December 1999 2-7
QUALIFIERS Intensity Intensity may be shown with most precipitation types.
A “-”denotes a light intensity level, no symbol denotes a moderate intensity level, and a “+” denotes a heavy intensity level. When more than one type of precipitation is present, the intensity refers to the first precipitation type (most predominant). (See Table 2-2.)
Example:
+SHRASN indicates heavy rainshowers and snow.
Table 2-2 Intensity Qualifiers Intensity Qualifiers
- Light Moderate + Heavy Proximity Proximity is applied to and reported only for weather phenomena occurring in the vicinity of the airport. Vicinity of the airport is defined to be between 5 and 10 miles of the usual point of observation for obscuration and just beyond to point of observation to 10 miles for precipitation. It is denoted by VC. Intensity and VC will never be shown in the same group.
Examples:
VCSH indicates showers in the vicinity of the airport.
VCFG indicates fog in the vicinity of the airport.
Descriptor The eight descriptors shown in Table 2-3 further identify weather phenomena and are used with certain types of precipitation and obscurations. Although TS and SH are used with precipitation and may be preceded with an intensity symbol, the intensity still applies to the precipitation and not the descriptor.
Example:
+TSRA is a thunderstorm with heavy rain and not a heavy thunderstorm with rain.
December 1999 2-8 Table 2-3 Descriptor Qualifiers Descriptor MI1 Shallow BC2 Patches DR3 Low drifting BL4 Blowing SH Showers TS Thunderstorm FZ Freezing PR Partial 1MI shall be used only to further describe fog that has little vertical extent (less than 6 feet).2BC shall be used only to further describe fog that has little vertical extent and reduces horizontal visibility.3DR shall be used when dust, sand, or snow is raised by the wind to less than 6 feet.4BL shall be used when dust, sand, snow, and/or spray is raised by the wind to a height of 6 feet or more.
WEATHER PHENOMENA If more than one significant weather phenomenon is observed, entries will be listed in the following order: Tornadic activity, thunderstorms, and weather phenomena in order of decreasing predominance
(i.e., the most dominant type is reported first).
If more than one significant weather phenomenon is observed, except precipitation, separate weather groups will be shown in the report. No more than three weather groups will be used to report weather phenomena at or in the vicinity of the station. If more than one type of precipitation is observed, the appropriate contractions are combined into a single group with the predominant type being reported first. In such a group, any intensity will refer to the first type of precipitation in the group.
Refer to Table 2-4 while reading the rest of this section.
Examples:
TSRA indicates thunderstorm with moderate rain.
+SHRA indicates heavy rainshowers.
-FZRA indicates light freezing rain.
Precipitation The types of precipitation in the METAR code are shown in Table 2-4. Precipitation is any form of water particle, whether liquid or solid, that falls from the atmosphere and reaches the ground.
December 1999 2-9 Examples:
GR is used to indicate hail ¼ inch in diameter or larger.
GS is used to indicate hail less than ¼ inch in diameter.
UP is unknown precipitation and is used only at automated sites. This occurs when light precipitation is falling but the precipitation discriminator cannot determine the precipitation type. This situation usually occurs when rain and snow are falling at the same time.
Obscurations The types of obscuration phenomena in the METAR code are shown in Table 2-4. They are any phenomena in the atmosphere, other than precipitation, that reduce horizontal visibility.
Examples:
BR is used to indicate mist restricting visibility and is used only when the visibility is from 5/8 mile to 6 miles.
FG is used to indicate fog restricting visibility and is used only when visibility is less than 5/8 mile.
Other The other weather phenomena, shown in the table, are reported when they occur.
Examples:
SQ is a sudden increase in wind speed of at least 16 knots, the speed rising to 22 knots or more, and lasting at least 1 minute.
+FC is used to denote a tornado or waterspout.
FC is used to denote a funnel cloud.
Table 2-4 Weather Phenomena Precipitation Obscuration Other DZ Drizzle BR Mist PO Dust/Sand whirls RA Rain FG Fog SQ Squalls SN Snow DU Dust FC Funnel cloud SG Snow grains SA Sand +FC Tornado or Waterspout IC Ice crystals HZ Haze SS Sandstorm PL Ice pellets PY Spray DS Dust storm GR Hail VA Volcanic ash GS Small hail or Snow pellets FU Smoke UP Unknown precipitation
December 1999 2-10 Weather Begins/Ends When weather begins or ends, the Remarks element will show the beginning and ending times of any type of precipitation or thunderstorms. Types of precipitation may be combined if beginning or ending times are the same.
Example:
RAB05E30SNB30E45 This means that rain began at 5 minutes past the hour and ended at 30 minutes past the hour, snow began at 30 minutes past the hour and ended at 45 minutes past the hour.
Example:
TSB05E45 This means a thunderstorm began at 5 minutes past the hour and ended at 45 minutes past the hour.
Hailstone Size When hailstones, GR, are shown in the body of a report, the largest hailstone size is shown in the Remarks element in 1/4-inch increments and identified with the contraction GR. Hailstones less than 1/4 inch are shown in the body of a report as GS and no remarks are entered indicating hailstone size.
Example:
GR 1 ¾
December 1999 2-11
SKY CONDITION METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK AO2 Sky condition is reported in the following format:
Amount/Height/Type (as required) or Indefinite Ceiling/Height (Vertical Visibility) AMOUNT A clear sky, a layer of clouds, or an obscuring phenomenon is reported by one of the six sky cover contractions. (See Table 2-5.) When more than one layer is reported, they are reported in ascending order of height. For each layer above a lower layer or layers, the sky cover for that higher layer will be the total sky cover that includes that higher layer and all lower layers. In other words, the summation of the cloud layers from below and at that higher level determines what sky cover is reported. This summation includes both clouds and obscuration. The amount of sky cover is reported in eighths of the sky, using the contractions in Table 2-5.
Table 2-5 Reportable Contractions for Sky Cover Reportable Contractions Meaning Summation Amount *SKC or CLR Clear 0 or 0 below 12,000 FEW Few >0 but < 2/8 SCT Scattered 3/8-4/8 BKN Broken 5/8-7/8 OVC Overcast 8/8 VV Vertical Visibility (indefinite ceiling) 8/8 *SKC will be reported at manual stations. The abbreviation CLR shall be used at automated stations when no clouds below 12,000 feet are detected.
Note: For aviation purposes, the ceiling is defined as the height (AGL) of the lowest broken or overcast layer aloft or vertical visibility into an obscuration.
HEIGHT Cloud bases are reported with three digits in hundreds of feet above ground level.
Example:
SCT020 Clouds above 12,000 feet cannot be detected by automated reporting systems. At reporting stations located in the mountains, if the cloud layer is below the station level, the height of the layer will be shown as three solidi (///).
Example:
SCT///
December 1999 2-12
HORIZON EARTH 1/8 5000 4000 3000 2000 1000
SURFACE Figure 2-1. Few sky cover at 2,000 feet (2/8) and scattered sky cover at 4,000 feet (4/8). The summation of sky cover would be coded as FEW020 SCT040.
HORIZON EARTH 1/8 5000 4000 3000 2000 1000
SURFACE Cloud not seen due to lower cloud layer.
Figure 2-2. The sky cover consists of few clouds at 1,000 feet (2/8), scattered clouds at 3,000 feet (3/8), and broken clouds at 5,000 feet (6/8). This is coded as FEW010 SCT030 BKN050.
December 1999 2-13
TYPE (AS REQUIRED) If towering cumulus clouds, TCU, or cumulonimbus clouds, CB, are present, they are reported after the height that represents their base.
Example:
BKN025CB or SCT040TCU Figure 2-3. Towering Cumulus (TCU). The significance of this cloud is that it indicates the atmosphere in the lower altitudes is unstable and conducive to turbulence. (Photo courtesy of National Severe Storms Laboratory/University of Oklahoma.)
December 1999 2-14 Figure 2-4. Cumulonimbus (CB). The anvil portion of a CB is composed of ice crystals. The CB or thunderstorm cloud contains most types of aviation weather hazards, particularly turbulence, icing, hail, and low-level wind shear (LLWS). (Photo courtesy of Doug Streu.)
INDEFINITE CEILING/HEIGHTS (VERTICAL VISIBILITY) The height into an indefinite ceiling is preceded with VV followed by three digits indicating the vertical visibility in hundreds of feet above ground level. The layer is spoken as “indefinite ceiling” and indicates total obscuration.
Example:
VV002 Partial Obscurations The amount of obscuration is reported in the body of the METAR when the sky is partially obscured by a surface-based phenomenon by indicating the amount of obscuration as FEW, SCT, or BKN followed with three zeros (000). The type of obscuring phenomenon is stated in the Remarks element and precedes the amount of obscuration and three zeros. For example, if fog is hiding >1/8 to 2/8 of the sky, it will be coded in the body of the METAR as “FEW000.” Because the fog is partially obscuring the sky, a remark is required. (See Figure 2-5.)
Example of Remark:
FG FEW000.
December 1999 2-15
HORIZON EARTH 1/8 5000 4000 3000 2000 1000
SURFACE Cloud not seen due to lower cloud layer.
Figure 2-5. The sky cover consists of surface-based obscuration and an overcast layer at 3,000 feet.
This is coded as SCT000 OVC030 with FG SCT000 in remarks.
The sky cover and ceiling, as determined from the ground, represent as nearly as possible what the pilot should experience in flight. In other words, a pilot flying at or above a reported ceiling layer (BKN- OVC) should see less than half the surface below. A pilot descending through a surface-based total obscuration should first see the ground directly below from the height reported as vertical visibility into the obscuration. However, due to the differing viewing points of the pilot and the observer, the observed values and what the pilot sees do not always exactly agree. Figure 2-6 illustrates the effect of an obscured sky on the vision from a descending aircraft.
December 1999 2-16 RUNWAY
REPORTED
VERTICAL
VISIBILITY
MISSED APPROACH A B
SLANT RANGE
VISIBILITY
SLANT RANGE
VISIBILITY Figure 2-6. The obscuration limits runway acquisition due to slant range effects (A). This pilot would be able to see the ground but not the runway. The pilot will not be able to see the runway until position B, which is at a much lower altitude. If position A represented approach minimums, the approach could not be continued and a missed approach must be executed.
ADDITIONAL SKY CONDITION REMARKS Whenever the ceiling is below 3,000 feet and is variable, the remark CIG will be shown in the Remarks element followed with the lowest and highest ceiling heights separated with a V.
Example:
CIG 005V010 When an automated station uses meteorological discontinuity sensors, site-specific sky conditions that differ from the ceiling height in the body of the report will be shown in the Remarks element.
Example:
CIG 002 RWY 11 When a layer is varying in sky cover, the variability range will be shown in the Remarks element. If there is more than one cloud layer of the same coverage, the variable layer will be identified by including the layer height.
Example:
BKN014 V OVC When significant clouds are observed, they are shown in the Remarks element. The following cloud types are shown:
December 1999 2-17 Towering cumulus, TCU, and direction from the station.
Example:
TCU W Cumulonimbus, CB; or cumulonimbus mammatus, CBMAM; direction from the station; and direction of movement (if known). If the clouds are beyond 10 miles from the airport, DSNT will indicate that they are distant. (See Figure 2-7.)
Examples:
CB DSNT E or CBMAM E MOV NE (For TCU and CB see Figures 2-3 and 2-4.)
Figure 2-7. Cumulonimbus Mammatus (CBMAM). This characteristic cloud can result from violent up- and downdrafts. This cloud type indicates possible severe or greater turbulence.
(Photo courtesy of Grant Goodge taken at Asheville, NC on 4/15/87.)
December 1999 2-18 Altocumulus castellanus, ACC; standing lenticular (stratocumulus, SCSL; altocumulus, ACSL; or cirrocumulus, CCSL); or rotor clouds, ROTOR CLD, will show a remark describing the clouds (if needed) and the direction from the station.
Examples:
ACC NW or ACSL SW (Figure 2-8 for ACC; see Figure 2-9 for standing lenticular clouds.)
Figure 2-8. Altocumulus Castellanus (ACC). ACC indicates unstable conditions aloft, but not necessarily below the base of the cloud. (Photo courtesy of National Severe Storms Laboratory/University of Oklahoma.)