks Section

Everything after RMK is the remarks section. ASOS/AWOS remarks can include peak wind (PK WND), variable ceiling height (CIG), sea-level pressure (SLP), and precipitation accumulation. Thunderstorm location and movement may also appear here. Remote pilots should scan remarks for any automated station advisory that the sensor data may be incomplete or that a particular element was not observed.

Why This Matters for Part 107 Operations

Unlike manned aircraft pilots who have cockpit instruments and can adapt in flight, a remote pilot must make a go/no-go decision before launch based largely on pre-flight weather evaluation. A METAR provides the most current, standardized snapshot of conditions at the reporting station. Because ASOS/AWOS sites are usually at airports, and Part 107 operations often occur at fields or sites away from airports, remote pilots must also consider that conditions may vary between the reporting station and their actual operating area. A METAR showing 7 SM visibility at the airport 5 miles away does not guarantee identical conditions at a construction site surrounded by industrial haze.

Key Numbers and Rules

3 SM — minimum flight visibility required under Part 107 without a waiver
500 ft below clouds — required cloud clearance (vertical)
2,000 ft horizontally from clouds — required cloud clearance (lateral)
400 ft AGL — standard maximum altitude for sUAS operations
METAR issued every hour; SPECIs issued on significant change
BKN or OVC = ceiling; FEW and SCT are not ceilings
Temperature/dew point spread ≤ 2-3°C — fog and low cloud risk is high

Common Test Traps

Confusing statute miles with nautical miles: METAR visibility is in statute miles in the U.S. Do not mix these up when assessing whether the 3 SM minimum is met.
Misidentifying a ceiling: FEW and SCT layers are not ceilings. Only BKN and OVC constitute an official ceiling. A METAR showing SCT015 does not mean the ceiling is 1,500 ft — there may be no ceiling at all if no BKN or OVC layer exists.
Forgetting cloud clearance applies both vertically and horizontally: Students often remember the 500-ft-below rule but forget the 2,000-ft horizontal requirement. Both apply simultaneously under Part 107.
Assuming a nearby METAR perfectly represents your site: Automated stations report conditions at the sensor location only. Microclimates, terrain effects, and urban heat can create meaningful differences even a few miles away.
Overlooking the SPECI: A test question may present a situation where the hourly METAR shows acceptable conditions but a SPECI issued 20 minutes later shows deterioration. Always use the most recent observation.