Block 01 SW-I-1 MET I

Cloud

A visible accumulation of minute water droplets and/or ice particles suspended in the atmosphere above the Earth's surface.

Low étage

Clouds between the Earth's surface and 6,500 feet.

Middle étage

Clouds between 6,500 feet and 23,000 feet.

High étage

Clouds between 16,500 feet and 45,000 feet.

Cumulus (CU)

Small to medium-sized clouds with slight vertical extent, popcorn-shaped, and bright white in appearance.

Cumulonimbus (CB)

Large to huge clouds with great vertical extent, cauliflower or anvil-shaped tops, and very dark gray to black bases.

Stratocumulus (SC)

Closely spaced, oval-shaped clouds with little vertical extent, often forming in groups, lines, or waves with lumpy tops and flat bases.

Stratus (ST)

Wide clouds with diffuse edges, forming in a uniform sheet with no vertical extent, appearing as light gray or medium gray.

Altocumulus (AC)

Resembling stratocumulus clouds but with much smaller individual elements, widely spaced and circular in shape with little to no vertical extent.

Nimbostratus (NS)

A thick, dark gray cloud with little to moderate vertical extent, forming in the middle étage and sometimes lowering into the low étage.

Cirrus (CI)

Thin and wispy clouds forming in hooks or filaments, with no vertical extent and bright white in color.

Cirrostratus (CS)

Thin, fibrous veil clouds forming in a uniform sheet, with no vertical extent and bright white in color.

Cirrocumulus (CC)

Extremely small cumulus clouds in sheets or bands, with a small vertical extent and white to light gray in color.

Obscuring Phenomena

Surface-based meteorological elements that reduce horizontal visibility, such as haze.

Layer

A cloud and/or obscuring phenomena with bases at approximately the same height above the ground.

Layer height

The distance between the Earth's surface and the layer's base.

Layer Amount

The amount of celestial dome covered by a layer measured in eighths or oktas in meteorology.

Layer amount

The amount of cloud layers present in the sky.

Okta

A unit of measurement used to describe the amount of cloud cover in the sky.

Clear (SKC or CLR)

Corresponds to 0 oktas of cloud cover.

Few (FEW)

Corresponds to 1-2 oktas of cloud cover.

Scattered (SCT)

Corresponds to 3-4 oktas of cloud cover.

Broken (BKN)

Corresponds to 5-7 oktas of cloud cover.

Overcast (OVC)

Corresponds to 8 oktas of cloud cover.

Layer

A distinct horizontal section of clouds in the sky.

Ceiling

The height above the ground of the lowest cloud layer.

Vertical visibility

The distance one can see vertically from a given point.

Horizon circle

The meeting point of the Earth's surface and the sky.

Point of observation

The center point of the horizon circle.

Visibility

The maximum horizontal distance at which objects can be identified.

Prevailing visibility

The greatest visibility observed in at least half of the horizon circle.

Tower visibility

The prevailing visibility determined by air traffic controllers.

Runway Visual Range (RVR)

The maximum distance a pilot can see along the runway.

Visibility aids

Charts, lists, or pictures identifying visibility markers.

Visibility markers

Natural or human-made structures used as reference points for visibility.

Daytime markers

Dark or nearly dark colored objects used as visibility markers during the day.

Nighttime markers

Unfocused lights of moderate intensity used as visibility markers at night.

Celestial dome

The imaginary dome representing the sky.

Atmospheric phenomena

Short-term variations affecting visibility or sky conditions.

Precipitation

Water particles falling from the atmosphere to the ground.

Precipitation rate

The amount of water reaching the ground at a specific location over time.

Precipitation intensity

Categorized as light, moderate, or heavy based on accumulation rates.

Precipitation amount

The total accumulation of precipitation over a given time.

Precipitation character

Describes the intensity and duration of precipitation.

Precipitation types

Different forms of precipitation such as rain, snow, drizzle, etc.

Obscurations to Vision

Visible collections of minute particles in the atmosphere that reduce visibility.

Hydrometeors

Water droplets suspended in the atmosphere.

Lithometeors

Solid, dry particles suspended in the atmosphere.

Mist

Minute water droplets reducing visibility to less than 7 statute miles but greater than or equal to 5/8 statute miles.

Fog

Similar to mist, but reduces visibility to less than 5/8 statute miles.

Spray

Water droplets raised into the atmosphere by strong winds.

Haze

Consists of microscopic dry particles or pollutants with an opalescent appearance.

Smoke

Small combustion particles raised into the atmosphere by large fires.

Dust

Microscopic solid particles of earth raised by strong winds.

Sand

Microscopic sand particles raised by surface winds.

Atmospheric Pressure

The force per unit area exerted on a surface by the weight of the air above that surface.

Altimeter Setting

A value that, when set on an aircraft's altimeter, adjusts the display to indicate altitude above a specific pressure level.

Sea-level Pressure

The atmospheric pressure at sea level, used as a reference point for weather observations and forecasts.

METAR

Meteorological Aerodrome Report, a coded weather observation used worldwide to forecast weather conditions and issue warnings.

Wind Direction

The direction from which the wind is blowing, measured in degrees clockwise from true north.

Wind Speed

The rate at which air is moving horizontally past a given point, typically measured in knots or meters per second.

Zulu Time

Coordinated Universal Time (UTC), the global standard time reference based on the prime meridian (0 degrees longitude).

Wind Speed and Gusts

When decoding wind speed and gusts, include their units of measure. For example, 16010MPS is wind from 160 degrees at 10 meters per second, and 030102G110KT is wind from 30 degrees at 102 gusting to 110 knots.

Variable Wind Direction

A variable wind direction occurs when the wind direction fluctuates 60 degrees or more, and the wind speed is greater than 6KT or 3MPS. It is denoted by two wind directions separated by "V", like 180V240 for wind from 180 to 240 degrees.

Prevailing Visibility

Prevailing visibility can be up to five digits and suffixed with SM (statute miles). Decode visibility based on atmospheric phenomena reported or not. For example, 7SM can mean unrestricted visibility or 7 statute miles depending on the observation.

Runway Visual Range (RVR)

RVR may be reported as a single value (RDRDR/VRVRVRVRFT) or a range (RDRDR/VNVNVNVNVVXVXVXVXFT). It includes the runway indicator, visual range, and measurement unit (feet or meters).

Present Weather

Present weather includes different weather phenomena codes like precipitation, obscurations to vision, and other phenomena. Intensity, type, and qualifiers are used to decode weather conditions like rain, fog, snow, and more.

Vicinity (VC) Phenomena

Refers to a phenomenon occurring within 10 nautical miles of the observer but not at the point of observation. Examples include VCFG (Fog in vicinity) and VCTS (Thunderstorm in vicinity).

Sky Condition

Refers to the amount of clouds and obscuring phenomena covering the celestial dome in weather observations. It includes layer amount, layer height, and significant cloud type in the standard format.

Partial Obscuration

Refers to a partial obscuration of the sky with FEW, SCT, or BKN and a layer height of 000 denoting the surface. The type of obscuration is noted in the remarks section of the observation.

Total Obscuration

Refers to total obscuration with the format VVhshshs, where VV indicates vertical visibility and the height is the highest visible height the observer can look vertically into the phenomenon.

International METAR

Refers to some international observations that may use CAVOK (Ceiling and visibility ok) or NSC (No significant cloud above 5,000 feet) instead of reporting cloud layers.

Ambient Air and Dew-Point Temperatures

Two-digit temperatures in whole degree Celsius (°C) separated by a solidus (/). The letter "M" before a number indicates a temperature below freezing.

Pressure

METAR observations report barometric pressure using altimeter setting (APhPhPhPh) for inches of mercury or station pressure (QPhPhPhPh) for millibars.

Winter Solstice

The time of year when the sun is at its southernmost point, resulting in the shortest day and longest night in the Northern Hemisphere.

Summer Solstice

The time of year when the sun is at its northernmost point, resulting in the longest day and shortest night in the Northern Hemisphere.

Vernal Equinox

The time when the sun crosses the equator in a northward direction, resulting in equal day and night lengths in both hemispheres.

Autumnal Equinox

The time when the sun crosses the equator in a southward direction, resulting in equal day and night lengths in both hemispheres.

Troposphere

The lowest layer of Earth's atmosphere where weather phenomena occur, with temperatures decreasing with altitude.

Stratosphere

The layer of the atmosphere above the troposphere containing the ozone layer, where temperatures increase with altitude.

Mesosphere

The third layer of the atmosphere above the stratosphere, where temperatures decrease with altitude.

Thermosphere

The fourth layer of the atmosphere above the mesosphere, where temperatures increase with altitude due to absorption of solar radiation.

Exosphere

The outermost layer of the atmosphere where it gradually transitions into space, with temperatures decreasing with altitude.

Ocean Currents

Horizontal movements of seawater that are large features extending across the oceans hundreds of miles wide and thousands of miles long.

Current Intensity

The speed or drift of a current measured in knots, with components of speed and direction.

Cold Currents

Occur where colder water moves into warmer water, found off the west coasts of continents in middle latitudes and off the east coasts of continents in high latitudes.

Warm Currents

Found off the east coast of continents in middle latitudes and off the west coast of continents in high latitudes.

Subtropical Gyres

Large oval or circular ocean currents near 30 degrees latitude that rotate clockwise in the Northern hemisphere and counterclockwise in the Southern hemisphere.

Boundary Currents

Four currents associated with each gyre - Equatorial, Western, Polar, and Eastern currents.

Coastal Upwelling

Forced upward movement of cold, sub-surface water to the ocean's surface, strongest where wind direction parallels the coastline.

Coastal Downwelling

Where warm, surface water is forced to sink, strongest when wind direction parallels the coast.

Vertical Movement of Water

Cold water is denser than warm water, leading to natural sinking of cold water and rising of warm water.

Gyres

Circular ocean currents associated with subtropical regions, with specific boundary currents.

Drift

The movement or flow of ocean currents, measured in nautical miles per day.

Temperature

The degree of hotness or coldness of a body or environment, influencing the movement of ocean currents.

Set

The direction of movement of an ocean current, often indicated using compass points.

Upwelling

The process of cold, sub-surface water rising to the ocean's surface due to specific wind patterns.

Downwelling

The process of warm, surface water sinking below the surface due to particular wind directions.

Equatorial Current

A boundary current near the Equator with a west set and a drift of 10 to 50 nautical miles per day.

Western Boundary Current

A warm current with a north set in the Northern hemisphere and a south set in the Southern hemisphere, with a drift of 25 to 75 nautical miles per day.