Aviation Weather Symbols
Standard weather symbols used on METAR reports, synoptic charts, and aviation weather maps — decoded and explained.
Last reviewed: March 2026Part of the Aviation Weather Reference — the complete hub for METAR, TAF, SIGMETs, icing, turbulence, ISA, and weather decision-making.
Weather symbols are standardised by the World Meteorological Organization (WMO) and adopted globally through ICAO Annex 3. These symbols ensure that pilots, forecasters, and dispatchers everywhere interpret weather information consistently, regardless of language or nationality.
METAR Weather Codes
Weather phenomena in METAR reports are encoded as text codes constructed by combining up to three elements: an intensity prefix, a descriptor, and a precipitation or obscuration type. For example, +TSRA means heavy (+) thunderstorm (TS) with rain (RA).
Intensity Prefixes
| Prefix | Meaning | Notes |
|---|---|---|
| - | Light | Precipitation is light; visibility generally not severely reduced |
| (none) | Moderate | No prefix indicates moderate intensity — the default |
| + | Heavy | Significant impact on visibility and operations |
| VC | In the vicinity | Within 8 km of the aerodrome reference point, but not at the station |
Descriptor Codes
| Code | Meaning | Usage Notes |
|---|---|---|
| MI | Shallow | Used with FG only — fog extending less than 2 m above ground |
| BC | Patches | Used with FG only — patchy fog across the aerodrome |
| PR | Partial | Used with FG only — fog covering part of the aerodrome |
| DR | Low drifting | Used with DU, SA, SN — below eye level (below ~2 m) |
| BL | Blowing | Used with DU, SA, SN — raised above eye level by wind |
| SH | Shower(s) | Used with RA, SN, GR, GS, PL — convective precipitation |
| TS | Thunderstorm | May appear alone or with precipitation types (e.g. TSRA, TSGR) |
| FZ | Freezing | Used with FG, DZ, RA — supercooled water freezing on contact |
Precipitation Types
| Code | Meaning | Notes |
|---|---|---|
| RA | Rain | Liquid precipitation, droplet diameter > 0.5 mm |
| SN | Snow | Frozen precipitation in the form of ice crystals |
| DZ | Drizzle | Fine droplets < 0.5 mm diameter, close together |
| GR | Hail | Ice balls or irregular ice ≥ 5 mm diameter |
| GS | Small hail / snow pellets | Ice particles < 5 mm; includes graupel |
| PL | Ice pellets | Transparent or translucent pellets of ice; also called sleet |
| SG | Snow grains | Very small, white, opaque ice particles; the frozen equivalent of drizzle |
| IC | Ice crystals | Also called diamond dust; tiny crystals suspended in air, common at very low temperatures |
| UP | Unknown precipitation | Used at automated (AUTO) stations when the sensor cannot determine the type |
Obscuration Types
| Code | Meaning | Notes |
|---|---|---|
| FG | Fog | Visibility < 1,000 m; composed of water droplets |
| BR | Mist | Visibility 1,000–5,000 m; similar to fog but less dense |
| HZ | Haze | Fine dry particles; visibility generally 1,000–5,000 m |
| FU | Smoke | Combustion particles suspended in air |
| VA | Volcanic ash | Fine rock particles from volcanic eruption; severe hazard to engines |
| DU | Widespread dust | Fine particles of earth raised by wind |
| SA | Sand | Sand particles raised by wind; coarser than dust |
| PY | Spray | Water droplets torn from a water surface by wind |
Other Weather Phenomena
| Code | Meaning | Notes |
|---|---|---|
| SQ | Squall | Sudden increase in wind speed ≥16 kt, sustained ≥22 kt for ≥1 min |
| SS | Sandstorm | Sand raised by strong wind; visibility severely reduced. Use + for severe. |
| DS | Duststorm | Dust raised by strong wind; visibility severely reduced. Use + for severe. |
| FC | Funnel cloud | Tornado or waterspout when preceded by +; funnel cloud (not surface) otherwise |
| PO | Dust/sand whirls | Well-developed dust devils or sand pillars |
Synoptic Chart Symbols
Synoptic weather charts depict large-scale weather systems using standardised symbols for fronts, pressure systems, and boundaries. The following frontal symbols are used on aviation and meteorological charts worldwide.
Frontal Symbols
Cold Front
Blue line with triangles pointing in the direction of movement. Cold air advances and undercuts warmer air, causing rapid lifting. Often associated with cumulonimbus, heavy showers, and gusty winds. Passage marked by a wind shift, pressure rise, and temperature drop.
Warm Front
Red line with semicircles pointing in the direction of movement. Warm air overrides cooler air ahead, producing a broad zone of cloud (cirrus, altostratus, nimbostratus) and prolonged, steady precipitation. Approach is signalled by lowering cloud bases.
Occluded Front
Purple line with alternating triangles and semicircles pointing in the direction of movement. Occurs when a cold front overtakes a warm front. Weather combines characteristics of both fronts — may produce heavy precipitation and embedded thunderstorms.
Stationary Front
Alternating blue triangles and red semicircles on opposite sides of the line. Neither air mass is advancing. Can persist for days, producing prolonged areas of cloud and precipitation along the boundary.
Pressure Systems
| Symbol | Meaning | Notes |
|---|---|---|
| L | Low pressure centre | Counterclockwise circulation (N. hemisphere); associated with cloud and precipitation |
| H | High pressure centre | Clockwise circulation (N. hemisphere); generally fair weather |
| TROUGH | Trough of low pressure | Elongated area of low pressure; may trigger convection along its axis |
| RIDGE | Ridge of high pressure | Elongated area of high pressure; generally fair weather |
Cloud Type Symbols
Cloud types are classified by the WMO into ten genera, grouped into three height bands. On aviation charts and in weather reports, standard abbreviations are used to identify cloud types. Cumulonimbus (CB) and towering cumulus (TCU) are always reported in METARs when present, regardless of amount.
CICirrus — thin, wispy, fibrousCCCirrocumulus — small white patches, rippledCSCirrostratus — thin, whitish veil, halo phenomenaACAltocumulus — white/grey patches, rounded massesASAltostratus — greyish sheet, sun visible as through ground glassNSNimbostratus — thick, dark grey layer, continuous rain/snowSCStratocumulus — grey/white layer with rounded massesSTStratus — uniform grey layer, may produce drizzleCUCumulus — detached, dense, vertical developmentCBCumulonimbus — heavy, dense, great vertical extent; thunderstormsMETAR cloud reporting: Cloud amounts are given in oktas (eighths of sky) using the codes FEW (1–2), SCT (3–4), BKN (5–7), OVC (8/8). Heights are in hundreds of feet AGL. The suffixes CB and TCU are appended when cumulonimbus or towering cumulus are observed — e.g. BKN040CB.
Wind Symbols
Station model wind barbs are used on synoptic charts and significant weather (SIGWX) charts to depict wind speed and direction. The barb points in the direction the wind is coming from, with speed indicated by half barbs, full barbs, and pennants attached to the end of the shaft.
| Element | Value | Appearance |
|---|---|---|
| Circle only | Calm (0 kt) | Empty circle at station position |
| Half barb (short line) | 5 kt | Short tick on the shaft |
| Full barb (long line) | 10 kt | Full-length tick on the shaft |
| Pennant (filled triangle) | 50 kt | Solid triangular flag on the shaft |
Wind barbs are additive — combine pennants, full barbs, and half barbs to read the total wind speed. For example: one pennant + one full barb + one half barb = 50 + 10 + 5 = 65 knots.
Visibility and Ceiling Symbols
The following codes appear in METAR and TAF reports to indicate special visibility or cloud conditions. These codes replace the standard cloud and visibility groups when applicable.
| Code | Meaning | Conditions |
|---|---|---|
| CAVOK | Ceiling and Visibility OK | Visibility ≥10 km, no cloud below 5,000 ft or below minimum sector altitude (whichever higher), no CB or TCU, and no significant weather |
| SKC | Sky Clear | No cloud at any level; used at manual observation stations |
| NSC | No Significant Cloud | No cloud below 5,000 ft or below MSA, no CB/TCU; used when CAVOK criteria are not fully met (e.g. significant weather present) |
| NCD | No Cloud Detected | Automated station (AUTO) — ceilometer detected no cloud; does not guarantee clear sky beyond sensor range |
| VV | Vertical Visibility | Sky obscured; followed by a three-digit height in hundreds of feet. Example: VV005 = vertical visibility 500 ft. Used when a ceiling cannot be determined due to obscuration (fog, heavy snow, etc.) |
IFR ceiling definition: A ceiling exists when the lowest layer is reported BKN (broken) or OVC (overcast), or when vertical visibility (VV) is reported. For IFR planning, the ceiling is the height of the lowest BKN/OVC layer or the VV value.
Turbulence and Icing Symbols
Turbulence and icing are reported on Significant Weather (SIGWX) prognostic charts, PIREPs (pilot reports), and AIRMETs/SIGMETs. The following intensity scales and type classifications are standardised by ICAO.
Turbulence Intensity
| Intensity | PIREP Code | Effect on Aircraft |
|---|---|---|
| Light | LGT | Slight, erratic changes in altitude/attitude; occupants may feel slight strain against belts. Unsecured objects displaced slightly. |
| Moderate | MOD | Changes in altitude/attitude occur, but aircraft remains in positive control. Occupants feel definite strain against belts. Unsecured objects dislodged. |
| Severe | SEV | Large, abrupt changes in altitude/attitude. Large airspeed variations. Aircraft may be momentarily out of control. Occupants forced violently against belts. |
| Extreme | EXTRM | Aircraft is violently tossed about and practically impossible to control. May cause structural damage. |
Turbulence Types on Charts
| Type | Abbreviation | Description |
|---|---|---|
| Clear Air Turbulence | CAT | Occurs in clear air, typically near the jet stream or in areas of strong wind shear at high altitude |
| Mechanical | MECH | Caused by terrain or obstructions disrupting airflow; common at low levels near mountains |
| Convective | CONV | Associated with cumulonimbus and thunderstorms; updrafts/downdrafts |
| Mountain wave | MTW | Standing waves on the lee side of mountains; may extend to great heights and include rotor turbulence at lower levels |
Icing Intensity
| Intensity | PIREP Code | Accumulation Rate / Effect |
|---|---|---|
| Trace | TRACE | Ice becomes perceptible. Rate of accumulation slightly greater than sublimation. Not hazardous unless encountered for extended period. |
| Light | LGT | Rate of accumulation may create a problem for prolonged flight (>1 hour). Occasional use of de-icing equipment removes accumulation. |
| Moderate | MOD | Rate of accumulation is such that even short encounters become potentially hazardous. Use of de-icing/anti-icing or diversion is necessary. |
| Severe | SEV | Rate of accumulation is such that de-icing/anti-icing equipment fails to reduce or control the hazard. Immediate exit from the icing environment is required. |
Icing Types
| Type | Description | Typical Conditions |
|---|---|---|
| Rime ice | Rough, milky-white, opaque ice formed by rapid freezing of small supercooled droplets | Stratiform cloud, temperatures -10 to -20 °C, small droplets |
| Clear ice (glaze) | Smooth, transparent, dense ice formed by slow freezing of large supercooled droplets | Cumuliform cloud or freezing rain, temperatures 0 to -10 °C, large droplets |
| Mixed ice | Combination of rime and clear ice, rough and irregular | Mixed droplet sizes; varying temperature zones within cloud |
| SLD (Supercooled Large Droplets) | Freezing drizzle or rain; droplets > 50 microns. Extremely hazardous — ice can accumulate aft of protected surfaces. | Warm layer aloft producing rain that becomes supercooled below; also in deep convective cloud |
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