8.1 General

Present weather includes precipitation, obscurations, well-developed dust/sand whirls, squalls, tornadic activity, sandstorms, and duststorms. Present weather may be evaluated instrumentally, manually, or through a combination of instrumental and manual methods.

8.2 Scope

This chapter prescribes the standards for observing and reporting present weather. The types of present weather reported vary according to the type of station defined by the responsible agency.

8.3 Present Weather Parameters

8.3.1 Precipitation. Precipitation is any of the forms of water particles, whether liquid or solid, that fall from the atmosphere and reach the ground. The types of precipitation are:

  a. Drizzle.  Fairly uniform precipitation composed exclusively
     of fine drops with diameters of less than 0.02 inch (0.5 mm) very
     close together.  Drizzle appears to float while following air currents,
     although unlike fog droplets, it falls to the ground.

  b. Rain.  Precipitation, either in the form of drops larger
     than 0.02 inch (0.5 mm), or smaller drops which, in contrast to
     drizzle, are widely separated.

  c. Snow.  Precipitation of snow crystals, mostly branched
     in the form of six-pointed stars.

  d. Snow Grains.  Precipitation of very small, white, and
     opaque grains of ice.

  e. Ice Crystals (Diamond Dust).  A fall of unbranched
     (snow crystals are branched) ice crystals in the form of needles,
     columns, or plates.

  f. Ice Pellets.  Precipitation of transparent or translucent
     pellets of ice, which are round or irregular, rarely conical, and
     which have a diameter of 0.2 inch (5 mm), or less.

     There are two main types:

     (1) Hard grains of ice consisting of frozen raindrops,
         or largely melted and refrozen snowflakes.

     (2) Pellets of snow encased in a thin layer of ice which
         have formed from the freezing, either of droplets intercepted
         by the pellets, or of water resulting from the partial
         melting of the pellets.

  g. Hail.  Precipitation in the form of small balls or other
     pieces of ice falling separately or frozen together in irregular
     lumps.

  h. Small Hail and/or Snow Pellets.  Precipitation of white, opaque
     grains of ice.  The grains are round or sometimes conical.  Diameters
     range from about 0.08 to 0.2 inch (2 to 5 mm).

  i. Unknown Precipitation.  Precipitation type that is reported
     if the automated station detects the occurrence of light precipitation
     but the precipitation discriminator cannot recognize the type.

8.3.2 Obscurations. Any phenomenon in the atmosphere, other than precipitation, that reduces the horizontal visibility.

  a. Mist.  A visible aggregate of minute water particles suspended
     in the atmosphere that reduces visibility to less than 7 statute miles
     but greater than or equal to 5/8 statute miles.

  b. Fog.  A visible aggregate of minute water particles (droplets)
     which are based at the Earth's surface and reduces horizontal visibility
     to less than 5/8 statute mile and, unlike drizzle, it does not fall to
     the ground.

  c. Smoke.  A suspension in the air of small particles produced by
     combustion.  A transition to haze may occur when smoke particles have
     traveled great distances (25 to 100 miles or more) and when the larger
     particles have settled out and the remaining particles have become widely
     scattered through the atmosphere.

  d. Volcanic Ash.  Fine particles of rock powder that originate
     from a volcano and that may remain suspended in the atmosphere for
     long periods.

  e. Widespread Dust.  Fine particles of earth or other matter
     raised or suspended in the air by the wind that may have occurred at
     or far away from the station which may restrict horizontal visibility.

  f. Sand.  Sand particles raised by the wind to a height sufficient
     to reduce horizontal visibility.

  g. Haze.  A suspension in the air of extremely small, dry particles
     invisible to the naked eye and sufficiently numerous to give the air an
     opalescent appearance.

  h. Spray.  An ensemble of water droplets torn by the wind from the
     surface of an extensive body of water, generally from the crests of waves,
     and carried up a short distance into the air.

8.3.3 Other Weather Phenomena

  a. Well-developed Dust/Sand Whirl.  An ensemble of particles of dust
     or sand, sometimes accompanied by small litter, raised from the ground
     in the form of a whirling column of varying height with a small diameter
     and an approximately vertical axis.

  b. Squall.  A strong wind characterized by a sudden onset in which
     the wind speed increases at least 16 knots and is sustained at 22 knots
     or more for at least one minute (see paragraph 12.6.8.e.(1)).

  c. Funnel Cloud (Tornadic Activity)

     (1) Tornado.  A violent, rotating column of air touching the ground.

     (2) Funnel Cloud.  A violent, rotating column of air which does not
         touch the surface.

     (3) Waterspout.  A violent, rotating column of air that forms over
         a body of water, and touches the water surface.

  d. Sandstorm.  Particles of sand carried aloft by a strong wind.  The
     sand particles are mostly confined to the lowest ten feet, and rarely rise
     more than fifty feet above the ground.

  e. Duststorm.  A severe weather condition characterized by strong winds
     and dust-filled air over an extensive area.

8.4 Present Weather Observing Standards

8.4.1 Qualifiers. Present weather qualifiers fall into two categories: intensity or proximity and descriptors. Qualifiers may be used in various combinations to describe weather phenomena.

  a. Intensity/Proximity.  The intensity qualifiers are:  light,
     moderate, and heavy.  The proximity qualifier is vicinity.

     (1) Intensity of Precipitation.  When more than one form of
         precipitation is occurring at a time or precipitation is occurring
         with an obscuration, the intensities determined shall be no greater
         than that which would be determined if any forms were occurring alone.

         The intensity of precipitation shall be identified as light, moderate,
         or heavy in accordance with one of the following:

         (a) Intensity of Rain or Ice Pellets.  The intensity of rain
             and ice pellets shall be based on the criteria given in Table 8-1,
             Table 8-2, and Table 8-3.

          (b) Intensity of Snow and Drizzle.  The intensity of snow
              and drizzle shall be based on the reported surface visibility
              in accordance with Table 8-4 when occurring alone.

      (2) Proximity.  Unless otherwise directed elsewhere in this
          Handbook, weather phenomena occurring beyond the point of observation
          (between 5 and 10 statute miles) shall be reported as (in the)
          vicinity.

  b. Descriptors.  Descriptors are qualifiers which further amplify
     weather phenomena and are used with certain types of precipitation and
     obscurations.  The descriptor qualifiers are:  shallow, partial, patches,
     low drifting, blowing, shower(s), thunderstorm, and freezing.

     (1) Shallow.  The descriptor shallow shall only be used to further
         describe fog that has little vertical extent (less than 6 feet).

     (2) Partial and Patches.  The descriptors partial and patches
         shall only be used to further describe fog that has little vertical
         extent (normally greater than or equal to 6 feet but less than 20 feet),
         and reduces horizontal visibility, but to a lesser extent vertically.
         The stars may often be seen by night and the sun by day.

     (3) Low Drifting.  When dust, sand, or snow is raised by the wind
         to less than 6 feet, "low drifting" shall be used to further describe
         the weather phenomenon.

     (4) Blowing.  When dust, sand, snow, and/or spray is raised by the
         wind to a height of 6 feet or more, "blowing" shall be used to further
         describe the weather phenomenon.

     (5) Shower(s).  Precipitation characterized by the suddenness with
         which they start and stop, by the rapid changes of intensity, and
         usually by rapid changes in the appearance of the sky.

     (6) Thunderstorm.  A local storm produced by a cumulonimbus cloud
         that is accompanied by lightning and/or thunder.

     (7) Freezing.  When fog is occurring and the temperature is below
         0°C, "freezing" shall be used to further describe the phenomena.  When
         drizzle and/or rain freezes upon impact and forms a glaze on the ground
         or other exposed objects, "freezing" shall be used to further describe
         the precipitation.

8.4.2 Weather Phenomena. Weather phenomena fall into three categories: precipitation, obscurations, and other phenomena. The three categories of weather phenomena shall be combined with the qualifiers listed in the preceding paragraphs, to identify present weather that is occurring.

8.5 Present Weather Reporting Standards

Present weather is reported when it is occurring at, or in the vicinity of, the station and at the time of observation. Unless directed elsewhere in the Handbook, the location of weather phenomena shall be reported as:

• "occurring at the station" when within 5 statute miles of the point(s) of observation.
• "in the vicinity of the station" when between 5 and 10 statute miles of the point(s) of obsesvation.
• "distant from the station" when beyond 10 statute miles of the point(s) of observation.

With the exception of volcanic ash, low drifting dust, low drifting sand, low drifting snow, shallow fog, partial fog, and patches (of) fog, obscurations are reported only when the prevailing visibility is less than 7 statute miles or considered operationally significant. Volcanic ash shall always be reported when observed.

When more than one type of present weather are reported at the same time, present weather shall be reported in the following order:

• Tornadic activity--Tornado, Funnel Cloud, or Waterspout.
• Thunderstorm(s) with or without associated precipitation.
• Present weather in order of decreasing dominance, i.e., the most dominant type is reported first.
• Left-to-right in Table 8-6 (Columns 1 through 5).

8.5.1 Precipitation. Precipitation shall be reported when occurring at the point of observation. Precipitation not occurring at the point of observation but within 10 statute miles shall be reported as showers in the vicinity.

  a. Liquid Precipitation

     (1) Drizzle. (see paragraphs 12.6.8.a(1), 12.6.8.c(1), and 12.7.1.l).

     (2) Rain. (see paragraphs 12.6.8.a(1), 12.6.8.c(1), and 12.7.1.l).

     (3) Rainshower(s). (see paragraphs 12.6.8.a(1), 12.6.8.b(3), 12.6.8.c(1),
         and 12.7.1.l).

  b. Freezing Precipitation

     (1) Freezing Rain. (see paragraphs 12.6.8.a(1),  12.6.8.b(5), 12.6.8.c(1),
         12.7.1.l).

     (2) Freezing Drizzle. (see paragraphs 12.6.8.a(1), 12.6.8.b(5),
         12.6.8.c(1), and 12.7.1.l).

  c. Solid Precipitation

     (1) Snow. (see paragraphs 12.6.8.a(1), 12.6.8.c(1), 12.7.1.l).

     (2) Snowshower(s). (see paragraphs 12.6.8.a(1), 12.6.8.b(3), 12.6.8.c(1),
         and 12.7.1.l).

     (3) Blowing Snow. (see paragraphs 12.6.8.a(1), 12.6.8.b(2), and 12.6.8.c(1)).

     (4) Low Drifting Snow. (see paragraphs 12.6.8.a(1), 12.6.8.b(2), and
         12.6.8.c(1)).

     (5) Snow Grains. (see paragraphs 12.6.8.a(1), 12.6.8.c(1), 12.7.1.l).

     (6) Ice Crystals. (see paragraphs 12.6.8.a(1), 12.6.8.c(1), and 12.7.1.l).

     (7) Ice Pellets. (see paragraphs 12.6.8.c(1) and 12.7.1.l).

         Ice Pellet shower(s). (see paragraphs 12.6.8.b(3), 12.6.8.c(1), and
         12.7.1.l).

     (8) Hail. Hail shall be reported, at designated stations. (see paragraph
         12.7.1.k and 12.7.1.n).

         Hail shower(s). (see paragraphs 12.6.8.b(3), 12.6.8.c(1), 12.7.1.l,
         and 12.7.1.n).

     (9) Small Hail and/or Snow Pellets. (see paragraphs 12.6.8.c(1)
         and 12.7.1.n).

         Small Hail and/or Snow Pellets Shower(s). (see paragraphs
         12.6.8.b(3), 12.6.8.c(1), and 12.7.1.n).

  d. Unknown Precipitation.  Unknown precipitation shall only be reported by
     automated stations to indicate precipitation of unknown type when the automated
     system cannot identify the precipitation with any greater precision (see
     paragraph 12.6.8.c(2)).

 - Light
   Moderate
   (see note 2)
 + Heavy
VC In the
   Vicinity
   (see note 3)

MI Shallow
PR Partial
BC Patches
DR Low Drifting
BL Blowing
SH Shower(s)
TS Thunderstorm
FZ Freezing

DZ Drizzle
RA Rain
SN Snow
SG Snow Grains
IC Ice Crystals
PE Ice Pellets
GR Hail
GS Small Hail
   and/or Snow
   Pellets
UP Unknown
   Precipitation

BR Mist
FG Fog
FU Smoke
VA Volcanic Ash
DU Widespread
   Dust
SA Sand
HZ Haze
PY Spray

PO Well-
   Developed
   Dust/Sand
   Whirls
SQ Squalls
FC Funnel Cloud
   Tornado
   Waterspout
   (see note 4)
SS Sandstorm
SS Duststorm

1. The weather groups shall be constructed by considering columns 1 to 5 in the table
   above in sequence, i.e. intensity, followed by description, followed by weather phenomena,
   e.g. heavy rain shower(s) is coded as +SHRA
2. To denote moderate intensity no entry or symbol is used.
3. See paragraph 8.4.1.a.(2), 8.5, and 8.5.1 for vicinity definitions.
4. Tornados and waterspouts shall be coded as +FC.

8.5.2 Obscuration.

  a. Mist. (see paragraph 12.6.8.d(1)).

  b. Fog. (see paragraphs 12.6.8.a(2) and 12.6.8.d(1)).

     (1) Shallow (Ground) Fog. (see paragraphs 12.6.8.b(1) and 12.6.8.d(1)).

     (2) Partial Fog. (see paragraphs 12.6.8.b(1) and 12.6.8.d(2)).

     (3) Patches (of) Fog. (see paragraphs 12.6.8.b(1) and 12.6.8.d(2)).

     (4) Freezing Fog. (see paragraph 12.6.8.b(5) and 12.6.8.d(1)).

  c. Smoke. (see paragraph 12.6.8.d(1)).

  d. Volcanic Ash. (see paragraph 12.6.8.d(1)).

  e. Widespread Dust. (see paragraph 12.6.8.d(1)).

     (1) Blowing Dust. (see paragraphs 12.6.8.a(1), 12.6.8.a(2),
         12.6.8.b(2), and 12.6.8.d(1)).

     (2) Low Drifting Dust. (see paragraphs 12.6.8.b(2) and 12.6.8.d(1)).

  f. Sand. (see paragraph 12.6.8.d(1)).

     (1) Blowing Sand. (see paragraphs 12.6.8.a(1), 12.6.8.a(2),
         12.6.8.b(2), and 12.6.8.d(1)).

     (2) Low Drifting Sand. (see paragraphs 12.6.8.b(2) and 12.6.8.d(1)).

  g. Haze. (see paragraph 12.6.8.d(1)).

  h. Blowing Spray. (see paragraphs 12.6.8.b(2) and 12.6.8.d(3)).

8.5.3 Other Weather Phenomena

  a. Well-Developed Dust/Sand Whirls. (see paragraphs 12.6.8.a(2) and
     12.6.8.e(1)).

  b. Squalls. (see paragraph 12.6.8.e(1)).

  c. Tornado, Waterspout, or Funnel Cloud. (see paragraphs 12.6.8.a(1),
     12.6.8.e(2), and 12.7.1.b).

  d. Sandstorm. (see paragraphs 12.6.8.a(1) and 12.6.8.e(1)).

  e. Duststorm. (see paragraphs (12.6.8.a(1) and 12.6.8.e(1)).

8.5.4 Thunderstorm. A thunderstorm occurring with or without accompanying precipitation shall be reported when observed to begin, to be in progress, or to end. In addition to reporting a thunderstorm in the body of the METAR/SPECI, remarks may be added to report the time, location, and movement of the storm (see paragraphs 8.5.5.c, 12.7.1.l, and 12.7.1.m).

  a. Beginning of Thunderstorm.  The beginning of a thunderstorm shall
     be reported as the earliest time:

     (1) thunder is heard;

     (2) lightning is observed at the station when the local noise level is
         sufficient to prevent hearing thunder; or

     (3) lightning is detected by an automated sensor.

  b. Ending of Thunderstorm.  The ending of a thunderstorm shall be
     reported as 15 minutes after the last occurrence of any of the above
     criteria.

8.5.5 Beginning/Ending Times of Precipitation, Tornadic Activity, and Thunderstorms.

  a. Precipitation.  At designated stations, the time precipitation begins
     or ends shall be reported to the nearest minute.  The beginning and ending
     times shall be reported in the next METAR after the event.  Beginning and
     ending times for separate periods shall be reported only if the intervening
     time exceeds 15 minutes (see paragraph 12.7.1.k).

  b. Tornadic Activity.  At designated stations, the time tornadic activity
     begins or ends shall be reported to the nearest minute.  The beginning and
     ending times shall be reported in a SPECI and the next METAR after the event
    (see paragraphs 12.6.8.e(2) and 12.7.1.b).

  c. Thunderstorm.  At designated stations, the time thunderstorm(s) begins
     or ends shall be reported to the nearest minute.  The beginning and ending
     times shall be reported in a SPECI and the next METAR after the event.
     Beginning and ending times of separate thunderstorm(s) shall be reported only
     in a METAR if the intervening time exceeds 15 minutes (see paragraphs 12.6.8.a(1),
     12.7.1.l, and 12.7.1.m).

8.5.6 Other Significant Weather Phenomena. Observers shall be alert to weather phenomena that are visible from the station but not occurring at the station. Examples of such phenomena are fog banks, localized rain, snow blowing over runways, etc. These phenomena shall be reported whenever they are considered to be operationally significant. Volcanic eruptions shall be reported in remarks (see paragraph 12.7.1.a).

8.6 Summary of Weather. Table 8-6 contains a summary of the present weather observing and reporting standards according to the type of station.